Anatomical Study of the First Dorsal Extensor Compartment

The first dorsal extensor compartment (1st EC) of the wrist is important in treating de Quervain’s disease, which causes stenosing tenosynovitis of the abductor pollicis longus (APL) and extensor pollicis brevis (EPB) muscles. Its anatomical variations are commonly noted, and hand surgeons should be aware of this possibility during the procedures.

Forty cadaver hands were dissected to define the anatomic variations of the 1st EC. Through the gross findings, we classified the contents into several ways, according to the presence of septation, subcompartment, and variation of tendons. Bony cross-section of the wrist was also performed to reveal any bony ridge or groove within the 1st EC. We measured the anatomical structures of the 1st EC based on the radial styloid process.

A septum that results in subcompartments in the 1st EC was present in 24 (60%); complete in 2 (8.3%), and incomplete in 22 (91.7%) distally. The mean size of the 1st EC was 21.2 ± 3.2 mm in length, and 7.9 ± 1.6 mm in width. The mean length of the septum was 10.7 ± 5.5 mm, while the mean width of the subcompartment was 3.0 ± 0.9 mm. All the subcompartments enclosed only EPB tendons. The mean number of APL and EPB tendon slips was 2.6 ± 0.5 and 1.1 ± 0.2, respectively. The bony floor of the 1st EC was classified into 5 types. Two distinctive grooves separating 2 tendons with protruding osseous ridge (type I, n=8), two distinctive grooves separating 2 tendons without protruding osseous ridge (type II, n=10), a single distinct groove with osteophytes (type III, n=13), indistinct groove with fibrous septum separating 2 tendons (type IV, n=6), and indistinct groove without fibrous septum (type V, n=3).

Based on our study, the 1st EC revealed relatively high anatomical variations, and acknowledgement of this abnormality is mandatory for the successful treatment of de Quervain’s disease.