<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:bf1dceb6-bbc6-41e2-a5fa-11c6732fa35f,g:e1016b3d-bcba-48ea-8ff9-fb8b242587b9-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://si-bone.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="sibn-20251231.xsd#CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/CONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_b354b20b-d335-4815-8412-ab0cb3d3f41a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_3337c5c3-8181-4ca0-b69a-59b1f89cd81d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_b354b20b-d335-4815-8412-ab0cb3d3f41a" xlink:to="loc_us-gaap_StatementTable_3337c5c3-8181-4ca0-b69a-59b1f89cd81d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_123c09e0-5227-4456-ae20-657abf4160f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_3337c5c3-8181-4ca0-b69a-59b1f89cd81d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_123c09e0-5227-4456-ae20-657abf4160f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_123c09e0-5227-4456-ae20-657abf4160f9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_123c09e0-5227-4456-ae20-657abf4160f9" xlink:to="loc_us-gaap_EquityComponentDomain_123c09e0-5227-4456-ae20-657abf4160f9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_123c09e0-5227-4456-ae20-657abf4160f9" xlink:to="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_34521211-34b7-46ea-83d0-005336e906d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:to="loc_us-gaap_CommonStockMember_34521211-34b7-46ea-83d0-005336e906d5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_aa392a46-6b0e-4442-b6a3-c17165d59e6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_aa392a46-6b0e-4442-b6a3-c17165d59e6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_264375f2-4f20-4743-820c-2f1205fcdc73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_264375f2-4f20-4743-820c-2f1205fcdc73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_e7a69d59-8ace-419a-9d5a-3ca0dfee1e22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_d4b795e9-d0b5-4ba9-b864-c73bc40f5c43" xlink:to="loc_us-gaap_RetainedEarningsMember_e7a69d59-8ace-419a-9d5a-3ca0dfee1e22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_b354b20b-d335-4815-8412-ab0cb3d3f41a" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_f95335e0-b869-48d8-b571-71c953916625" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_f95335e0-b869-48d8-b571-71c953916625" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_b3c8ec04-6df4-449b-a617-a588ee2bae37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockholdersEquity_b3c8ec04-6df4-449b-a617-a588ee2bae37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_8743d87f-d6f3-46c2-b65c-868f081385cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_8743d87f-d6f3-46c2-b65c-868f081385cc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_937b3d21-9d95-46f7-a6ff-5511ab9f39c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_937b3d21-9d95-46f7-a6ff-5511ab9f39c8" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_823e57c7-0b78-49d4-a6e9-fc90b9a443aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_823e57c7-0b78-49d4-a6e9-fc90b9a443aa" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c5141312-fc99-4088-984f-77cff3d1dcb9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_c5141312-fc99-4088-984f-77cff3d1dcb9" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_246113f8-cc54-4232-a914-35840acf4c7f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_246113f8-cc54-4232-a914-35840acf4c7f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ff737ceb-052a-455f-b0c1-c4a16db2f3c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_ff737ceb-052a-455f-b0c1-c4a16db2f3c5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_StockIssuedDuringPeriodSharesRestrictedStockUnits_8564630a-a997-4420-bf60-560fcdbb4526" xlink:href="sibn-20251231.xsd#sibn_StockIssuedDuringPeriodSharesRestrictedStockUnits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_sibn_StockIssuedDuringPeriodSharesRestrictedStockUnits_8564630a-a997-4420-bf60-560fcdbb4526" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants_9d646af4-a8db-43b3-9eca-1629e486ddc3" xlink:href="sibn-20251231.xsd#sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants_9d646af4-a8db-43b3-9eca-1629e486ddc3" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f77a5d95-cf5c-46ff-8730-7d6998dd09cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_f77a5d95-cf5c-46ff-8730-7d6998dd09cb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_c6a08cb5-22f0-4c18-8c00-09b8fb5965bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_c6a08cb5-22f0-4c18-8c00-09b8fb5965bc" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax_9dfba462-2623-4c5a-8204-4ffaf80202df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsNetOfTax_9dfba462-2623-4c5a-8204-4ffaf80202df" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_69ebebe7-e694-4891-8691-f5867b1097aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_f5db089a-d1b1-4609-a4a7-3a48e4cc2a8d" xlink:to="loc_us-gaap_NetIncomeLoss_69ebebe7-e694-4891-8691-f5867b1097aa" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_48a5270f-d567-4cd6-a7a6-1ae7fda0b253" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_aafee075-7856-49c9-89cc-228f6a71e7d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesScheduleofRevenuebyGeographyDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofRevenuebyGeographyDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesScheduleofRevenuebyGeographyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_63d1cb40-fd90-42ad-9c80-d35b26fae75c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_c667c680-589e-42b3-8ab9-34a4435eb027" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_63d1cb40-fd90-42ad-9c80-d35b26fae75c" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_c667c680-589e-42b3-8ab9-34a4435eb027" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_3227bd99-9349-4dcd-8da3-1dd55cb448b5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_c667c680-589e-42b3-8ab9-34a4435eb027" xlink:to="loc_srt_StatementGeographicalAxis_3227bd99-9349-4dcd-8da3-1dd55cb448b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_3227bd99-9349-4dcd-8da3-1dd55cb448b5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_3227bd99-9349-4dcd-8da3-1dd55cb448b5" xlink:to="loc_srt_SegmentGeographicalDomain_3227bd99-9349-4dcd-8da3-1dd55cb448b5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_f352441c-e9c2-4266-8782-c446cd5f51c9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_3227bd99-9349-4dcd-8da3-1dd55cb448b5" xlink:to="loc_srt_SegmentGeographicalDomain_f352441c-e9c2-4266-8782-c446cd5f51c9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_093736ba-2026-4e54-979a-1411c2780987" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_f352441c-e9c2-4266-8782-c446cd5f51c9" xlink:to="loc_country_US_093736ba-2026-4e54-979a-1411c2780987" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_534f28a5-ffc4-4d77-be40-433f415b7fa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_f352441c-e9c2-4266-8782-c446cd5f51c9" xlink:to="loc_us-gaap_NonUsMember_534f28a5-ffc4-4d77-be40-433f415b7fa1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2862c56a-d250-469a-afac-1556b9b5ab71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_63d1cb40-fd90-42ad-9c80-d35b26fae75c" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_2862c56a-d250-469a-afac-1556b9b5ab71" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesScheduleofPropertyandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c0d6253-0553-4b5d-9ff1-0e27f05f2c50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a45575f2-4de4-44fd-b2c9-8f7ff98d2867" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c0d6253-0553-4b5d-9ff1-0e27f05f2c50" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a45575f2-4de4-44fd-b2c9-8f7ff98d2867" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_92e8493d-6790-4bb5-8614-bc575236936a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a45575f2-4de4-44fd-b2c9-8f7ff98d2867" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_92e8493d-6790-4bb5-8614-bc575236936a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_92e8493d-6790-4bb5-8614-bc575236936a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_92e8493d-6790-4bb5-8614-bc575236936a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_92e8493d-6790-4bb5-8614-bc575236936a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_92e8493d-6790-4bb5-8614-bc575236936a" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ComputerAndOfficeEquipmentMember_c382506c-5fd9-4dab-94a3-23f7a4f51b48" xlink:href="sibn-20251231.xsd#sibn_ComputerAndOfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:to="loc_sibn_ComputerAndOfficeEquipmentMember_c382506c-5fd9-4dab-94a3-23f7a4f51b48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_InstrumentTraysMember_f0dc47fc-060e-46b6-bb43-165903fecd24" xlink:href="sibn-20251231.xsd#sibn_InstrumentTraysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:to="loc_sibn_InstrumentTraysMember_f0dc47fc-060e-46b6-bb43-165903fecd24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_323e4219-fd54-4b97-9c3e-7b517228984b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_323e4219-fd54-4b97-9c3e-7b517228984b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_f7b7df2c-b19d-42d5-a762-b134ecbbaa8d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f6068ff0-e1d6-469b-9f04-33e6857479dc" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_f7b7df2c-b19d-42d5-a762-b134ecbbaa8d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_5b87c307-330d-4e1a-a991-83392415eeaa" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_a45575f2-4de4-44fd-b2c9-8f7ff98d2867" xlink:to="loc_srt_RangeAxis_5b87c307-330d-4e1a-a991-83392415eeaa" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_5b87c307-330d-4e1a-a991-83392415eeaa_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_5b87c307-330d-4e1a-a991-83392415eeaa" xlink:to="loc_srt_RangeMember_5b87c307-330d-4e1a-a991-83392415eeaa_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c39d26a7-b401-4efb-8314-b10e57302191" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_5b87c307-330d-4e1a-a991-83392415eeaa" xlink:to="loc_srt_RangeMember_c39d26a7-b401-4efb-8314-b10e57302191" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_f7cfc475-6094-44df-8f33-32bb05349d9b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c39d26a7-b401-4efb-8314-b10e57302191" xlink:to="loc_srt_MinimumMember_f7cfc475-6094-44df-8f33-32bb05349d9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_c941070f-a066-4824-b824-faea2d704e8b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c39d26a7-b401-4efb-8314-b10e57302191" xlink:to="loc_srt_MaximumMember_c941070f-a066-4824-b824-faea2d704e8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_e28db16d-489f-4d12-92d7-88b651d5c223" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_4c0d6253-0553-4b5d-9ff1-0e27f05f2c50" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_e28db16d-489f-4d12-92d7-88b651d5c223" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#SummaryofSignificantAccountingPoliciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_1f381d19-12e1-47c2-9f19-6f85f9c0c6c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_1f381d19-12e1-47c2-9f19-6f85f9c0c6c1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