Attachments

Pronator teres has humeral and ulna attachments (Fig. 49.3, Fig. 49.12, Fig. 49.13). The humeral head, the larger and more superficial of the two, arises just proximal to the medial epicondyle, from the common tendon of origin of the flexor muscles, from the intermuscular septum between it and flexor carpi radialis, and from antebrachial fascia. The smaller ulnar head springs from the medial side of the coronoid process of the ulna, distal to the attachment of flexor digitorum superficialis, and joins the humeral head at an acute angle. The muscle passes obliquely across the forearm to end in a flat tendon that is attached to a rough area midway along the lateral surface of the radial shaft at the ‘summit’ of its lateral curve. The coronoid attachment may be absent. Accessory slips may arise from a supracondylar process of the humerus, if it is present, or from biceps, brachialis or the medial intermuscular septum.

Fig. 49.13 The deep flexor muscles of the left forearm.

(From Sobotta 2006.)

Relations

The median nerve usually enters the forearm between the two heads of pronator teres, and is separated from the ulnar artery by the ulnar head. The lateral border of pronator teres is the medial limit of the cubital fossa, the triangular hollow anterior to the elbow joint.

Vascular supply

The humeral head of pronator teres is supplied by the inferior ulnar collateral artery and the anterior ulnar recurrent artery. The ulnar head is supplied by the common interosseous artery. The mid portion of the muscle belly is supplied by direct branches from the ulnar artery, while the attachment to the radius is supplied by the radial artery.

Innervation

Pronator teres is innervated by the median nerve, C6 and 7.

Action

Pronator teres rotates the radius on the ulna (pronation of the forearm), turning the palm medially so that it faces backwards. It acts with pronator quadratus (which is always active in pronation) only in rapid or forcible pronation. Like all of the muscles which arise from the medial epicondyle, pronator teres acts as a weak flexor of the elbow joint.

Clinical anatomy: testing

Pronator teres is tested by palpating its contracting fibres during pronation against resistance.

Attachments

Flexor carpi radialis lies medial to pronator teres, and arises from the medial epicondyle via the common flexor tendon, from the antebrachial fascia and from adjacent intermuscular septa (Fig. 49.12). Its fusiform belly ends, rather more than halfway to the wrist, in a long tendon which passes within a synovial sheath through a lateral canal, formed by the flexor retinaculum above and a groove on the trapezium beneath. It inserts on the palmar surface of the base of the second metacarpal, sending a slip to the third metacarpal. These distal attachments are hidden by the oblique head of adductor pollicis. The muscle rarely may be absent. It may have accessory slips from the biceps tendon, bicipital aponeurosis, coronoid process or radius. Distally it may also be attached to the flexor retinaculum, trapezium or fourth metacarpal.

Relations

In the lower part of the forearm the radial artery lies between the tendon of flexor carpi radialis and that of brachioradialis. The surface groove for the radial pulse is well known to all physicians.

Vascular supply

Flexor carpi radialis is supplied by a single dominant proximal pedicle and several distal minor pedicles. The dominant pedicle is formed by a branch which arises from either the anterior or posterior ulnar recurrent artery. The latter passes deep to pronator teres to enter the deep surface of flexor carpi radialis, whereupon it divides into a small ascending branch and a larger descending branch. The distal minor pedicles amount to six to eight branches from the radial artery which enter the muscle on the anterolateral side.

Innervation

Flexor carpi radialis is innervated by the median nerve, C6 and 7.

Action

Acting with flexor carpi ulnaris, and sometimes flexor digitorum superficialis, flexor carpi radialis flexes the wrist, and helps radial extensors of the wrist in abducting the hand.

Clinical anatomy: testing

Flexor carpi radialis is tested by palpating its contracting fibres during flexion of the wrist against resistance.

Attachments

Flexor digitorum superficialis (sublimis) lies deep to the preceding muscles (Fig. 49.12). It is the largest of the superficial flexors, and arises by two heads. The humero-ulnar head arises from the medial epicondyle of the humerus via the common tendon; the anterior band of the ulnar collateral ligament; adjacent intermuscular septa, and from the medial side of the coronoid process proximal to the ulnar origin of pronator teres. The radial head, a thin sheet of muscle, arises from the anterior radial border extending from the radial tuberosity to the insertion of pronator teres. The median nerve and ulnar artery descend between the heads. The muscle usually separates into two strata, directed to digits 2–5. The superficial stratum, joined laterally by the radial head, divides into two tendons for the middle and ring finger. The deep stratum gives off a muscular slip to join the superficial fibres directed to the ring finger, and then ends in two tendons for the index and little finger. As the tendons pass behind the flexor retinaculum they are arranged in pairs: the superficial pair pass to the middle and ring fingers, the deep to the index and little finger. Distal to the carpal tunnel the four tendons diverge. Each passes towards a finger superficial to the corresponding flexor digitorum profundus tendon. The two tendons for each finger enter the digital flexor sheath (which starts over the metacarpophalangeal joint) in this relationship. The superficialis tendon then splits into two bundles which pass around the profundus to lie posteriorly. They subsequently reunite and insert into the anterior surface of the middle phalanx. Some fibres interchange from one bundle to another.

