Anatomical variations in the first extensor compartment: a cadaver study

BACKGROUND: Anatomical variations in the first extensor compartment are associated with the pathogenesis of de Quervain's disease. Here, we report two novel anatomical variations of the first extensor compartment. METHODS: The wrists of two adult cadavers were dissected to reveal the anatomical variations in the first extensor compartment. RESULTS: In one of the cadavers, no septum was present in the first extensor compartment. However, the extensor pollicis brevis tendon and its proximal muscle belly were absent. The abductor pollicis longus (APL) tendon had multiple slips, and one of them inserted on the dorsal base of the proximal thumb phalanx. In another cadaver, a septum was present in the first extensor compartment. One of the multiple APL tendon slips ran into the septum alongside the extensor pollicis brevis tendon for 4 mm, which then exited the septum and inserted into the base of the first phalanx together with the APL tendon. CONCLUSION: Our findings may help to improve the awareness of the anatomical variations in the first extensor compartment.