M90.521
BillableOsteonecrosis in diseases classified elsewhere, right upper arm
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M90.521 an HCC code?
Yes. M90.521 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 M90.521
For M90.521 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 M90.521 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M90.521 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, right upper arm. Death of bone tissue in the right upper arm caused by another disease. M90.521 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, M90.521 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, M90.521 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.
Code the underlying disease condition separately (e.g., sickle cell disease, systemic lupus erythematosus). Because M90.521 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 M90.521 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Code the underlying disease condition separately (e.g., sickle cell disease, systemic lupus erythematosus)
- •Ensure documentation specifies right upper arm; this code is specific to that anatomical location
Clinical Significance
Secondary osteonecrosis of the right upper arm represents bone death in the humerus caused by underlying systemic disease, potentially leading to fracture risk and functional impairment. This condition requires careful monitoring and management of both the primary disease and skeletal complications.
Documentation Requirements
- ✓Primary disease causing osteonecrosis documented and sequenced first
- ✓Right upper arm/humerus specifically identified as affected site
- ✓Clinical or radiographic evidence of bone tissue death
- ✓Imaging studies supporting osteonecrosis diagnosis
- ✓Functional assessment of right arm strength and mobility
- ✓Risk assessment for pathological fracture
- ✓Treatment plan addressing underlying condition and bone pathology