M90.549
BillableOsteonecrosis in diseases classified elsewhere, unspecified hand
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M90.549 an HCC code?
Yes. M90.549 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 M90.549
For M90.549 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 M90.549 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M90.549 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, unspecified hand. Death of bone tissue in the hand (side not specified) caused by another disease or condition affecting the body. M90.549 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, M90.549 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, M90.549 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.
Avoid using this code if laterality can be determined; it reduces specificity. Because M90.549 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 M90.549 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Avoid using this code if laterality can be determined; it reduces specificity
- •Clarify with documentation whether right, left, or bilateral involvement exists
Clinical Significance
This diagnosis indicates secondary osteonecrosis affecting an unspecified hand, representing bone death caused by an underlying classified disease condition. The diagnosis significantly impacts risk adjustment calculations and reflects ongoing complex medical management needs with potential functional limitations.
Documentation Requirements
- ✓Clear documentation of underlying disease causing the secondary osteonecrosis
- ✓Clinical evidence of hand involvement without specific laterality documentation
- ✓Radiological confirmation of osteonecrotic changes (MRI, bone scan, CT)
- ✓Provider statement establishing causal relationship to classified disease
- ✓Current management approach for both primary and secondary conditions
- ✓Functional impact assessment on hand use and daily activities
- ✓Documentation excluding primary osteonecrosis or traumatic causes
- ✓Treatment monitoring and response documentation
Commonly Confused Codes
- •M87.049 — Primary osteonecrosis of unspecified hand, not disease-related
- •M90.541 — Same condition but specifically documented as right hand
- •M90.542 — Same condition but specifically documented as left hand
- •M86.149 — Chronic osteomyelitis of unspecified hand involving infection
- •M25.549 — Pain in unspecified hand, which is symptomatic rather than structural