_31430627-6838-48d8-88a5-14de1a7310b3" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_1f381d19-12e1-47c2-9f19-6f85f9c0c6c1" xlink:to="loc_srt_RangeAxis_31430627-6838-48d8-88a5-14de1a7310b3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_31430627-6838-48d8-88a5-14de1a7310b3_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_31430627-6838-48d8-88a5-14de1a7310b3" xlink:to="loc_srt_RangeMember_31430627-6838-48d8-88a5-14de1a7310b3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_89c51c87-e0ed-40e4-9dc2-fdcf2f464573" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_31430627-6838-48d8-88a5-14de1a7310b3" xlink:to="loc_srt_RangeMember_89c51c87-e0ed-40e4-9dc2-fdcf2f464573" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_ecfb9d1c-7e6e-42b4-96f5-7e50f1dff242" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_89c51c87-e0ed-40e4-9dc2-fdcf2f464573" xlink:to="loc_srt_MinimumMember_ecfb9d1c-7e6e-42b4-96f5-7e50f1dff242" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_865bca03-6273-425f-8c08-4df60abd9865" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_89c51c87-e0ed-40e4-9dc2-fdcf2f464573" xlink:to="loc_srt_MaximumMember_865bca03-6273-425f-8c08-4df60abd9865" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_d2479fc8-33b2-4820-8561-46405534fc32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ImpairmentOfLongLivedAssetsHeldForUse"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_us-gaap_ImpairmentOfLongLivedAssetsHeldForUse_d2479fc8-33b2-4820-8561-46405534fc32" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfReportableSegments_3053d063-99af-4ea5-82ad-1a801ac3bf73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfReportableSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_us-gaap_NumberOfReportableSegments_3053d063-99af-4ea5-82ad-1a801ac3bf73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NumberOfOperatingSegments_87cf77e6-0b82-4366-988c-942d69f525e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NumberOfOperatingSegments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_us-gaap_NumberOfOperatingSegments_87cf77e6-0b82-4366-988c-942d69f525e1" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_RevenueRecognitionStandardPaymentTerms_da6591cd-b0fc-41a0-880f-b9c0e5977e01" xlink:href="sibn-20251231.xsd#sibn_RevenueRecognitionStandardPaymentTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_sibn_RevenueRecognitionStandardPaymentTerms_da6591cd-b0fc-41a0-880f-b9c0e5977e01" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_StandardProductWarrantyTerm_9c7ba87d-8926-4147-9b1c-9bac1d603483" xlink:href="sibn-20251231.xsd#sibn_StandardProductWarrantyTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_sibn_StandardProductWarrantyTerm_9c7ba87d-8926-4147-9b1c-9bac1d603483" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_SalesCreditReservePeriod_56865084-3f17-44cb-8187-2a2446cf7ea6" xlink:href="sibn-20251231.xsd#sibn_SalesCreditReservePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_sibn_SalesCreditReservePeriod_56865084-3f17-44cb-8187-2a2446cf7ea6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdvertisingExpense_c1dcdb73-0f10-4451-bb2f-dabe278a0ddd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdvertisingExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_042c5d28-7827-402e-ab52-fd71311c160e" xlink:to="loc_us-gaap_AdvertisingExpense_c1dcdb73-0f10-4451-bb2f-dabe278a0ddd" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#MarketableSecuritiesScheduleofMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/MarketableSecuritiesScheduleofMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MarketableSecuritiesTable_4d7a66bf-03f6-492b-8b25-3276d04e8dec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MarketableSecuritiesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_us-gaap_MarketableSecuritiesTable_4d7a66bf-03f6-492b-8b25-3276d04e8dec" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019becc1-eebb-75ad-bf18-09ebb928c53e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_4d7a66bf-03f6-492b-8b25-3276d04e8dec" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019becc1-eebb-75ad-bf18-09ebb928c53e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-75ad-bf18-09ebb928c53e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019becc1-eebb-75ad-bf18-09ebb928c53e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-75ad-bf18-09ebb928c53e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-7019-80be-8dea944f7695" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019becc1-eebb-75ad-bf18-09ebb928c53e" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-7019-80be-8dea944f7695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019becc2-1c69-7229-95a0-75728a7d4720" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-7019-80be-8dea944f7695" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019becc2-1c69-7229-95a0-75728a7d4720" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_019bfee4-b493-7f83-8729-a94dc18fe859" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019becc1-eebb-7019-80be-8dea944f7695" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_019bfee4-b493-7f83-8729-a94dc18fe859" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_505b39ff-8b01-449c-abf5-b40d972022d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MarketableSecuritiesTable_4d7a66bf-03f6-492b-8b25-3276d04e8dec" xlink:to="loc_us-gaap_FinancialInstrumentAxis_505b39ff-8b01-449c-abf5-b40d972022d0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_505b39ff-8b01-449c-abf5-b40d972022d0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_505b39ff-8b01-449c-abf5-b40d972022d0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_505b39ff-8b01-449c-abf5-b40d972022d0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c4fc9cd-9031-45be-bd93-87e7e8dbd2f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_505b39ff-8b01-449c-abf5-b40d972022d0" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c4fc9cd-9031-45be-bd93-87e7e8dbd2f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_7eeebdac-2993-46e9-baee-0a1f431fe6bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c4fc9cd-9031-45be-bd93-87e7e8dbd2f3" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_7eeebdac-2993-46e9-baee-0a1f431fe6bf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_f07703ca-b6f5-439d-840c-b689543299e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_6c4fc9cd-9031-45be-bd93-87e7e8dbd2f3" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_f07703ca-b6f5-439d-840c-b689543299e9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValueAbstract_35a81c3f-08e4-4b1d-9c90-44f0a0dda34c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashEquivalentsAtCarryingValueAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValueAbstract_35a81c3f-08e4-4b1d-9c90-44f0a0dda34c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashEquivalentsAtCarryingValue_879a180b-34e0-4282-b09a-ab3ac8be4272" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsAtCarryingValueAbstract_35a81c3f-08e4-4b1d-9c90-44f0a0dda34c" xlink:to="loc_us-gaap_CashEquivalentsAtCarryingValue_879a180b-34e0-4282-b09a-ab3ac8be4272" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_CashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax_019c77ff-2e89-7330-9124-31bbe18d2fb9" xlink:href="sibn-20251231.xsd#sibn_CashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsAtCarryingValueAbstract_35a81c3f-08e4-4b1d-9c90-44f0a0dda34c" xlink:to="loc_sibn_CashEquivalentsAccumulatedGrossUnrealizedGainBeforeTax_019c77ff-2e89-7330-9124-31bbe18d2fb9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019c77ff-e034-74d7-b2bc-a119df274f99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashEquivalentsAtCarryingValueAbstract_35a81c3f-08e4-4b1d-9c90-44f0a0dda34c" xlink:to="loc_us-gaap_CashAndCashEquivalentsFairValueDisclosure_019c77ff-e034-74d7-b2bc-a119df274f99" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_013387b2-e7b4-47c6-abe3-72b015e9ffdf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleAmortizedCostExcludingAccruedInterestBeforeAllowanceForCreditLoss_013387b2-e7b4-47c6-abe3-72b015e9ffdf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_64e7c6bc-9220-4cda-8eca-aa1b3754cedf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_64e7c6bc-9220-4cda-8eca-aa1b3754cedf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_0925f4c6-23df-4e40-b514-c18d666207ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_0925f4c6-23df-4e40-b514-c18d666207ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_e1ba6307-23ec-4f21-a66d-e4267679a283" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesFairValueToAmortizedCostBasisAbstract_f68e39a5-6e67-47ca-a064-1ebfbc57762c" xlink:to="loc_us-gaap_DebtSecuritiesAvailableForSaleExcludingAccruedInterest_e1ba6307-23ec-4f21-a66d-e4267679a283" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_MarketableSecuritiesAmortizedCost_be1efdf1-f1d5-4e91-9afb-bb1c3093bff9" xlink:href="sibn-20251231.xsd#sibn_MarketableSecuritiesAmortizedCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_sibn_MarketableSecuritiesAmortizedCost_be1efdf1-f1d5-4e91-9afb-bb1c3093bff9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_CashCashEquivalentsAndShortTermInvestmentsAccumulatedGrossUnrealizedGainBeforeTax_019c7804-8278-7827-b9f1-6e13c38489b6" xlink:href="sibn-20251231.xsd#sibn_CashCashEquivalentsAndShortTermInvestmentsAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_sibn_CashCashEquivalentsAndShortTermInvestmentsAccumulatedGrossUnrealizedGainBeforeTax_019c7804-8278-7827-b9f1-6e13c38489b6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_0cff101e-8574-496b-98d5-56ca0868945b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashCashEquivalentsAndShortTermInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MarketableSecuritiesLineItems_8511d904-a9ea-47bb-8052-5aa00ca5a6ca" xlink:to="loc_us-gaap_CashCashEquivalentsAndShortTermInvestments_0cff101e-8574-496b-98d5-56ca0868945b" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/FairValueMeasurementDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#FairValueMeasurementDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/FairValueMeasurementDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_1e570d8e-51cd-43b3-b6a7-bfe01631acaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b505b535-169f-4c2b-b1d4-cc1fe725d4cd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_1e570d8e-51cd-43b3-b6a7-bfe01631acaf" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b505b535-169f-4c2b-b1d4-cc1fe725d4cd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b000f48e-8eb8-48c9-a1f3-26560618865c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b505b535-169f-4c2b-b1d4-cc1fe725d4cd" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b000f48e-8eb8-48c9-a1f3-26560618865c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b000f48e-8eb8-48c9-a1f3-26560618865c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b000f48e-8eb8-48c9-a1f3-26560618865c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b000f48e-8eb8-48c9-a1f3-26560618865c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5647b545-a225-4886-8d46-5e8ada380fb8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_b000f48e-8eb8-48c9-a1f3-26560618865c" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