M86.9 ICD-10-CM Code: Osteomyelitis, unspecified

Coding instructions

Official Tabular Instructional Notes: the inclusion, exclusion and sequencing notes published for M86.9 in the official ICD-10-CM tabular list, quoted as published.

Source: CMS/CDC — ICD-10-CM Tabular ListRelease: FY2026Effective: October 1, 2025

Notes without a marker are published on M86.9 itself; “inherited from” names the category or block whose note applies here.

Coder workflow for M86.9

MedCoder structured workflow — derived from this code’s own official record

Before you code M86.9

1. Unspecified does not mean incorrect. When the record gives no greater specificity, M86.9 may be the appropriate code. Check the record for detail that supports a more specific sibling. An unspecified code is for records that do not provide the detail a more specific code needs; a query, not an assumption, is the route to specificity (Guidelines I.A.9.b, I.B.18).

   ReviewM86.8

   See the relationships section · Guide: Other vs unspecified (NEC vs NOS) →

2. Check the Excludes1 note: if the documentation supports a condition named there, do not simply proceed with M86.9. Excludes1 conditions are not reported together with this code unless the record shows they are unrelated (Guidelines I.A.12.a).

   See the official tabular notes

Choose the right path

1. Does the record document the detail a more specific sibling code needs?
   Yes → Review the specific siblings in this subcategory.
   No → Continue — M86.9 is appropriate when the documentation goes no further.

   ReviewM86.8

2. Does the documentation support a condition named in M86.9’s Excludes1 note?
   Yes → Do not simply proceed: review the excluded code. Both are reported only when the record shows the two conditions are unrelated.
   No → Continue.

   ReviewB67.2, A54.43, A02.24, M96

Consider M86.9. Then work the Use Additional Code note, and confirm the code is valid for the date of service in the Verify section.

Documentation check

The provider’s diagnostic statement

Codes are assigned from the provider’s documented diagnosis, not from clinical criteria, test values or a medication list (Guidelines I.A.19).

The conditions the Use Additional Code note names

Reported with this code when documented; a conditional instruction (“if applicable”, “if known”) applies only when the record supports it.

Any detail beyond this code’s title

What the record states that a more specific sibling code would capture — or its absence, which itself supports the unspecified code.

Official instructions as workflow

• Excludes1 — check before selecting M86.9(5 notes)

  Coding workflow: If the documentation supports a condition named in this note, do not simply proceed with M86.9: the two are not reported together. The one exception is when the record shows the two conditions are unrelated to each other.

  CompareB67.2, A54.43, A02.24, M96

  See the official tabular notes · Guidelines I.A.12.a

• Excludes2 — not part of M86.9(4 notes)

  Coding workflow: The conditions named in this note are not included in M86.9. When the record documents both, both may be reported; the note is a boundary, not a prohibition.

  CompareH05.0, H70.2, M46.2

  See the official tabular notes · Guidelines I.A.12.b

• Use Additional Code — after identifying M86.9(2 notes)

  Coding workflow: Check whether the documentation supports the additional code(s) the note names, and report them with M86.9 when it does. Where the instruction is conditional (“if applicable”, “if known”), it applies only when the record documents the condition.

  ReviewM89.7

  See the official tabular notes · Guidelines I.A.13

Coding decision scenarios

Pattern scenarios for this code’s structure — decision rules, not clinical cases

Every row is derived from this code’s own record — its title, tabular notes, 7th-character family and same-category siblings — with fixed MedCoder wording; nothing is inferred about a patient. The official notes and guideline text are in the sections each row links to, and they control.

Indexed Clinical Terms (1)

Official source data — entries quoted as published, in the Index’s own lookup phrasing

Clinical term phrases from the official ICD-10-CM Index to Diseases and Injuries that map to this code. These are alphabetic-index entries shown as the Index writes them — lookup phrasing, not necessarily the wording of a final diagnosis.

