M86.479
BillableChronic osteomyelitis with draining sinus, unspecified ankle and foot
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.479 an HCC code?
Yes. M86.479 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 M86.479
For M86.479 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 M86.479 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.479 is the ICD-10-CM diagnosis code for chronic osteomyelitis with draining sinus, unspecified ankle and foot. A chronic bone infection of the ankle and foot bones with an unspecified side that has created an open drainage channel through the skin, allowing infected material to drain continuously. M86.479 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, M86.479 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, M86.479 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 this code only when the medical record does not specify right or left ankle and foot. Because M86.479 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 M86.479 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use this code only when the medical record does not specify right or left ankle and foot
- •Query the provider if laterality can be determined from imaging or clinical documentation to assign a more specific code
Clinical Significance
Chronic osteomyelitis with draining sinus of unspecified ankle and foot represents a serious bone infection with persistent external drainage requiring intensive medical management. Although laterality is unspecified, this condition indicates significant morbidity affecting lower extremity function and mobility, necessitating comprehensive treatment and long-term monitoring.
Documentation Requirements
- ✓Documentation of chronic osteomyelitis diagnosis
- ✓Clear evidence of draining sinus tract presence
- ✓Ankle and foot involvement specified without laterality designation
- ✓Description of drainage characteristics and management
- ✓Microbiological studies and culture results when available
- ✓Imaging studies confirming osteomyelitis and sinus tract
- ✓Treatment protocols including antibiotic therapy duration
- ✓Assessment of functional impact and treatment response