An intermediate tendon is always found in the central branching area of the muscle belly and is an important landmark in deep dissection: it can initially be confused with the median nerve. The radial head of flexor digitorum superficialis may be absent and the muscular slip from the deep stratum may provide most or all of the fibres acting on the index finger. The fibres associated with the little finger may be absent, when they are replaced by a separate slip from the ulna, flexor retinaculum or palmar fascia. Variations occur in the arrangement of the tendons.

Relations

The median nerve and ulnar artery descend between the heads of flexor digitorum superficialis.

Vascular supply

The humeral head of flexor digitorum superficialis is supplied by the anterior ulnar recurrent artery. The main part of the muscle is supplied on its anterior surface by three or four branches from both the ulnar and radial arteries. The posterior surface is supplied by the ulnar artery and median artery, and the lateral surface by additional branches from the radial artery.

Innervation

Flexor digitorum superficialis is innervated by the median nerve, C8 and T1.

Action

Flexor digitorum superficialis is potentially a flexor of all the joints over which it passes, i.e. proximal interphalangeal, metacarpophalangeal and wrist joints. Its precise action depends on which other muscles are acting. It has independent muscle slips to all four fingers, unlike flexor digitorum profundus, which has a muscle group common to the middle, ring and little fingers. It is therefore able to flex the proximal interphalangeal joints individually.

Clinical anatomy: testing

The independent action of flexor digitorum superficialis for a particular finger is tested by flexing that digit while holding the three other fingers in full extension. This eliminates any simultaneous contraction of the flexor digitorum profundus which might flex the digit.

Attachments

Palmaris longus is a slender, fusiform muscle medial to flexor carpi radialis (Fig. 49.12). It springs from the medial epicondyle by the common tendon, and from adjacent intermuscular septa and deep fascia. It converges on a long tendon, which passes anterior (superficial) to the flexor retinaculum. A few fibres leave the tendon and interweave with the transverse fibres of the retinaculum, but most of the tendon passes distally. As the tendon crosses the retinaculum it broadens out to become a flat sheet which becomes incorporated into the palmar aponeurosis. Palmaris longus is often absent on one or both sides.

Relations

The median nerve at the wrist lies partly under the cover of the tendon of palmaris longus, and partly between the tendons of palmaris longus and flexor carpi radialis.

Vascular supply

The muscle belly of palmaris longus is supplied by a small branch from the anterior ulnar recurrent artery. A small contribution is sometimes made by the median artery, if this is well developed.

Innervation

Palmaris longus is innervated by the median nerve, C7 and 8.

Action

It has been suggested that palmaris longus is a phylogenetically degenerate metacarpophalangeal joint flexor. Although consideration of the line of action would suggest that it plays a role in carpal flexion, its main function appears to be as an anchor for the skin and fascia of the hand, in resisting horizontal shearing forces in a distal direction (e.g. as in holding a golf club), which would tend to deglove the skin of the palm.

Clinical anatomy: testing

If the wrist is flexed against resistance, the taut tendon of palmaris longus will be seen in the midline of the flexor wrist crease as the tendon passes superficial to the flexor retinaculum. When testing palmaris longus it helps to oppose the thumb to the middle fingertip at the same time as the wrist is flexed in order to make palmaris stand out.

Attachments

Flexor carpi ulnaris is the most medial of the superficial forearm flexors (Fig. 49.12). It arises by two heads, humeral and ulnar, connected by a tendinous arch. The small humeral head arises from the medial epicondyle via the common tendon. The ulnar head has an extensive origin from the medial margin of the olecranon and proximal two-thirds of the posterior border of the ulna, an aponeurosis (which it shares with extensor carpi ulnaris and flexor digitorum profundus), and from the intermuscular septum between it and flexor digitorum superficialis. Occasionally there is a slip from the coronoid process. A thick tendon forms along its anterolateral border in its distal half. The tendon is attached to the pisiform, and thence prolonged to the hamate and fifth metacarpal by pisohamate and pisometacarpal ligaments. The attachment to the flexor retinaculum and the fourth or fifth metacarpal bones is sometimes substantial.

Relations

The ulnar nerve and posterior ulnar recurrent artery pass under the tendinous arch between the humeral and ulnar heads of flexor carpi ulnaris. Ulnar vessels and nerve lie lateral to the tendon of insertion.

Vascular supply

The main arterial supply of flexor carpi ulnaris is derived from three pedicles. The proximal pedicle arises from a branch of the posterior ulnar recurrent artery as it passes between the humeral and ulnar heads. The middle and distal pedicles arise from the ulnar artery and enter the muscle at the junction of the upper and middle thirds, and the musculotendinous junctions, respectively. Flexor carpi ulnaris also receives a small supply near its origin which arises from the inferior ulnar collateral artery.