5647b545-a225-4886-8d46-5e8ada380fb8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_bd367ba9-a0d4-4b3f-9577-175e84e79101" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5647b545-a225-4886-8d46-5e8ada380fb8" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_bd367ba9-a0d4-4b3f-9577-175e84e79101" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_b5de2299-f142-4148-ada4-90c579f18234" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5647b545-a225-4886-8d46-5e8ada380fb8" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_b5de2299-f142-4148-ada4-90c579f18234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_743a3361-5704-40ba-9927-50ad10edff23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_5647b545-a225-4886-8d46-5e8ada380fb8" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_743a3361-5704-40ba-9927-50ad10edff23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable_b505b535-169f-4c2b-b1d4-cc1fe725d4cd" xlink:to="loc_us-gaap_FinancialInstrumentAxis_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_35ab579d-fcb9-4666-a503-a7ab24340a77" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_a1fd8689-ce5e-4b91-9e1e-6c5c7d426457" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_35ab579d-fcb9-4666-a503-a7ab24340a77" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_329813dc-2486-463c-9529-72899e0a223a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_35ab579d-fcb9-4666-a503-a7ab24340a77" xlink:to="loc_us-gaap_MoneyMarketFundsMember_329813dc-2486-463c-9529-72899e0a223a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USTreasurySecuritiesMember_0e992d90-1565-42ec-86de-030598f5c53c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USTreasurySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_35ab579d-fcb9-4666-a503-a7ab24340a77" xlink:to="loc_us-gaap_USTreasurySecuritiesMember_0e992d90-1565-42ec-86de-030598f5c53c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_0f3c2026-cb06-4130-b9b3-737c203e0497" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_USGovernmentAgenciesDebtSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_35ab579d-fcb9-4666-a503-a7ab24340a77" xlink:to="loc_us-gaap_USGovernmentAgenciesDebtSecuritiesMember_0f3c2026-cb06-4130-b9b3-737c203e0497" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsFairValueDisclosureAbstract_93dfe605-bae9-4c37-86f6-92f728c11be6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_1e570d8e-51cd-43b3-b6a7-bfe01631acaf" xlink:to="loc_us-gaap_AssetsFairValueDisclosureAbstract_93dfe605-bae9-4c37-86f6-92f728c11be6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_39cb820b-d564-452f-ab5a-fa7232ff256b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentsFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsFairValueDisclosureAbstract_93dfe605-bae9-4c37-86f6-92f728c11be6" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_39cb820b-d564-452f-ab5a-fa7232ff256b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#BalanceSheetComponentsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/BalanceSheetComponentsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_225ad587-361b-4b3a-903c-b54f6a3aa587" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_225ad587-361b-4b3a-903c-b54f6a3aa587" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_40e738c7-0d9e-4b9a-b255-1828e2ea600d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_225ad587-361b-4b3a-903c-b54f6a3aa587" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_40e738c7-0d9e-4b9a-b255-1828e2ea600d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_40e738c7-0d9e-4b9a-b255-1828e2ea600d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_40e738c7-0d9e-4b9a-b255-1828e2ea600d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_40e738c7-0d9e-4b9a-b255-1828e2ea600d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f85a34d6-08a2-413b-9439-13e0421f1c48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_40e738c7-0d9e-4b9a-b255-1828e2ea600d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f85a34d6-08a2-413b-9439-13e0421f1c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ConstructionInProgressSurgicalPlacementInstrumentSetMember_d6a4d953-7c9e-49ea-a2a3-72f0015ea3c5" xlink:href="sibn-20251231.xsd#sibn_ConstructionInProgressSurgicalPlacementInstrumentSetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f85a34d6-08a2-413b-9439-13e0421f1c48" xlink:to="loc_sibn_ConstructionInProgressSurgicalPlacementInstrumentSetMember_d6a4d953-7c9e-49ea-a2a3-72f0015ea3c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ConstructionInProgressSoftwareCostsMember_82bff87c-0981-4424-8609-2865bbf8665f" xlink:href="sibn-20251231.xsd#sibn_ConstructionInProgressSoftwareCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f85a34d6-08a2-413b-9439-13e0421f1c48" xlink:to="loc_sibn_ConstructionInProgressSoftwareCostsMember_82bff87c-0981-4424-8609-2865bbf8665f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryFinishedGoods_ceba21b6-312b-4383-affa-5df1dbe719cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryFinishedGoods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:to="loc_us-gaap_InventoryFinishedGoods_ceba21b6-312b-4383-affa-5df1dbe719cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryWorkInProcess_9eeb3372-5ed4-44a6-8c46-f39d2ae2ddb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InventoryWorkInProcess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:to="loc_us-gaap_InventoryWorkInProcess_9eeb3372-5ed4-44a6-8c46-f39d2ae2ddb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_68b41d6f-97a5-4b2b-8ace-c1d61375ae0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_68b41d6f-97a5-4b2b-8ace-c1d61375ae0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_c9702d0a-e978-4d21-95ef-e1dc8a6a423d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_acb1de7a-a2bf-4215-9c78-530bf6e76c58" xlink:to="loc_us-gaap_Depreciation_c9702d0a-e978-4d21-95ef-e1dc8a6a423d" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/BalanceSheetComponentsPropertyandEquipmentNetDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#BalanceSheetComponentsPropertyandEquipmentNetDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/BalanceSheetComponentsPropertyandEquipmentNetDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d4f90bb4-ff54-4384-8abb-bf4920a74146" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_36c92309-0722-46a6-9752-90e2040d0f28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d4f90bb4-ff54-4384-8abb-bf4920a74146" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_36c92309-0722-46a6-9752-90e2040d0f28" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6597646d-854b-4032-81b5-a0586ef12419" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_36c92309-0722-46a6-9752-90e2040d0f28" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6597646d-854b-4032-81b5-a0586ef12419" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6597646d-854b-4032-81b5-a0586ef12419_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6597646d-854b-4032-81b5-a0586ef12419" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_6597646d-854b-4032-81b5-a0586ef12419_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_6597646d-854b-4032-81b5-a0586ef12419" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_InstrumentTraysMember_7fc91ecc-3f65-4c51-8b3f-8ec8765d2ff9" xlink:href="sibn-20251231.xsd#sibn_InstrumentTraysMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_sibn_InstrumentTraysMember_7fc91ecc-3f65-4c51-8b3f-8ec8765d2ff9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_9eb0fb02-3dff-420c-af31-0cff9eae979e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_9eb0fb02-3dff-420c-af31-0cff9eae979e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_5f423660-c75e-4fae-aef9-b7d33727860b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_us-gaap_ConstructionInProgressMember_5f423660-c75e-4fae-aef9-b7d33727860b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ComputerAndOfficeEquipmentMember_570f13b8-d28a-4952-8f1f-0114689c0af2" xlink:href="sibn-20251231.xsd#sibn_ComputerAndOfficeEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_sibn_ComputerAndOfficeEquipmentMember_570f13b8-d28a-4952-8f1f-0114689c0af2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_f200c8b8-132a-4c5c-bd6a-d5d41452c86f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_f200c8b8-132a-4c5c-bd6a-d5d41452c86f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_4d9e2852-04af-4b7a-a2a6-297de4f57c31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_32d67298-e43f-45a9-90b4-5af13c3db710" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_4d9e2852-04af-4b7a-a2a6-297de4f57c31" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_084eb079-459e-41ad-9a9b-bf7c2154e292" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d4f90bb4-ff54-4384-8abb-bf4920a74146" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_084eb079-459e-41ad-9a9b-bf7c2154e292" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_8145de48-acb2-4b31-be3a-a55364274df3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d4f90bb4-ff54-4384-8abb-bf4920a74146" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_8145de48-acb2-4b31-be3a-a55364274df3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_24f18bd3-2407-40ce-bd07-f026ea91dc2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_d4f90bb4-ff54-4384-8abb-bf4920a74146" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_24f18bd3-2407-40ce-bd07-f026ea91dc2e" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#CommitmentsandContingenciesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/CommitmentsandContingenciesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCommitmentsTable_c295db33-6ade-491e-b9d6-d0c2f402ed2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCommitmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_OtherCommitmentsTable_c295db33-6ade-491e-b9d6-d0c2f402ed2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f0b3ea06-b95c-4cf3-986f-27229cddb5c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OtherCommitmentsTable_c295db33-6ade-491e-b9d6-d0c2f402ed2e" xlink:to="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f0b3ea06-b95c-4cf3-986f-27229cddb5c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_f0b3ea06-b95c-4cf3-986f-27229cddb5c1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f0b3ea06-b95c-4cf3-986f-27229cddb5c1" xlink:to="loc_us-gaap_LossContingencyNatureDomain_f0b3ea06-b95c-4cf3-986f-27229cddb5c1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyNatureDomain_190b9ad7-3ba6-40b5-b5f8-8594c304a66d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyNatureDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LossContingenciesByNatureOfContingencyAxis_f0b3ea06-b95c-4cf3-986f-27229cddb5c1" xlink:to="loc_us-gaap_LossContingencyNatureDomain_190b9ad7-3ba6-40b5-b5f8-8594c304a66d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndemnificationGuaranteeMember_de5b93b1-ac7b-4eda-a5c3-2d162a173199" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndemnificationGuaranteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingencyNatureDomain_190b9ad7-3ba6-40b5-b5f8-8594c304a66d" xlink:to="loc_us-gaap_IndemnificationGuaranteeMember_de5b93b1-ac7b-4eda-a5c3-2d162a173199" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeaseRenewalTerm_5fede739-e5a8-4cf1-9b44-8c903653