What is ICD-10 code M87.873?

M87.873 is the ICD-10-CM diagnosis code for Other osteonecrosis, unspecified ankle. Death of bone tissue in the ankle when the specific side is not documented or affects both ankles. It belongs to the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99). M87.873 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M87.873 is part of the FY2026 ICD-10-CM code set published by the CMS National Center for Health Statistics and used on Medicare, Medicaid, and commercial claims in the United States.

Yes. M87.873 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M87.873 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Which HCC does M87.873 map to under V28?

M87.873 maps to CMS-HCC V28 HCC 92 (Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis). The category numbers, labels, and conditions come from the CMS-HCC V28 model file for payment year 2026.

2026 ICD-10-CM M87.873: Other osteonecrosis

M87.873 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 Buddy coding tools

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Code lookupM87.873

Effective periodFY2026 Apr Update (Apr 1-Sep 30)

FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Other osteopathies (M86-M90)

M87.873

Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidance

Other osteonecrosis, unspecified ankle

Death of bone tissue in the ankle when the specific side is not documented or affects both ankles.

Buddy Insight

Unspecified ankle osteonecrosis represents avascular bone death in a critical weight-bearing joint without documented laterality, suggesting bilateral involvement or incomplete documentation.

Overview Risk Models Code Book Documentation Audit Notes Edition comparison

CMS-HCC V28

Mapped

HCC 92

Bone/Joint/Muscle/Severe Soft...

Code-level coefficient reference

CMS-HCC V24

Historical

Not used for standard CY2026 Medicare Advantage payment. Select a historical period to review V24.

Not used for CY2026 payment

ACA/HHS

Mapped

HCC 055

HHS-HCC 055 adult, RAF varies...

Code-level coefficient reference

ESRD/PACE

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

Code-level coefficient reference

RXHCC

Mapped

HCC 80

Aseptic Necrosis of Bone

Code-level coefficient reference

Code Book Path

Official

M87.8Other osteonecrosis M87.87Other osteonecrosis, ankle, foot and toes M87.873Other osteonecrosis, unspecified ankle

Inclusion Terms

Official

No inclusion terms are included in this display for M87.873. Check the code and parent instructions in the Code Book.

Excludes 2

Official

arthropathic psoriasis (L40.5-)Inherited from M00-M99
certain conditions originating in the perinatal period (P04-P96)Inherited from M00-M99
certain infectious and parasitic diseases (A00-B99)Inherited from M00-M99
compartment syndrome (traumatic) (T79.A-)Inherited from M00-M99
complications of pregnancy, childbirth and the puerperium (O00-O9A)Inherited from M00-M99
congenital malformations, deformations, and chromosomal abnormalities (Q00-Q99)Inherited from M00-M99
endocrine, nutritional and metabolic diseases (E00-E88)Inherited from M00-M99
injury, poisoning and certain other consequences of external causes (S00-T88)Inherited from M00-M99
neoplasms (C00-D49)Inherited from M00-M99
symptoms, signs and abnormal clinical and laboratory findings, not elsewhere classified (R00-R94)Inherited from M00-M99

Related Codes

Official

M87.871Other osteonecrosis, right ankle M87.872Other osteonecrosis, left ankle M87.874Other osteonecrosis, right foot M87.875Other osteonecrosis, left foot M87.876Other osteonecrosis, unspecified foot

Includes

Official

avascular necrosis of boneInherited from M87

Excludes 1

Official

postprocedural osteopathies (M96.-)Inherited from M86-M90, M87
juvenile osteonecrosis (M91-M92)Inherited from M86-M90, M87
osteochondropathies (M90-M93)Inherited from M86-M90, M87

Code First

Official

No Code First sequencing instructions are included in this display for M87.873. Check the code and parent instructions in the Code Book.

Use Additional

Official

code to identify major osseous defect, if applicable (M89.7-)Inherited from M87

Code Also

Official

No Code Also instructions are included in this display for M87.873. Check the code and parent instructions in the Code Book.

Buddy Documentation Tip

HCC Buddy guidance

Documentation of ankle osteonecrosis without side specification

Comprehensive imaging studies of both ankles if bilateral

Exclusion of trauma, infection, and radiation as causes

Bilateral functional assessment if both ankles affected

MEAT Support

HCC Buddy guidance

Documentation of ankle osteonecrosis without side specification

Comprehensive imaging studies of both ankles if bilateral

Exclusion of trauma, infection, and radiation as causes

Bilateral functional assessment if both ankles affected

Audit Caution

HCC Buddy guidance

Using unspecified codes when laterality is documented elsewhere

Confusing symptomatic joint pain with structural osteonecrosis

Missing bilateral involvement that should be coded separately

Failing to query providers for laterality clarification

Common Mistakes

HCC Buddy guidance

M87.373 — Drug-induced osteonecrosis requires specific medication documentation

M87.173 — Post-traumatic osteonecrosis needs clear trauma history

M87.073 — Idiopathic osteonecrosis has no identifiable underlying etiology

M19.079 — Unspecified ankle osteoarthritis is degenerative joint disease

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 M87.873 an HCC code?

Yes. M87.873 (Other osteonecrosis, unspecified ankle) 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: M87.873 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: M87.873
Description: Other osteonecrosis, unspecified ankle
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

V28HCC 92, Bone/Joint/Muscle/Severe Soft Tissue Infections/Necrosis

0.479

ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis

Not separately weighted

RxHCCHCC 80, Aseptic Necrosis of Bone

Not separately weighted

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 M87.873 in the Code Book — tabular path, V28 RAF reference, and MEAT checklist →

MEAT review for M87.873

For M87.873, 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

M87.873 is the ICD-10-CM diagnosis code for other osteonecrosis, unspecified ankle. Death of bone tissue in the ankle when the specific side is not documented or affects both ankles. M87.873 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, M87.873 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. No V24 mapping is shown for M87.873; use the applicable model and payment year when reviewing the V28 mapping. 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.

Query provider for laterality when not specified, as unilateral codes are preferred. For M87.873, 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 M87.873 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Query provider for laterality when not specified, as unilateral codes are preferred
•Use this code only when bilateral involvement is confirmed or laterality is truly indeterminate

Clinical Significance

Unspecified ankle osteonecrosis represents avascular bone death in a critical weight-bearing joint without documented laterality, suggesting bilateral involvement or incomplete documentation. This condition poses significant risk for joint collapse and functional disability.