S66.317A Strain of extensor muscle, fascia and tendon of left little finger at wrist and hand level, initial encounter

ICD-10-CM S66.317A: Strain of left little finger extensor at wrist and hand level, initial encounter

ICD-10-CM code S66.317A identifies an initial encounter for a strain affecting the extensor muscle, fascia, and tendon of the left little finger at the wrist and hand level. The terminology record classifies this concept as an injury or poisoning, and Medicare billing articles include this specific diagnosis code within injection-related coding specifications. 1 4

Plain-language overview

This diagnosis code represents an injury to the extensor muscle, fascia, and tendon of the left little finger at the wrist and hand level, specifically for an initial encounter. 1

What this code represents

The semantic type assigned to S66.317A is Injury or Poisoning, and the terminology record maintains an active status for this concept within the ICD-10-CM version 2026. 1

S66.317A is a narrower concept derived from the parent code S66.317, which describes the same left little finger extensor strain without specifying the encounter type. 1

Coding details

The seventh character A in S66.317A specifies an initial encounter, distinguishing it from S66.317D, which represents a subsequent encounter for the same left little finger injury. 1 5

Documentation considerations

Clinical evaluation of hand extensor tendon injuries requires a detailed history including the mechanism of injury, patient age, occupation, and hand dominance. 2

An open wound on the dorsum of the hand warrants suspicion of extensor tendon injury, and physical examination can include checking for normal tenodesis and digital cascade. 2

Coverage and utilization context

A Medicare billing and coding article for tendon and ligament injections includes S66.317A as an ICD-10-CM diagnosis code within its listed specifications. 4

What the sources add

While the terminology record defines the specific diagnosis, the clinical text adds that hand extensor tendons are prone to injury due to superficial location and minimal soft tissue coverage. 1 2

The Medicare article lists S66.317A alongside related left index finger extensor strain codes within the same billing and coding document for tendon and ligament injections. 3 4

Sources

1. ICD-10-CM S66.317A terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
3. Article - Billing and Coding: Injections - Tendon, Ligament, Ganglion Cyst, Tunnel Syndromes and Morton's Neuroma (A57079) — cms.gov; accessed 2026-07-27.
4. Article - Billing and Coding: Injections - Tendon, Ligament, Ganglion Cyst, Tunnel Syndromes and Morton's Neuroma (A57079) — cms.gov; accessed 2026-07-27.
5. S66.317D - Strain of extensor muscle, fascia and tendon of left little finger at wrist and hand level [subsequent encounter] | ICD-10-CM — unboundmedicine.com; accessed 2026-07-27.