Innervation

Flexor carpi ulnaris is innervated by the ulnar nerve, C7 and 8 and T1.

Action

Acting with flexor carpi radialis, flexor carpi ulnaris flexes the wrist. Acting with extensor carpi ulnaris, it adducts (ulnar deviates) the hand.

Clinical anatomy: testing

Flexor carpi ulnaris is tested by palpating its fibres while the wrist is flexed against resistance. A more positive test is to palpate the tendon while the patient abducts the little finger against resistance. FCU synergistically contracts to stabilize the pisiform, giving abducted digiti minimi a stable origin.

Attachments

Flexor digitorum profundus arises deep to the superficial flexors from about the upper three-quarters of the anterior and medial surfaces of the ulna (Fig. 49.13, see Fig. 49.19). It embraces the attachment of brachialis above and extends distally almost to pronator quadratus. It also arises from a depression on the medial side of the coronoid process, the upper three-quarters of the posterior ulnar border (by an aponeurosis which it shares with flexor and extensor carpi ulnaris), and the anterior surface of the ulnar half of the interosseous membrane. The muscle ends in four tendons, which run initially posterior (deep) to the tendons of flexor digitorum superficialis and the flexor retinaculum. The part of the flexor digitorum profundus muscle which acts on the index finger is usually distinct throughout. The tendons for the other fingers are interconnected by areolar tissue and tendinous slips as far as the palm. Anterior to their proximal phalanges, the tendons pass through the tendons of flexor digitorum superficialis to insert on the palmar surfaces of the bases of the distal phalanges. The tendons of the profundus undergo fascicular rearrangement as they pass through those of superficialis.

Fig. 49.19 The deep flexor aspect of the left forearm.

(From Sobotta 2006.)

Flexor digitorum profundus may be joined by accessory slips from the radius (which act on the index finger), flexor superficialis, flexor pollicis longus, the medial epicondyle or the coronoid process.

Relations

Flexor digitorum profundus forms most of the surface elevation medial to the palpable posterior ulnar border. In the palm, the lumbrical muscles are attached to its tendons.

Vascular supply

The origin of flexor digitorum profundus is supplied by the inferior ulnar collateral and ulnar recurrent arteries. The proximal part is supplied by one or two branches from either the ulnar or common interosseous arteries. The distal part is supplied by a series of branches from the ulnar artery, the anterior interosseous artery and the median artery.

Innervation

The medial part of flexor digitorum profundus, i.e. the muscle bellies to the little and ring fingers, is innervated by the ulnar nerve. The lateral part, i.e. the muscle bellies to the middle and index fingers, is innervated by the anterior interosseous branch of the median nerve, C8 and T1.

Action

Flexor digitorum profundus is capable of flexing any or all of the joints over which it passes. It therefore has a role in coordinated finger flexion, but it is the only muscle capable of flexing the distal interphalangeal joints. The index finger tendon is usually capable of independent function, whereas the other three work together. Electromyographically flexor digitorum profundus acts alone in gentle digital flexion and is reinforced by superficialis for greater force and/or velocity.

Clinical anatomy: testing

Flexor digitorum profundus is tested by flexing the distal interphalangeal joint while holding the proximal interphalangeal joint in extension.

Attachments

Flexor pollicis longus is lateral to flexor digitorum profundus (Fig. 49.13). It arises from the grooved anterior surface of the radius, and extends from below its tuberosity to the upper attachment of pronator quadratus. It also arises from the adjacent interosseous membrane, and frequently by a variable slip from the lateral, or more rarely medial, border of the coronoid process, or from the medial epicondyle of the humerus. The muscle ends in a flattened tendon, which passes behind the flexor retinaculum, between opponens pollicis and the oblique head of adductor pollicis, to enter a synovial sheath. It inserts on the palmar surface of the base of the distal phalanx of the thumb.

Flexor pollicis longus is sometimes connected to flexor digitorum superficialis, or profundus, or pronator teres. The interosseous attachment, and indeed the whole muscle, may be absent. Anomalous tendon slips from the flexor pollicis longus to the flexor digitorum profundus are common.

Relations

The anterior interosseous nerve and vessels descend on the interosseous membrane between flexor pollicis longus and flexor digitorum profundus.

Vascular supply

The medial half of flexor pollicis longus is supplied by the anterior interosseous artery, while the lateral half is supplied by branches of the radial artery. The median artery may contribute if it is well developed.

Innervation

Flexor pollicis longus is innervated by the anterior interosseous branch of the median nerve, C7 and 8.

Action

Flexor pollicis longus flexes the phalanges of the thumb and the carpometacarpal joint of the thumb, especially if the more distal joints are stiff or fused.

Clinical anatomy: testing

Flexor pollicis longus is tested by flexing the interphalangeal joint of the thumb against resistance.

