Palmaris profundus in the carpal tunnel.

Carpal tunnel release is a routinely performed operation to relieve pressure caused by compression on the median nerve. In the majority of cases, the causation of the compression will be idiopathic. Among the secondary causes of median nerve compression is the palmaris profundus, a rare anatomical variant separate to the palmaris longus tendon. It has been suggested that it may cause carpal tunnel syndrome as it courses underneath the flexor retinaculum with the contents of the carpal tunnel reducing the space available to the median nerve. Several cases have found it intimately associated with the median nerve within the carpal tunnel. Raising awareness of this anatomical variant is therefore important for those undertaking carpal tunnel decompression in order to avoid unintended damage.