• Osteomyelitis (general) (infective) (localized) (neonatal) (purulent) (septic) (staphylococcal) (streptococcal) (suppurative) (with periostitis)

Don’t confuse M86.9 with…

MedCoder analysis — pairs from this code’s official notes, distinctions written by MedCoder

The codes most likely to be picked instead of M86.9 — named in its own official notes, or sharing its laterality or encounter family — with what separates them and which documentation moves the case. Each links to the full comparison.

• B67.2— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of echinococcus moves the case to B67.2; the two are not reported together unless documented as unrelated.

  Full comparison: M86.9 vs B67.2 →

• A54.43— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of gonococcus moves the case to A54.43; the two are not reported together unless documented as unrelated.

  Full comparison: M86.9 vs A54.43 →

• A02.24— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of salmonella moves the case to A02.24; the two are not reported together unless documented as unrelated.

  Full comparison: M86.9 vs A02.24 →

• M96— Excludes1 conflict (Excludes1 — generally not reported together)

  Not coded here — the tabular list excludes this pair for the same encounter.

  Not reported together with this code, except where the two conditions are documented as unrelated.

  What moves you there: Documentation of postprocedural osteopathies moves the case to M96; the two are not reported together unless documented as unrelated.

  Full comparison: M86.9 vs M96 →

• H05.0— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of orbit adds H05.0; it is not part of this code and both may be reported when both are documented.

  Full comparison: M86.9 vs H05.0 →

• H70.2— Excludes2 relationship (Informational)

  Distinct conditions — both may be reported.

  A distinct condition — both may be reported when both are documented.

  What moves you there: Documentation of petrous bone adds H70.2; it is not part of this code and both may be reported when both are documented.

  Full comparison: M86.9 vs H70.2 →

Relationships are read from this code's own official notes, its laterality siblings and its encounter family; the wording of each distinction is MedCoder editorial, and the documentation named in each “what moves you there” line is the official note phrase or sibling title itself. Source: CMS ICD-10-CM tabular instructional notes; ICD-10-CM Official Guidelines, Section I.A.12.a.

Decision Points

The directives on this code's own record, as a pre-claim checklist.

1. 2 Use Additional Code instructions — report the named additional code(s) when the documentation supports them. See the Use Additional Code notes
2. 5 Excludes1 entries — codes named there are generally not reported together with this code (Guidelines I.A.12.a). See the Excludes1 notes
3. 4 Excludes2 entries — those conditions are not part of this code and may be reported additionally when documented. See the Excludes2 notes

Checklist rows are derived from this code's own official directives; the wording of each check is MedCoder editorial. The official notes themselves are in the sections each row links to.

Verify Before Coding

• CC as a secondary diagnosis (FY2026). Can raise the stay's MS-DRG severity tier.

From the code registry, the Medicare Code Editor, and the MS-DRG Definitions Manual. Check it against a full claim in Claim Check.

Relationships & Classification

MedCoder structured relationships — computed from published CMS and AHRQ datasets

Other codes that name M86.9 or its code family, from the CMS ICD-10-CM tabular instructional notes. Tabular-note edges are stored at the code family level that carries each note.

Referenced by 1 Code First instruction: M89.7 — Major osseous defect (via M86.-).

Each of these codes carries a Code First note naming this condition — when that code is reported, THIS code is sequenced first, ahead of it.

MS-DRG Grouper Relationships (FY2026)

Potential MS-DRG participation — not a DRG assignment.

FY2026 MS-DRG: CC — Complication or Comorbidity. Reported as a secondary diagnosis, this code raises the stay's MS-DRG severity tier — except when the principal diagnosis is one of 152 clinically related codes on its CMS exclusion list.

Named in the grouper logic of 6 MS-DRGs: DRG 456 (MDC 08), DRG 457 (MDC 08), DRG 458 (MDC 08), DRG 539 (MDC 08), DRG 540 (MDC 08), DRG 541 (MDC 08).

From the CMS MS-DRG Definitions Manual (Appendices B and C). Actual DRG assignment depends on the complete claim.

Clinical classification (AHRQ CCSR):MUS002 — Osteomyelitis (default).

Clinical Classifications Software Refined (CCSR) for ICD-10-CM Diagnoses. Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality.