Attachments

Pronator quadratus is a flat, quadrilateral muscle which extends across the front of the distal parts of the radius and ulna (Fig. 49.13, see Fig. 49.19). It arises from the oblique ridge on the anterior surface of the shaft of the ulna, the medial part of this surface, and a strong aponeurosis which covers the medial third of the muscle. The fibres pass laterally and slightly downwards to the distal quarter of the anterior border and surface of the shaft of the radius. Deeper fibres insert into the triangular area above the ulnar notch of the radius.

Vascular supply

Pronator quadratus receives its main arterial supply from the anterior interosseous artery as it passes through the interosseous membrane.

Innervation

Pronator quadratus is innervated by the anterior interosseous branch of the median nerve, C7 and 8.

Action

Pronator quadratus is the principal pronator of the forearm, and is assisted by pronator teres only in rapid or forceful pronation. The deeper fibres oppose separation of the distal ends of the radius and ulna when upward thrusts are transmitted through the carpus.

Clinical anatomy: testing

Pronator quadratus is tested by pronation of the forearm against resistance while the wrist finger flexors are relaxed. The simultaneous contraction of pronator teres makes it difficult to test the independent action of pronator quadratus.

Attachments

Brachioradialis is the most superficial muscle along the radial side of the forearm, and forms the lateral border of the cubital fossa (Fig. 49.14). It arises from the proximal two-thirds of the lateral supracondylar ridge of the humerus and the anterior surface of the lateral intermuscular septum. The muscle fibres end above mid-forearm level in a flat tendon which inserts on the lateral side of the distal end of the radius, usually just proximal to its styloid process. Occasionally this attachment may be much more proximal.

Fig. 49.14 The superficial extensor muscles of the left forearm.

The muscle is often fused proximally with brachialis. Its tendon may divide into two or three separately attached slips. In rare instances it is double or absent.

Relations

The radial nerve and the anastomosis between the profunda brachii artery and the radial recurrent artery lie between the lateral intermuscular septum and brachialis. The tendon is crossed near its distal termination by the tendons of abductor pollicis longus and extensor pollicis brevis. The radial artery is on its ulnar (medial) side.

Vascular supply

Brachioradialis is supplied by branches of the radial recurrent artery which pierce the posteromedial surface of the muscle. It also receives branches from the radial collateral branch of the profunda brachii and directly from the radial artery in the distal part of the muscle.

Innervation

Brachioradialis is innervated by the radial nerve, C5 and 6.

Action

Brachioradialis is a flexor of the elbow (despite being supplied by an ‘extensor’ nerve). It acts most effectively with the forearm in mid-pronation. It is minimally active in slow, easy flexions, or with the forearm supine, but generates a powerful burst of activity in both flexion and extension when movement is rapid. Under these conditions it develops a pronounced transarticular component of its force which helps to stabilize the elbow joint by balancing the centrifugal force of rapid swings in either direction.

Clinical anatomy: testing

Brachioradialis can be seen and felt when the semi-pronated forearm is flexed against resistance.

Attachments

Extensor carpi radialis longus arises mainly from the distal third of the lateral supracondylar ridge of the humerus and the front of the lateral intermuscular septum. Some fibres come from the common tendon of origin of the forearm extensors. The belly ends at the junction of the proximal and middle thirds of the forearm in a flat tendon which runs along the lateral surface of the radius, deep to abductor pollicis longus and extensor pollicis brevis. The tendon then passes under the extensor retinaculum, where it lies in a groove on the back of the radius just behind the styloid process. It inserts on the radial side of the dorsal surface of the base of the second metacarpal, and may send slips to the first or third metacarpal bones. It contributes to the intermetacarpal ligaments.

Relations

Extensor carpi radialis longus is partly overlapped by brachioradialis (Fig. 49.14).

Vascular supply

Extensor carpi radialis longus receives its principal arterial supply from a single branch from the radial recurrent artery. Additional blood supply comes from branches from the radial collateral branch of the profunda brachii and directly from the radial artery in the distal part of the muscle.

Innervation

Extensor carpi radialis longus is innervated by the radial nerve, C6 and 7.

Action

Extensor carpi radialis longus acts as an extensor and abductor of the wrist and midcarpal joints. It acts in synergism with the finger flexors when making a fist.

Clinical anatomy: testing

The muscle belly and tendon of extensor carpi radialis longus can be palpated when the wrist is extended and abducted against resistance with the forearm pronated.

Attachments

Extensor carpi radialis brevis arises from the lateral epicondyle of the humerus by a tendon of origin which it shares with other forearm extensors, the radial collateral ligament of the elbow joint, a strong aponeurosis which covers its surface, and adjacent intermuscular septa. Its belly ends at about mid-forearm in a flat tendon which closely accompanies that of the longer carpal extensor to the wrist. The tendon passes under the extensor retinaculum and is attached to the dorsal surface of the base of the third metacarpal on its radial side, distal to its styloid process, and on adjoining parts of the second metacarpal base.

The tendons of both extensor carpi radialis longus and brevis may split into slips, which are variably attached to the second and third metacarpal bones. The muscles themselves may be united or may exchange muscular slips.

