M86.642
BillableOther chronic osteomyelitis, left hand
Last updated: FY2026 ICD-10-CM (Oct 1, 2025 – Sep 30, 2026) | CMS-HCC V28 (100% phase-in, PY2026)
Is M86.642 an HCC code?
Yes. M86.642 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 M86.642
For M86.642 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 M86.642 during that encounter — not just copy-forwarded from a problem list.
What This Code Means
M86.642 is the ICD-10-CM diagnosis code for other chronic osteomyelitis, left hand. A chronic bone infection affecting the bones of the left hand with ongoing inflammation and potential loss of hand function. M86.642 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, M86.642 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, M86.642 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 'left hand' is documented and identify specific carpal, metacarpal, or phalangeal involvement if available. Because M86.642 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 M86.642 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Verify 'left hand' is documented and identify specific carpal, metacarpal, or phalangeal involvement if available
- •Document any associated complications such as contractures or limited range of motion
Clinical Significance
Chronic osteomyelitis of the left hand represents a serious bone infection affecting the complex hand anatomy, severely compromising hand function and manual dexterity. This condition significantly impacts quality of life and may require extensive rehabilitation and adaptive strategies for daily activities.
Documentation Requirements
- ✓Confirmation of chronic nature (minimum 6 weeks duration or recurrent)
- ✓Specific documentation of left hand bone involvement
- ✓Non-hematogenous etiology (contiguous spread or direct inoculation)
- ✓Radiographic evidence of bone infection or destruction in hand
- ✓Laboratory studies supporting chronic infection process
- ✓Functional assessment of left hand including grip and pinch strength
- ✓Documentation of antibiotic therapy and surgical interventions
- ✓Assessment of occupational impact and need for adaptive equipment
Commonly Confused Codes
- •M86.542 — Other chronic hematogenous osteomyelitis, left hand (hematogenous origin)
- •M86.641 — Other chronic osteomyelitis, right hand (different laterality)
- •M86.442 — Chronic osteomyelitis with draining sinus, left hand (has sinus tract)
- •M86.142 — Other acute osteomyelitis, left hand (acute presentation)
- •L03.032 — Cellulitis of left finger (soft tissue infection without bone involvement)