Related Codes

Same clinical process (MS-DRG)

Acts as CC — raises the severity of other admissions. CMS groups these diagnoses into one MS-DRG principal-diagnosis exclusion process — a CC/MCC on this list never raises severity when the principal diagnosis is also on it.

M86.8X0 — Other osteomyelitis, multiple sites, M86.8X1 — Other osteomyelitis, shoulder, M86.8X2 — Other osteomyelitis, upper arm, M86.8X3 — Other osteomyelitis, forearm, M86.8X4 — Other osteomyelitis, hand, M86.8X5 — Other osteomyelitis, thigh, M86.8X6 — Other osteomyelitis, lower leg, M86.8X7 — Other osteomyelitis, ankle and foot, M86.8X8 — Other osteomyelitis, other site, M86.8X9 — Other osteomyelitis, unspecified sites, M88.0 — Osteitis deformans of skull, M88.1 — Osteitis deformans of vertebrae, M88.811 — Osteitis deformans of right shoulder, M88.812 — Osteitis deformans of left shoulder, M88.819 — Osteitis deformans of unspecified shoulder, M88.821 — Osteitis deformans of right upper arm, M88.822 — Osteitis deformans of left upper arm, M88.829 — Osteitis deformans of unspecified upper arm, M88.831 — Osteitis deformans of right forearm, M88.832 — Osteitis deformans of left forearm, +131 more

Same CMS-HCC risk category (V28)

CMS maps these diagnoses to the same Hierarchical Condition Category (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis) for risk-adjusted payment.

M86.8X0 — Other osteomyelitis, multiple sites, M86.8X1 — Other osteomyelitis, shoulder, M86.8X2 — Other osteomyelitis, upper arm, M86.8X3 — Other osteomyelitis, forearm, M86.8X4 — Other osteomyelitis, hand, M86.8X5 — Other osteomyelitis, thigh, M86.8X6 — Other osteomyelitis, lower leg, M86.8X7 — Other osteomyelitis, ankle and foot, M86.8X8 — Other osteomyelitis, other site, M86.8X9 — Other osteomyelitis, unspecified sites, M87.00 — Idiopathic aseptic necrosis of unspecified bone, M87.011 — Idiopathic aseptic necrosis of right shoulder, M87.012 — Idiopathic aseptic necrosis of left shoulder, M87.019 — Idiopathic aseptic necrosis of unspecified shoulder, M87.021 — Idiopathic aseptic necrosis of right humerus, M87.022 — Idiopathic aseptic necrosis of left humerus, M87.029 — Idiopathic aseptic necrosis of unspecified humerus, M87.031 — Idiopathic aseptic necrosis of right radius, M87.032 — Idiopathic aseptic necrosis of left radius, M87.033 — Idiopathic aseptic necrosis of unspecified radius, +588 more

Same clinical category (CCSR)

AHRQ's Clinical Classifications Software groups these diagnoses under the same clinical category (Osteomyelitis).

M86.652 — Other chronic osteomyelitis, left thigh, M86.659 — Other chronic osteomyelitis, unspecified thigh, M86.661 — Other chronic osteomyelitis, right tibia and fibula, M86.662 — Other chronic osteomyelitis, left tibia and fibula, M86.669 — Other chronic osteomyelitis, unspecified tibia and fibula, M86.671 — Other chronic osteomyelitis, right ankle and foot, M86.672 — Other chronic osteomyelitis, left ankle and foot, M86.679 — Other chronic osteomyelitis, unspecified ankle and foot, M86.68 — Other chronic osteomyelitis, other site, M86.69 — Other chronic osteomyelitis, multiple sites, M86.8X0 — Other osteomyelitis, multiple sites, M86.8X1 — Other osteomyelitis, shoulder, M86.8X2 — Other osteomyelitis, upper arm, M86.8X3 — Other osteomyelitis, forearm, M86.8X4 — Other osteomyelitis, hand, M86.8X5 — Other osteomyelitis, thigh, M86.8X6 — Other osteomyelitis, lower leg, M86.8X7 — Other osteomyelitis, ankle and foot, M86.8X8 — Other osteomyelitis, other site, M86.8X9 — Other osteomyelitis, unspecified sites, +174 more

Same Index main term, other category

The ICD-10-CM Index to Diseases and Injuries files this code under the main term “Osteomyelitis”; these codes share that main term but sit in a different category of the Tabular List.

