Overview of the upper limb

The upper limb functions as a series of articulated segments, which act in a coordinated manner to allow the hand to manipulate and sense its surrounding environment. The degree of coordination of these movements is such that the hand can be positioned with remarkable precision. The freedom of movement allowed by the highly mobile thoracoscapular and glenohumeral joints means that, when combined with the actions of the elbow and wrist joint, the hands can reach virtually anywhere in a sphere defined by the reach of the arms.

Skin and fascia

The skin of the neck and upper limb is thin and mobile, whereas the skin of the back of the neck, shoulder, arm and forearm is thicker and more hirsute. In the hand, the thick, hairless palmar skin is anchored to the palmar aponeurosis, while the skin over the dorsum of the hand is thinner and more mobile. The skin creases on the preaxial surface of the elbow, wrist and hand indicate where the skin is tethered to the deep fascia. The skin of the axilla is particularly mobile to allow for the extensive range of movement of the glenohumeral joint.

The superficial fascia is also thicker over the dorsal aspect of the neck and upper limb, and allows gliding to take place between the skin and deep fascia.

The deep fascia of the upper limb, the intermuscular septa of the arm and the interosseous membrane of the forearm divide the limb into discrete compartments. They also increase the area for the attachment of muscles. This compartmental arrangement is particularly important in limiting the spread of local infection and tumour but also acts to contain pathological swelling within the compartment.

A compartment syndrome may occur in the arm, forearm or hand. It arises, usually as the result of injury, when the tissue pressure in a compartment is elevated to a level that decreases the perfusion gradient across the capillary bed. Consequently, the peripheral pulses may remain palpable. Pain is often severe, disproportionate to the degree of injury and exacerbated by stretching the muscles in the affected compartment. Muscle and nerve ischaemia can occur within hours, leading to muscle necrosis and irreversible damage to the affected nerves. Treatment is by thorough decompression of the affected compartment (fasciotomy).

Bones and joints

The bones of the upper limb consist of the clavicle, scapula, humerus, radius, ulna, eight carpal bones, five metacarpals and 14 phalanges.

The pectoral girdle, formed by the clavicle, scapula and acromioclavicular joint, is linked to the axial skeleton only by the sternoclavicular joint and a series of powerful flat muscles: principally, serratus anterior, trapezius and the two rhomboids, and, to a lesser extent, levator scapulae. Its function is to act as a powerful, mobile but stable base on which the rest of the upper limb can move. Paralysis of these muscles significantly impairs upper limb function in terms of range and stability.

The glenohumeral joint is a synovial joint between the near-hemispherical head of the humerus and the shallow glenoid fossa of the scapula. The glenoid fossa is deepened by the glenoid labrum. The joint is surrounded by a fibrous capsule lined with synovium. The capsule is attached medially to the neck of the glenoid and laterally to the anatomical neck of the humerus just distal to its articular margin. It encloses the supraglenoid tubercle to which the intracapsular long head of biceps brachii is attached. The lateral part of the capsule is thickened by the tendons of supraspinatus superiorly, infraspinatus and teres minor posteriorly, and subscapularis anteriorly. The insertion of the long head of triceps to the infraglenoid tubercle blends with it inferiorly.

The elbow consists of a hinge joint between the humerus and the ulna, and two pivot joints: the humeroradial and proximal radioulnar joints. It is stabilized by a fibrous capsule that is reinforced by the radial and ulnar collateral ligaments of the elbow and by the anular ligament, which surrounds the radial head and stabilizes the proximal radioulnar joint. The elbow joint allows flexion from 0° to 150° and 180° of pronation/supination in conjunction with the distal radioulnar joint.

The shafts of the radius and ulna are connected by two syndesmoses: the oblique cord, the function of which is uncertain, and the interosseous membrane. The fibres of the interosseous membrane pass obliquely and distally from the radius to the ulna and give origin to the deep muscles of the forearm. Their central portion is thought to act, in conjunction with the radial head, to prevent proximal migration of the radius.

The distal radioulnar joint is a pivot joint between the head of the ulna and the ulnar notch of the radius. It contains an articular disc and is stabilized by a fibrous capsule that is thickest anteriorly and posteriorly.

The wrist (radiocarpal joint) is a synovial ellipsoid joint between the distal end of the radius and the articular portion of the triangular fibrocartilage complex (TFCC), and the scaphoid, lunate and triquetrum of the proximal carpal row. It is surrounded by a fibrous capsule that is reinforced by palmar radiocarpal and ulnocarpal ligaments, dorsal radiocarpal ligaments, and radial and ulnar collateral ligaments. The palmar ligaments are notably stronger than the dorsal. The radiocarpal joint can achieve approximately 140° of flexion/extension and 70° of combined abduction and adduction.

