In the human wrist there is a sheath of tough connective tissue which envelopes and protects one nerve (median nerve) and tendons, which attach muscles to the wrist and hand bones. The carpal tunnel is the space between this sheath (above) and the bones (below) making up the wrist and hand (carpal bones). The term 'carpal tunnel' is also used quite commonly to refer to 'carpal tunnel syndrome' which is a condition where the median nerve is pinched within the tunnel and causes pain and/or numbness of the wrist/hand, once thought to be a result of repetitive motion such as painting or typing.

Medical/Anatomical definition

---

The carpal tunnel is a fibro-osseous tunnel on the palmar surface of the carpal bones which transmits a number of tendons (flexor pollicis longus, flexor digitorum superficialis and profondus) and the median nerve from the forearm into the hand.

Surface markings are, proximally, the distal wrist crease; distally, the hook of the hamate bone.

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, then curves back over the flexor retinaculum to reach the thenar eminence. It is endangered in carpal tunnel surgery if the incision over the carpal tunnel is made too far laterally (thumb side).

Boundaries

The 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, and to the pisiform and hook of the hamate medially.

Contents

The carpal tunnel transmits 9 tendons and one nerve:

• Median nerve
• Flexor digitorum superficialis contributes 4 tendons that insert on the middle phalanx of digits 2-5.
• Flexor digitorum profundus contributes 4 tendons that insert on the distal phalanx of digits 2-5.
• Flexor pollicis longus

From superficial to deep, the structures encountered in exposing the carpal tunnel, are:

• Skin
• Palmaris longus tendon merging with palmar aponeurosis
• Flexor retinaculum
• Flexor digitorum superficialis
• Flexor pollicis longus
• Flexor digitorum profundus

The median nerve is just deep to the flexor retinaculum on the lateral side.

Relevance

---

The carpal tunnel is important because the median nerve can be compressed in cases such as the following:

• Carpal tunnel syndrome
• Wrist dislocations
• Fractures around the wrist

Wrist

Karpaltunnel