Entrapment Syndromes of the Median Nerve

Abstract

13.1 Anatomy [ 5 ] It's a mixed nerve (motor, sensorial, and neurovegetative role). It comes from the roots C6 to T1 and passes through the posterior cord (C6–C7) and medial cord (C8–T1) and then through the brachial canal until the Struthers ligament (inconstant) above the medial epicondyle, to reach the bicipital groove. It then passes between the two heads of the pronator teres where it gives off the anterior interosseous branch. This nerve innervates the fl exor indicis profundus, the fl exor pollicis longus, and the pronator quadratus, as well as a part of the wrist joints. The median nerve then passes under the fl exor digitorum superfi cialis. The palmar cutaneous branch of the median nerve arises from its lateral side 6 cm above the palmar fl exion crease of the wrist, passes between the fl exor carpi radialis and the palmaris longus, and then passes through the antebrachial aponeu-rosis above the wrist to give off its terminal branches (sensitivity of the thenar com-partment) (Fig. 13.1). It enters the hand at the level of the carpal tunnel, which is an hourglass-shaped inextensible osteofi brous tunnel. Its narrow part is the hamulus. It's formed dorsally by the palmar concave osteo-ligamentous groove and closed in the front by the fl exor retinaculum composed by two layers: • The superfi cial layer and the antebrachial fascia prolonged distally by the palmar aponeurosis [ 9 ]. • The deep layer with the carpi volare proximally, then from the distal palmar crease of the wrist, from the fl exor retinaculum [ 8 , 11 ] that spreads from the pisiform bone to the apophysis of the sesamoid bone inward, and from the scaph-oid's tubercle to the trapezium bone outward. Its distal part is covered by fat tissues that form the fat pad of Kaplan and Milford, which contains the superfi -cial palmar arch. Between these two layers and the two compartments, there is the fascia of Mirza. Its most internal part forms the fl oor of Guyon's canal, limited inward by the insertion of the fl exor carpi ulnaris on the pisiform bone and in the front by the antebrachial fascia.