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Pectoral girdle and upper limb: Overview and surface anatomy
The upper limb is, in mechanical terms, a series of powered, articulated segments which enable the hand to be positioned accurately in space so that it can sense and manipulate its surrounding environment. It is attached to the bony thorax at the sternoclavicular joint, and to the chest wall by a series of powerful flat muscles which stabilize the scapula, allowing it to act as a stable but mobile base on which the limb can function. An extensive range of movement is enabled by a number of factors. The glenohumeral joint is remarkably little constrained and the muscles that both stabilize and move it are powerful. Elbow flexion allows movements close to the trunk, such as eating and attention to personal hygiene, while extension achieves a wide arc of reach for daily activities. Pronation and supination markedly increase the functional capacity of the hand by rotating the forearm through nearly 180°.
In the soft tissues, the deep fascial planes and the synovial sheaths permit the excursion of muscles and tendons against each other and their adjacent structures. Condensations of fascia around the neurovascular bundles segregate them and enhance gliding.
The innervation of the upper limb is complex and rich. There is a particular concentration of specialized sensory organelles in the wrist and hand, not only in the skin but also in the deep afferent system from muscles, tendons and joints. The postganglionic sympathetic vasomotor and sudomotor nerves are especially dense in the palmar skin. The basis of stereognosis, the ability to recognize the qualities of objects and textures, is a combination of stimuli from skin, tendon, muscle and joints. Movement is vital; blindfolded patients cannot identify the nature of an object if it is simply placed on the finger, but recognize it immediately if allowed to create spatial and temporal patterns by feeling the object or material between moving fingers and thumb.
Bones and Joints
The bones of the upper limb include the scapula, clavicle, humerus, radius and ulna (connected by the interosseous membrane along most of their length), the eight bones forming the carpus, five metacarpals and fourteen phalanges ( Figs 48.1 – 48.2 ). There are two phalanges in the thumb and three in each finger.
The thoracoscapular joint is the platform for function of the upper limb: paralysis of either of the two great muscles, trapezius and serratus anterior, is crippling. The limb is directly attached to the axial skeleton by one bony articulation, the sternoclavicular joint. The glenohumeral joint is shallow and little constrained, whereas the acromioclavicular joint is a plane joint stabilized by strong ligaments. The range of movements provided by these joints and the muscles acting across them is enormous. Arthrodesis of the thoracoscapular joint for facioscapulohumeral dystrophy improves flexion and abduction of the glenohumeral joint, but protraction and retraction are lost. A correctly performed glenohumeral arthrodesis retains powerful adduction, protraction and retraction, but rotation and the limited elevation achieved is dependent on rotation of the scapula. The elbow includes a hinge between the humerus and ulna, and two pivot joints, between the humerus and radius, and between the proximal radius and ulna. This permits a range of about 150° of flexion and extension, and 180° of pronosupination in conjunction with the distal radio-ulnar joint. The wrist complex allows a range of flexion and extension of about 140°, supplemented by some 70° of adduction and abduction. The condylar metacarpophalangeal joint enables 120° of flexion and extension, about 40° of abduction and adduction, and some rotation. Pronation and supination are unique to the primate upper limb. The range of movement of the thumb ray, which rests on the ‘saddle’ carpometacarpal joint, the qualities of the long muscles and the thenar muscles acting on the ray and the skin of the web space, are unique to humans.
Skin and Fascia
The skin over the front of the neck and posterior triangle is mobile and is sustained by the underlying platysma. Large flaps may be raised safely when platysma is included with the skin. The postaxial skin of the posterior aspect of the neck, shoulder, arm and forearm is thicker and hairy, whereas the glabrous preaxial skin on the anterior surface of the arm and forearm is thinner and more mobile. The situation is reversed in the hand, where the thick palmar skin is firmly secured by a fibrous skeleton to the palmar aponeurosis, whereas the dorsal skin is thinner and more mobile, especially across the joints. The characteristic furrows or creases at the elbow, wrist and interphalangeal joints represent places of anchorage of the deep fascia. The hairy skin of the axilla is especially mobile, permitting the extensive range of movement at the glenohumeral joint; it is rich in sweat glands and their sympathetic nerves. The dense sympathetic innervation in the axilla, the hand and forearm is important in temperature homeostasis. The consequences of scarring from burns or other injury, or badly placed incisions, are severe, and nowhere more so than after a deep burn of the axilla.
The superficial fascia is generally thicker on the dorsal aspect of the neck, shoulder, arm and forearm. Measurement of its thickness in the arm provides a useful measure of obesity. It is an important gliding plane between the skin and the underlying deep fascia. Nerves and vessels are at risk of entrapment or even rupture where they perforate the deep fascia to ramify into the superficial fascia and skin.
The deep fascia, intermuscular septa and the interosseous membrane between the radius and ulna define discrete compartments that enable gliding of segregated structures against one another. The medial and lateral intermuscular septa of the arm and the interosseous membrane also provide wide areas for the attachment of muscles. The various fascial compartments are relevant to the spread of infection and tumour, and are especially important in ischaemia (compartment syndrome).