The intercarpal joints link the bones of the carpus. They are divided into a proximal row consisting of the scaphoid, lunate and triquetrum, and a distal row consisting of the trapezium, trapezoid, capitate and hamate. The pisiform articulates with the volar aspect of the triquetrum. The joint between proximal and distal row is designated the mid-carpal joint.

Of the carpometacarpal joints, the first is a saddle joint that allows opposition of the thumb. The second to fifth are synovial ellipsoid joints that become progressively more mobile towards the fifth. The metacarpophalangeal joints are almost bicondylar; the interphalangeal joints are uniaxial hinge joints.

Muscles

The muscles of the shoulder girdle may be divided into two groups: those that suspend the scapula and those that move it.

Muscles of scapular suspension

The principal muscles of scapular suspension are trapezius, which is attached to the spine of the scapula, the acromion and the lateral third of the clavicle; and pectoralis minor, which is attached to the coracoid. Trapezius stabilizes and suspends the scapula, whereas pectoralis minor depresses and protracts it. They are assisted in this by subclavius, which stabilizes the medial end of the clavicle. The acromion and coracoid are linked by the coracoacromial ligament, which completes the coracoacromial arch. Scapular suspension is impaired if there is disruption of any part of this system.

Muscles of scapular motion

The muscles of scapular motion are levator scapulae, the rhomboids and serratus anterior. Each is attached to the medial border of the scapula. Levator scapulae elevates the superomedial corner of the scapula, the rhomboids retract its medial border, and serratus anterior protracts the scapula around the chest wall: it is mainly involved in movements involving reaching or pushing. Paralysis of serratus anterior results in ‘winging’ of the scapula and is characterized by prominence of its medial border and an inability to sustain elevation of the arm. It can be elicited by asking a patient to push against a wall with both hands.

Muscles acting across the shoulder joint

The muscles acting across the shoulder joint also fall into three groups: a group of large muscles that arise from the axial skeleton, a second group that arise from the shoulder girdle, and a third group of smaller muscles that arise from the scapula and act to stabilize and centre the humeral head in the concavity of the glenoid.

Muscles that arise from the axial skeleton to act across the shoulder joint are the sternal head of pectoralis major, pectoralis minor and latissimus dorsi. Muscles arising from the shoulder girdle are deltoid, the clavicular head of pectoralis major and coracobrachialis. The tendons of the group of smaller muscles arising from the scapula are collectively known as the rotator cuff. This consists of supraspinatus, infraspinatus, teres minor and subscapularis, all of which are attached to the head of the humerus. Subscapularis is principally an internal rotator, whereas infraspinatus and teres minor are external rotators. Supraspinatus abducts the shoulder.

The subacromial space lies between the upper surface of the rotator cuff and the lower surface of the coracoacromial arch. It contains the subacromial bursa, which extends laterally under deltoid as the subdeltoid bursa. Their function is to allow the rotator cuff to move smoothly beneath the coracoacromial arch. If the inferior aspect of the coracoacromial arch becomes roughened, usually as a result of degeneration of the acromioclavicular joint, or if the rotator cuff is degenerate or injured, the subacromial bursa can become inflamed, causing an impingement syndrome. This results in a painful arc of movement on abduction of the shoulder at around 90°. Treatment is by the injection of local anaesthetic and depot steroid, which reduces the inflammation of the bursa but does not affect the underlying problem; if the condition is more severe, treatment is by subacromial decompression, removing the undersurface of the acromion and, if necessary, part of the distal end of the clavicle.

Muscles acting principally across the elbow joint

Muscles that act principally across the elbow are biceps and triceps, which flex and extend the elbow, respectively. The long heads of each of these also cross the glenohumeral joint and insert into the superior (biceps) and inferior (triceps) aspects of the glenoid neck. Consequently, the tendon of the long head of biceps is intra-articular. Brachialis lies deep to biceps and also flexes the elbow.

Biceps is a flexor of the elbow and a supinator of the forearm. Its arterial supply is highly variable but is mainly from branches of the brachial artery. It is innervated by the musculocutaneous nerve (C5/6).

Triceps forms most of the extensor compartment of the arm and is the principal extensor of the elbow joint. Its blood supply is mainly from the profunda brachii artery and the superior ulnar collateral artery. It is innervated by the radial nerve (C6/7/8), one branch supplying each of its three heads.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here