What is ICD-10 code M87.171?

M87.171 is the ICD-10-CM diagnosis code for Osteonecrosis due to drugs, right ankle. Death of bone tissue in the right ankle caused by medication side effects, potentially affecting mobility and joint function. M87.171 is a billable code, meaning it can be reported on a claim as a primary or secondary diagnosis when supported by documentation. M87.171 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. M87.171 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. M87.171 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.

What is the V28 vs V24 difference for M87.171?

CMS phased in the V28 risk adjustment model over payment years 2024 (33%), 2025 (67%), and 2026 (100%), replacing V24. V28 consolidates HCC categories, removes some lower-acuity conditions, and recalibrates RAF weights across the entire model. M87.171 was a payment HCC under V24 (Bone/Joint/Muscle Infections/Necrosis) but the V28 recalibration removed it from the risk adjustment model. Both models can still appear in legacy data and in payer-specific lookback periods.

What should coders know when reporting M87.171?

Verify whether the osteonecrosis affects the talus or other ankle bones and document accordingly Correlate with imaging findings to confirm drug-induced etiology versus other causes Because M87.171 maps to a payment HCC, the documentation must also satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's risk adjustment score.

M87.171: Osteonecrosis due to drugs, right ankle —

ICD-10-CM Code View

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Code lookupM87.171Effective 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)

M87.171

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

Osteonecrosis due to drugs, right ankle

Death of bone tissue in the right ankle caused by medication side effects, potentially affecting mobility and joint function.

Buddy Insight

Drug-induced osteonecrosis of the right ankle involves medication-related bone death affecting the complex joint structure, potentially compromising mobility and weight-bearing capacity.

CMS-HCC V28

Not risk-adjusted for this model/period.

RAF 0

CMS-HCC V24

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.482

ACA/HHS

Not risk-adjusted for this model/period.

RAF 0

ESRD/PACE

Mapped

HCC 39

Bone/Joint/Muscle Infections/...

RAF 0.0

RXHCC

Mapped

HCC 80

Bone/Joint/Muscle Infections/...

RAF 0.0

Code Trumping

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Code Book Path

Official

M87.1Osteonecrosis due to drugs

M87.17Osteonecrosis due to drugs, ankle, foot and toes

M87.171Osteonecrosis due to drugs, right ankle

Inclusion Terms

Official

ICD-10-CM does not list inclusion terms for M87.171 in this effective period.

Excludes 2

Official

ICD-10-CM does not list Excludes 2 notes for M87.171 in this effective period.

Related Child Codes

Official

M87.172Osteonecrosis due to drugs, left ankle

M87.173Osteonecrosis due to drugs, unspecified ankle

M87.174Osteonecrosis due to drugs, right foot

M87.175Osteonecrosis due to drugs, left foot

M87.176Osteonecrosis due to drugs, unspecified foot

Includes

Official

ICD-10-CM does not list Includes notes for M87.171 in this effective period.

Excludes 1

Official

ICD-10-CM does not list Excludes 1 notes for M87.171 in this effective period.

Code First

Official

ICD-10-CM does not list Code First sequencing instructions for M87.171 in this effective period.

Use Additional

Official

ICD-10-CM does not list Use Additional Code instructions for M87.171 in this effective period.

Code Also

Official

ICD-10-CM does not list Code Also instructions for M87.171 in this effective period.

Buddy Documentation Tip

HCC Buddy guidance

Specific documentation of right ankle involvement in osteonecrosis

Causative medication identification with exposure details

Advanced imaging confirming ankle osteonecrosis

Assessment of ankle joint function and range of motion

MEAT Support

HCC Buddy guidance

Specific documentation of right ankle involvement in osteonecrosis

Causative medication identification with exposure details

Advanced imaging confirming ankle osteonecrosis

Assessment of ankle joint function and range of motion

Audit Caution

HCC Buddy guidance

Confusing ankle joint with broader foot involvement

Using unspecified laterality when right side is clearly documented

Missing drug causation in patients with multiple ankle problems

Using acute injury codes for chronic drug-induced conditions

Common Mistakes

HCC Buddy guidance

M87.172 — Left ankle osteonecrosis, opposite laterality

M87.173 — Unspecified ankle when right side is documented

M87.174 — Right foot osteonecrosis involves broader foot structures

M87.271 — Post-traumatic right ankle requires injury history

Last updated: FY2026 ICD-10-CM Apr update, Apr 1, 2026 through Sep 30, 2026. CMS-HCC V28 is 100% phased in for payment year 2026.

Is M87.171 an HCC code?

Yes. M87.171 maps to Bone/Joint/Muscle Infections/Necrosis under the V24 model but is not retained in V28.

HCC Category Mapping

V24HCC 39, Bone/Joint/Muscle Infections/Necrosis

0.482

ESRDHCC 39, Bone/Joint/Muscle Infections/Necrosis

0.000

RxHCCHCC 80, Bone/Joint/Muscle Infections/Necrosis

0.000

RAF weights shown are the community, non-dual, aged base weights from the CMS risk adjustment model file. Actual per-patient RAF contribution depends on member segment, interactions, and the model year used by the payer. V28 is the CMS-HCC model phased in over payment years 2024–2026; V24 remains in use during the transition and for historical data.

MEAT Criteria for M87.171

For M87.171to count as a valid HCC diagnosis in a given encounter, the provider's documentation must show MEAT: Monitor, Evaluate, Assess, or Treat. A diagnosis from a prior year does not carry forward automatically, it has to be re-documented and supported each calendar year.

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

Only one of M/E/A/T is required to support the code, but the documentation must be specific enough to show that the provider actually addressed M87.171 during that encounter, not just copy-forwarded from a problem list.

Coder workflow notes

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What This Code Means

M87.171 is the ICD-10-CM diagnosis code for osteonecrosis due to drugs, right ankle. Death of bone tissue in the right ankle caused by medication side effects, potentially affecting mobility and joint function. M87.171 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 older CMS-HCC V24 model, M87.171 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 39) with a community, non-dual, aged base RAF weight of 0.482. V28 is the CMS-HCC risk adjustment model that reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition.

Verify whether the osteonecrosis affects the talus or other ankle bones and document accordingly. Because M87.171 maps to a payment HCC, the provider's documentation must satisfy MEAT criteria (Monitor, Evaluate, Assess, or Treat) for the encounter to count toward the patient's Medicare Advantage risk adjustment score. 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, RAF weights, and MEAT documentation criteria for M87.171 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.

Coding Tips

•Verify whether the osteonecrosis affects the talus or other ankle bones and document accordingly
•Correlate with imaging findings to confirm drug-induced etiology versus other causes

Clinical Significance

Drug-induced osteonecrosis of the right ankle involves medication-related bone death affecting the complex joint structure, potentially compromising mobility and weight-bearing capacity. This condition may require specialized orthopedic intervention and can significantly impact daily activities and ambulation.