M86.8X9
BillableOther osteomyelitis, unspecified sites
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.8X9 an HCC code?
Yes. M86.8X9 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 M86.8X9
For M86.8X9 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 M86.8X9 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.8X9 is the ICD-10-CM diagnosis code for other osteomyelitis, unspecified sites. A bone infection (osteomyelitis) affecting an unspecified location that doesn't fit into other specific osteomyelitis categories. M86.8X9 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, M86.8X9 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, M86.8X9 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 is the least specific code in the 'other osteomyelitis' category; use only when the site cannot be determined. Because M86.8X9 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 M86.8X9 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •This is the least specific code in the 'other osteomyelitis' category; use only when the site cannot be determined
- •Query the provider if possible to obtain a more specific anatomical location for better coding accuracy
Clinical Significance
Other osteomyelitis at unspecified sites represents bone infection that doesn't fit standard acute or chronic patterns and lacks specific anatomical documentation. This indicates complex clinical scenarios where infection characteristics don't conform to typical classifications, requiring careful evaluation to determine appropriate treatment approaches despite incomplete localization information.
Documentation Requirements
- ✓Documentation of osteomyelitis diagnosis with atypical features
- ✓Clinical justification for 'other' versus acute or chronic classification
- ✓Available information about potential anatomical involvement
- ✓Supporting diagnostic studies confirming bone infection
- ✓Laboratory markers supporting infection diagnosis
- ✓Treatment plan addressing diagnostic uncertainty
- ✓Explanation for why specific anatomical site cannot be determined
- ✓Documentation of unique clinical characteristics