M90.539
BillableOsteonecrosis in diseases classified elsewhere, unspecified forearm
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M90.539 an HCC code?
Yes. M90.539 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 M90.539
For M90.539 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 M90.539 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M90.539 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, unspecified forearm. Death of bone tissue in the forearm (side not specified) caused by another disease or condition affecting the body. M90.539 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, M90.539 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, M90.539 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 (left or right) is not documented in the medical record. Because M90.539 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 M90.539 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 (left or right) is not documented in the medical record
- •Query the provider if laterality is missing, as it affects specificity of coding
Clinical Significance
Secondary osteonecrosis of unspecified forearm indicates bone tissue death resulting from an underlying systemic condition, requiring comprehensive medical management. This diagnosis reflects significant medical complexity and ongoing care needs that substantially impact risk stratification and resource allocation.
Documentation Requirements
- ✓Documentation of underlying disease process causing the secondary osteonecrosis
- ✓Clinical evidence of bone necrosis in forearm location
- ✓Imaging confirmation of osteonecrotic changes (MRI, bone scan, or CT)
- ✓Provider documentation establishing causal relationship to primary disease
- ✓Current management plan for both underlying condition and osteonecrosis
- ✓Assessment of functional limitations or complications
- ✓Exclusion of primary or traumatic causes of bone necrosis
- ✓Treatment response documentation or progression monitoring