FASCIA AND SUPERFICIAL ANATOMY OF THE HAND
The fascia of the palm of the hand is continuous with the antebrachial fascia of the flexor aspect of the forearm and with the palmar carpal ligament. At the borders of the hand, it is continuous with the fascia of the dorsum at attachments to the first and fifth metacarpals. The hypothenar fascia invests the muscles of the little finger and bounds the hypothenar compartment of the hand by means of a palmar attachment to the radial side of the fifth metacarpal. In a similar manner, the fascia over the thumb muscles dips deeply to attach to the palmar aspect of the first metacarpal and bounds, with the metacarpal, a thenar compartment in the hand. The central compartment of the palm is covered by the intervening part of the fascia of the palm, but this portion is reinforced superficially by the palmar aponeurosis, an expansion of the tendon of the palmaris longus muscle. Recognizable in the palmar aponeurosis are a superficial stratum of longitudinally running fibers (which is continuous with the tendon of the palmaris longus muscle) and a deeper layer of transverse fibers. The transverse fibers are continuous with the thenar and hypothenar fasciae; proximally, they are continuous with the flexor retinaculum and the transverse carpal ligament. The palmar aponeurosis broadens distally in the palm and divides into four digital slips, some of its fibers meanwhile attaching to the overlying skin at the skin creases of the palm. The central parts of these slips pass into the digits, attaching superficially to the skin of the crease at the base of each digit; deeply, they attach to the fibrous sheath of the digit. The marginal fibers sink deeply between the heads of the metacarpals and attach to the metacarpophalangeal joint capsules, the deep transverse metacarpal ligaments, and the proximal phalanges of the digits. There is usually no digital slip for the thumb, but longitudinal fibers of the aponeurosis usually curve over onto the thenar fascia.
The deep attachments of the margins of the digital slips of the palmar aponeurosis define the entrance to the fibrous sheath of each digit, but they are also continued proximally into the palm for varying distances. They attach to the palmar interosseous fascia and to the shafts of the metacarpals, thus providing communicating subcompartments for each pair of flexor tendons and the associated lumbrical muscles (see Plate 4-15). The septum reaching the third metacarpal is stronger and more constant; it separates a surgical thenar space under the aponeurosis to its radial side and a midpalmar space to its ulnar side.
Accumulations of the deeper transverse fibers of the aponeurosis appear between the diverging digital slips. Located at the level of the heads of the metacarpals, these fibers are designated as the superficial transverse metacarpal ligament. Distally, the webs of the fingers are reinforced by another accumulation of transverse fibers designated as transverse fasciculi.
The fascia of the dorsum of the hand is continuous with the antebrachial fascia of the extensor surface of the forearm and with the extensor retinaculum. It encloses the tendons of the extensor muscles as they pass to the digits and continues into the extensor expansions on the dorsum of the digits; deep to it is a subaponeurotic space. This interfascial cleft separates the fascia of the dorsum from the deeper dorsal interosseous fascia covering the dorsal interosseous muscles and the descending branches of the dorsal carpal arterial arch (see Plate 4-16).
The superficial lymphatic vessels of the upper limb begin in the hand and pervade the skin and subcutaneous tissues (see Plates 4-16 and 4-17). The dense digital lymphatic plexuses are drained by channels accompanying the digital arteries. At the interdigital clefts (and also more distally), collecting vessels of the palmar surfaces of the fingers pass to join dorsal collecting vessels and empty into the plexus of the dorsum of the hand.
Drainage of the thumb, index finger, and radial portion of the third finger is by collecting vessels that ascend along the radial side of the forearm; channels draining the ulnar fingers ascend along the ulnar side. Vessels from the lymphatic plexus of the palm radiate to the sides of the hand and also upward through the wrist, coalescing into two or three collecting vessels that ascend in the middle of the anterior surface of the forearm. The radial and ulnar channels turn onto the anterior surface of the forearm, lying parallel to the middle group, and all continue subcutaneously through the forearm and arm to reach the axillary nodes.
Some of the ulnar lymphatic channels are efferent to the cubital lymph nodes. This superficial group of one or two nodes is located 3 to 4 cm above the medial epicondyle of the humerus and below the aperture in the brachial fascia for the basilic vein. The afferent vessels of these nodes include channels originating in the ulnar three fingers and the ulnar portion of the forearm. The efferent vessels accompany the basilic vein under the brachial fascia and reach the lateral and central groups of axillary lymph nodes.
