Anatomy of the extensor pollicis brevis associated with an extension mechanism of the thumb metacarpophalangeal joint.

This study aimed to determine whether the extensor pollicis longus (EPL) or abductor pollicis longus (APL) can replace the function of thumb extension in hands in which the extensor pollicis brevis (EPB) is absent. Cadaver dissection was performed to examine anatomical association between the interphalangeal (IP) joint and metacarpophalangeal (MP) joint of the thumb, as well as extension mechanism in clinical cases. EPB insertion could be classified into eight types, and the EPB was absent in 7.6% of all cases. In hands without an EPB, the width of the EPL tendon tended to be wider, and the number of APL tendons was significantly greater than in hands with an EPB. In hands without an EPB, the EPL and APL may replace the function of the EPB. As a result, a greater load is imposed on these two tendons than in hands with the EPB.