bf34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LessorOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_LessorOperatingLeaseRenewalTerm_5fede739-e5a8-4cf1-9b44-8c903653bf34" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_a0da0ea1-1e60-4182-951e-5542067222f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceSheetAmount_a0da0ea1-1e60-4182-951e-5542067222f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PurchaseObligation_d895bc6e-afbd-4919-b3a5-78734b948728" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PurchaseObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_PurchaseObligation_d895bc6e-afbd-4919-b3a5-78734b948728" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementExpense_6bf24a49-5f9c-4062-89b8-5ae98ca6754b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_LitigationSettlementExpense_6bf24a49-5f9c-4062-89b8-5ae98ca6754b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationReserve_2e4465c1-f7b8-4be7-b8ec-e8de3b177282" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OtherCommitmentsLineItems_1b03bed8-a301-4307-8e3e-1bf607a67b85" xlink:to="loc_us-gaap_LitigationReserve_2e4465c1-f7b8-4be7-b8ec-e8de3b177282" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/BorrowingsNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#BorrowingsNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/BorrowingsNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_0e008ef7-5d2b-4a41-9e67-93009cb3237f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_DebtInstrumentTable_0e008ef7-5d2b-4a41-9e67-93009cb3237f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_1a9b5432-fd09-4610-8af0-ed137c2433d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0e008ef7-5d2b-4a41-9e67-93009cb3237f" xlink:to="loc_us-gaap_DebtInstrumentAxis_1a9b5432-fd09-4610-8af0-ed137c2433d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_1a9b5432-fd09-4610-8af0-ed137c2433d5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_1a9b5432-fd09-4610-8af0-ed137c2433d5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_1a9b5432-fd09-4610-8af0-ed137c2433d5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_1a9b5432-fd09-4610-8af0-ed137c2433d5" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_SVBTermLoanMember_baad4de1-f521-4b65-9dc1-ccb3fedec88a" xlink:href="sibn-20251231.xsd#sibn_SVBTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:to="loc_sibn_SVBTermLoanMember_baad4de1-f521-4b65-9dc1-ccb3fedec88a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_FirstCitizensTermLoanMember_7036dd42-86e5-4b2c-9c33-3b97e75f7cd4" xlink:href="sibn-20251231.xsd#sibn_FirstCitizensTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:to="loc_sibn_FirstCitizensTermLoanMember_7036dd42-86e5-4b2c-9c33-3b97e75f7cd4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ThirdAmendmentTermLoanMember_d02c1023-8a67-4063-ac12-845c4ca9eb5c" xlink:href="sibn-20251231.xsd#sibn_ThirdAmendmentTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:to="loc_sibn_ThirdAmendmentTermLoanMember_d02c1023-8a67-4063-ac12-845c4ca9eb5c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_FirstAmendmentTermLoanMember_8bddddd1-ac3c-4934-9f3d-1ca9be3f8b9c" xlink:href="sibn-20251231.xsd#sibn_FirstAmendmentTermLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_d46454cd-d3bf-43d4-9e0e-33d16455833a" xlink:to="loc_sibn_FirstAmendmentTermLoanMember_8bddddd1-ac3c-4934-9f3d-1ca9be3f8b9c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_85d0e280-78dc-4143-9202-014336db01e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0e008ef7-5d2b-4a41-9e67-93009cb3237f" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_85d0e280-78dc-4143-9202-014336db01e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_85d0e280-78dc-4143-9202-014336db01e0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_85d0e280-78dc-4143-9202-014336db01e0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_85d0e280-78dc-4143-9202-014336db01e0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_94e7ce2f-f6f1-4467-912f-cbfed8cba49d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_85d0e280-78dc-4143-9202-014336db01e0" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_94e7ce2f-f6f1-4467-912f-cbfed8cba49d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_6fe36e63-cf9a-4310-afa8-1621f431f8ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_94e7ce2f-f6f1-4467-912f-cbfed8cba49d" xlink:to="loc_us-gaap_SecuredDebtMember_6fe36e63-cf9a-4310-afa8-1621f431f8ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_f55549d8-7cbc-4155-9d9f-38ed689dd7fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_94e7ce2f-f6f1-4467-912f-cbfed8cba49d" xlink:to="loc_us-gaap_LineOfCreditMember_f55549d8-7cbc-4155-9d9f-38ed689dd7fb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_d47c2594-cfda-44e4-9c47-2eaee215c9ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_0e008ef7-5d2b-4a41-9e67-93009cb3237f" xlink:to="loc_us-gaap_CreditFacilityAxis_d47c2594-cfda-44e4-9c47-2eaee215c9ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_d47c2594-cfda-44e4-9c47-2eaee215c9ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_d47c2594-cfda-44e4-9c47-2eaee215c9ff" xlink:to="loc_us-gaap_CreditFacilityDomain_d47c2594-cfda-44e4-9c47-2eaee215c9ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_2f159ba1-b86b-4139-b04d-2a8c2fe7cacc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_d47c2594-cfda-44e4-9c47-2eaee215c9ff" xlink:to="loc_us-gaap_CreditFacilityDomain_2f159ba1-b86b-4139-b04d-2a8c2fe7cacc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_368d07c7-e6d7-4068-8630-ed1c9bb100ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_2f159ba1-b86b-4139-b04d-2a8c2fe7cacc" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_368d07c7-e6d7-4068-8630-ed1c9bb100ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_76fffa01-0a1a-404d-8ffe-c32f02e48219" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_76fffa01-0a1a-404d-8ffe-c32f02e48219" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfSecuredDebt_6407e9b8-e08f-4a70-afa6-400e8d570312" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromRepaymentsOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfSecuredDebt_6407e9b8-e08f-4a70-afa6-400e8d570312" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_f92a8134-86c6-4fc0-a278-027cce47e8c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_f92a8134-86c6-4fc0-a278-027cce47e8c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65004e19-8692-47a9-a3f1-1b701fb38255" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_65004e19-8692-47a9-a3f1-1b701fb38255" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchaseAmount_4f1ef44e-ef90-4682-aa1c-1f6396d47b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentRepurchaseAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_DebtInstrumentRepurchaseAmount_4f1ef44e-ef90-4682-aa1c-1f6396d47b8f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_DebtInstrumentFinalPaymentFee_019beccf-ab37-7169-8cdf-1664644827e3" xlink:href="sibn-20251231.xsd#sibn_DebtInstrumentFinalPaymentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_sibn_DebtInstrumentFinalPaymentFee_019beccf-ab37-7169-8cdf-1664644827e3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_53f0d237-b745-46ef-baee-4c325f328979" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_53f0d237-b745-46ef-baee-4c325f328979" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_DebtInstrumentPrimeRateAdjustment_d557f381-e0ec-4d35-8100-182d2eb4959a" xlink:href="sibn-20251231.xsd#sibn_DebtInstrumentPrimeRateAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_sibn_DebtInstrumentPrimeRateAdjustment_d557f381-e0ec-4d35-8100-182d2eb4959a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_DebtInstrumentFeeAmountAsPercentageOfAggregatePrincipal_6ab1ff46-fdd6-460e-9d31-42af76bf3d5d" xlink:href="sibn-20251231.xsd#sibn_DebtInstrumentFeeAmountAsPercentageOfAggregatePrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_sibn_DebtInstrumentFeeAmountAsPercentageOfAggregatePrincipal_6ab1ff46-fdd6-460e-9d31-42af76bf3d5d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_DebtInstrumentFeeThresholdPeriodFollowingClosing_ac26d2dd-24cd-49eb-8cdf-2bcc81bede3c" xlink:href="sibn-20251231.xsd#sibn_DebtInstrumentFeeThresholdPeriodFollowingClosing"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_sibn_DebtInstrumentFeeThresholdPeriodFollowingClosing_ac26d2dd-24cd-49eb-8cdf-2bcc81bede3c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_7ab98334-d2e9-4178-b18c-045ee8e78709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateDuringPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_d113af9b-9260-47f7-b80d-9feb099433ab" xlink:to="loc_us-gaap_DebtInstrumentInterestRateDuringPeriod_7ab98334-d2e9-4178-b18c-045ee8e78709" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/WarrantsDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#WarrantsDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/WarrantsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightLineItems_33f41dbf-f43a-4885-8ee1-a96d90a66730" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightTable_08d25be3-1a33-4da4-9e10-88f382c2f7d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_33f41dbf-f43a-4885-8ee1-a96d90a66730" xlink:to="loc_us-gaap_ClassOfWarrantOrRightTable_08d25be3-1a33-4da4-9e10-88f382c2f7d8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_0d0356c1-5326-46f9-833f-65c96ddec25a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ClassOfWarrantOrRightTable_08d25be3-1a33-4da4-9e10-88f382c2f7d8" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_0d0356c1-5326-46f9-833f-65c96ddec25a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_0d0356c1-5326-46f9-833f-65c96ddec25a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_0d0356c1-5326-46f9-833f-65c96ddec25a" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_0d0356c1-5326-46f9-833f-65c96ddec25a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_0d0356c1-5326-46f9-833f-65c96ddec25a" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_WarrantsIssuedMarchFirstTwentySeventeenMember_08a1651d-ef62-45f5-865e-e9b06be4ee82" xlink:href="sibn-20251231.xsd#sibn_WarrantsIssuedMarchFirstTwentySeventeenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:to="loc_sibn_WarrantsIssuedMarchFirstTwentySeventeenMember_08a1651d-ef62-45f5-865e-e9b06be4ee82" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_WarrantsIssuedOctoberTwentiethTwentyFifteenMember_36cefde3-7ce3-4c60-9e36-86317b889285" xlink:href="sibn-20251231.xsd#sibn_WarrantsIssuedOctoberTwentiethTwentyFifteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:to="loc_sibn_WarrantsIssuedOctoberTwentiethTwentyFifteenMember_36cefde3-7ce3-4c60-9e36-86317b889285" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_WarrantsIssuedNovemberNinthTwentyFifteenMember_7059e2ec-eb07-4ffe-8093-e603bb0e8778" xlink:href="sibn-20251231.xsd#sibn_WarrantsIssuedNovemberNinthTwentyFifteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:to="loc_sibn_WarrantsIssuedNovemberNinthTwentyFifteenMember_7059e2ec-eb07-4ffe-8093-e603bb0e8778" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_WarrantsIssuedDecemberTwentySecondTwentySixteenMember_44a2a3b1-cdb9-453f-9cab-dbef63a3fda0" xlink:href="sibn-20251231.xsd#sibn_WarrantsIssuedDecemberTwentySecondTwentySixteenMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_3251aee8-e9b1-4475-b36d-920f6d27329a" xlink:to="loc_sibn_WarrantsIssuedDecemberTwentySecondTwentySixteenMember_44a2a3b1-cdb9-453f-9cab-dbef63a3fda0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants_1b66d88d-904a-4e51-9557-b7669c8984cf" xlink:href="sibn-20251231.xsd#sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_33f41dbf-f43a-4885-8ee1-a96d90a66730" xlink:to="loc_sibn_StockIssuedDuringPeriodSharesExerciseOfWarrants_1b66d88d-904a-4e51-9557-b7669c8984cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:href="sibn-20251231.xsd#sibn_ClassOfWarrantOrRightRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightLineItems_33f41dbf-f43a-4885-8ee1-a96d90a66730" xlink:to="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_79cda7a5-90a2-4eff-93ef-b0258e1a8fb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightOutstanding_79cda7a5-90a2-4eff-93ef-b0258e1a8fb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_bc8f0cbf-546f-4f2f-bf3e-e93b4ff054d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_bc8f0cbf-546f-4f2f-bf3e-e93b4ff054d8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ClassOfWarrantOrRightSharesIssued_2fc12a16-726a-4f46-a765-a512b8df5c73" xlink:href="sibn-20251231.xsd#sibn_ClassOfWarrantOrRightSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:to="loc_sibn_ClassOfWarrantOrRightSharesIssued_2fc12a16-726a-4f46-a765-a512b8df5c73" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ClassOfWarrantOrRightSharesExercised_e12862b2-ae4b-401a-9f1e-79347c3d1519" xlink:href="sibn-20251231.xsd#sibn_ClassOfWarrantOrRightSharesExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:to="loc_sibn_ClassOfWarrantOrRightSharesExercised_e12862b2-ae4b-401a-9f1e-79347c3d1519" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ClassOfWarrantOrRightSharesExpired_14a1ea48-478a-45fd-8ca0-192571d10bae" xlink:href="sibn-20251231.xsd#sibn_ClassOfWarrantOrRightSharesExpired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_sibn_ClassOfWarrantOrRightRollForward_1255fe41-2516-43e4-92e9-668c742b8cc9" xlink:to="loc_sibn_ClassOfWarrantOrRightSharesExpired_14a1ea48-478a-45fd-8ca0-192571d10bae" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightOutstanding_00b82b20-ff25-4def-ad34-8ef5da890f66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_474c7c44-eecf-48de-a248-2c5cde3c0c40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:to="loc_us-gaap_PlanNameAxis_474c7c44-eecf-48de-a248-2c5cde3c0c40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_474c7c44-eecf-48de-a248-2c5cde3c0c40_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_474c7c44-eecf-48de-a248-2c5cde3c0c40" xlink:to="loc_us-gaap_PlanNameDomain_474c7c44-eecf-48de-a248-2c5cde3c0c40_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_135f7858-2427-40b8-8a94-a33e75fc14a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_474c7c44-eecf-48de-a248-2c5cde3c0c40" xlink:to="loc_us-gaap_PlanNameDomain_135f7858-2427-40b8-8a94-a33e75fc14a7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_A2008StockOptionPlanMember_a93335e8-d1c4-4835-a81c-1b627223992d" xlink:href="sibn-20251231.xsd#sibn_A2008StockOptionPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_135f7858-2427-40b8-8a94-a33e75fc14a7" xlink:to="loc_sibn_A2008StockOptionPlanMember_a93335e8-d1c4-4835-a81c-1b627223992d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_A2018EquityIncentivePlanMember_1e87b69a-30ae-424c-a41c-3d2e735245b5" xlink:href="sibn-20251231.xsd#sibn_A2018EquityIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_135f7858-2427-40b8-8a94-a33e75fc14a7" xlink:to="loc_sibn_A2018EquityIncentivePlanMember_1e87b69a-30ae-424c-a41c-3d2e735245b5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_A2018EmployeeStockPurchasePlanMember_822d638e-e726-415a-8014-d13da03519a2" xlink:href="sibn-20251231.xsd#sibn_A2018EmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_135f7858-2427-40b8-8a94-a33e75fc14a7" xlink:to="loc_sibn_A2018EmployeeStockPurchasePlanMember_822d638e-e726-415a-8014-d13da03519a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_134a53cd-8c71-4194-8591-e8cfbd543d85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:to="loc_us-gaap_AwardTypeAxis_134a53cd-8c71-4194-8591-e8cfbd543d85" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_134a53cd-8c71-4194-8591-e8cfbd543d85_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_134a53cd-8c71-4194-8591-e8cfbd543d85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_134a53cd-8c71-4194-8591-e8cfbd543d85_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_134a53cd-8c71-4194-8591-e8cfbd543d85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_471dc8a6-41c2-4dea-adeb-3936bc7717fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:to="loc_us-gaap_EmployeeStockOptionMember_471dc8a6-41c2-4dea-adeb-3936bc7717fc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_IncentiveStockOptionMember_b4c3b6a9-2190-4d06-aabc-8e31add45f2c" xlink:href="sibn-20251231.xsd#sibn_IncentiveStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:to="loc_sibn_IncentiveStockOptionMember_b4c3b6a9-2190-4d06-aabc-8e31add45f2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_NonqualifiedStockOptionMember_86c215da-636d-4a2e-861e-4b8a64ea0542" xlink:href="sibn-20251231.xsd#sibn_NonqualifiedStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:to="loc_sibn_NonqualifiedStockOptionMember_86c215da-636d-4a2e-861e-4b8a64ea0542" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_16ca96ad-798b-4f50-a5c6-ee1fbed57caf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_16ca96ad-798b-4f50-a5c6-ee1fbed57caf" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_d64b3e1b-ccab-4b4a-be5a-adba705704fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ca8a71c7-ae64-497d-a53a-64c9139a3410" xlink:to="loc_us-gaap_PerformanceSharesMember_d64b3e1b-ccab-4b4a-be5a-adba705704fe" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_265bc214-d6d2-459a-8b92-6fa076005279" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:to="loc_srt_RangeAxis_265bc214-d6d2-459a-8b92-6fa076005279" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_265bc214-d6d2-459a-8b92-6fa076005279_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_265bc214-d6d2-459a-8b92-6fa076005279" xlink:to="loc_srt_RangeMember_265bc214-d6d2-459a-8b92-6fa076005279_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_f8fac5ad-4b9c-4b45-b1fa-ade06451b221" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_265bc214-d6d2-459a-8b92-6fa076005279" xlink:to="loc_srt_RangeMember_f8fac5ad-4b9c-4b45-b1fa-ade06451b221" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_c76c8582-9826-460d-ae9f-8f2f62dd4c93" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f8fac5ad-4b9c-4b45-b1fa-ade06451b221" xlink:to="loc_srt_MinimumMember_c76c8582-9826-460d-ae9f-8f2f62dd4c93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_31dcc2a8-cb54-4d18-b246-671587c60608" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_f8fac5ad-4b9c-4b45-b1fa-ade06451b221" xlink:to="loc_srt_MaximumMember_31dcc2a8-cb54-4d18-b246-671587c60608" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019becd1-f85b-725b-87cb-51bc62d6bcc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_b1edbd7c-059c-4d51-bc1a-deb88e114893" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019becd1-f85b-725b-87cb-51bc62d6bcc5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019becd1-f85b-725b-87cb-51bc62d6bcc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019becd1-f85b-725b-87cb-51bc62d6bcc5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019becd1-f85b-725b-87cb-51bc62d6bcc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019becd1-f85b-7b3f-80b9-43b61fc16989" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019becd1-f85b-725b-87cb-51bc62d6bcc5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019becd1-f85b-7b3f-80b9-43b61fc16989" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019becd2-2129-7048-896f-5fa1801a371f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019becd1-f85b-7b3f-80b9-43b61fc16989" xlink:to="loc_us-gaap_SubsequentEventMember_019becd2-2129-7048-896f-5fa1801a371f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_9fd1c674-aae0-453d-a88a-06b2b4683165" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_9fd1c674-aae0-453d-a88a-06b2b4683165" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedAsPercentageOfPriorYearSharesOutstanding_58a4b7a3-6ec9-4a30-ad88-9c961a62cb24" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedAsPercentageOfPriorYearSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardAnnualIncreaseInSharesReservedAsPercentageOfPriorYearSharesOutstanding_58a4b7a3-6ec9-4a30-ad88-9c961a62cb24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_c7f7c429-7fc2-488b-9c72-2598f1463f25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_c7f7c429-7fc2-488b-9c72-2598f1463f25" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_fb6ae0d6-53d0-4549-a794-4613a4647c9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_fb6ae0d6-53d0-4549-a794-4613a4647c9b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOwnershipOfOutstandingSharesThresholdForAlternateTerms_00997cd9-cb6a-4ae8-86b1-3fa96ca0ac58" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOwnershipOfOutstandingSharesThresholdForAlternateTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardPercentageOwnershipOfOutstandingSharesThresholdForAlternateTerms_00997cd9-cb6a-4ae8-86b1-3fa96ca0ac58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValueForIndividualOwningMoreThanTenPercentOfOutstandingShares_f08f2dee-a6d6-4289-a3f0-48564eb20a62" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValueForIndividualOwningMoreThanTenPercentOfOutstandingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValueForIndividualOwningMoreThanTenPercentOfOutstandingShares_f08f2dee-a6d6-4289-a3f0-48564eb20a62" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValue_6201362c-39cf-456c-915b-53ad94a8e36f" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisePriceAsPercentOfFairMarketValue_6201362c-39cf-456c-915b-53ad94a8e36f" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_1ad1feb8-77e0-4335-8537-4b82fc14811f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_1ad1feb8-77e0-4335-8537-4b82fc14811f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodForIndividualOwningMoreThanTenPercentOfOutstandingShares_96e9f02b-0cd9-4bb1-8bab-b8de713bbc47" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodForIndividualOwningMoreThanTenPercentOfOutstandingShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardExpirationPeriodForIndividualOwningMoreThanTenPercentOfOutstandingShares_96e9f02b-0cd9-4bb1-8bab-b8de713bbc47" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_461e6b4a-8b1b-4e52-8e2a-82b3205d8afa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_461e6b4a-8b1b-4e52-8e2a-82b3205d8afa" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_80d1a855-d4c9-4de7-b3de-94832a26f1f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisesInPeriodTotalIntrinsicValue_80d1a855-d4c9-4de7-b3de-94832a26f1f6" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_873490c6-f602-4a81-83a5-981810cb0f1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_873490c6-f602-4a81-83a5-981810cb0f1d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019c6e8a-a736-