S66.321 Laceration of extensor muscle, fascia and tendon of left index finger at wrist and hand level

ICD-10-CM S66.321: Laceration of extensor muscle, fascia and tendon of left index finger at wrist and hand level

ICD-10-CM code S66.321 identifies a laceration of the extensor muscle, fascia, and tendon of the left index finger at the wrist and hand level. This active diagnosis concept is classified as an injury or poisoning. General clinical literature notes that hand extensor tendon lacerations can cause functional impairment. 1 2

Plain-language overview

Code S66.321 describes an injury involving a cut to the extensor muscle, fascia, and tendon of the left index finger at the wrist and hand level, classified specifically as an injury or poisoning concept. 1

What this code represents

The official preferred name for S66.321 is laceration of extensor muscle, fascia and tendon of left index finger at wrist and hand level, and the terminology record indicates this code currently has no narrower child concepts. 1

Coding details

In the ICD-10-CM hierarchy, S66.321 is a child of parent code S66.32, which broadly covers lacerations of extensor muscle, fascia, and tendon of other and unspecified finger at wrist and hand level. 1 4

Documentation considerations

Clinical literature emphasizes that obtaining a detailed history for hand tendon lacerations is necessary, including the mechanism of injury, position of the hand and fingers at the time, patient age, occupation, and hand dominance. 2

Clinical context

Extensor tendon lacerations of the hand can lead to significant functional impairment if not properly managed, and these injuries often result in an extensor lag that can interfere with the performance of myriad activities. 2

While the middle finger tends to be most commonly affected by extensor tendon lacerations, followed by the thumb and index finger, the dominant hand is more likely to be injured overall. 2

Coverage and utilization context

A Medicare billing and coding article for tendon and ligament injections lists various S66 series codes, such as strains of the right index finger, but the supplied excerpt does not specify coverage criteria for S66.321. 3

What the sources add

The National Cancer Institute terminology record establishes the official code status and hierarchy for S66.321, while the clinical bookshelf source provides general background on the functional impact and history-taking for hand extensor tendon lacerations. 1 2

The EVS Explore source mirrors the official S66.321 code description and places it alongside related left finger extensor laceration codes like S66.327, illustrating the available coding options within this specific category. 4

Sources

1. ICD-10-CM S66.321 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. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-27.