M86.662
BillableOther chronic osteomyelitis, left tibia and fibula
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.662 an HCC code?
Yes. M86.662 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 M86.662
For M86.662 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 M86.662 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.662 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, left tibia and fibula. A chronic bone infection affecting the left shin bone (tibia) and the smaller bone next to it (fibula) that has been ongoing. M86.662 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, M86.662 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, M86.662 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 code is specific to the left lower leg; confirm laterality in documentation before coding. Because M86.662 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 M86.662 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This code is specific to the left lower leg; confirm laterality in documentation before coding
- •Consider documenting the duration and any previous treatment attempts for this chronic infection
Clinical Significance
Left tibia and fibula chronic osteomyelitis represents a serious bone infection affecting the primary weight-bearing bones of the left lower leg. This condition significantly impacts patient mobility, requires prolonged treatment courses, and carries substantial risk for complications including treatment resistance and bone destruction.
Documentation Requirements
- ✓Clear documentation of chronic osteomyelitis diagnosis
- ✓Specific identification of left tibia and fibula involvement
- ✓Evidence of chronic nature through duration or recurrent episodes
- ✓Supporting imaging studies showing chronic osteomyelitis changes
- ✓Laboratory markers of infection or inflammation
- ✓Documentation of antimicrobial treatment history
- ✓Functional assessment including weight-bearing limitations
- ✓Identification of predisposing factors or underlying conditions
Commonly Confused Codes
- •M86.162 — Acute osteomyelitis of left tibia/fibula represents initial acute phase
- •M87.065 — Aseptic necrosis of left fibula involves bone death without infection
- •M86.669 — Unspecified tibia/fibula osteomyelitis lacks laterality specification
- •M79.3 — Panniculitis affects subcutaneous tissue, not bone