Relations

Extensor carpi radialis brevis is shorter than extensor carpi radialis longus and is covered by it (Fig. 49.14). The tendon passes deep to abductor pollicis longus and extensor pollicis brevis, then under the extensor retinaculum, where it lies in a shallow groove on the back of the radius, medial to the tendon of extensor carpi radialis longus, and separated from it by a low ridge. These two tendons share a common synovial sheath.

Vascular supply

Extensor carpi radialis brevis receives its arterial supply principally from two pedicles. One is a single branch from the radial recurrent artery, and the other is a branch of the radial artery which arises about one third of the way down the forearm. There is an additional blood supply proximally from branches from the radial collateral branch of the profunda brachii.

Innervation

Extensor carpi radialis brevis is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor carpi radialis brevis acts with extensor carpi radialis longus as an extensor and abductor of the wrist and midcarpal joints. It acts in synergism with the finger flexors when making a fist.

Clinical anatomy: testing

The muscle belly and tendon of extensor carpi radialis brevis can be palpated when the wrist is extended and abducted against resistance with the forearm pronated.

Attachments

Extensor digitorum arises from the lateral epicondyle of the humerus via the common extensor tendon, the adjacent intermuscular septa and the antebrachial fascia (Fig. 49.14). It divides distally into four tendons, which pass, in a common synovial sheath with the tendon of extensor indicis, through a tunnel under the extensor retinaculum. The tendons diverge on the dorsum of the hand, one to each finger. The tendon to the index finger is accompanied by extensor indicis, which lies ulnar (medial) to it. On the dorsum of the hand, adjacent tendons are linked by three variable intertendinous connections (juncturae tendinae), which are inclined distally and radially. The digital attachments enter a fibrous expansion on the dorsum of the proximal phalanges to which lumbrical, interosseous and digital extensor tendons all contribute.

The tendons of extensor digitorum may be variably deficient. More commonly, they are doubled or even tripled in one or more digits, most often the index finger or the middle finger. Occasionally a slip of tendon passes to the thumb. The arrangement of the intertendinous connections on the dorsum of the hand is highly variable. The medial connection is strong and pulls the tendon of the little finger towards that of the ring finger, whereas the connection between the middle two tendons is weak and may be absent.

Relations

The extensor tendon to the index finger lies radial (lateral) to the tendon of extensor indicis. The extensor tendon to the little finger lies radial (lateral) to the tendon of extensor digiti minimi.

Vascular supply

The proximal third of extensor digitorum is supplied by branches from the radial recurrent artery, and the distal two-thirds are supplied by branches from the posterior interosseous artery. The very distal portion is supplied by a perforating branch from the anterior interosseous artery which passes through the interosseous membrane.

Innervation

Extensor digitorum is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor digitorum can extend any or all of the joints over which it passes, i.e. wrist, metacarpophalangeal, proximal and distal interphalangeal joints (the latter two via the extensor expansion of the digits). When acting on the metacarpophalangeal joints, extensor digitorum tends to spread the digits apart, an action that is due principally to the different axes of the individual joints imposed by the transverse arch of the hand. This is a ‘trick’ movement used by patients with interosseous muscle paralysis. The function of the intertendinous bands is not clear, but they may affect the independent extension of digits. Alternatively a junctura can maintain some active extension even when a tendon has been divided in the metacarpal section of the hand, although the extent to which this occurs will depend on the junctura’s orientation. For example, some extension of the ring finger may be possible in the absence of its own tendon via the junctura of the middle finger, but the converse does not occur

Testing

The tendons of extensor digitorum can be readily felt, and usually seen, when the fingers are extended against resistance and the forearm is pronated.

Attachments

Extensor digiti minimi is a slender muscle medial to, and usually connected with, extensor digitorum (Fig. 49.14). It arises from the common extensor tendon by a thin tendinous slip and adjacent intermuscular septa. It frequently has an additional origin from the antebrachial fascia. Its long tendon slides in a separate compartment of the extensor retinaculum just behind the inferior radio-ulnar joint. Distal to the retinaculum, the tendon typically splits into two, and the lateral slip is joined by a tendon from extensor digitorum. All three tendons are attached to the dorsal digital expansion of the fifth digit, and there may be a slip to the fourth digit.

Extensor digiti minimi is rarely absent, but sometimes it is fused with extensor digitorum.

Relations

The tendon of extensor digiti minimi lies ulnar (medial) to the common extensor tendon to the little finger.

Vascular supply

Extensor digiti minimi is supplied by branches from the radial recurrent and posterior interosseous arteries, and by terminal branches from the anterior interosseous artery after it has pierced the interosseous membrane.

Innervation

Extensor digiti minimi is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor digiti minimi can extend any of the joints of the little finger, or contribute to wrist extension. It permits extension of the little finger independently of the other digits even in extremes of ulnar or radial wrist deviation.