744e-8fff-eac35e16817a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_019c6e8a-a736-744e-8fff-eac35e16817a" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7a9d126d-20e0-414a-b843-6eb58b3e31c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_7a9d126d-20e0-414a-b843-6eb58b3e31c2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_f490e2e0-df33-406b-a467-8a7ee797c8fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_f490e2e0-df33-406b-a467-8a7ee797c8fb" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_62f8c3dc-2d88-4b0e-88ff-30c3299d9707" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_62f8c3dc-2d88-4b0e-88ff-30c3299d9707" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriodInterval_719bf49a-6485-4961-8c0a-5f8d3ef848a8" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriodInterval"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardOfferingPeriodInterval_719bf49a-6485-4961-8c0a-5f8d3ef848a8" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_08650536-e5c9-4cbd-8eef-ef39de17cf0a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_08650536-e5c9-4cbd-8eef-ef39de17cf0a" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_56db1575-d403-47d2-8a5e-aa63f2960b03" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueEmployeeStockPurchasePlan_56db1575-d403-47d2-8a5e-aa63f2960b03" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherEmployeeRelatedLiabilitiesCurrent_16508035-a459-4f8c-8fbc-cdb1f21cdfa1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherEmployeeRelatedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_OtherEmployeeRelatedLiabilitiesCurrent_16508035-a459-4f8c-8fbc-cdb1f21cdfa1" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_15b839de-b1a5-4621-a803-20074f0b99c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_5eb84799-b0c8-46ed-9bb3-b8f0491cbb2c" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_15b839de-b1a5-4621-a803-20074f0b99c0" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationOutstandingOptionsandExercisableOptionsInformationbyRangeofExercisePricesDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationOutstandingOptionsandExercisableOptionsInformationbyRangeofExercisePricesDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationOutstandingOptionsandExercisableOptionsInformationbyRangeofExercisePricesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_487a135a-711a-49d9-831f-43bc17650376" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_487a135a-711a-49d9-831f-43bc17650376" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_2f900bf9-85a8-4e79-ab81-e431d6abd87e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_487a135a-711a-49d9-831f-43bc17650376" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_2f900bf9-85a8-4e79-ab81-e431d6abd87e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_2f900bf9-85a8-4e79-ab81-e431d6abd87e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_2f900bf9-85a8-4e79-ab81-e431d6abd87e" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_2f900bf9-85a8-4e79-ab81-e431d6abd87e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_2f900bf9-85a8-4e79-ab81-e431d6abd87e" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_OptionsTrancheOneMember_fdceb677-f105-4400-8fde-5492a55f1493" xlink:href="sibn-20251231.xsd#sibn_OptionsTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:to="loc_sibn_OptionsTrancheOneMember_fdceb677-f105-4400-8fde-5492a55f1493" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_OptionsTrancheTwoMember_b2d2c69d-8e8f-4a02-93c7-62f28acdd825" xlink:href="sibn-20251231.xsd#sibn_OptionsTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:to="loc_sibn_OptionsTrancheTwoMember_b2d2c69d-8e8f-4a02-93c7-62f28acdd825" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_OptionsTrancheThreeMember_2619e606-7cdf-4de7-be0d-2294efa5a076" xlink:href="sibn-20251231.xsd#sibn_OptionsTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:to="loc_sibn_OptionsTrancheThreeMember_2619e606-7cdf-4de7-be0d-2294efa5a076" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_OptionsTrancheFourMember_07b58edb-6406-4c55-8fe5-394f362cf769" xlink:href="sibn-20251231.xsd#sibn_OptionsTrancheFourMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:to="loc_sibn_OptionsTrancheFourMember_07b58edb-6406-4c55-8fe5-394f362cf769" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_OptionsTrancheFiveMember_bc7ee1c0-4d7e-4aee-bb6d-4a4472e5f40b" xlink:href="sibn-20251231.xsd#sibn_OptionsTrancheFiveMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_78c47a6e-3f00-4ea8-b579-ac4222623d27" xlink:to="loc_sibn_OptionsTrancheFiveMember_bc7ee1c0-4d7e-4aee-bb6d-4a4472e5f40b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_9bd1308f-a96d-4c61-b335-678094b85a58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_9bd1308f-a96d-4c61-b335-678094b85a58" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_1896d910-becd-43e8-9250-6adb8843b292" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_1896d910-becd-43e8-9250-6adb8843b292" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_1ce31ad7-30c6-4a2e-9582-7a80e98a83bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_1ce31ad7-30c6-4a2e-9582-7a80e98a83bc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_8880d5db-a370-433c-85c6-43147549934e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_8880d5db-a370-433c-85c6-43147549934e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_21802153-dfdb-44e4-9a08-fd0d5f9c4107" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_21802153-dfdb-44e4-9a08-fd0d5f9c4107" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_c0b64b33-0894-4eca-b026-450152f5edcb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableNumber_c0b64b33-0894-4eca-b026-450152f5edcb" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_1a399e08-7044-43be-ba67-b0a72835d503" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_a543ee02-06e3-48e7-9396-31e530d733e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsVestedAndExpectedToVestExercisableWeightedAverageExercisePrice_1a399e08-7044-43be-ba67-b0a72835d503" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationValuationAssumptionsforStockOptionsDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationValuationAssumptionsforStockOptionsDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationValuationAssumptionsforStockOptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a2ad279f-b4ad-42b2-b133-de9b528e9506" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a2ad279f-b4ad-42b2-b133-de9b528e9506" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_869470a6-3e45-47f7-ba1d-26ea1f238c32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a2ad279f-b4ad-42b2-b133-de9b528e9506" xlink:to="loc_us-gaap_AwardTypeAxis_869470a6-3e45-47f7-ba1d-26ea1f238c32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_869470a6-3e45-47f7-ba1d-26ea1f238c32_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_869470a6-3e45-47f7-ba1d-26ea1f238c32" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_869470a6-3e45-47f7-ba1d-26ea1f238c32_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b71854d1-4511-4696-ba46-8fa2043475c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_869470a6-3e45-47f7-ba1d-26ea1f238c32" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b71854d1-4511-4696-ba46-8fa2043475c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_070b6852-ab62-4cfd-afde-e29497b23547" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b71854d1-4511-4696-ba46-8fa2043475c8" xlink:to="loc_us-gaap_PerformanceSharesMember_070b6852-ab62-4cfd-afde-e29497b23547" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e018975f-4c88-4dc0-a0e0-54563b57373a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_a2ad279f-b4ad-42b2-b133-de9b528e9506" xlink:to="loc_srt_RangeAxis_e018975f-4c88-4dc0-a0e0-54563b57373a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e018975f-4c88-4dc0-a0e0-54563b57373a_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e018975f-4c88-4dc0-a0e0-54563b57373a" xlink:to="loc_srt_RangeMember_e018975f-4c88-4dc0-a0e0-54563b57373a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e1bc6dd9-05bd-4e82-a949-d32f2313721e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e018975f-4c88-4dc0-a0e0-54563b57373a" xlink:to="loc_srt_RangeMember_e1bc6dd9-05bd-4e82-a949-d32f2313721e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_d21c6bb2-e995-4822-999f-0d00d2b51223" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e1bc6dd9-05bd-4e82-a949-d32f2313721e" xlink:to="loc_srt_MinimumMember_d21c6bb2-e995-4822-999f-0d00d2b51223" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_eaef263e-d604-4d54-9424-0399b9f76972" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e1bc6dd9-05bd-4e82-a949-d32f2313721e" xlink:to="loc_srt_MaximumMember_eaef263e-d604-4d54-9424-0399b9f76972" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_b9660cdc-7b2f-4c87-92ea-e97e63e18a01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_b9660cdc-7b2f-4c87-92ea-e97e63e18a01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_158066e1-a1d1-4c34-9e1c-e3277195b66c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_158066e1-a1d1-4c34-9e1c-e3277195b66c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMinimum_2b6845ae-16b9-4c71-b690-9a07111dd07b" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMinimum_2b6845ae-16b9-4c71-b690-9a07111dd07b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMaximum_f971182b-01b6-4915-a0d0-43b42eb2f777" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRatePeerCompaniesMaximum_f971182b-01b6-4915-a0d0-43b42eb2f777" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMinimum_1f63f8e0-4069-43cf-a6f3-a049fbc43524" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMinimum_1f63f8e0-4069-43cf-a6f3-a049fbc43524" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMaximum_432d1e6f-9397-421e-8611-56e890b53212" xlink:href="sibn-20251231.xsd#sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_sibn_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsCorrelationCoefficientOfPeerCompaniesMaximum_432d1e6f-9397-421e-8611-56e890b53212" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_34f4cf59-ceeb-4e32-999e-9465fed05562" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_34f4cf59-ceeb-4e32-999e-9465fed05562" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_f6b3f2d3-e60e-45ec-bbf3-12977fd853f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_f6b3f2d3-e60e-45ec-bbf3-12977fd853f0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_0aff331a-b7bc-48da-bf4c-20ce0de2f5c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_cf10a4f5-defa-4f47-88d1-c30210ee8a85" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_0aff331a-b7bc-48da-bf4c-20ce0de2f5c2" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationRestrictedStockUnitActivityDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationRestrictedStockUnitActivityDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationRestrictedStockUnitActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_68b8b97a-4922-464f-9a16-8d0565b1fcf3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d320a06b-5af6-4205-899c-134adc0f150b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_68b8b97a-4922-464f-9a16-8d0565b1fcf3" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d320a06b-5af6-4205