Hand Bones and Flexor Retinaculum

Hand Anatomy

• Carpal bones can be remembered using the mnemonic "She Looks Too Proud, Try To Chase Her"
• Proximal row of carpal bones: Scaphoid, Lunate, Triquetrum, Pisiform
• Distal row of carpal bones: Trapezium, Trapezoid, Capitate, Hamate

Flexor Retinaculum

• A thickening of deep fascia that holds long flexor tendons in position at the wrist
• Attaches medially to the pisiform bone and the hook of the hamate, and laterally to the tubercle of the scaphoid and the trapezium bones

Structures Passing Deep to Flexor Retinaculum

• Flexor digitorum superficialis tendons
• Median nerve
• Flexor pollicis longus tendon
• Flexor carpi radialis tendon

Structures Passing Superficial to Flexor Retinaculum

• Flexor carpi ulnaris tendon
• Ulnar nerve
• Ulnar artery
• Palmar cutaneous branch of the ulnar nerve
• Palmaris longus tendon
• Palmar cutaneous branch of the median nerve

Carpal Tunnel

• A fibro-osseous canal formed by the carpal bones and the flexor retinaculum
• Contents: tendons of FDS, FDP, and FPL, and the median nerve

Muscles of the Hand

• Divided into two groups: extrinsic and intrinsic
• Extrinsic group: muscles that originate outside the hand and insert into the hand bones
• Intrinsic group: arranged in five parts - thenar eminence, hypothenar eminence, adductor pollicis, interosseous muscles, and lumbrical muscles

Thenar Eminence

• Three muscles responsible for the prominent swelling on the lateral side of the palm at the base of the thumb
• Opponens pollicis, flexor pollicis brevis, and abductor pollicis brevis
• All supplied by the recurrent branch of the median nerve

Hypothenar Eminence

• Three muscles responsible for the swelling at the base of the little finger
• Branches: three palmar metacarpal arteries and three perforating branches

Dorsal Carpal Arch

• Formed by the radial artery before penetrating the back of the hand
• Gives rise to the dorsal carpal branch, which passes medially as the dorsal carpal arch, and subsequently divides to become small dorsal digital arteries

Veins of the Hand

• Deep veins follow the arteries
• Superficial veins drain into a dorsal venous network on the back of the hand over the metacarpal bones
• The Cephalic vein originates from the lateral side of the dorsal venous network and passes over the anatomical snuffbox into the forearm
• The Basilic vein originates from the medial side of the dorsal venous network and passes into the dorso-medial aspect of the forearm

Nerves of the Hand

• The hand is supplied by the ulnar, median, and radial nerves
• The ulnar nerve innervates all intrinsic muscles of the hand except for the three thenar muscles and the two lateral lumbricals, which are innervated by the median nerve
• The radial nerve only innervates skin on the dorsolateral side of the hand

Extensor Retinaculum

• A strong, fibrous band that extends obliquely across the back of the wrist
• Attached laterally to the anterior border of the radius, and medially to the triquetral and pisiform bones

Adductor Pollicis

• Originates as two heads: transverse head from the anterior aspect of the shaft of the 3rd metacarpal, and oblique head from the capitate and adjacent bases of the 2nd and 3rd metacarpals
• Inserts into the medial side of the base of the proximal phalanx of the thumb
• Supplied by the deep branch of the ulnar nerve
• Action: adduction of the thumb

Interosseous Muscles

• Divided into two groups: dorsal interossei and palmar interossei
• All are supplied by the deep branch of the ulnar nerve
• Action: PAD (palmar abduction of the fingers), DAB (dorsal abduction of the fingers)

Lumbrical Muscles

• Four worm-like muscles, each associated with one of the fingers
• Originate from the tendons of FDP in the palm
• The medial two lumbricals are innervated by the deep branch of the ulnar nerve; the lateral two lumbricals are innervated by digital branches of the median nerve
• Action: flex MPJ (metacarpophalangeal joint) and extend IPJ (interphalangeal joint)

Blood Vessels of the Hand

• Blood supply to the hand is by the radial and ulnar arteries
• These arteries form two interconnected vascular arches (superficial and deep) in the palm
• The radial artery contributes substantially to the supply of the thumb and the lateral side of the index finger
• The remaining digits and the medial side of the index finger are supplied mainly by the ulnar artery