M90.579
BillableOsteonecrosis in diseases classified elsewhere, unspecified ankle and foot
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M90.579 an HCC code?
Yes. M90.579 maps to Bone/Joint/Muscle Infections/Necrosis under the CMS-HCC V28 risk adjustment model (and Bone/Joint/Muscle Infections/Necrosis under V24).
HCC Category Mapping
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 M90.579
For M90.579 to 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 M90.579 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M90.579 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, unspecified ankle and foot. Bone death (osteonecrosis) in the ankle and foot caused by another disease, side not specified. The bone tissue in the ankle and foot dies as a secondary effect of an underlying condition. M90.579 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, M90.579 maps to Bone/Joint/Muscle Infections/Necrosis (HCC 92) with a community, non-dual, aged base RAF weight of 0.209. Under the older V24 model, M90.579 mapped to the same category but with a base RAF weight of 0.482 — V28 recalibrated weights across the entire model. 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.
Use only when the specific side of the ankle and foot is not documented or is bilateral. Because M90.579 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 M90.579 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use only when the specific side of the ankle and foot is not documented or is bilateral
- •Always pair with a secondary diagnosis code for the underlying disease causing the osteonecrosis
Clinical Significance
Secondary osteonecrosis of unspecified ankle and foot represents bone death in these critical weight-bearing structures caused by an underlying classified disease. This diagnosis significantly impacts risk adjustment modeling due to mobility limitations and the complex care coordination required for management.
Documentation Requirements
- ✓Documentation of underlying classified disease causing the osteonecrosis
- ✓Clinical evidence of ankle and/or foot bone involvement
- ✓Imaging confirmation of osteonecrotic changes (MRI, bone scan, or CT)
- ✓Provider documentation establishing causal relationship to primary disease
- ✓Comprehensive management plan for both conditions
- ✓Assessment of mobility and weight-bearing capacity
- ✓Documentation excluding primary or traumatic causes
- ✓Treatment monitoring and complication assessment documentation
Commonly Confused Codes
- •M87.079 — Primary osteonecrosis of unspecified ankle and foot, not disease-related
- •M90.571 — Same condition but specifically right ankle and foot rather than unspecified
- •M90.572 — Same condition but specifically left ankle and foot rather than unspecified
- •M86.179 — Chronic osteomyelitis of unspecified ankle and foot involving infection
- •M25.579 — Pain in unspecified ankle and foot, which is symptomatic rather than structural