Nerves

Carpal Tunnel Master And Beyond

Treatments for Carpal Tunnel Syndrome

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Median nerve

Proximal to the wrist joint the median nerve travels between the flexor digito-rum superficialis and FCR muscles. It then courses through the carpal tunnel along with the flexor tendons of the fingers and thumb. The carpal tunnel is a fibro-osseous canal bordered volarly by the flexor retinaculum, medially by the pisiform and the hook of the hamate, laterally by the scaphoid and trapezium, and dorsally by the carpal bones.

The flexor retinaculum is composed of three parts: the antebrachial fascia proximal to the wrist bones (see Fig. 4A), the transverse carpal ligament proper, extending from the scaphoid and trapezium to the pisiform and the hook of the hamate (see Fig. 4B), and, more distally, the palmar aponeurosis between the thenar and hypothenar muscles (see Fig. 4C) [24]. The carpal tunnel is narrowest at the level of the hook of hamate and trapezium.

The carpal tunnel contains synovium, the median nerve, and the nine extrinsic flexor tendons of the thumb and fingers, including the flexor pollicis longus tendon, the four flexor digitorum superficialis tendons, and the four flexor

Mri Flexor Pollicis Longus Tendon

Fig. 4. Normal anatomy—carpal tunnel. (A) Axial proton-density weighted image at the level of the proximal carpus demonstrates the median nerve (arrow) underneath the antebrachial fascia (arrowheads). Flexor carpi ulnaris indicated by open arrowhead. us, ulnar styloid. (B) Axial image at the level of the transverse carpal ligament proper (arrowheads). Median nerve indicated by arrow. t, trapezium; h, hook of the hamate. (C) Axial image at the level of the metacarpals demonstrates the palmar aponeurosis (arrowheads) extending between the thenar and hypothenar muscles. Median nerve indicated by arrow. fpl, flexor pollicis lon-gus tendon.

Fig. 4. Normal anatomy—carpal tunnel. (A) Axial proton-density weighted image at the level of the proximal carpus demonstrates the median nerve (arrow) underneath the antebrachial fascia (arrowheads). Flexor carpi ulnaris indicated by open arrowhead. us, ulnar styloid. (B) Axial image at the level of the transverse carpal ligament proper (arrowheads). Median nerve indicated by arrow. t, trapezium; h, hook of the hamate. (C) Axial image at the level of the metacarpals demonstrates the palmar aponeurosis (arrowheads) extending between the thenar and hypothenar muscles. Median nerve indicated by arrow. fpl, flexor pollicis lon-gus tendon.

digitorum profundus tendons. Intratunnel bursae are located along the radial aspect of the flexor pollicis longus and ulnar aspect of the flexor digitorum superficialis and profundus to the third and fourth digits.

At the wrist the median nerve supplies the thenar eminence muscles: the abductor pollicis brevis, opponens pollicis, and the superficial head of the flexor pollicis brevis. It also supplies the first and second lumbricals and provides sensation to the palmar and distal dorsal aspects of the radial three and a half fingers.

Ulnar nerve

At the wrist the ulnar nerve, accompanied by the more lateral ulnar artery, traverses superficial to the flexor retinaculum within Guyon's canal, also known as the ''pisohamate tunnel'' or the ''distal ulnar tunnel'' [25]. The triangular fi-bro-osseous tunnel is bordered by the pisiform medially, the hook of the hamate laterally, and the palmar carpal ligament volarly (Fig. 5). The tendons of the flexor digitorum profundus, the transverse carpal ligament, the pisoha-mate and pisometacarpal ligaments, and the opponens digiti minimi muscle form the floor of the canal.

The ulnar nerve supplies sensory branches to the dorsal ulnar hand and a palmar branch to the skin over the hypothenar eminence proximal to Guy-on's canal. Within the canal, the ulnar nerve gives off superficial and deep terminal branches. The superficial branch supplies a branch to the palmaris brevis muscle and provides sensation to the fifth finger and ulnar half of the fourth finger. The deep motor branch takes an acute lateral turn at the hook of the hamate and enters the pisohamate hiatus. This is the most vulnerable site for compression of the deep motor branch of the ulnar nerve. The deep motor branch innervates the hypothenar muscles, including the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi, as well as the adductor pollicis, the third and fourth lumbricals, and all the interossei muscles.

Axial Flexor Digiti Minimi
Fig. 5. Normal anatomy—ulnar nerve. Axial proton-density image demonstrates the ulnar nerve (arrow) within Guyon's canal. The ulnar nerve travels closer to the hook of the hamate than the adjacent artery and vein (black arrowhead). Median nerve indicated by white arrowhead.

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