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Body Surface

The primary surface landmarks of the anterior forearm and palmar hand are associated with the humerus (medial and lateral epicondyles), pisiform, hamate (hamulus), biceps brachii, flexor carpi ulnaris and flexor carpi radialis tendons, and thenar and hypothenar eminances. The skin overlying the anterior forearm and palmar hand is innervated by the medial and lateral cutaneous nerves of the forearm, and palmar and digital branches of median and ulnar nerves.

Skeleton and Joints

The bones and joints associated with the anterior forearm and palmar hand are the humerus, radius and ulna articulating at the elbow joint, the radius, ulna and carpals articulating at the wrist joint, the carpals and metacarpals at the metacarpal-phalangeal joints and the proximal, intermediate and distal phalanges at the interphalangeal joints. The elbow joint moves in flexion and extension and contributes to pronation and supination of the forearm. The wrist joint moves in flexion and extension, and abduction and adduction. The carpal-metacarpal joints move in flexion and extension, abduction and adduction, and opposition (1st only). The interphalangeal joints move in flexion and extension.

Fascial Organization

The antebrachial (deep) fascia, its two intermuscular septa and the interosseous membrane divide the forearm into two compartments and a third region, the mobile wad. The intermuscular septa attach to the radius and separate the mobile wad (brachioradialis, and extensor carpi radialis longus and brevis) from the anterior (flexor) and posterior (extensor) compartments.

The anterior compartment muscles are subdivided into a superficial group attaching in part to the medial epicondyle of the humerus, and a deep group attaching in part to the radius, ulna and interosseous membrane. The palmar aponeurosis (deep fascia) has distinct longitudinally, transversely and vertically oriented fibrous bands overlying the soft tissue structures. A common synovial sheath is deep to the palmar aponeurosis and is continuous with the digital synovial sheaths of the thumb and 5th finger. The 2nd, 3rd and 4th fingers have independent synovial sheaths. The digital synovial sheaths are covered by fibrous flexor sheaths. The intrinsic muscles of the hand are organized into three ( thenar, hypothenar and interosseous) compartments.

The flexor retinaculum is a strong, fibrous thickening of the anterior antebrachial fascia at the wrist. It splits into superficial and deep laminae. The ulnar artery and nerve pass between the two laminae ( Guyon's canal) adjacent to the hamulus. The deep lamina splits laterally to form a tunnel for the flexor carpi radialis tendon. The remaining flexor tendons (flexor digitorum superficialis, flexor digitorum profundus and flexor pollicus longus) and median nerve pass deep to the flexor retinaculum (transverse carpal ligament) as they traverse the carpal tunnel.

Muscles

The muscles of the anterior compartment of the forearm are active in pronation, flexion and pronation of the forearm ( pronator teres), flexion ( flexor carpi radialis, flexor carpi ulnaris, flexor digitorum superficialis and flexor digitorum profundus), abduction (flexor carpi radialis) and adduction (flexor carpi ulnaris) of the wrist, flexion of the 1st digit ( flexor pollicis longus) and flexion of the 2nd – 5th digits (flexor digitorum superficialis and flexor digitorum profundus). Thenar muscles are active in flexion (flexor pollicis brevis), abduction (abductor pollicis brevis), adduction ( adductor pollicis) and opposition ( opponens pollicis) of the 1st digit. Hypothenar muscles are active in flexion ( flexor digiti minimi brevis), abduction ( abductor digiti minimi) and opposition ( opponens digiti minimi) of the 5th digit. The interosseous compartment muscles are active in metacarpal – phalangeal flexion ( dorsal and palmar interosseous), interphalangeal extension (dorsal and palmar interosseous), abduction (dorsal interosseous) and adduction (palmar interosseous) of the 2nd – 5th digits.

Innervation

The median and ulnar nerves innervate the muscles of the anterior compartment of the forearm. The recurrent branch of the median nerve and deep branch of the ulnar nerve innervate the muscles of the thenar compartment of the hand. The deep branch of the ulnar nerve innervates the muscles of the hypothenar and interosseous compartments of the hand.

Blood Supply

Branches of the radial, ulnar and anterior interosseous arteries supply the anterior compartment of the forearm. Branches of the radial artery supply the thenar compartment of the hand. Branches of the superficial palmar arterial arch supply the hypothenar compartment and the 2nd – 5th digits. Branches of the deep palmar arterial arch supply the interosseous compartment of the hand.