Several lymphatic channels collecting from the dorsal surface of the arm follow the upper course of the cephalic vein to the deltopectoral triangle, perforate the costocoracoid membrane with the vein, and terminate in an apical node of the axillary group. In about 10% of cases, this channel is interrupted in the deltopectoral triangle by one or two small deltopectoral nodes.
AXILLARY LYMPH NODES
The axillary lymph nodes, usually large and numerous, are arranged in five subgroups, some related to the axillary walls and others to vessels.
A lateral group of three to five nodes lies medial and posterior to the distal segment of the axillary vein. These nodes are in the direct line of lymph drainage from the upper limb, except for the drainage lymphatics along the cephalic vein. Efferent vessels from these nodes drain to the central and apical nodes.
A pectoral group is located along the lateral thoracic artery adjacent to the axillary border of the pectoralis minor muscle. These three to five nodes receive the lymphatic drainage of the anterolateral part of the thoracic wall, including most of the lateral drainage from the mammary gland, and of the skin and muscles of the supraumbilical part of the abdominal wall. Efferent lymphatic vessels reach the central and apical groups.
A subscapular group of five or six nodes is stretched along the subscapular blood vessels, from their origin in the axillary vessels to their contact with the chest wall. These nodes drain the skin and muscles of the posterior thoracic wall and shoulder region and also the lower part of the back of the neck. Their efferent lymph channels pass to the central axillary nodes.
A central group of four or five nodes lies under the axillary fascia, embedded in its fat. Among the largest of the axillary nodes, these nodes receive some lymphatic vessels directly from the arm and mammary regions; but primarily, they receive lymph from the lateral, pectoral, and subscapular groups. Their efferent channels pass to the apical nodes.
The apical group, consisting of 6 to 12 nodes, lies along the axillary vein at the apex of the axilla and adjacent to the superior border of the pectoralis minor muscle. The apical nodes receive efferent vessels of all other axillary groups, lymphatic vessels that accompany the cephalic vein, and lymphatic vessels from the mammary gland. From lymph vessels interconnecting the apical nodes arises a larger common channel, the subclavian lymphatic trunk.
These vessels serve the upper limb, draining joint capsules, periosteum, tendons, nerves, and, to a lesser extent, muscles. Collecting vessels accompany the major arteries, along whose paths lie small intercalated lymph nodes. The deep lymphatics are afferent to the central and lateral axillary nodes.
The subcutaneous veins of the limb are interconnected with the deep veins of the limb via perforating veins. Certain prominent veins, unaccompanied by arteries, are found in the subcutaneous tissues of the limbs. The cephalic and basilic veins, the principal superficial veins of the upper limb, originate in venous radicals in the hand and digits.
Anastomosing longitudinal palmar digital veins empty at the webs of the fingers into longitudinally oriented dorsal digital veins. The dorsal veins of adjacent digits then unite to form relatively short dorsal metacarpal veins, which end in the dorsal venous arch. The radial continuation of the dorsal venous arch is the cephalic vein, which receives the dorsal veins of the thumb and then ascends at the radial border of the wrist. In the forearm, it tends to ascend at the anterior border of the brachioradialis muscle, with tributaries from the dorsum of the forearm. In the cubital space, the obliquely ascending median cubital vein connects the cephalic and basilic veins. Above the cubital fossa, the cephalic vein runs in the lateral bicipital groove and then in the interval between the deltoid and pectoralis major muscles, where it is accompanied by the small deltoid branch of the thoracoacromial artery. At the deltopectoral triangle, the cephalic vein perforates the costocoracoid membrane and empties into the axillary vein. An accessory cephalic vein passes from the dorsum of the forearm spirally laterally to join the cephalic vein at the elbow.
The basilic vein continues the ulnar end of the venous arch of the dorsum of the hand (see Plate 4-17). It ascends along the ulnar border of the forearm and enters the cubital fossa anterior to the medial epicondyle of the humerus. After receiving the median cubital vein, the basilic vein continues upward in the medial bicipital groove, pierces the brachial fascia a little below the middle of the arm, and enters the neurovascular compartment of the medial intermuscular septum, where it lies superficial to the brachial artery. In the distal axilla, it joins the brachial veins to form the axillary vein.
The median antebrachial vein is a frequent collecting vessel of the middle of the anterior surface of the forearm. It terminates in the cubital fossa in the median cubital vein or in the basilic vein. It sometimes divides into a median basilic vein and a median cephalic vein, which borders the biceps brachii laterally and joins the cephalic vein. The median antebrachial vein may be large or absent.