M86.559
BillableOther chronic hematogenous osteomyelitis, unspecified femur
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.559 an HCC code?
Yes. M86.559 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 M86.559
For M86.559 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 M86.559 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.559 is the ICD-10-CM diagnosis code for other chronic hematogenous osteomyelitis, unspecified femur. A chronic bone infection of the thighbone (femur) that developed from bacteria spreading through the bloodstream, with unspecified laterality. M86.559 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, M86.559 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, M86.559 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.
Use only when the side of the femur cannot be determined from documentation. Because M86.559 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 M86.559 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Use only when the side of the femur cannot be determined from documentation
- •Query the provider or review imaging to determine if right or left femur is affected
Clinical Significance
Chronic hematogenous osteomyelitis of unspecified femur represents a serious bone infection affecting the body's largest weight-bearing bone. The unspecified laterality suggests documentation gaps that should be addressed, though the condition still requires intensive management due to the femur's critical functional importance.
Documentation Requirements
- ✓Documentation of chronic duration (>6 weeks or recurrent pattern)
- ✓Evidence of hematogenous spread (bloodstream origin)
- ✓Femur bone involvement without laterality specification
- ✓Radiographic confirmation of bone infection
- ✓Laboratory studies supporting infection (inflammatory markers)
- ✓Assessment of weight-bearing capacity and mobility
- ✓Treatment plan including antibiotic therapy
- ✓Justification for unspecified laterality (unclear documentation or bilateral)
Commonly Confused Codes
- •M86.551 — Other chronic hematogenous osteomyelitis, right femur (specific side)
- •M86.552 — Other chronic hematogenous osteomyelitis, left femur (specific side)
- •M86.659 — Other chronic osteomyelitis, unspecified thigh (non-hematogenous)
- •M86.459 — Chronic osteomyelitis with draining sinus, unspecified femur (has sinus)
- •M86.159 — Other acute osteomyelitis, unspecified femur (acute phase)