Fig. 1.

Proximal portion of the carpal tunnel. The carpal tunnel is an osteofibrous canal situated in the volar wrist. The boundaries are the carpal bones and the flexor retinaculum (A). The carpal tunnel contains nine tendons: the flexor pollicis longus, the four flexor digitorum superficialis and the four flexor digitorum profundus as well as the median nerve (B, C). The retinaculum (arrows) appears as a ribbon-like structure, hypoechoic (B) or hypointense (C), proximally it inserts to the tuberosity of the scaphoid and the pisiform.