Question 1

What is ICD-10 code M66.142?

Accepted Answer

M66.142 is the ICD-10-CM diagnosis code for rupture of synovium, left hand. A tear or rupture of the synovium (joint lining) in the left hand, causing pain, swelling, and potential loss of hand function. M66.142 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).

M66.142 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.

Verify left hand is clearly documented in the clinical notes.

Question 2

Is M66.142 an HCC code?

Accepted Answer

No. M66.142 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 M66.142 billable?

Accepted Answer

Yes. M66.142 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. M66.142 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 M66.142?

Accepted Answer

M66.142 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 M66.142 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 M66.142?

Accepted Answer

Verify left hand is clearly documented in the clinical notes Differentiate between hand and finger involvement; use finger-specific codes if rupture is limited to finger joints

M66.142

Is M66.142 an HCC code?

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Open M66.142 in the Interactive Encoder