The prevertebral fascia (see Fig. 35.4A ) envelops the phrenic nerve, scalene muscles, cervical ventral rami, cervical sympathetic trunk, and subclavian and vertebral arteries. It projects below the clavicle as the axillary sheath, enveloping the divisions and cords of the brachial plexus with the axillary artery, and continues into the arm as the brachial sheath, surrounding the brachial artery with its venae comitantes, the median nerve and the proximal part of the radial and ulnar nerves. The great muscles of the shoulder and axilla, deltoid, pectoralis major and latissimus dorsi are covered by deep fascia that winds around their deep surfaces to blend with the deep fascia of the arm. This latter is drawn upwards by suspensory condensations of fascia to form the cone-shaped axillary space, an arrangement that is obvious to the reader who traces the anterior surface of pectoralis major with a finger, then follows it round and deep, before thrusting the finger upwards as far at least as the lateral part of the second rib.
The deep fascia of the arm and forearm forms a sleeve that is attached to the medial and lateral intermuscular septa in the arm, to the periosteum of the medial and lateral epicondyles and olecranon at the elbow, and to the periosteum of the ulna and radius. Important condensations, such as the bicipital aponeurosis at the elbow, and the flexor and extensor retinacula at the wrist, are, in turn, subdivided by septa. Discrete compartments within the forearm separate the superficial muscles from the deep. The reader will note the relative mobility of the extensor muscles that traverse the elbow: brachioradialis and the radial extensor muscles of the wrist form the ‘mobile wad’ of Henry, overlying the deeper compartment containing the posterior interosseous nerve and vessels, supinator, the digital extensors, extensor carpi ulnaris and the long muscles acting on the thumb ray.
Three compartments are found in the anterior aspect of the forearm. The deep flexor compartment contains the anterior interosseous nerve and vessels, flexor pollicis longus, flexor digitorum profundus and pronator quadratus. The superficial compartment contains the radial artery, pronator teres, flexor carpi radialis, palmaris longus and flexor digitorum superficialis. The ulnar nerve and vessels pass in a separate sheath close to the ulna. The anterior deep fascia of the forearm continues into the hand as the palmar aponeurosis, from which a complex arrangement of septa forms the fibrous skeleton of the hand (see Fig. 51.12A ). The range of excursion of the main nerves of the upper limb across fixed points such as the first rib, the distal humerus and the distal radius, is some 10–15 mm and is enabled by gliding between the adventitia and the epineurium. More movement occurs within the plane between the epineurium and perineurium, and also within the perineurium itself ( 
Commentary 6.1 ).
Cutaneous innervation
Bundles of nerves enter the skin deep in the dermis and course towards the skin surface, giving off axons, nearly all unmyelinated, that innervate the associated end organs. The few myelinated axons terminate at hair follicles, Meissner corpuscles and Merkel complexes. The density of innervation of the epidermis is greatest in the proximal segment of the limb and there is little change between the twentieth and eightieth years.
Muscles
The sensorimotor cortex controls movements, not individual muscles. Reaching out to catch a flying object, such as a cricket ball, requires the coordination and integrated action of every muscle group in the upper limb, and indeed beyond. This system of complex and refined muscle patterning depends on the integrity of the somatic afferent and efferent pathways in the central nervous system.
The muscles of the upper limb may be grouped according to their origin and the joints on which they act. Muscles arising from the axial skeleton to act on the scapula include trapezius, levator scapulae, the rhomboids and serratus anterior. Muscles arising from the axial skeleton to act on the glenohumeral joint include the sternal head of pectoralis major, pectoralis minor and latissimus dorsi. Muscles passing between the scapula and the proximal humerus control the glenohumeral joint. They include supra- and infraspinatus, subscapularis, teres major and minor, and coracobrachialis. Deltoid and the clavicular head of pectoralis major also belong here, even though they arise in part from the clavicle. The main muscles controlling the elbow include biceps brachii and triceps: the long heads of both muscles traverse the glenohumeral joint to insert on the scapula. The main muscles controlling supination and pronation are biceps brachii and supinator, pronator teres and pronator quadratus. The radiocarpal joint is controlled by extensors carpi radialis longus and brevis, extensor carpi ulnaris, flexors carpi ulnaris and radialis, and palmaris longus. The muscles acting on the thumb ray include the powerful flexor pollicis longus, the much weaker abductor pollicis longus, and extensors pollicis longus and brevis. These last three are essential for thumb function. The unopposed action of flexor pollicis longus leads to the virtually useless thumb in palm posture. The extension and flexion of the metacarpophalangeal and interphalangeal joints of the fingers rest on coordinated activity in extensor digitorum, flexors digitorum superficialis and profundus, and the interosseous and lumbrical muscles. Extensor digitorum alone extends the metacarpophalangeal joints; the long flexors alone flex the interphalangeal joints. The imbalance caused by paralysis of the small muscles leads to ‘clawing’ deformity (see Fig. 48.27 ). The small muscles of the hand may be considered as those controlling the thumb ray and web space; adductor pollicis lies deep to the first dorsal interosseous; abductor and flexor pollicis brevis and opponens pollicis are superficial and form the ball of the thumb. The interosseous muscles acting with the lumbricals flex, abduct and adduct the metacarpophalangeal joints and, in conjunction with the long flexor and extensor muscles, enable full extension of the proximal interphalangeal joints. Abductor and opponens digiti minimi and flexor digiti minimi brevis form the hypothenar eminence and act on the little finger.
Many muscles act on more than one joint, for example, the long heads of biceps and triceps flex and extend, respectively the glenohumeral joint as well as the elbow. In addition, biceps brachii is a powerful supinator of the forearm. Extensor carpi radialis longus not only extends the wrist, but also is a powerful abductor of that joint and a flexor of the elbow in pronation. Flexor carpi ulnaris is the most powerful muscle in the forearm; it contributes to elbow flexion, flexes and adducts the wrist, and is active in all sustained movements of the wrist.
