M86.171
BillableOther acute osteomyelitis, right ankle and foot
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.171 an HCC code?
Yes. M86.171 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 M86.171
For M86.171 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 M86.171 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.171 is the ICD-10-CM diagnosis code for other acute osteomyelitis, right ankle and foot. A rapidly developing bone infection affecting the right ankle and foot bones. M86.171 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, M86.171 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, M86.171 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.
Verify that the infection involves the ankle and/or foot structures, not the tibia/fibula. Because M86.171 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 M86.171 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify that the infection involves the ankle and/or foot structures, not the tibia/fibula
- •Document which specific foot bones are involved if possible for clinical clarity
Clinical Significance
Acute osteomyelitis of the right ankle and foot represents a complex infection affecting multiple small bones critical for weight-bearing and mobility. This condition poses significant risks for chronic disability and requires immediate intervention to preserve foot function and prevent systemic complications.
Documentation Requirements
- ✓Specific identification of right ankle and foot involvement
- ✓Documentation of acute onset bone infection
- ✓Clinical evidence of ankle/foot bone infection
- ✓Imaging confirmation of osteomyelitis in ankle/foot bones
- ✓Laboratory support for active infection
- ✓Assessment of weight-bearing capacity and gait
- ✓Documentation of pain and functional limitations
- ✓Treatment plan addressing complex foot anatomy