The fasciae of the forearm and the hand The antebrachial fascia

• The antebrachial fascia (fascia antebrachii/фасция предплечья) invests the forearm muscles and produces fibrous septa which projects between them.

• On the dorsal surface the antebrachial fascia forms a transverse thickening in the form of a ligament, which is called the extensor retinaculum (retinaculum musculorum extensorum/удерживатель мышц-разгибателей). Processes from the retinaculum fuse with the dorsal surface of the ulna and radius. Between the processes under ligament there are six dorsal carpal tendinous sheaths. These sheaths transmit the tendons of the finger and wrist extensors. If to count from the radial to the ulnar border:

• The first sheath transmits the tendons of the abductor pollicis longus and the extensor pollicis brevis.

• The second sheath transmits the tendons of the extensors carpi radials longus and brevis.

• The third sheath transmits the tendon of the extensor pollicis longus.

• The fourth sheath transmits the tendons of the extensor digitorum and extensor indicis.

• The fifth sheath transmits the tendons of the extensor digiti minimi.

• The sixth sheath transmits the tendons of the extensor carpi ulnaris.

The walls of the canals are lined with a synovial membrane, which, above and below the extensor retinaculum, folds over tendons and covers them. The sheaths protrude on the dorsal surface of the hand.

• On the palmar surface the antebrachial fascia forms a transverse thickening in the form of a ligament, which is called the flexor retinaculum (retinaculum musculorum flexorum/удерживатель мышц-сгибателей). The flexor retinaculum converts the carpal groove into the carpal canal or tunnel (canalis carpalis/канал запястья). In the carpal canal there are two separate palmar carpal tendinous sheaths:

• The common flexor sheath (vag. communis tendinum musculorum flexorum/общее влагалище сухожилий сгибателей) is a large medially located sac enclosing eight tendons of the deep and superficial flexors of the fingers. It protrudes 1-2 cm proximally of the flexor retinaculum superiorly, while inferiorly it reaches the middle of the palm. The sheath continues only on the tendons of the long flexors of the little finger and reaches the base of its distal phalanx.

• The tendinous sheath of flexor pollicis longus (vagina tendinis m. flexoris pollicis longi/влагалище сухожилия длинного сгибателя большого пальца кисти) is situated laterally. Superiorly this sheath protrudes 1-2 cm proximally of the flexor retinaculum, while inferiorly it extends on the tendon to the base of the distal phalanx of the thumb.

The remaining three fingers have separate sheaths, enclosing the tendons of the flexors of the corresponding finger. These sheaths extend from the line of the metacarpophalangeal joints to the base of the distal phalanges.

• The flexor retinaculum forms separating and running to the radial and ulnar sides, the radial carpal canal and the ulnar carpal canal respectively.

• The tendon of the flexor carpi radialis ensheathed in a synovial sheath lies in the radial carpal canal.

• The ulnar nerves and vessels pass in the ulnar carpal canal.

Palmar fascia

The palmar fascia covers the muscles of the hand.

• The thickened fascia in the middle of the palm forms a strong palmar aponeurosis (aponeurosis palmaris/ладонный апоневроз), which is a triangle extension of the tendon of the long palmar muscle. Its apex is directed to the flexor retinaculum, the base is directed to the fingers.

• The palmar aponeurosis forms on the palmar surface of the fingers osteofibrous canals called the fibrous sheaths of digits of hand (vaginae fibrosae digitorum manus/фиброзные влагалища пальцев кисти) that surrounds the tendons of flexors and their sheath. These sheaths has two types of fibres:

• The annular part of fibrous sheath (pars anularis vaginae fibrosae/кольцевая часть фиброзного влагалища) near the shaft of the phalanx.

• The cruciform part of fibrous sheath (pars cruciformis veginae fibrosae/крестообразная часть фиброзного влагалища) near the interphalangeal joints.

• The deep layer of the palmar fascia covers the middle muscles of the hand. Besides these muscles the deep layer fuses with the palmar aponeurosis.