Question 1

What is ICD-10 code M66.861?

Accepted Answer

M66.861 is the ICD-10-CM diagnosis code for spontaneous rupture of other tendons, right lower leg. A tendon in the right lower leg (calf or shin area) suddenly tears or breaks on its own without a specific injury. M66.861 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).

M66.861 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.

Achilles tendon ruptures are common in this location; document if this specific tendon is involved.

Question 2

Is M66.861 an HCC code?

Accepted Answer

No. M66.861 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 M66.861 billable?

Accepted Answer

Yes. M66.861 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. M66.861 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 M66.861?

Accepted Answer

M66.861 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 M66.861 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 M66.861?

Accepted Answer

Achilles tendon ruptures are common in this location; document if this specific tendon is involved Note any associated pain, swelling, or difficulty walking that accompanies the rupture

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M66.861

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M66.861 ICD-10-CM Code: Spontaneous rupture of other tendons, right lower leg

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M66.861

Is M66.861 an HCC code?

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Work M66.861 in HCC Buddy