Clinical anatomy: testing

Extensor digiti minimi is tested by extending the little finger while holding the remaining fingers flexed at the metacarpophalangeal joints. This eliminates any simultaneous contraction of extensor digitorum.

Attachments

Extensor carpi ulnaris arises from the lateral epicondyle via the common extensor tendon, the posterior border of the ulna (by an aponeurosis shared with flexor carpi ulnaris and flexor digitorum profundus), and overlying fascia (Fig. 49.14). It ends in a tendon that slides in a groove between the head and the styloid process of the ulna, in a separate compartment of the extensor retinaculum, and is ultimately attached to a tubercle on the medial side of the fifth metacarpal base.

Vascular supply

Proximally extensor carpi ulnaris receives branches from the radial recurrent artery. Distally, it is supplied by several branches from the posterior interosseous artery.

Innervation

Extensor carpi ulnaris is innervated by the posterior interosseous nerve, C7 and 8.

Action

Together with extensors carpi radialis longus and brevis, extensor carpi ulnaris acts synergistically with the digital flexors to extend and to fix the wrist when objects are being gripped or when the fist is clenched. Observation shows that it is impossible to grip strongly unless the wrist is extended. Acting with flexor carpi ulnaris, extensor carpi ulnaris adducts the hand.

Clinical anatomy: testing

If the wrist is extended and adducted against resistance, and the forearm is pronated and the fingers are extended, extensor carpi ulnaris can be felt lateral to the groove that overlies the posterior subcutaneous border of the ulna.

Attachments

Anconeus is a small, triangular muscle posterior to the elbow joint and is partially blended with triceps (Fig. 49.14). Anconeus arises by a separate tendon from the posterior surface of the lateral epicondyle of the humerus. Its fibres diverge medially towards the ulna, covering the posterior aspect of the annular ligament, and are attached to the lateral aspect of the olecranon and proximal quarter of the posterior surface of the shaft of the ulna.

The extent to which anconeus fuses with triceps or extensor carpi ulnaris is variable.

Vascular supply

Anconeus is supplied by branches from the posterior interosseous recurrent artery. A small number of musculocutaneous perforators reach the skin overlying the muscle.

Innervation

Anconeus is innervated by the radial nerve, C6, 7 and 8.

Action

Anconeus assists triceps in extending the elbow joint. Its major function is not clear, but it may be the control of ulnar abduction in pronation, which is necessary if the forearm is to turn over the hand without translating it medially. In this way a tool can be revolved ‘on the spot’ or it can be swept through an arc.

Attachments

Abductor pollicis longus arises from the posterior surface of the shaft of the ulna distal to anconeus, the adjoining interosseous membrane, and the middle third of the posterior surface of the radius distal to the attachment of supinator (Fig. 49.15). It descends laterally, becoming superficial in the distal forearm, where it is visible as an oblique elevation (Fig. 49.14). The muscle fibres end in a tendon just proximal to the wrist. The tendon runs in a groove on the lateral side of the distal end of the radius accompanied by the tendon of extensor pollicis brevis. It usually splits into two slips, one of which is attached to the radial side of the first metacarpal base, and the other is attached to the trapezium. Slips from the tendon may continue into opponens pollicis or abductor pollicis brevis. Occasionally the muscle itself may be wholly or partially divided.

Vascular supply

Abductor pollicis longus is supplied proximally by a lateral branch from the posterior interosseous artery. Distally it is supplied on the medial side by a perforating branch from the anterior interosseous artery.

Innervation

Abductor pollicis longus is innervated by the posterior interosseous nerve, C7 and 8.

Action

Abductor pollicis longus abducts the wrist joint. Acting with abductor pollicis brevis it aids abduction of the thumb radially (i.e. in the plane of the palm). Acting with the pollicial extensors it extends the thumb at its carpometacarpal joint. The tendon may also stabilize the trapezium upon which the first metacarpal can move.

Clinical anatomy: testing

The tendon of abductor pollicis longus can be seen and felt at the radial aspect of the anatomical snuff box when the thumb and wrist are abducted against resistance at the carpometacarpal joint.

Attachments

Extensor pollicis longus is larger than extensor pollicis brevis, whose proximal attachment it partly covers (Fig. 49.14, Fig. 49.15). It arises from the lateral part of the middle third of the posterior surface of the shaft of the ulna below abductor pollicis longus, and the adjacent interosseous membrane. The tendon passes through a separate compartment of the extensor retinaculum in a narrow, oblique groove on the back of the distal end of the radius. It turns around a bony fulcrum, Lister’s tubercle, which changes its line of pull from that of the forearm to that of the thumb, and is attached to the base of the distal phalanx of the thumb. The sides of the tendon are joined on the dorsum of the proximal phalanx by expansions from the tendon of abductor pollicis brevis laterally, and from the first palmar interosseous and adductor pollicis medially.

