M86.669
BillableOther chronic osteomyelitis, unspecified tibia and fibula
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.669 an HCC code?
Yes. M86.669 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 M86.669
For M86.669 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 M86.669 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.669 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, unspecified tibia and fibula. A chronic bone infection in the shin bone (tibia) and fibula where the specific side (left or right) is not specified. M86.669 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, M86.669 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, M86.669 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.
Only use this unspecified code when laterality cannot be determined from available documentation. Because M86.669 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 M86.669 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Only use this unspecified code when laterality cannot be determined from available documentation
- •Query the provider if documentation is unclear about whether the infection is unilateral or bilateral
Clinical Significance
Chronic osteomyelitis of unspecified tibia and fibula indicates a persistent bone infection in critical weight-bearing bones where laterality is not documented. This represents significant morbidity requiring extensive antibiotic therapy and potential surgical intervention, with high risk for treatment complications and functional impairment.
Documentation Requirements
- ✓Documentation of chronic osteomyelitis diagnosis
- ✓Evidence that tibia and/or fibula are involved
- ✓Proof of chronicity through time course or treatment history
- ✓Imaging studies confirming osteomyelitis
- ✓Laboratory studies supporting infection diagnosis
- ✓Treatment plan including antibiotics or surgical intervention
- ✓Assessment of functional impact on mobility
- ✓Documentation explaining why laterality cannot be determined