S66.019 Strain of long flexor muscle, fascia and tendon of unspecified thumb at wrist and hand level

ICD-10-CM S66.019: Strain of long flexor muscle, fascia and tendon of unspecified thumb at wrist and hand level

ICD-10-CM code S66.019 designates an injury diagnosis defined as a strain of the long flexor muscle, fascia, and tendon of an unspecified thumb at the wrist and hand level. The active terminology record classifies this concept under a broader parent category for similar thumb strains. 1 4

Plain-language overview

This diagnosis code identifies a strain affecting the long flexor muscle, fascia, and tendon of an unspecified thumb at the wrist and hand level, serving as a standardized way to document this specific injury. 1

What this code represents

The code S66.019 represents a diagnosis classified semantically as an injury or poisoning, specifically detailing a strain of the long flexor musculature and tendons of the thumb. 1 4

S66.019 is a child concept to the parent code S66.01, which broadly covers strains of the long flexor muscle, fascia, and tendon of the thumb at the wrist and hand level. 1

The terminology record for S66.019 indicates that this specific code has no narrower subcategories within the ICD-10-CM system, meaning it currently represents the most specific level available for this exact unspecified designation. 1

Documentation considerations

The official preferred name for S66.019 explicitly includes the term unspecified thumb, directly reflecting the terminology used to define this particular injury diagnosis within the coding system. 1

Coverage and utilization context

The code S66.019 appears within a Medicare billing and coding article for outpatient occupational therapy, showing its inclusion in payer documentation lists for these specific healthcare services. 6

What the sources add

A Medicare outpatient occupational therapy article lists a distinct sequela code for an unspecified thumb flexor strain, providing a comparative example of related terminology appearing in payer documentation. 6

A Medicare billing article for injections references a related sequela code for a right thumb flexor strain, illustrating the existence of laterality-specific codes adjacent to the unspecified S66.019 code. 5

National health statistics reports classify strains and muscle or tendon injuries within specific nature-of-injury categories, providing a broader surveillance framework that contrasts with the precise code-level detail found in the S66.019 terminology record. 1 2

Sources

1. ICD-10-CM S66.019 terminology record — National Cancer Institute Enterprise Vocabulary Services; accessed 2026-07-27.
2. National Health Statistics Reports — cdc.gov; accessed 2026-07-27.
3. Bookshelf — ncbi.nlm.nih.gov; accessed 2026-07-27.
4. EVS Explore — evsexplore.semantics.cancer.gov; accessed 2026-07-27.
5. Article - Billing and Coding: Injections - Tendon, Ligament, Ganglion Cyst, Tunnel Syndromes and Morton's Neuroma (A57079) — cms.gov; accessed 2026-07-27.
6. Article - Billing and Coding: Outpatient Occupational Therapy (A53064) — cms.gov; accessed 2026-07-27.