M86.659 ICD-10-CM Code: Other chronic osteomyelitis, unspecified thigh
M86.659 maps to CMS-HCC V28 92. A source-labeled RAF reference is available. Confirm the documented diagnosis and applicable coding requirements. MEAT criteria · RAF Calculator · HCC coding software
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)
M86.659
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceOther chronic osteomyelitis, unspecified thigh
A chronic bone infection in the thigh bone that has persisted over time, where the specific side is not specified.
Buddy Insight
Chronic osteomyelitis represents a persistent bone infection that significantly impacts patient morbidity and healthcare utilization.
CMS-HCC V28
MappedHCC 92
Coefficient HCC 92: 0.479 (Community Non-Dual Aged (CNA))
CMS-HCC V24
HistoricalHistorical
Not used for CY2026 payment
ACA/HHS
MappedHCC 055
Code-level coefficient reference
ESRD/PACE
MappedHCC 39
Code-level coefficient reference
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialNo inclusion terms are included in this display for M86.659. Check the code and parent instructions in the Code Book.
Excludes 2
Official- arthropathic psoriasis (L40.5-)Inherited from M00-M99, M86
- certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99, M86
- certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99, M86
- compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99, M86
- complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99, M86
- congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99, M86
- endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99, M86
- injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99, M86
- neoplasms (C00-D49)Inherited from M00-M99, M86
- symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99, M86
- ostemyelitis of:Inherited from M00-M99, M86
- orbit (H05.0-)Inherited from M00-M99, M86
- petrous bone (H70.2-)Inherited from M00-M99, M86
- vertebra (M46.2-)Inherited from M00-M99, M86
Related Codes
Includes
OfficialNo Includes notes are included in this display for M86.659. Check the code and parent instructions in the Code Book.
Excludes 1
Official- postprocedural osteopathies (M96.-)Inherited from M86-M90, M86
- osteomyelitis due to:Inherited from M86-M90, M86
- echinococcus (B67.2)Inherited from M86-M90, M86
- gonococcus (A54.43)Inherited from M86-M90, M86
- salmonella (A02.24)Inherited from M86-M90, M86
Code First
OfficialNo Code First sequencing instructions are included in this display for M86.659. Check the code and parent instructions in the Code Book.
Use Additional
Official- code (B95-B97) to identify infectious agentInherited from M86
- code to identify major osseous defect, if applicable (M89.7-)Inherited from M86
Code Also
OfficialNo Code Also instructions are included in this display for M86.659. Check the code and parent instructions in the Code Book.
Buddy Documentation Tip
MEAT Support
Audit Caution
Common Mistakes
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is M86.659 an HCC code?
Yes. M86.659 (Other chronic osteomyelitis, unspecified thigh) maps to HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis under the CMS-HCC V28 risk adjustment model, with a source-labeled community non-dual aged reference coefficient of 0.479. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes. It is billable for payment year 2026.
Coder answer: M86.659 is billable and maps to V28 HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis. Open it in the Code Book for the tabular path, RAF, and MEAT checklist.
- Code
- M86.659
- Description
- Other chronic osteomyelitis, unspecified thigh
- HCC (V28)
- HCC 92 — Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis
- RAF reference coefficient
- 0.479
- Billable
- Yes
- Payment year
- 2026
HCC Category Mapping
These are source-labeled model coefficients, not member totals. A category may still be removed by hierarchy or model cleanup rules. Weights are not directly comparable across models: CMS-HCC V28 and V24 use Community, Non-Dual, Aged; ESRD uses the dialysis continuing-enrollee model; RxHCC is the Part D continuing-enrollee, non-low-income, aged weight (a larger scale than CMS-HCC). ACA/HHS has no single weight — it varies by metal level. Actual per-patient RAF contribution depends on member context, hierarchy and cleanup rules, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains available for historical review.
Work M86.659 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →
MEAT review for M86.659
For M86.659, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule.
- MMonitor: signs, symptoms, disease progression, or lab trending documented in the note
- EEvaluate: test results, medication response, or physical findings reviewed by the provider
- AAssess: explicit mention in the assessment or plan with acknowledgment of status
- TTreat: medication, referral, procedure, therapy, or counseling tied to the diagnosis
Coder workflow notes
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What This Code Means
M86.659 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, unspecified thigh. A chronic bone infection in the thigh bone that has persisted over time, where the specific side is not specified. M86.659 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering other osteopathies (m86-m90).
Under the CMS-HCC V28 risk adjustment model, M86.659 maps to Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis (HCC 92) with a source-labeled community, non-dual, aged reference coefficient of 0.479. For CY2026 non-PACE Medicare Advantage, CMS uses 100% of the 2024 CMS-HCC model (V28). PACE uses a separate model blend. Source-labeled code-level coefficients are references, not member totals. Actual contribution depends on complete member context, hierarchy and cleanup rules, interactions, and model year. HCC Buddy's RAF Calculator supports CMS-HCC V28 PY2026 and shows no score unless every required source and calculation check passes.
Use this code only when the thigh location is documented but laterality (left/right) cannot be determined from the medical record. For M86.659, confirm that the documentation supports the diagnosis and meets the applicable coding, encounter, program and payer requirements. MEAT (Monitor, Evaluate, Assess, or Treat) is a review mnemonic, not a universal CMS coding rule. When documentation is ambiguous, coders should issue a provider query rather than assume the highest-specificity variant.
HCC Buddy maintains structured V28 and V24 mapping, source-labeled coefficient references, and MEAT documentation criteria for M86.659 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
Clinical Significance
Chronic osteomyelitis represents a persistent bone infection that significantly impacts patient morbidity and healthcare utilization. This condition indicates a compromised immune status and bone integrity, requiring long-term antibiotic therapy and potentially surgical intervention, making it a high-risk condition for complications.
Documentation Requirements
- ✓Clear documentation of chronic osteomyelitis diagnosis
- ✓Specification of thigh location (femur involvement)
- ✓Evidence of chronicity through duration or recurrent episodes
- ✓Supporting diagnostic imaging (MRI, bone scan, or CT)
- ✓Laboratory evidence such as elevated ESR, CRP, or positive cultures
- ✓Documentation of antibiotic therapy or surgical treatment
- ✓Assessment of functional impact on patient mobility
- ✓Identification of underlying risk factors or comorbidities
Commonly Confused Codes
- •M86.10: Acute osteomyelitis lacks the chronic time component and represents initial bone infection
- •M87.9: Aseptic necrosis is bone death without infection, while osteomyelitis involves active bacterial infection
- •M86.20: Subacute osteomyelitis represents intermediate stage between acute and chronic phases
- •M86.9: Unspecified osteomyelitis lacks the chronic designation and anatomical specificity