-899c-134adc0f150b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_b8ee94f2-891e-4629-915a-873332fbb97f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_d320a06b-5af6-4205-899c-134adc0f150b" xlink:to="loc_us-gaap_AwardTypeAxis_b8ee94f2-891e-4629-915a-873332fbb97f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b8ee94f2-891e-4629-915a-873332fbb97f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_b8ee94f2-891e-4629-915a-873332fbb97f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_b8ee94f2-891e-4629-915a-873332fbb97f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec66a5b7-1f26-4950-a51a-796366289d5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_b8ee94f2-891e-4629-915a-873332fbb97f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec66a5b7-1f26-4950-a51a-796366289d5f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_003ee3eb-6bc0-4f55-9b7f-de5331fea5c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec66a5b7-1f26-4950-a51a-796366289d5f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_003ee3eb-6bc0-4f55-9b7f-de5331fea5c5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_5e18574f-6a52-4ef9-9acd-b1840d3b518b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_ec66a5b7-1f26-4950-a51a-796366289d5f" xlink:to="loc_us-gaap_PerformanceSharesMember_5e18574f-6a52-4ef9-9acd-b1840d3b518b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_68b8b97a-4922-464f-9a16-8d0565b1fcf3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_d957fa6e-2e72-4138-b4db-8f5285818577" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_d957fa6e-2e72-4138-b4db-8f5285818577" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_63d2a608-b98d-4e81-b57b-0e233d7e3611" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_63d2a608-b98d-4e81-b57b-0e233d7e3611" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_dd454ec5-8c8e-41b6-8cd7-700a0493fcd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_dd454ec5-8c8e-41b6-8cd7-700a0493fcd3" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_33f4d85d-a3f0-42b7-8672-ac109ba88715" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_39af58cd-18f9-4fa6-8fa5-2335b0f825d9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_33f4d85d-a3f0-42b7-8672-ac109ba88715" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_357d1ca8-9ab9-4d45-a026-187543311524" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_68b8b97a-4922-464f-9a16-8d0565b1fcf3" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a09d55d1-f21d-4a02-a9c7-9cd45efc0349" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a09d55d1-f21d-4a02-a9c7-9cd45efc0349" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_aa7181a8-14e7-444c-9297-c68be1888c40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_aa7181a8-14e7-444c-9297-c68be1888c40" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_239d6ede-adaf-4ed6-80f4-4f12705a3c62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_239d6ede-adaf-4ed6-80f4-4f12705a3c62" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_4978a429-a5cd-4de8-95b9-c4a26dcb9cb4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_04137b41-e643-4f19-a85f-b9e00d333050" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_4978a429-a5cd-4de8-95b9-c4a26dcb9cb4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_a5d3439b-873c-4caf-a48c-37199d6befe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationValuationAssumptionsforESPPPurchaseRightsDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationValuationAssumptionsforESPPPurchaseRightsDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationValuationAssumptionsforESPPPurchaseRightsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_3e46b3d1-69b4-4236-aaa6-82f525ca6656" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_3e46b3d1-69b4-4236-aaa6-82f525ca6656" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_6e7a9702-474e-45bb-952c-7c41e7631695" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_3e46b3d1-69b4-4236-aaa6-82f525ca6656" xlink:to="loc_us-gaap_AwardTypeAxis_6e7a9702-474e-45bb-952c-7c41e7631695" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e7a9702-474e-45bb-952c-7c41e7631695_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_6e7a9702-474e-45bb-952c-7c41e7631695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_6e7a9702-474e-45bb-952c-7c41e7631695_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9dc1c9-aefa-4a5a-af03-97d84da2d709" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_6e7a9702-474e-45bb-952c-7c41e7631695" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9dc1c9-aefa-4a5a-af03-97d84da2d709" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_ESPPPurchaseRightsMember_6c248182-f0c3-4cb7-9306-90fde02682d3" xlink:href="sibn-20251231.xsd#sibn_ESPPPurchaseRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_af9dc1c9-aefa-4a5a-af03-97d84da2d709" xlink:to="loc_sibn_ESPPPurchaseRightsMember_6c248182-f0c3-4cb7-9306-90fde02682d3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_92f73769-09b2-4d9c-b934-d3364a40373b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_92f73769-09b2-4d9c-b934-d3364a40373b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_df9b4a9c-c9ad-4206-b35a-e0658c226d2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMinimum_df9b4a9c-c9ad-4206-b35a-e0658c226d2b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_0c483dc1-43bd-4ccf-b344-f0a7daa51abb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRateMaximum_0c483dc1-43bd-4ccf-b344-f0a7daa51abb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_230325b8-397e-48d3-8d64-c59af9eb32ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMinimum_230325b8-397e-48d3-8d64-c59af9eb32ba" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_c69ce829-21dd-41c1-b0e6-21d2f673d088" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRateMaximum_c69ce829-21dd-41c1-b0e6-21d2f673d088" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e4ba8eb2-f53a-42e1-be3e-b4bbb218aa8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_78013323-4bcc-41b7-baf6-21b91371d9fa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_e4ba8eb2-f53a-42e1-be3e-b4bbb218aa8c" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/StockBasedCompensationStockBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#StockBasedCompensationStockBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/StockBasedCompensationStockBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_dcc364b2-0e00-419e-9e78-80e2a92129fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58e86c31-7053-4dd5-b11b-b3eb565b4d47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_dcc364b2-0e00-419e-9e78-80e2a92129fe" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58e86c31-7053-4dd5-b11b-b3eb565b4d47" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_d8db659a-567e-487b-8032-d3128c93eac5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_58e86c31-7053-4dd5-b11b-b3eb565b4d47" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_d8db659a-567e-487b-8032-d3128c93eac5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_d8db659a-567e-487b-8032-d3128c93eac5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d8db659a-567e-487b-8032-d3128c93eac5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_d8db659a-567e-487b-8032-d3128c93eac5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_d8db659a-567e-487b-8032-d3128c93eac5" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_7410b683-f02a-45eb-8990-407d759ad55d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:to="loc_us-gaap_CostOfSalesMember_7410b683-f02a-45eb-8990-407d759ad55d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingAndMarketingExpenseMember_701ddb1f-78bb-478a-9afa-bba085e85fce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingAndMarketingExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:to="loc_us-gaap_SellingAndMarketingExpenseMember_701ddb1f-78bb-478a-9afa-bba085e85fce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_9f77abfc-c9aa-4e1a-b20f-9a1677fed38f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_9f77abfc-c9aa-4e1a-b20f-9a1677fed38f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a9880cd2-e322-43fa-82a1-1336bb36f01b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeneralAndAdministrativeExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_cff22ed8-6edf-47dc-8d05-bf1944e532a6" xlink:to="loc_us-gaap_GeneralAndAdministrativeExpenseMember_a9880cd2-e322-43fa-82a1-1336bb36f01b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_27737587-de84-43fd-abab-fe6ee68d2c62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_dcc364b2-0e00-419e-9e78-80e2a92129fe" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_27737587-de84-43fd-abab-fe6ee68d2c62" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/EmployeeBenefitPlanDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#EmployeeBenefitPlanDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/EmployeeBenefitPlanDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_6ed53951-94d4-411a-8694-63cf496a8c4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanTable_4a126a4f-07a3-4fb2-aee6-af9216de87b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_6ed53951-94d4-411a-8694-63cf496a8c4c" xlink:to="loc_us-gaap_DefinedContributionPlanTable_4a126a4f-07a3-4fb2-aee6-af9216de87b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameAxis_37db1437-45d4-4108-ab09-34b9c423226d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_4a126a4f-07a3-4fb2-aee6-af9216de87b4" xlink:to="loc_us-gaap_RetirementPlanNameAxis_37db1437-45d4-4108-ab09-34b9c423226d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameDomain_37db1437-45d4-4108-ab09-34b9c423226d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RetirementPlanNameAxis_37db1437-45d4-4108-ab09-34b9c423226d" xlink:to="loc_us-gaap_RetirementPlanNameDomain_37db1437-45d4-4108-ab09-34b9c423226d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetirementPlanNameDomain_f034e4c7-c970-4a5a-b071-9f4759e63c60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetirementPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RetirementPlanNameAxis_37db1437-45d4-4108-ab09-34b9c423226d" xlink:to="loc_us-gaap_RetirementPlanNameDomain_f034e4c7-c970-4a5a-b071-9f4759e63c60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_Company401KPlanMember_064706af-c094-4da4-948a-125ae481ade9" xlink:href="sibn-20251231.xsd#sibn_Company401KPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RetirementPlanNameDomain_f034e4c7-c970-4a5a-b071-9f4759e63c60" xlink:to="loc_sibn_Company401KPlanMember_064706af-c094-4da4-948a-125ae481ade9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_3d166704-7a28-46b0-aeb3-23cf689f09d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_6ed53951-94d4-411a-8694-63cf496a8c4c" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_3d166704-7a28-46b0-aeb3-23cf689f09d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_DefinedContributionPlanEmployerMatchingContributionMaximumAmountPerEmployee_019bfb4f-c287-7588-9978-af321d9de39e" xlink:href="sibn-20251231.xsd#sibn_DefinedContributionPlanEmployerMatchingContributionMaximumAmountPerEmployee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_6ed53951-94d4-411a-8694-63cf496a8c4c" xlink:to="loc_sibn_DefinedContributionPlanEmployerMatchingContributionMaximumAmountPerEmployee_019bfb4f-c287-7588-9978-af321d9de39e" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/NetLossPerShareofCommonStockAntidilutiveCommonStockEquivalentsExcludedfromComputationofEarningsPerShareDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#NetLossPerShareofCommonStockAntidilutiveCommonStockEquivalentsExcludedfromComputationofEarningsPerShareDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/NetLossPerShareofCommonStockAntidilutiveCommonStockEquivalentsExcludedfromComputationofEarningsPerShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1e025e96-3506-494c-ad60-974e2b1479e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_e9e8d427-e2ec-4826-b24e-8a13df576ad1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1e025e96-3506-494c-ad60-974e2b1479e1" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_e9e8d427-e2ec-4826-b24e-8a13df576ad1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_9924bed2-9987-4b80-a524-fb0f550188d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_e9e8d427-e2ec-4826-b24e-8a13df576ad1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_9924bed2-9987-4b80-a524-fb0f550188d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9924bed2-9987-4b80-a524-fb0f550188d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_9924bed2-9987-4b80-a524-fb0f550188d3" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_9924bed2-9987-4b80-a524-fb0f550188d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_9924bed2-9987-4b80-a524-fb0f550188d3" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_6dd58af7-ff68-498b-b0bf-9cde266baca1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:to="loc_us-gaap_EmployeeStockOptionMember_6dd58af7-ff68-498b-b0bf-9cde266baca1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_4f3e68df-ee0c-4fbf-880b-3f606f06cf2c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_4f3e68df-ee0c-4fbf-880b-3f606f06cf2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_EmployeeStockPurchasePlanSharesMember_a0c1ff39-28df-4e30-9455-cbef23595793" xlink:href="sibn-20251231.xsd#sibn_EmployeeStockPurchasePlanSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:to="loc_sibn_EmployeeStockPurchasePlanSharesMember_a0c1ff39-28df-4e30-9455-cbef23595793" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_CommonStockWarrantsMember_7bdc75b6-a513-48ae-8413-17c1a0a084f0" xlink:href="sibn-20251231.xsd#sibn_CommonStockWarrantsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_daf9db48-e4a4-42ef-8108-3224898ffeb6" xlink:to="loc_sibn_CommonStockWarrantsMember_7bdc75b6-a513-48ae-8413-17c1a0a084f0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_0b231e4d-0dfa-42fa-a947-211f4ec9236e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_1e025e96-3506-494c-ad60-974e2b1479e1" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_0b231e4d-0dfa-42fa-a947-211f4ec9236e" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/IncomeTaxesNarrativeDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#IncomeTaxesNarrativeDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/IncomeTaxesNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_019c2742-13b5-7fe3-8875-07817cea975e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_019c2742-13b5-75ab-aeeb-896afbfb50e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019c2742-13b5-7fe3-8875-07817cea975e" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_019c2742-13b5-75ab-aeeb-896afbfb50e2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019c2742-13b5-727f-8f28-c189bf3f0019" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_019c2742-13b5-75ab-aeeb-896afbfb50e2" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019c2742-13b5-727f-8f28-c189bf3f0019" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-727f-8f28-c189bf3f0019_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c2742-13b5-727f-8f28-c189bf3f0019" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-727f-8f28-c189bf3f0019_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-7ebc-b639-1fe7689f5749" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019c2742-13b5-727f-8f28-c189bf3f0019" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-7ebc-b639-1fe7689f5749" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019c2742-13b5-7892-b63f-3e3fa9e9ad59" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-7ebc-b639-1fe7689f5749" xlink:to="loc_us-gaap_DomesticCountryMember_019c2742-13b5-7892-b63f-3e3fa9e9ad59" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019c2742-13b5-7ab7-a0f4-fd89030d4c12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019c2742-13b5-7ebc-b639-1fe7689f5749" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019c2742-13b5-7ab7-a0f4-fd89030d4c12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019c2ef1-e1a4-713f-a08e-19d947567a88" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StateAndLocalJurisdictionMember_019c2742-13b5-7ab7-a0f4-fd89030d4c12" xlink:to="loc_stpr_CA_019c2ef1-e1a4-713f-a08e-19d947567a88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_019c2742-13b5-705f-ad67-f7d712f132ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_019c2742-13b5-75ab-aeeb-896afbfb50e2" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_019c2742-13b5-705f-ad67-f7d712f132ee" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019c2742-13b5-705f-ad67-f7d712f132ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019c2742-13b5-705f-ad67-f7d712f132ee" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019c2742-13b5-705f-ad67-f7d712f132ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_019c2742-13b5-71dc-8e53-eed50e6f9abd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_019c2742-13b5-705f-ad67-f7d712f132ee" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_019c2742-13b5-71dc-8e53-eed50e6f9abd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchMember_019c2742-13b5-7a5a-913d-4d75c5d08e28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_019c2742-13b5-71dc-8e53-eed50e6f9abd" xlink:to="loc_us-gaap_ResearchMember_019c2742-13b5-7a5a-913d-4d75c5d08e28" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwards_019c2ef0-dad5-738f-9fc5-69f8ec569fbb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwards"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019c2742-13b5-7fe3-8875-07817cea975e" xlink:to="loc_us-gaap_OperatingLossCarryforwards_019c2ef0-dad5-738f-9fc5-69f8ec569fbb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAmount_019c2742-13b5-7b57-9d5c-f5643bd854e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_019c2742-13b5-7fe3-8875-07817cea975e" xlink:to="loc_us-gaap_TaxCreditCarryforwardAmount_019c2742-13b5-7b57-9d5c-f5643bd854e8" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://si-bone.com/role/SubsequentEventsDetails" xlink:type="simple" xlink:href="sibn-20251231.xsd#SubsequentEventsDetails"/>
  <link:definitionLink xlink:role="http://si-bone.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventLineItems_019c64aa-d3d8-7820-bd2c-7640b652d907" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTable_019c64aa-d3d8-7f99-97b8-3fed99b26c4b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_019c64aa-d3d8-7820-bd2c-7640b652d907" xlink:to="loc_us-gaap_SubsequentEventTable_019c64aa-d3d8-7f99-97b8-3fed99b26c4b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_019c64aa-d3d8-71ce-b698-9ae334b5601c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_019c64aa-d3d8-7f99-97b8-3fed99b26c4b" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_019c64aa-d3d8-71ce-b698-9ae334b5601c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019c64aa-d3d8-71ce-b698-9ae334b5601c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019c64aa-d3d8-71ce-b698-9ae334b5601c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019c64aa-d3d8-71ce-b698-9ae334b5601c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_019c64aa-d3d8-70b3-b4bf-ebacfae4cd64" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_019c64aa-d3d8-71ce-b698-9ae334b5601c" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_019c64aa-d3d8-70b3-b4bf-ebacfae4cd64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubsequentEventMember_019c64aa-d3d8-741b-acfa-1d46969d3a90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_019c64aa-d3d8-70b3-b4bf-ebacfae4cd64" xlink:to="loc_us-gaap_SubsequentEventMember_019c64aa-d3d8-741b-acfa-1d46969d3a90" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_LesseeOperatingLeaseAreaLeased_019c64aa-d3d8-7ccd-95f8-e616508f6614" xlink:href="sibn-20251231.xsd#sibn_LesseeOperatingLeaseAreaLeased"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019c64aa-d3d8-7820-bd2c-7640b652d907" xlink:to="loc_sibn_LesseeOperatingLeaseAreaLeased_019c64aa-d3d8-7ccd-95f8-e616508f6614" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_LesseeOperatingLeaseMonthlyBaseRent_019c64aa-d3d8-7bda-b058-e26b8a1e6ab9" xlink:href="sibn-20251231.xsd#sibn_LesseeOperatingLeaseMonthlyBaseRent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019c64aa-d3d8-7820-bd2c-7640b652d907" xlink:to="loc_sibn_LesseeOperatingLeaseMonthlyBaseRent_019c64aa-d3d8-7bda-b058-e26b8a1e6ab9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019c6e41-6a32-7d78-8da3-69c8baaf0e8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseTermOfContract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_019c64aa-d3d8-7820-bd2c-7640b652d907" xlink:to="loc_us-gaap_LesseeOperatingLeaseTermOfContract_019c6e41-6a32-7d78-8da3-69c8baaf0e8b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:type="arc" order="101"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_AnshulMaheshwariMember_6de03f92-74ed-4206-973a-68411c12ede9" xlink:href="sibn-20251231.xsd#sibn_AnshulMaheshwariMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_sibn_AnshulMaheshwariMember_6de03f92-74ed-4206-973a-68411c12ede9" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#TradingArrangmentsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/TradingArrangementsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllTradingArrangementsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllTradingArrangementsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_AnshulMaheshwariTradingArrangementCommonStockMember_c2ec3b3a-ae98-4a61-9dca-0e2b49d761b6" xlink:href="sibn-20251231.xsd#sibn_AnshulMaheshwariTradingArrangementCommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_sibn_AnshulMaheshwariTradingArrangementCommonStockMember_c2ec3b3a-ae98-4a61-9dca-0e2b49d761b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_AnshulMaheshwariTradingArrangementRestrictedStockUnitsMember_6ef622ad-49b6-45a5-a006-7ee5434fe22d" xlink:href="sibn-20251231.xsd#sibn_AnshulMaheshwariTradingArrangementRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_sibn_AnshulMaheshwariTradingArrangementRestrictedStockUnitsMember_6ef622ad-49b6-45a5-a006-7ee5434fe22d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_sibn_AnshulMaheshwariTradingArrangementPerformanceBasedRestrictedStockUnitsMember_417882a3-7dd5-4437-853d-5e411b44d896" xlink:href="sibn-20251231.xsd#sibn_AnshulMaheshwariTradingArrangementPerformanceBasedRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllTradingArrangementsMember" xlink:to="loc_sibn_AnshulMaheshwariTradingArrangementPerformanceBasedRestrictedStockUnitsMember_417882a3-7dd5-4437-853d-5e411b44d896" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