A01.05 — Typhoid osteomyelitis (typhoid), A02.24 — Salmonella osteomyelitis (Salmonella), A50.02 — Early congenital syphilitic osteochondropathy (syphilitic, congenital), A52.77 — Syphilis of bone and joint (syphilitic), B67.2 — Echinococcus granulosus infection of bone (echinococcal), H05.02 — Osteomyelitis of orbit (orbit), M27.2 — Inflammatory conditions of jaws (jaw), M46.20 — Osteomyelitis of vertebra, site unspecified (vertebra), M46.21 — Osteomyelitis of vertebra, occipito-atlanto-axial region (vertebra, occipito-atlanto-axial region), M46.22 — Osteomyelitis of vertebra, cervical region (vertebra, cervical region), M46.23 — Osteomyelitis of vertebra, cervicothoracic region (vertebra, cervicothoracic region), M46.24 — Osteomyelitis of vertebra, thoracic region (vertebra, thoracic region), M46.25 — Osteomyelitis of vertebra, thoracolumbar region (vertebra, thoracolumbar region), M46.26 — Osteomyelitis of vertebra, lumbar region (vertebra, lumbar region), M46.27 — Osteomyelitis of vertebra, lumbosacral region (vertebra, lumbosacral region), M46.28 — Osteomyelitis of vertebra, sacral and sacrococcygeal region (vertebra, sacrococcygeal region)

Lab tests where this diagnosis supports Medicare coverage (NCD)

Medicare's National Coverage Determination (NCD) program lists this diagnosis as medical justification for these lab tests.

Blood Glucose Test, Thyroid Stimulating Hormone (TSH)

Contextual Map

Every relationship of M86.9 in one view: hierarchy, official tabular instructions in both directions, clinical classification, risk adjustment, MS-DRG participation, index terms and change history — each edge carrying the CMS source it derives from.

Run M86.9 with this related code in Claim Check

Hierarchy

• M00-M99 — Chapter 13: Diseases of the Musculoskeletal System and Connective Tissue (M00-M99) (M00-M99)[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86-M90 — Other osteopathies[Hierarchy]— CMS ICD-10-CM tabular structure · icd10cm-fy2026

Referenced by Code First instructions

• M89.7 — Major osseous defect[Code First](via M86.-): “osteomyelitis (M86.-)”— CMS ICD-10-CM tabular instructional notes · icd10cm-fy2026

Clinical classification (CCSR)

• MUS002 — Osteomyelitis[CCSR]— AHRQ CCSR for ICD-10-CM Diagnoses (HCUP)

Risk adjustment (CMS-HCC)

• HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis [CMS-HCC]— CMS-HCC V28 · 2026

MS-DRG Grouper

• CC — Complication or Comorbidity [MS-DRG severity]: “As a secondary diagnosis this code can raise the stay's MS-DRG severity tier (CC).”— CMS MS-DRG Definitions Manual (Appendix C) · FY2026
• DRG 456 — SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITH MCC[MS-DRG]: “SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITH MCC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 457 — SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITH CC[MS-DRG]: “SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITH CC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 458 — SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITHOUT CC/MCC[MS-DRG]: “SPINAL FUSION EXCEPT CERVICAL WITH SPINAL CURVATURE, MALIGNANCY, INFECTION OR EXTENSIVE FUSIONS WITHOUT CC/MCC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 539 — OSTEOMYELITIS WITH MCC[MS-DRG]: “OSTEOMYELITIS WITH MCC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 540 — OSTEOMYELITIS WITH CC[MS-DRG]: “OSTEOMYELITIS WITH CC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026
• DRG 541 — OSTEOMYELITIS WITHOUT CC/MCC[MS-DRG]: “OSTEOMYELITIS WITHOUT CC/MCC (MDC 08)”— CMS MS-DRG Definitions Manual (Appendix B) · FY2026

