An Introduction to the Carpal Tunnel

In the human wrist, a sheath of tough connective tissue envelops and protects the nerve, median and tendons. It is attached to the muscles, wrist and hand bones. This is the carpal tunnel, which is the space between the sheath above and the bones below making up the wrist and hand.

The term carpal tunnel is also used quite commonly to refer to carpal tunnel syndrome. It is a condition where the median nerve is pinched within the tunnel and causes pain. It is also experienced in the numbness of the wrist or hand, once thought to be a result of repetitive motion such as painting or typing. This is a painful condition caused by continuous flexing or stressing over a long time. This flexing or stressing causes pressure on the median nerve, which carries nervous impulses back and forth between the hand and the spinal cord.

Carpal tunnel is a fibro- osseous tunnel on the palmar surface of the carpal bones. It transmits a number of tendons and the median nerve from the forearm into the hand. Surface markings are proximally the distal wrist crease or distally the hook of the hamate bone.

Both base and walls of the carpal tunnel are a concave bony channel formed by the carpal bones. The flexor retinaculum or transverse carpal ligament forms the roof of the carpal tunnel. It attaches to the scaphoid tubercle and ridge of the trapezium laterally, to the pisiform and hook the hamate medially.

The recurrent thenar branch of the median nerve, the motor branch to the thenar eminence, leaves the median nerve in or beyond the carpal tunnel. It curves back over the flexor retinaculum to reach the thenar eminence. If the incision over the carpal tunnel is made too far laterally, it is dangerous making surgery.

The carpal tunnel transmits to the median nerve and nine tendons. They are the following: flexor digitorum superficialis which contributes to the four tendons that insert on the middle phalanx; flexor digitorum profundus which contributes to the four tendons that insert on the distal phalanx; flexor pollicis longus; palmaris longus which is a tendon merging with palmar aponeurosis; flexor retinaculum; flexor digitorum superficialis; flexor pollicis longus; flexor digitorum profundus and skin.

In addition to carpal tunnel syndrome, the median nerve can also become compressed with wrist dislocations and bone fractures. The carpal tunnel is important because it serves to protect this important nerve.

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