M86.579
BillableOther chronic hematogenous osteomyelitis, unspecified ankle and foot
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.579 an HCC code?
Yes. M86.579 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 M86.579
For M86.579 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 M86.579 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.579 is the ICD-10-CM diagnosis code for other chronic hematogenous osteomyelitis, unspecified ankle and foot. A long-term bone infection in the ankle or foot from bloodstream bacteria, but the specific side (left or right) is not documented. M86.579 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, M86.579 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, M86.579 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 laterality cannot be determined from documentation. Because M86.579 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 M86.579 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 laterality cannot be determined from documentation
- •Query provider if possible to obtain specific laterality information
Clinical Significance
This code represents chronic hematogenous osteomyelitis of the ankle and foot when laterality is not specified. Despite the unspecified laterality, this condition represents a serious bone infection that significantly impacts mobility and weight-bearing function, requiring intensive medical management and potentially surgical intervention.
Documentation Requirements
- ✓Documentation of chronic osteomyelitis duration (>6 weeks or recurrent)
- ✓Evidence of hematogenous origin (bloodstream spread)
- ✓Ankle and/or foot bone involvement without laterality specification
- ✓Imaging studies confirming bone infection
- ✓Laboratory evidence of infection or inflammatory response
- ✓Assessment of ambulation and weight-bearing capacity
- ✓Treatment documentation including antibiotic therapy
- ✓Justification for unspecified laterality (bilateral involvement or unclear documentation)