M86.18
BillableOther acute osteomyelitis, other site
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.18 an HCC code?
Yes. M86.18 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 M86.18
For M86.18 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 M86.18 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.18 is the ICD-10-CM diagnosis code for other acute osteomyelitis, other site. A rapidly developing bone infection occurring in a body location not covered by the other acute osteomyelitis codes. M86.18 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, M86.18 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, M86.18 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.
Clearly document the specific anatomical site affected to justify use of this 'other site' code. Because M86.18 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 M86.18 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Clearly document the specific anatomical site affected to justify use of this 'other site' code
- •Consider if the site might fit into a more specific category before assigning this code
Clinical Significance
Acute osteomyelitis at other specified sites represents bone infections in locations not covered by standard anatomical codes, such as ribs, sternum, or skull bones. These infections require careful evaluation as they may indicate underlying systemic issues or unusual pathogen involvement.
Documentation Requirements
- ✓Clear identification of specific anatomical site not covered by other codes
- ✓Documentation of acute infection onset
- ✓Clinical evidence of bone infection at specified site
- ✓Imaging confirmation of osteomyelitis at the documented location
- ✓Laboratory support for active infection
- ✓Exclusion of more common anatomical sites
- ✓Documentation of causative factors when known
- ✓Treatment plan appropriate for anatomical location