Certain muscles are functionally segregated, e.g. the anterior part of deltoid is a powerful flexor of the glenohumeral joint, whereas the posterior part is the most powerful extensor of that joint.
Vascular Supply and Lymphatic Drainage
The detailed regional descriptions of these systems in the upper limb are found in Chapter 49, Chapter 50, Chapter 51 .
Arteries
The axial vessel is the subclavian artery, which arises from the brachiocephalic trunk on the right and directly from the arch of the aorta on the left ( Fig. 48.3 ). The artery is described in three parts that are successively anteromedial, deep and lateral to scalenus anterior. The second and third parts are in close relation to the seventh and eighth cervical and first thoracic ventral rami, and to the middle and lower trunks of the brachial plexus. The subclavian artery becomes the axillary artery at the outer border of the first rib. The axillary artery is closely related to the divisions of the brachial plexus deep to the clavicle, and to the cords below it. It continues deep to pectoralis minor and becomes the brachial artery at the inferior margin of teres major.
The brachial artery is closely related to the median nerve; both move from the medial side of the arm to the anterior aspect of the elbow, lying medial to the tendon of biceps brachii and deep to the bicipital aponeurosis. The artery divides into the radial and ulnar arteries just distal to the elbow. The ulnar artery is consistently the larger of the two. The common interosseous artery arises close to its origin and subsequently divides into the anterior and posterior interosseous arteries. The anterior interosseous artery, accompanied by the anterior interosseous nerve, lies on the interosseous membrane in the deepest part of the deep flexor compartment. The posterior interosseous artery is separated from the membrane by the deep extensor muscles. The radial and ulnar arteries remain in the flexor compartment of the forearm, the ulnar artery moving towards the ulnar nerve in the proximal quarter of the forearm; it is usually the dominant vessel for the hand. At the wrist, the radial artery passes dorsally and crosses the scaphoid and trapezium.
Important branches from the main axial vessels form extensive anastomoses that provide a collateral circulation. For example, the collateral circulation formed by branches of the thyrocervical trunk with the circumflex humeral and subscapular arteries permits survival of the limb after occlusion of either the third part of the subclavian artery, or of the axillary artery deep to the clavicle and pectoralis minor. The profunda brachii is an important channel for the posterior muscles of the arm. It accompanies the radial nerve and contributes to the collateral circulation about the elbow with the ulnar collateral and recurrent vessels and the radial collateral and recurrent vessels. The anterior interosseous artery is effectively an end artery. A series of anastomoses between the radial and ulnar arteries, such as the transversely orientated palmar and dorsal arches and the superficial and deep palmar arches, maintain a rich blood supply to the wrist and hand. There are extensive interconnections between these arches and between the dorsal and palmar phalangeal arteries.
Pulses
The pulsation of the subclavian artery is palpable at the lateral margin of sternocleidomastoid and is easily blocked by digital pressure against the first rib. This simple maoeuvre has saved lives and limbs, and should be widely known and rehearsed because it is the best method for emergency control of bleeding from the deeply placed axillary artery. The method was used successfully for high amputation or disarticulation of the shoulder in the Napoleonic wars.
The brachial artery is palpable in the arm in the groove, or valley, between biceps brachii anteriorly and the medial head of triceps brachii posteriorly; it can be traced down to the anterior aspect of the elbow, where it moves towards the midline. The radial and ulnar pulses are palpable at the wrist, where the vessels emerge from under the cover of overlying muscles.
Veins
The upper limb is drained by superficial and deep groups of vessels.
The superficial group starts as an irregular dorsal arch on the back of the hand. The cephalic vein begins at the radial extremity of the arch, and ascends along the lateral aspect of the arm within the superficial fascia to enter the deltopectoral groove. It pierces the deep fascia above the superior margin of pectoralis minor and enters the axillary vein near the tip of the coracoid ( Fig. 48.4 ). The basilic vein drains the ulnar end of the arch, passes along the medial aspect of the forearm, pierces the deep fascia at the elbow, and joins the venae comitantes of the brachial artery to form the axillary vein. The prominent median cubital vein links the cephalic and basilic veins on the flexor aspect of the elbow. It receives a number of tributaries from the flexor aspect of the forearm and gives off the deep median vein, which pierces the fascial roof of the antecubital fossa to join the venae comitantes of the brachial artery.
The deep group of veins drains the tissues beneath the deep fascia of the upper limb and is connected to the superficial system by perforating veins. The deep veins accompany the arteries, usually as venae comitantes, ultimately becoming the axillary, and subsequently the subclavian, vein.
The subclavian vein is the central continuation of the axillary vein. It starts at the outer border of the first rib, which it crosses. Initially deep to the clavicular head of pectoralis major and then to subclavius, which is a buffer between it and the overlying medial portion of the clavicle, the vein then runs deep to the insertion of sternocleidomastoid. Sometimes, only the superior margins of the vein rise above the medial end of the clavicle; sometimes, the entire vein does so. The phrenic nerve and the inferior part of scalenus anterior lie posteriorly. The subclavian vein joins the internal jugular vein to form the brachiocephalic vein at the medial border of scalenus anterior, behind the sternoclavicular joint (see Fig. 35.14 ). A pair of valves usually lies within 2 cm of this junction. The subclavian vein receives, as tributaries, the external jugular, dorsal scapular and, sometimes, the anterior jugular veins. The trifurcation of subclavian, external and internal jugular veins is demonstrable by a forced expiration (Valsalva) manœuvre, when the distended veins rise up above the sternoclavicular joint, filling the fossa above the jugular notch of the sternum ( ). Main lymphatic vessels join the subclavian veins at, or very close to, this junction with the internal jugular vein. The left subclavian vein receives the thoracic duct; the right receives the right lymphatic duct (see Fig. 35.16 ). There is a risk of air embolism after wounding of the subclavian, external or internal jugular veins.
