Question 1

What is ICD-10 code M65.979?

Accepted Answer

M65.979 is the ICD-10-CM diagnosis code for unspecified synovitis and tenosynovitis, unspecified ankle and foot. Inflammation of the tissue lining the tendons in the ankle and foot area, with unspecified cause and unspecified side. M65.979 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering disorders of synovium and tendon (m65-m67).

M65.979 is a billable ICD-10-CM code but does not map to a payment HCC under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can be reported on Medicare Advantage encounter data submissions but it does not contribute to a beneficiary's RAF score and therefore does not affect risk-adjusted payments to the plan.

This code should only be used when laterality (left, right, or bilateral) cannot be determined from documentation.

Question 2

Is M65.979 an HCC code?

Accepted Answer

No. M65.979 is a billable ICD-10-CM code but does not map to any payment HCC category under the CMS-HCC V28, V24, ESRD, or RxHCC risk adjustment models. It can still be reported on Medicare Advantage encounter data submissions, but it does not contribute to the beneficiary's Risk Adjustment Factor (RAF) score and therefore does not affect the risk-adjusted capitation payment to the plan. V28 reached 100% phase-in for payment year 2026.

Question 3

Is M65.979 billable?

Accepted Answer

Yes. M65.979 is a billable ICD-10-CM code that can be reported on professional and institutional claims as a primary or secondary diagnosis when the provider documentation supports the specific condition described. Billable codes in ICD-10-CM are coded to the highest level of specificity available for the documented diagnosis. M65.979 is current for fiscal year 2026 and remains in the active CMS ICD-10-CM code set published by the National Center for Health Statistics.

Question 4

What is the V28 vs V24 difference for M65.979?

Accepted Answer

M65.979 does not map to a payment HCC under either the CMS-HCC V28 risk adjustment model or the older V24 model. V28 reached 100% phase-in for payment year 2026, replacing V24 which was used during the PY2024–PY2025 transition. Because neither model rewards M65.979 with a risk adjustment factor, it contributes zero to a Medicare Advantage beneficiary's RAF score in either version. Coders should check whether provider documentation supports a more specific child code that does map to a payment HCC.

Question 5

What should coders know when reporting M65.979?

Accepted Answer

This code should only be used when laterality (left, right, or bilateral) cannot be determined from documentation If laterality can be determined, use the more specific codes M65.971 (right) or M65.972 (left) instead

M65.979

Is M65.979 an HCC code?

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Open M65.979 in the Interactive Encoder