M86.179
BillableOther acute 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 M86.179 an HCC code?
Yes. M86.179 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 M86.179
For M86.179 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 M86.179 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.179 is the ICD-10-CM diagnosis code for other acute osteomyelitis, unspecified ankle and foot. A rapidly developing bone infection in the ankle and foot area, but the specific side is not documented. M86.179 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, M86.179 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, M86.179 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.
Attempt to obtain laterality information from clinical documentation or imaging reports. Because M86.179 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 M86.179 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Attempt to obtain laterality information from clinical documentation or imaging reports
- •Use this code only when side cannot be determined despite documentation review
Clinical Significance
Acute osteomyelitis of unspecified ankle and foot represents incomplete documentation of a complex multi-bone infection affecting weight-bearing structures. The foot's complex anatomy and functional importance make laterality specification crucial for treatment planning and prognosis assessment.
Documentation Requirements
- ✓Documentation of ankle/foot bone infection without laterality
- ✓Evidence of acute infection in foot/ankle bones
- ✓Clinical presentation of complex foot bone infection
- ✓Imaging confirmation of ankle/foot involvement
- ✓Laboratory evidence of active bone infection
- ✓Provider query for laterality specification
- ✓Assessment of weight-bearing and gait impact
- ✓Treatment plan for complex foot anatomy
Commonly Confused Codes
- •L03.119 — Cellulitis of unspecified lower limb (soft tissue)
- •M86679 — Chronic osteomyelitis with draining sinus of unspecified ankle and foot
- •M86279 — Subacute osteomyelitis of unspecified ankle and foot
- •M86171/172 — Right/left specific codes when laterality available
- •S92.909A — Unspecified fracture of unspecified foot