M86.639
BillableOther chronic osteomyelitis, unspecified radius and ulna
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.639 an HCC code?
Yes. M86.639 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 M86.639
For M86.639 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 M86.639 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.639 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, unspecified radius and ulna. A chronic bone infection in the forearm bones (radius and ulna) where the specific side is not identified or documented. M86.639 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, M86.639 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, M86.639 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.
This is a less specific code; attempt to clarify laterality through provider query when possible. Because M86.639 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 M86.639 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is a less specific code; attempt to clarify laterality through provider query when possible
- •Use only when medical record does not specify right or left forearm involvement
Clinical Significance
This code represents chronic osteomyelitis of the radius and ulna when laterality is unspecified. While still capturing the serious nature of chronic forearm bone infection that impacts upper extremity function, the lack of laterality specification suggests documentation improvements could enhance care coordination and treatment planning.
Documentation Requirements
- ✓Documentation of chronic osteomyelitis (>6 weeks or recurrent pattern)
- ✓Radius and/or ulna involvement without laterality specification
- ✓Non-hematogenous etiology (contiguous or direct inoculation)
- ✓Imaging confirmation of bone infection in forearm
- ✓Laboratory markers of infection or inflammation
- ✓Assessment of forearm and hand function
- ✓Treatment history and current management approach
- ✓Justification for unspecified laterality (bilateral or unclear documentation)