APL, Abductor pollicis longus; ECRB, extensor carpi radialis brevis; ECRL, extensor carpi radialis longus; ECU, extensor carpi ulnaris; EDC, extensor digitorum communis; EDM, extensor digiti minimi; EIP, extensor indicis proprius; EPB, extensor pollicis brevis; EPL, extensor pollicis longus.

Cross-sectional anatomy (see Fig. 4-9) at the following levels: (1) distal radioulnar joint, (2) proximal carpal row, (3) distal carpal row, and (4) proximal metacarpal.

Landmarks (see Fig. 4-10): palpable anatomic landmarks: the pisiform, the hook of the hamate, Lister’s tubercle, and the palmaris.

Muscles

Best considered in groups (Table 4-2)

Table 4-2

Hand Musculature

GROUP	MUSCLES	ORIGIN	INSERTION	INNERVATION	ACTION
Thenar	Opponens pollicis	Flexor retinaculum and tubercle of trapezium	Radial border of the first metacarpal	Recurrent motor branch of the median nerve	Thumb opposition
	Abductor pollicis brevis	Scaphoid tubercle and flexor retinaculum	Base of the thumb proximal phalanx and the tendon of EPL	Recurrent motor branch of the median nerve	Thumb abduction
	Flexor pollicis brevis	Flexor retinaculum and tubercle of trapezium	Base of the thumb proximal phalanx	Dual innervation—deep head ulnar, superficial head median nerves	Flexion of the thumb MCP joint
	Adductor pollicis	Transverse head—third MC; oblique head—trapezium, trapezoid, capitate, and bases of the second and third MC	Ulnar side of the thumb proximal phalanx base	Deep branch of the ulnar nerve	Thumb adduction
Hypothenar	Abductor digiti minimi	Pisiform and pisohamate ligament, flexor retinaculum	Fifth digit proximal phalanx base and extensor hood	Deep branch of the ulnar nerve	Abducts the fifth digit
	Flexor digiti minimi	Hook of hamate and flexor retinaculum	Fifth digit proximal phalanx base	Deep branch of the ulnar nerve	Flexes the fifth digit at the MCP joint
	Opponens digiti minimi	Hook of hamate and flexor retinaculum	Ulnar border of the fifth MC shaft	Deep branch of the ulnar nerve	Opposes the fifth finger
Intrinsic hand muscles	Lumbrical muscles	FDP tendons—first and second lumbricals are unipennate and arise on radial side of tendon; third and fourth lumbricals are bipennate and arise from adjacent tendons	Radial side of the extensor hood at the level of the proximal phalanx	First and second—median nerve; third and fourth—deep branch of the ulnar nerve	Flex MCP and extend PIP joints
	DI muscles	4 muscles—bipennate on metacarpal shafts	Proximal phalanges and extensor hood; first DI—radial side of index finger; second DI—radial side of middle finger; third DI—ulnar side of middle finger; fourth DI—ulnar side of ring finger	Deep branch of the ulnar nerve	Abduct from the axis of the middle finger; flex MCP joints and extend PIP joints
	PI muscles	3 muscles—unipennate on MC shafts; first PI—ulnar shaft of the second MC; second PI—radial shaft of the fourth MC; third PI—radial shaft of the fifth MC	Proximal phalanges and extensor hoods; first PI—ulnar side of index finger; second PI—radial side of ring finger; third PI—radial side of small finger	Deep branch of the ulnar nerve	Adduct toward the middle finger; flex MCP joints and extend PIP joints

DI, Dorsal interossei; EPL, extensor pollicis longus; FDP, flexor digitorum profundus; MC, metacarpal; MCP, metacarpophalangeal; PI, palmar interossei; PIP, proximal interphalangeal.