Question 1

What is ICD-10 code M23.642?

Accepted Answer

M23.642 is the ICD-10-CM diagnosis code for other spontaneous disruption of lateral collateral ligament of left knee. A spontaneous tear or rupture of the lateral collateral ligament (the ligament on the outer side of the knee) on the left knee that occurs without a specific injury. M23.642 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering other joint disorders (m20-m25).

M23.642 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 laterality is documented as left knee; if not specified, use M23.649 instead.

Question 2

Is M23.642 an HCC code?

Accepted Answer

No. M23.642 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 M23.642 billable?

Accepted Answer

Yes. M23.642 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. M23.642 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 M23.642?

Accepted Answer

M23.642 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 M23.642 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 M23.642?

Accepted Answer

Verify laterality is documented as left knee; if not specified, use M23.649 instead Confirm this is a spontaneous disruption rather than traumatic; review clinical notes for mechanism of injury

M23.642

Is M23.642 an HCC code?

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