Cutaneous blood supply
The blood supply of the skin of the upper limb is generally abundant ( Fig. 48.5 ) and rather more robust than that in the lower limb. Proximally based flaps of skin caused by ‘degloving’ injury are more likely to survive; even a distally based flap of palmar skin may do so. The skin of the lower leg is notoriously sensitive to the effects of fracture because of rupture of the vessels perforating the deep fascia; this problem is less severe in the upper limb. Three interconnected pathways may be recognized in the upper limb, namely: muscle perforators, deep fasciocutaneous vessels and the direct cutaneous supply.
Muscle perforators
Vessels pass from the deep axial vessels through muscle, perforate the deep fascia and supply the overlying skin. The latissimus dorsi myocutaneous flap based on the thoracodorsal vessels was an important development in plastic and reconstructive surgery, not only for the replacement of lost skin or reconstruction of the breast, but also in the evolution of the free-functioning muscle transfer.
Fasciocutaneous system
The fasciocutaneous system rests on branches that arise from deep vessels and pass along the intermuscular septa to perforate the deep fascia and ramify over its surface: extensive areas of skin are supplied in this way. The development of fasciocutaneous flaps, either as pedicle flaps or free grafts, has been a revolutionary advance in the treatment of severe wounds. Not only is it possible to replace large areas of lost skin, but also to improve the tissue bed that supports the main nerves thereby enhancing regeneration and relieving neuropathic pain.
Direct cutaneous supply
The direct cutaneous supply is exemplified in the palmar skin, where branches from the underlying digital vessels pass directly into the overlying skin.
Lymphatic drainage
Superficial tissues
The subcutaneous tissues of the limbs can be divided into five layers: skin (layer 1); subcutaneous fat (2); superficial fascia (3); loose areolar tissue (4) and deep fascia (5). Layer 2 can be subdivided into a superficial (2a) and deep layer (2c) by a thin transparent horizontal septum (2b) ( ). The main superficial veins and the superficial nerves are found in layer 4 and the lymphatic collectors in layer 2c and layer 4.
Superficial lymphatic vessels begin in cutaneous plexuses. In the hand, the palmar plexus is denser than the dorsal plexus. Digital plexuses drain along the digital borders to their webs, where they join the distal palmar vessels, which pass back to the dorsal aspect of the hand. The proximal palm drains towards the carpus, medially by vessels that run along its ulnar border, and laterally to join vessels draining the thumb. Several vessels from the central palmar plexus form a trunk that winds round the second metacarpal bone to join the dorsal vessels that drain the index finger and thumb.
In the forearm and arm, superficial vessels run with the superficial veins. Collecting vessels from the hand pass into the forearm on all carpal aspects. Dorsal vessels, after running proximally in parallel, curve successively round the borders of the limb to join the ventral vessels. Anterior carpal vessels run through the forearm parallel with the median vein of the forearm to the cubital region, then follow the medial border of biceps brachii before piercing the deep fascia at the anterior axillary fold to end in the lateral axillary lymph nodes.
Lymph vessels that lie laterally in the forearm receive vessels that curve round the lateral border from the dorsal aspect of the limb. They follow the cephalic vein to the level of the tendon of deltoid, where most incline medially to reach the lateral axillary nodes; a few continue with the vein and drain into the infraclavicular nodes. Vessels lying medially in the forearm are joined by vessels that curve round the medial border of the limb and follow the basilic vein. Proximal to the elbow, some end in supratrochlear lymph nodes whose efferents, together with the medial vessels that have bypassed them, pierce the deep fascia with the basilic vein and end in the lateral axillary nodes or deep lymphatic vessels.
Collecting vessels from the deltoid region pass round the anterior and posterior axillary folds to end in the axillary nodes. The scapular skin drains either to subscapular axillary nodes or by channels that follow the transverse cervical vessels to the inferior deep cervical nodes.
Deeper tissues
Deep lymph vessels follow the main neurovascular bundles (radial, ulnar, interosseous and brachial) to the lateral axillary nodes. They are less numerous than the superficial vessels and communicate with them at intervals. A few lymph nodes occur along the vessels. Scapular muscles drain mainly to the subscapular axillary nodes, and pectoral muscles drain mainly to the pectoral, central and apical nodes.
Efferent vessels from the deep cervical nodes form the jugular trunk. The right jugular trunk drains the right upper limb, the right half of the thorax and the right head and neck, and enters the right thoracic duct or directly enters the right subclavian vein close to its junction with the internal jugular. The left jugular trunk usually enters the thoracic duct, but it may directly enter either the subclavian or internal jugular vein (see Figure 35.16, Figure 49.45 ).
Acute Ischaemia and Compartment Syndromes in the Upper Limb
Common examples of the classical compartment syndrome in the upper limb occur in the flexor and extensor compartments of the forearm. Although nerve conduction is lost before muscle contractility, ischaemia is more likely to produce infarction of muscle than necrosis of nerve. Decompression of a nerve embedded within muscle that has become fibrosed by ischaemia usually leads to relief of pain and considerable improvement in sensation and sympathetic function, even when delayed for some months.
