The lumbricals pass dorsally around the lateral side of each finger, and insert into the extensor hood (Fig. 7.108). The tendons of the muscles are anterior to the deep transverse metacarpal ligaments.
The lumbricals are unique because they link flexor tendons with extensor tendons. Through their insertion into the extensor hoods, they participate in flexing the metacarpophalangeal joints and extending the interphalangeal joints.
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 (Table 7.15).
The blood supply to the hand is by the radial and ulnar arteries, which form two interconnected vascular arches (superficial and deep) in the palm (Fig. 7.109). Vessels to the digits, muscles, and joints originate from the two arches and the parent arteries:
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.
The ulnar artery and ulnar nerve enter the hand on the medial side of the wrist (Fig. 7.110). The vessel lies between the palmaris brevis and the flexor retinaculum and is lateral to the ulnar nerve and the pisiform bone. Distally, the ulnar artery is medial to the hook of the hamate bone and then swings laterally across the palm, forming the superficial palmar arch, which is superficial to the long flexor tendons of the digits and just deep to the palmar aponeurosis. On the lateral side of the palm, the arch communicates with a palmar branch of the radial artery.
One branch of the ulnar artery in the hand is the deep palmar branch (Figs. 7.109 and 7.110), which arises from the medial aspect of the ulnar artery, just distal to the pisiform, and penetrates the origin of the hypothenar muscles. It curves medially around the hook of the hamate to access the deep plane of the palm and to anastomose with the deep palmar arch derived from the radial artery.
Branches from the superficial palmar arch include: a palmar digital artery to the medial side of the little finger, and three large, common palmar digital arteries, which ultimately provide the principal blood supply to the lateral side of the little finger, both sides of the ring and middle fingers, and the medial side of the index finger (Fig. 7.110); they are joined by palmar metacarpal arteries from the deep palmar arch before bifurcating into the proper palmar digital arteries, which enter the fingers.
The radial artery curves around the lateral side of the wrist and passes over the floor of the anatomical snuffbox and into the deep plane of the palm by penetrating anteriorly through the back of the hand (Figs. 7.109 and 7.111). It passes between the two heads of the first dorsal interosseous muscle and then between the two heads of the adductor pollicis to access the deep plane of the palm and form the deep palmar arch.
The deep palmar arch passes medially through the palm between the metacarpal bones and the long flexor tendons of the digits. On the medial side of the palm, it communicates with the deep palmar branch of the ulnar artery (Figs. 7.109 and 7.111).
Before penetrating the back of the hand, the radial artery gives rise to two vessels: a dorsal carpal branch, which passes medially as the dorsal carpal arch, across the wrist and gives rise to three dorsal metacarpal arteries, which subsequently divide to become small dorsal digital arteries, which enter the fingers; and the first dorsal metacarpal artery, which supplies adjacent sides of the index finger and thumb.