MDC crossing

• MDC 08 — Diseases and Disorders of the Musculoskeletal System and Connective Tissue[MDC crossing]: “Diseases and Disorders of the Musculoskeletal System and Connective Tissue — the grouper's crossing between diagnoses and procedures: a principal diagnosis sets the MDC, and same-MDC procedures move the stay to its surgical DRGs. 18,508 same-MDC procedures group here; browse them on the MDC page.”— CMS MS-DRG Definitions Manual · FY2026

Index entries

• Osteomyelitis (general) (infective) (localized) (neonatal) (purulent) (septic) (staphylococcal) (streptococcal) (suppurative) (with periostitis)[Index term]— CMS ICD-10-CM Index to Diseases and Injuries · icd10cm-fy2026

Nearest codes (40)

• M86 — Osteomyelitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.672 — Other chronic osteomyelitis, left ankle and foot[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.679 — Other chronic osteomyelitis, unspecified ankle and foot[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.68 — Other chronic osteomyelitis, other site[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.69 — Other chronic osteomyelitis, multiple sites[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.8 — Other osteomyelitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.8X — Other osteomyelitis[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• M86.8X0 — Other osteomyelitis, multiple sites[Sibling]— CMS ICD-10-CM tabular structure · icd10cm-fy2026
• and 32 more

Change history

• FY2016 — In the code set at ICD-10-CM adoption [Change history]— CMS release files (code change ledger) · icd10cm-fy2016

Sources for this page

Codes, titles, notes, index terms and mappings on this page are transcribed from the datasets below. Relationships MedCoder computed and text MedCoder wrote are labelled where they appear.

Code, title, tabular notes and index terms Official source data

CMS/CDC ICD-10-CM FY2026 tabular list, index and tables, effective October 1, 2025 Release, file and checksum · Publisher’s page

Claim edits Official source data

CMS Definitions of Medicare Code Edits — v43.1 (April 2026) Release, file and checksum · Publisher’s page

Inpatient payment groups Official source data

CMS MS-DRG Definitions Manual (incl. Appendix B diagnosis index, Appendix C CC/MCC list, Appendix E procedure index) and IPPS Final Rule tables — v43 Release, file and checksum · Publisher’s page

Risk adjustment Official source data

2026 Mid-Year Final ICD-10 Mappings + Model Software (cms.gov/files/zip/2026-midyear-final-icd-10-mappings.zip, 2026-midyear-final-model-software.zip) — CMS-HCC V28, PY2026 mid-year final release Release, file and checksum · Publisher’s page

Change history and date-of-service validity Official source data

CMS ICD-10-CM release addenda, ingested release by release into the change ledger Release, file and checksum · Publisher’s page

Comparisons, relationships and the contextual map MedCoder structured relationship

Computed by MedCoder from the tabular notes and tables above; every derived relationship is marked as derived where it appears

Summary and FAQ answers MedCoder explanation

Written by MedCoder to explain the sources above: drafted with AI assistance, checked by a person against the release files, and labelled as MedCoder text where it appears. Not official text.

Labels on this page: Official source data · MedCoder structured relationship · MedCoder explanation. How to read the labels · All data sources and release dates

Nearest Codes in This Family

Official ICD-10-CM classifications closest to M86.9 in its code family, with their registry titles.

• M86.8X62 — Other osteomyelitis, left lower leg
• M86.8X69 — Other osteomyelitis, unspecified lower leg
• M86.8X7 — Other osteomyelitis, ankle and foot
• M86.8X71 — Other osteomyelitis, right ankle and foot
• M86.8X72 — Other osteomyelitis, left ankle and foot
• M86.8X79 — Other osteomyelitis, unspecified ankle and foot
• M86.8X8 — Other osteomyelitis, other site
• M86.8X80 — Other osteomyelitis, skull
• M86.8X81 — Other osteomyelitis, face and sinuses
• M86.8X89 — Other osteomyelitis, other site

View all codes in the M86 family