M66.371 ICD-10-CM Code: Spontaneous rupture of flexor tendons, right ankle and foot
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FY 2026 Apr update / Diseases of the musculoskeletal system and connective tissue (M00-M99) / Disorders of synovium and tendon (M65-M67)
M66.371
Billable / SpecificICD-10-CMOfficial ICD-10-CMCodebook guidanceSpontaneous rupture of flexor tendons, right ankle and foot
A spontaneous breaking or tearing of the flexor tendons in the right ankle and foot that occurs without a known injury.
CMS-HCC V28
N/A—
Not mapped
CMS-HCC V24
N/A—
Not mapped
ACA/HHS
N/A—
Not mapped
ESRD/PACE
N/A—
Not mapped
RXHCC
N/A—
Not mapped
Code Book Path
Inclusion Terms
OfficialICD-10-CM does not list inclusion terms for M66.371 in this effective period.
Excludes 2
OfficialICD-10-CM does not list Excludes 2 notes for M66.371 in this effective period.
Related Child Codes
Includes
OfficialICD-10-CM does not list Includes notes for M66.371 in this effective period.
Excludes 1
OfficialICD-10-CM does not list Excludes 1 notes for M66.371 in this effective period.
Code First
OfficialICD-10-CM does not list Code First sequencing instructions for M66.371 in this effective period.
Use Additional
OfficialICD-10-CM does not list Use Additional Code instructions for M66.371 in this effective period.
Code Also
OfficialICD-10-CM does not list Code Also instructions for M66.371 in this effective period.
Buddy Documentation Tip
Current with CMS: FY2026 ICD-10-CM Apr 1 update (effective Apr 1 – Sep 30, 2026) · CMS-HCC V28, 100% phased in for payment year 2026. FY2027 code set already staged for October 1, 2026. How HCC Buddy stays current →
Is M66.371 an HCC code?
No. M66.371 is a billable ICD-10-CM code but does not map to any HCC category in V28, V24, ESRD, or RxHCC.
- Code
- M66.371
- Description
- Spontaneous rupture of flexor tendons, right ankle and foot
- HCC (V28)
- No CMS-HCC V28 mapping
- RAF
- —
- Billable
- Yes
- Payment year
- 2026
Coder workflow notes
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This code does not map to an HCC category in any model (V28, V24, ESRD, RxHCC).
What This Code Means
M66.371 is the ICD-10-CM diagnosis code for spontaneous rupture of flexor tendons, right ankle and foot. A spontaneous breaking or tearing of the flexor tendons in the right ankle and foot that occurs without a known injury. M66.371 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).
M66.371 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.
Ensure right side is documented; use M66.372 for left ankle and foot.
HCC Buddy maintains structured V28 and V24 mapping, RAF weights, and MEAT documentation criteria for M66.371 sourced directly from the CMS-HCC risk adjustment model files and the CMS ICD-10-CM code set.
Coding Tips
- •Ensure right side is documented; use M66.372 for left ankle and foot
- •Consider documenting which specific flexor tendon ruptured (flexor hallucis longus, flexor digitorum longus, etc.)