Anoxia occurs either because of cessation of flow through a main axial artery or as a result of increasing pressure within an osseofascial compartment caused by bleeding, infusion of fluid or sepsis. It destroys the integrity of the cell membrane and capillary endothelium, which means that the homeostatic balance between the intravascular, extracellular and intracellular spaces is lost. Tissue death is imminent.
The increased permeability of the vascular endothelium leads to an increase in intracompartmental pressure by exudation, which collapses the low-pressure lymphatic and venous systems. The final event is the closure or obstruction of perfusing arterioles to muscles and the extrinsic supply to nerves, when tissue or extravascular pressure exceeds the cortical closing pressure of those vessels. The vicious circle is complete. The fluid entering the compartment cannot get out and continues to leak into the compartment until the pressure is so high that inflow is blocked. Increasing intracompartmental pressure occurs when the collateral circulation is inadequate after occlusion of the main artery or after restoration of flow through that vessel, unless the compartments have been decompressed adequately by fasciotomy. The vascular anastomoses about the joints of the upper limb provide a richer collateral circulation than those found in the lower limb. In a study of nearly 2500 World War II battle casualties, at a time when ligation of damaged arteries was common, ligation of the popliteal artery led to amputation in 346 of 502 limbs. By contrast, the incidence of amputation after ligation was about one-quarter for the subclavian artery, one-third for the axillary artery and more than one-half when the brachial artery was ligated proximal to the profunda brachii artery. These figures are certainly lower in the less contaminated injuries of civilian life, but some degree of post-ischaemic fibrosis is almost inevitable after failure to repair these vessels. The principles of arterial repair include urgent restoration of flow by repair of the artery and restoration of tissue perfusion by decompression. Temporary intraluminal shunts are invaluable, as they buy time and permit adequate stabilization of the skeleton. Application of these principles in current conflicts ensures a remarkably high rate of limb survival and a remarkably low incidence of post-ischaemic fibrosis.
Flow through the brachial artery in adults and in children has been measured by high-resolution ultrasonography. Flow was calculated by the Laplace equation: BF (blood flow)= [π×(D/2)] 2 ×FV (flow velocity). The mean diameter of the brachial artery in children aged between 4 and 5 years is 2.7 mm, which provides a resting flow of about 200 ml per minute. The significance of the diameter of the vessel is emphasized by Poiseuille’s law. This is the physical law describing the volume of flow (Φ) of an incompressible uniform viscous liquid, where R is the internal radius of the tube, P the pressure difference between the two ends, ɳ the dynamic fluid viscosity and L the total length of the tube.
The diameter of the superior ulnar collateral artery at the elbow in a 5-year-old child is, at most, 1 mm. This calibre provides flow of about 20 ml per minute, assuming that the pressure gradient is the same as that in the brachial artery itself. These facts must be borne in mind by any clinician inclined to the view that cessation of flow through the brachial artery is a matter of little consequence. The collateral channels take hours or days to develop and may be compromised by the original injury or during operation. The radial and ulnar nerves are often entrapped or compressed in fracture dislocations at the elbow, blocking flow through the ulnar and radial collateral systems that accompany these nerves.
The presence of peripheral pulses does not indicate adequate perfusion of the deep intracompartmental tissues, neither does the perfusion of skin or the nail bed when pulses are absent. The cardinal symptom of ischaemic anoxia is severe pain and the cardinal sign is loss of nerve conduction. This can be confirmed during exposure of limb nerves with an inflated tourniquet cuff in position proximally. For about 20 minutes, stimulation of the nerve evokes a brisk muscular response as a consequence of transmission through the neuromuscular junction. This response diminishes and disappears after about 30 minutes, although conduction within the nerve itself can still be detected for up to another 20 minutes. However, direct stimulation of the muscle provokes a twitch that can be elicited for up to several hours. Indeed, it is the loss of this direct response that signifies impending death of the muscle, and with it, death of the limb. The earliest nerve fibres to suffer are the largest, i.e. those conveying vibration and proprioception sense.
Ischaemia and acute compression within neurovascular fascial compartments
Sleeves of fascia surround main nerves and main vessels in some regions, an arrangement that predisposes nerves to injury from ischaemia or compression, or both. The seventh and eighth cervical and first thoracic ventral rami are enclosed in semi-rigid space after they enter the posterior triangle of the neck. This is bounded, posteriorly, by the dorsal part of the first rib, the transverse processes of the cervical vertebrae and by the fascia of levator scapulae. The nerves are embraced by scalenus anterior and scalenus medius, both of which are invested in an unyielding fascia. This is one envelope of the prevertebral fascia that also serves to bind the phrenic nerve down to the anterior face of scalenus anterior. The prevertebral fascia is particularly well developed in front of the vertebral column and also at the base of the posterior triangle, where it envelops the seventh and eighth cervical and first thoracic ventral rami, the phrenic nerve, the cervical sympathetic chain, and the subclavian and vertebral arteries. Infusion of relatively large volumes of fluid, from 10 to 20 ml, deep to the prevertebral fascia for the purpose of inducing regional block may cause tamponade of the radicular vessels that enter the spinal canal and contribute to the anterior spinal artery. has described the medial brachial fascial compartment, which extends from the axilla to the elbow and is bounded by the tough medial intramuscular septum and the axillary sheath. Bleeding into this compartment is responsible for the majority of infraclavicular plexopathies that follow regional block, and for many of the neurological lesions that result from closed or even open injuries in this region. The anterior interosseous nerve and its accompanying artery may be damaged by compression because of swelling in the deepest part of the flexor compartment of the forearm. The ulnar nerve, accompanied by the ulnar artery, lies in a discrete fascial compartment in the distal two-thirds of the forearm.