Relations

After passing around Lister’s tubercle, the tendon of extensor pollicis longus crosses the tendons of extensor carpi radialis brevis and longus obliquely (Fig. 49.14). When the thumb is fully extended the tendon is separated from extensor pollicis brevis by a triangular depression or fossa, the so-called ‘anatomical snuff-box’. Bony structures can be felt in the floor of this fossa by deep palpation. In proximal to distal order they are the radial styloid, the smooth convex articular surface of the scaphoid, the trapezium, and the base of the first metacarpal. The latter are more easily felt during metacarpal movement, while the scaphoid is more easily felt during adduction and abduction of the hand.

Vascular supply

Extensor pollicis longus is supplied on its superficial surface by branches from the posterior interosseous artery, and on its deep surface by perforating branches from the anterior interosseous artery.

Innervation

Extensor pollicis longus is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor pollicis longus extends the distal phalanx of the thumb. Acting in association with extensor pollicis brevis and abductor pollicis longus, it extends the proximal phalanx and the metacarpal. In continued action, as a consequence of the obliquity of its tendon, extensor pollicis longus adducts the extended thumb and rotates it laterally.

Clinical anatomy: testing

The tendon of extensor pollicis longus can be palpated at the ulnar border of the anatomical snuff-box when the thumb is extended at the interphalangeal joint against resistance. When the thumb is opposed and adducted, abductor pollicis brevis can extend the interphalangeal joint of the thumb, mimicking the action of extensor pollicis longus.

Attachments

Extensor pollicis brevis arises from the posterior surface of the radius distal to abductor pollicis longus, and from the adjacent interosseous membrane (Fig. 49.14, Fig. 49.15). The tendon is inserted into the base of the proximal phalanx of the thumb, and commonly has an additional attachment to the base of the distal phalanx, usually through a fasciculus which joins the tendon of extensor pollicis longus. Extensor pollicis brevis may be absent or fused completely with abductor pollicis longus.

Relations

Extensor pollicis brevis is ulnar (medial) to, and closely connected with, abductor pollicis longus (Fig. 49.14, Fig. 49.15). In the distal forearm, the two muscles emerge between extensor carpi radialis brevis and extensor digitorum, and pass obliquely across the tendons of the radial extensors of the wrist. They cover the distal part of brachioradialis, and pass through the most lateral compartment of the extensor retinaculum in a single synovial sheath, sharing a groove in the distal radius. Ultimately they cross, superficial to the radial styloid process and radial artery, to reach the dorsolateral base of the proximal phalanx of the thumb.

Vascular supply

Extensor pollicis brevis is supplied from branches from the posterior interosseous artery together with perforating branches from the anterior interosseous artery.

Innervation

Extensor pollicis brevis is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor pollicis brevis extends the proximal phalanx and metacarpal of the thumb.

Clinical anatomy: testing

The tendon of extensor pollicis brevis can be felt at the radial border of the anatomical snuff-box, lying medial to the tendon of abductor pollicis longus, when the metacarpophalangeal joint of the thumb is extended against resistance.

Attachments

Extensor indicis is a narrow, elongated muscle which lies medial and parallel to extensor pollicis longus (Fig. 49.15). It arises from the posterior surface of the ulna distal to extensor pollicis longus, and the adjacent interosseous membrane. Its tendon passes under the extensor retinaculum in a common compartment with the tendons of extensor digitorum. Opposite the head of the second metacarpal it joins the ulnar side of the tendon of extensor digitorum which serves the index finger.

Extensor indicis occasionally sends accessory slips to the extensor tendons of other digits. Rarely its tendon may be interrupted on the dorsum of the hand by an additional muscle belly (extensor indicis brevis manus).

Relations

The tendon of extensor indicis lies on the ulnar aspect of the extensor digitorum tendon to the index finger on the dorsum of the hand.

Vascular supply

Extensor indicis is supplied on its superficial surface by branches from the posterior interosseous artery, and on its deep surface by perforating branches from the anterior interosseous artery.

Innervation

Extensor indicis is innervated by the posterior interosseous nerve, C7 and 8.

Action

Extensor indicis helps to extend the index finger and the wrist. It permits extension of the index finger independently of the other digits, even in extremes of ulnar or radial wrist deviation.

Clinical anatomy: testing

Extensor indicis is tested by extending the index finger while holding the remaining fingers flexed at the metacarpophalangeal joints. This eliminates the effects of any simultaneous contraction of extensor digitorum.

Attachments

Supinator surrounds the proximal third of the radius and has superficial and deep layers (Fig. 49.15). The two parts arise together, the superficial by tendinous, and the deep by muscular fibres, from the lateral epicondyle of the humerus; the radial collateral ligament of the elbow joint and the anular ligament of the superior radio-ulnar joint; the supinator crest of the ulna and the posterior part of the triangular depression in front of it; and an aponeurosis which covers the muscle. Supinator is attached distally to the lateral surface of the proximal third of the radius, down to the insertion of pronator teres. The radial attachment extends on to the anterior and posterior surfaces between the anterior oblique line and the fainter posterior oblique ‘ridge’ (Fig. 49.4).

