The carpal tunnel (carpal canal) is the passageway on the palmar side of the wrist that connects the forearm to the middle compartment of the deep plane of the palm.
The carpus, the bony elements of the wrist, form an arch which is convex on the dorsal side of the hand and concave on the palmar side. The groove on the palmar side, the sulcus carpi, is covered by the flexor retinaculum, a sheath of tough connective tissue, thus forming the carpal tunnel. The flexor retinaculum is attached radially to the scaphoid tubercle and the ridge of trapezium, and on the ulna side to the pisiform and hook of hammate.
The narrowest section of the tunnel is located a centimetre beyond the mid-line of the distal row of carpal bones where the sectional area is limited to 1.6 cm2.
The tendons of the flexor digitorum superficialis and profundus pass through a common ulnar sheath, while the tendon of the flexor pollicis longus passes through a separate radial sheath. The mesotendon shared by these tendons is attached to the radial and palmar walls of the carpal tunnel.
A total of nine flexor tendons pass through the carpal tunnel:
A single nerve passes through the tunnel: the median nerve between tendons of flexor digitorum profundus and flexor digitorum superficialis.
Superficial to the carpal tunnel and the flexor retinaculum, the ulnar artery and ulnar nerve pass through the ulnar tunnel.