M90.561
BillableOsteonecrosis in diseases classified elsewhere, right lower leg
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M90.561 an HCC code?
Yes. M90.561 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 M90.561
For M90.561 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 M90.561 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M90.561 is the ICD-10-CM diagnosis code for osteonecrosis in diseases classified elsewhere, right lower leg. Bone death (osteonecrosis) in the right lower leg caused by another disease. The bone tissue in the lower leg dies as a secondary effect of an underlying condition. M90.561 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, M90.561 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, M90.561 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.
Requires a secondary diagnosis code for the underlying disease causing the osteonecrosis. Because M90.561 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 M90.561 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Requires a secondary diagnosis code for the underlying disease causing the osteonecrosis
- •Laterality is specified as right; do not use this code for left-sided or bilateral involvement
Clinical Significance
Secondary osteonecrosis of the right lower leg represents bone death in the tibia or fibula caused by an underlying classified disease, requiring comprehensive medical management. This diagnosis significantly impacts risk adjustment modeling due to potential mobility limitations and complex care coordination needs.
Documentation Requirements
- ✓Clear documentation of underlying disease causing secondary osteonecrosis
- ✓Specific identification of right lower leg (tibia/fibula) involvement
- ✓Radiological evidence of bone necrosis (MRI, bone scan, or CT imaging)
- ✓Clinical correlation between primary disease and secondary bone death
- ✓Current management plan for both underlying condition and osteonecrosis
- ✓Assessment of weight-bearing status and mobility limitations
- ✓Provider statement confirming secondary rather than primary cause
- ✓Documentation of treatment response and complication monitoring