Bleeding into the axillary fascia (the medial antebrachial compartment) causes a characteristic, progressive lesion. There is, almost always, pain accompanied by dysaesthesiae; loss of sensation soon follows and then, over the next 2–3 hours, paralysis ensues. Wilbourn’s comment bears repeating: Distal pulses are normal as they are with most compartment syndromes because the elevated pressure, although sufficient to collapse the vasa nervorum, is far below mean arterial pressure. Ultrasound, MR and CT may reveal the vascular lesion, but, considering the very brief time available for surgical decompression before irreversible nerve damage occurs, obtaining these is rarely justified.
In one series of 16 patients ( ), there was, in all cases, an injury to the axillary artery or one of its offsets, caused by dislocation of the shoulder or fracture of the proximal humerus. The diagnosis of continuing bleeding into the axillary sheath was made by the delayed onset of nerve palsy or the deepening of the lesion whilst under observation. A favourable outcome was seen in 87 nerve palsies, where urgent repair of the artery and decompression of the axillary sheath were performed. However, delay in diagnosis and treatment may lead to permanent loss of function.
Case report
After a fracture/dislocation of the shoulder in a 59-year-old man, the patient’s complaints of pain and the signs of a deepening nerve lesion were not appreciated for several days. Angiography showed bleeding from the subscapular artery. Two unsuccessful attempts were made to occlude this by embolization. The patient was reviewed at six weeks in right heart failure; haemoglobin was 4.9 g/litre (49 g/dl). He was in great pain and there was a total and deep plexopathy. MRI scan showed an enormous haematoma occupying the axilla and the arm, and suggested continuing bleeding. Treatment was simple: the axillary artery was exposed and controlled above pectoralis minor and the brachial artery exposed and controlled in the arm. More than 4 litres of altered blood were removed from the sac. The defect in the axillary artery was, at most, 2 mm in diameter and it was closed by direct suture. The pain was relieved and there was gradual recovery of the nerves, but the small muscles of the hand never recovered.
Innervation
The accessory nerve, dorsal scapular nerve, long thoracic nerve (nerve to serratus anterior), suprascapular nerve and nerve to subclavius all innervate muscles that act on the scapulothoracic ‘joint’ and will therefore be summarized here.
Accessory nerve
The integrity of the accessory nerve is fundamental to thoracoscapular function and essential for scapulohumeral rhythm ( ). The intraspinal and intracranial course of the accessory nerve and of the segment of the nerve that lies in the anterior triangle of the neck are described in Chapter 35 .
The accessory nerve passes either deep to or through sternocleidomastoid, to enter the posterior triangle in a consistent and important relation to the ascending nerves of the cervical plexus. The great auricular nerve is the key to exposure of the accessory nerve, which emerges, usually as one trunk, 5–10 mm cephalad to the point where the great auricular nerve winds around sternocleidomastoid, and moves from a plane posterior to the muscle to one that is anterior. The general relations of the posterior triangle vary with individual physique, but this relation between the two nerves is reliably consistent. The nerve now runs across the fatty areolar tissue at the apex of the posterior triangle, in close relation to the superior superficial cervical lymph nodes deep to platysma. It is separated from the underlying levator scapulae by this areolar tissue, and then, more deeply, by the prevertebral fascia. One slender branch passes to the upper fibres of trapezius either deep to sternocleidomastoid or just beyond it. The nerve pierces the fascia covering the deep surface of trapezius close to the anterior border of the muscle and then runs caudally about 2 cm from that border. The nerve passes down in a characteristic sinuous fashion, accompanied by slender vessels to the deep, inner face of trapezius. A branch from the cervical plexus (third and fourth cervical ventral rami) joins the nerve just above the clavicle. Intraoperative stimulation of this branch rarely evokes a muscular response; it probably conveys afferent fibres from the middle and lower parts of trapezius. The nerve now turns medially, continuing in parallel to the spine of the scapula about 4 cm above it. At the medial end of the spine, the nerve turns caudally again, passing down parallel to the medial border of the scapula. It divides into terminal muscular branches about 7 cm distal to the scapular spine. Although sternocleidomastoid, and the middle and the lower portions of trapezius, may be partially supplied by branches from the cervical plexus, the upper part of trapezius is innervated solely by the accessory nerve.
Dorsal scapular nerve
The dorsal scapular nerve arises above the clavicle from the proximal segment of the the fifth cervical ventral ramus. It passes posteriorly, piercing scalenus medius, to run down in the plane between levator scapulae and serratus posterior superior and the posterior scalene muscles. It continues along the anterior border of the rhomboid muscles about 1.5 cm medial to the vertebral border of the scapula and is closely related to the dorsal scapular artery. The dorsal scapular nerve innervates the rhomboid muscles and, together with branches from the third and fourth cervical ventral rami, it supplies levator scapulae.
Long thoracic nerve (nerve to serratus anterior)
The long thoracic nerve is formed by branches that arise above the clavicle from the proximal segments of the fifth, sixth and seventh cervical ventral rami. It innervates serratus anterior, a muscle that is essential for the function of the thoracoscapular joint. The muscular branches from the rami join deep to scalenus medius, and the trunk passes down posterolateral to the muscle, on the floor of the posterior triangle deep to the suprascapular nerve. The branches from the fifth and sixth cervical ventral rami are the largest. The nerve follows a sinuous course deep to the investing fascia covering the anterior faces of the digitations of serratus anterior. It is accompanied here by a branch of the thoracodorsal artery, and inclines posterolaterally towards the mid-axillary line.
