In the human body, the carpal tunnel or carpal canal is a flattened body cavity on the flexor (palmar/volar) side of the wrist, bounded by the carpal bones and flexor retinaculum. It forms the passageway that transmits the median nerve and the tendons of the extrinsic flexor muscles of the hand from the forearm to the hand. The median artery is an anatomical variant (increasingly found). When present it lies between the radial artery, and the ulnar artery and runs with the median nerve supplying the same structures innervated.
When swelling or degeneration occurs in the tendons and sheaths of any of the nine flexor muscles (flexor pollicis longus, four flexor digitorum profundus and four flexor digitorum superficialis) passing through the carpal tunnel, the canal can narrow and compress/entrap the median nerve, resulting in a compression neuropathy known as carpal tunnel syndrome (CTS). If untreated, neuropraxia, parasthesia and muscle atrophy (especially of the thenar muscles) can occur. The condition often requires surgical division of the retinaculum to relieve the pressure upon the nerve.