anatomy

Last reviewed 07/2023

The carpal tunnel lies deep to the flexor retinaculum on the anterior aspect of the wrist, overlying the carpal bones.

The single soft-tissue structure in the carpal tunnel is the median nerve. The median nerve is therefore susceptible to damage by any lesion compressing the contents of the carpal tunnel.

The other structures in the carpal tunnel are the long flexor tendons of the fingers.

Sensory supply of the median nerve:

The median nerve supplies sensation to the palmar surface of the hand, including the thumb, index, middle and radial half of the ring fingers.

A palmar branch of the median nerve actually runs superficial to the flexor retinaculum, unlike the main part of the nerve, so sensation to the palm may be preserved in carpal tunnel syndrome.

Motor supply of the median nerve:

The median nerve provides motor supply to the muscles of the thenar eminence, recalled with the acronym "LOAF" -

• L = lateral two lumbricals
• O = opponens pollicis
• A = abductor pollicis brevis
• F = flexor pollicis brevis

Opposition of the thumb is particularly affected in carpal tunnel syndrome as other movements are assisted by muscles not innervated by the median nerve.