Suprascapular nerve
The suprascapular nerve, from the fifth and sixth cervical ventral rami, is usually the first branch of the upper trunk, but frequently arises directly from the fifth cervical ventral ramus. It gives motor branches to supraspinatus and infraspinatus and articular branches to the glenohumeral and acromioclavicular joints
Nerve to subclavius
The slender nerve to subclavius, from the fifth and sixth cervical ventral rami, springs from the upper trunk and passes anteriorly. It descends anterior to the plexus and the subclavian artery and passes above the subclavian vein to supply subclavius.
Brachial plexus
The muscles, joints and skin of the upper limb are innervated by the fifth, sixth, seventh and eighth cervical ventral rami and nearly all of the first thoracic ventral ramus, collectively forming the brachial plexus ( Figs 48.6 – 48.7 ). A branch from the fourth to the fifth cervical ventral ramus which contributes to the innervation of the glenohumeral and elbow flexor muscles is seen occasionally at operation. A muscular contribution from the second thoracic ventral ramus is rare. The rami enter the posterior triangle of the neck between scalenus anterior and medius. Rami from the seventh and eight cervical ventral rami are the largest (C8 contains about 30,000 myelinated axons) and those from the fifth cervical and the first thoracic ventral rami are the smallest (between 15,000 and 20,000 myelinated axons). An adult brachial plexus contains between 120,000 and 150,000 myelinated axons, of which 25% innervate the shoulder girdle and glenohumeral joint. The proportion of motor fibres is greatest in the fifth and eighth cervical ventral rami; the sensory contribution is greatest in the seventh cervical ventral ramus. A complex interchange of branches, before the main nerves of the upper limb are formed, produces the trunks, divisions and cords of the brachial plexus.
Blood supply
The blood supply to the brachial plexus is derived from vessels which arise from the subclavian and vertebral arteries. Important branches pass from the vertebral artery to the fifth and sixth cervical ventral rami and the more proximal cervical nerves. Branches from the costocervical trunk provide a rich supply to the eighth cervical and first thoracic ventral rami. Extensive contributions come from the suprascapular and superficial cervical arteries that arise from the thyrocervical trunk. In at least one-third of cases, the superficial cervical and dorsal scapular arteries arise from the thyrocervical trunk as the transverse cervical artery. In clinical terms, the arteries arising from the thyrocervical trunk have become the lifeline to the upper limb and must be preserved during operations in cases when the ruptured subclavian artery has not been repaired. The dorsal scapular artery may arise from the third part of the subclavian artery to pass between the upper and middle trunks of the brachial plexus.
Trunks of the brachial plexus
The upper trunk is formed by the fifth and sixth cervical ventral rami, where these nerves emerge from deep to scalenus anterior. The middle trunk is the continuation of the seventh cervical ventral ramus. The lower trunk is formed by the eighth cervical and first thoracic ventral rami, and passes over the anterosuperior surface of the first rib. The first thoracic ventral ramus takes an upward course across the deep face of the neck of the first rib behind the pleura and the vertebral and subclavian arteries towards the lower trunk. The formation of the trunks is fairly consistent; they lie in front of one another rather than side by side, with the subclavian artery passing anteromedially. The phrenic nerve crosses the fifth cervical ventral ramus to pass anteromedially on the surface of scalenus anterior. The upper trunk, its divisions and the suprascapular nerve can all be palpated in the supraclavicular fossa in a subject of normal physique. The examining finger identifies first the subclavian pulse and then the nerves, whilst rolling the fingertip laterally (see ).
Divisions of the brachial plexus
The trunks divide into anterior and posterior divisions. The upper trunk divides 2–3 cm above the clavicle, and the divisions of the middle and lower trunk are formed deep to the clavicle. The posterior divisions of the upper and middle trunks are consistently larger than their anterior divisions. The posterior division of the lower trunk is consistently smaller than the anterior division and is absent in about 10% of cases.
Cords of the brachial plexus
The cords are formed by the confluence of divisions: the lateral cord from the anterior divisions of the upper and middle trunks; the posterior cord by all three posterior divisions; and the medial cord by the anterior division of the lower trunk and, sometimes, by a branch from the anterior division of the middle trunks. The divisions of the trunks and the formation of the cords represent an important anatomical and functional differentiation. The posterior divisions and posterior cord innervate postaxial (extensor) musculature; the anterior divisions and the lateral and medial cords innervate preaxial (flexor) musculature.
The formation and relations of the three cords are variable and, indeed, their designations somewhat misleading. Immediately inferior to the clavicle, the posterior cord is lateral, the medial cord is posterior, and the lateral cord is anterior, in relation to the axillary artery; the cords assume their appropriate relations about the axillary artery deep to pectoralis minor. There is considerable variation in this arrangement; most commonly, the axillary artery lies anterior to the three cords and the median nerve.
