Question 1

What is ICD-10 code M85.431?

Accepted Answer

M85.431 is the ICD-10-CM diagnosis code for solitary bone cyst, right ulna and radius. A fluid-filled cavity or hollow space in the right forearm bones (radius and ulna) that is not associated with other bone conditions. M85.431 sits in the ICD-10-CM chapter for diseases of the musculoskeletal system and connective tissue (m00-m99), within the section covering disorders of bone density and structure (m80-m85).

M85.431 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.

Confirm whether the cyst involves the radius, ulna, or both bones before coding.

Question 2

Is M85.431 an HCC code?

Accepted Answer

No. M85.431 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 M85.431 billable?

Accepted Answer

Yes. M85.431 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. M85.431 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 M85.431?

Accepted Answer

M85.431 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 M85.431 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 M85.431?

Accepted Answer

Confirm whether the cyst involves the radius, ulna, or both bones before coding Document right-sided location clearly to avoid confusion with left-sided variants

M85.431

Is M85.431 an HCC code?

What This Code Means

Coding Tips

Code Hierarchy

Open M85.431 in the Interactive Encoder