The branches of the posterior cord, the largest of the three trunks, are consistent. In sequence, they are the upper subscapular, thoracodorsal, lower subscapular, axillary and radial nerves. The branches of the medial cord are usually predictable; the medial pectoral nerve and medial cutaneous nerve of the forearm are succeeded by the division into the medial root of the median nerve and the ulnar nerve. The ulnar nerve may arise as two or three branches. The greatest variation in formation of trunk nerves is found within the lateral cord. Occasionally, the musculocutaneous nerve arises more distally than usual, either directly from the lateral cord as two or three branches or even from the median nerve itself. Sometimes, the highest of these branches enters coracobrachialis no more than 2 or 3 cm below the coracoid process. The lateral root of the median nerve may arise as two or three branches, and in some cases, it appears as a branch of the musculocutaneous nerve.
Terminal branches of the brachial plexus
Axillary (circumflex) nerve
The axillary nerve (fifth and sixth cervical ventral rami) ( Fig. 48.8 ) runs freely in loose fatty tissue in the axilla before turning around subscapularis to pass almost horizontally through the quadrilateral tunnel, where it is accompanied by the posterior circumflex humeral vessels (see Fig. 49.33 ). It innervates teres minor and deltoid, and the skin overlying deltoid on the lateral aspect of the shoulder. FLOAT NOT FOUND
Radial nerve
The radial nerve (fifth, sixth, seventh and eighth cervical and first thoracic ventral rami) is the terminal branch of the posterior cord ( Fig. 48.9 ). It is the largest nerve in the upper limb and the most commonly damaged. Between its origin at the level of the base of the coracoid and its entrance into the spiral groove, where it is accompanied by the profunda brachii artery, the radial nerve is supplied by fewer arteries than elsewhere along its course. The first 8–10 cm of the nerve may not have a nutrient artery and will, therefore, be relatively avascular if the nerve is transected at its origin. The nerve lies closest to the bone where it pierces the lateral intermuscular septum to pass through a short tunnel bounded by bone and unyielding fascia. The nerve is tethered here, a common level of rupture, entrapment or compression. FLOAT NOT FOUND
The nerve to the medial head of triceps arises in the axilla and accompanies the main nerve as it passes through the intermuscular septum. The nerve(s) to the lateral head of triceps arise(s) within the spiral groove; that to the lateral head just before the radial nerve re-enters the anterior compartment. Two cutaneous nerves, the lower lateral cutaneous nerve of the arm and the posterior cutaneous nerve of the forearm, pass away from the main nerve in the final part of the spiral groove and course along the anterior face of the lateral head of triceps to perforate the deep fascia about four fingers’-breadths above the lateral epicondyle. They innervate the skin of the lower lateral arm and the posterior aspect of the forearm. The nerve to brachioradialis is formed about three fingers’-breadths proximal to the lateral epicondyle; the nerve to extensor carpi radialis longus about one finger’s-breadth more distal; and that to extensor carpi radialis brevis about one finger’s-breadth above the epicondyle. These branches spring from the main nerve as it runs in the valley between brachialis anteriorly and brachioradialis posteriorly, where the nerve may be palpated. At the level of the tip of the lateral epicondyle, the radial nerve divides into the posterior interosseous and superficial radial nerves. Another branch to extensor carpi radialis brevis is usually given off here. The superficial radial nerve innervates the skin over the dorsum of the radial half of the ring, middle and index fingers, and that of the thumb as far as the distal interphalangeal joint. It often provides important sensation on the skin of the thumb web space and the skin on the adjacent sides of the thumb and index.
Median nerve
The median nerve is formed by the union of the lateral root from the lateral cord (sixth and seventh cervical ventral rami), and the medial root from the medial cord (eighth cervical and first thoracic ventral rami), which meet anterior to the third part of the axillary artery ( Fig. 48.10 ). Fibres in the lateral root innervate the palmar skin of the thumb, index and most of the middle finger, pronator teres, flexor carpi radialis and some of flexor digitorum superficialis ( Fig. 48.11 ). The lateral root conveys most of the sympathetic fibres to the median distribution in the hand. The medial root carries fibres to the skin of the medial side of the middle and the lateral side of the ring finger, and also fibres to palmaris longus, flexor digitorum superficialis and the lateral part of flexor digitorum profundus, flexor pollicis longus, pronator quadratus and the median innervated muscles within the hand.
The first branch of the median nerve, to pronator teres, arises 2–3 cm above the medial epicondyle. A second branch, or leash of branches, arises at the level of the tip of the medial epicondyle and innervates palmaris longus, flexor carpi radialis and flexor digitorum superficialis. Just proximal to the tendinous arcade of flexor digitorum superficialis, the median nerve gives off the anterior interosseous nerve. Accompanied by the anterior interosseous vessels, this large branch dives deeply to pass down along the interosseous membrane and supplies flexor pollicis longus, the radial half of flexor digitorum profundus and pronator quadratus. There is no cutaneous distribution. The main nerve continues in the plane between the superficial and deep digital flexors, supplying two or three branches to the former. The palmar cutaneous nerve arises about 3 cm proximal to the proximal wrist crease (when there are two creases), and passes lateral to the main nerve and superficial to the flexor retinaculum to innervate the skin of the proximal palm. The median nerve passes deep to the flexor retinaculum, into the carpal tunnel, to enter the palm. The nerve to the thenar muscles arises within, or just distal to, the tunnel, usually on the lateral side of the main nerve. The palmar digital nerves are formed within the palm of the hand.
The nerve is palpable along its course in the arm, where it is covered by deep fascia and skin, after emerging from deep to coracobrachialis. It is palpable on the flexor aspect of the elbow, deep to the bicipital aponeurosis, and is accompanied by the brachial artery in this segment of the limb. The median nerve is palpable at the wrist where it emerges from behind the superficial flexor tendons, just lateral to palmaris longus.
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