Supinator is subject to frequent variation, and small parts of the muscle have acquired individual names, e.g. lateral and medial tensors of the annular ligament.

Relations

The posterior interosseous nerve enters the forearm by passing between the superficial and deep heads of supinator.

Vascular supply

The superficial part of supinator is supplied by branches from the radial recurrent artery. The deep part of supinator is supplied by branches from the posterior interosseous artery and the posterior interosseous recurrent artery.

Innervation

Supinator is innervated by the posterior interosseous nerve, C6 and 7 as it traverses the muscle.

Action

Supinator rotates the radius so as to bring the palm to face anteriorly. It acts alone in slow, unopposed supination, and together with biceps brachii in fast or forceful supination. An object which may potentially be heavy is often picked up with the forearm initially pronated. The more powerful supinators lift the object against gravity, and rotation is often combined with increasing elbow flexion to bring the object towards the eyes.

Clinical anatomy: testing

Supinator is too deep to be palpated and independent testing is difficult. Biceps is inactive on supination with the elbow fully extended, therefore this must be produced by supination alone and can be used to test its function.

Radial recurrent artery

The radial recurrent artery is discussed on page 835.

Cutaneous branches

Cutaneous branches emerge between brachioradialis and pronator teres in the proximal third of the forearm. The largest perforator, which is also the largest in the forearm, has been named the inferior cubital artery. It reaches the deep fascia by passing superficially between brachioradialis and pronator teres in the apex of the antecubital fossa. It lies lateral to the tendon of biceps, emerging between the median cubital vein and its communicating branch to the venae comitantes of the radial artery. In the distal two-thirds of the forearm, the cutaneous perforators emerge through the fascia between brachioradialis and flexor carpi radialis and between flexor carpi radialis and flexor digitorum superficialis and fan out at the level of the deep fascia. These vessels anastomose with their counterparts from the ulnar artery and the posterior interosseous artery.

The fasciocutaneous branches provide the anatomical basis for raising a skin flap containing the whole width of forearm skin, either pedicled or as a free flap, based on the radial artery and its venae comitantes. Known as the radial forearm fasciocutaneous flap, it is used for reconstructing areas of missing tissue elsewhere in the body. It is possible to incorporate the lateral aspect of the radius with the flap because a few fascioperiosteal branches supply this part of the bone.

Muscular branches

Muscular branches are distributed to the muscles on the radial side of the forearm.

Anterior and posterior ulnar recurrent arteries

The anterior and posterior ulnar recurrent arteries are described on page 835.

Common interosseous artery

The common interosseous artery is a short branch of the ulnar artery (Fig. 49.13, see Fig. 49.19). It arises just distal to the radial tuberosity and passes back to the proximal border of the interosseous membrane, where it divides into the anterior and posterior interosseous arteries. Occasionally, the common interosseous artery is a branch of the radial artery.

Anterior interosseous artery

The anterior interosseous artery descends on the anterior aspect of the interosseous membrane with the anterior interosseous branch of the median nerve (see Fig. 49.19). It is overlapped by contiguous sides of flexor digitorum profundus and flexor pollicis longus. Shortly after its origin, it usually gives off a slender median artery. This accompanies and supplies the median nerve as far as the palm, where it may join the superficial palmar arch or end as one or two palmar digital arteries. (The median artery can also arise from the ulnar or the common interosseous artery.)

Muscular and nutrient branches from the anterior interosseous artery pierce the interosseous membrane to supply deep extensor muscles and the radius and ulna respectively. A branch descends deep to pronator quadratus before piercing the interosseous membrane to join the anterior ‘carpal’ arch.

The anterior interosseous artery proper leaves the anterior compartment by piercing the interosseous membrane proximal to pronator quadratus. It anastomoses with the posterior interosseous artery in the posterior compartment of the forearm, and travels through a tunnel under the extensor retinaculum with the tendons of the digital extensors before joining the dorsal carpal arch. Three small cutaneous perforating branches supply the skin over the lower lateral border of the forearm.

Posterior interosseous artery

The posterior interosseous artery is usually smaller than the anterior (Fig. 49.15, Fig. 49.17, Fig. 49.18). It passes dorsally between the oblique cord and proximal border of the interosseous membrane and then between supinator and abductor pollicis longus. It descends deep in the groove between extensor carpi ulnaris and the extensor digiti minimi part of extensor digitorum. While in the groove it gives rise to multiple muscular branches which supply these muscles and fasciocutaneous perforators which travel in the intermuscular septum between extensor carpi ulnaris and extensor digiti minimi. These fasciocutaneous vessels provide the anatomical basis for raising a dorsal forearm skin flap, which is usually pedicled, based on the posterior interosseous artery and its venae comitantes. Known as the posterior interosseous artery flap, it is used for reconstructing areas of missing tissue in the forearm and proximal part of the hand.

Fig. 49.18 Axial MRI through middle of left forearm. 1. Flexor digitorum superficialis. 2. Flexor carpi ulnaris. 3. Ulnar artery. 4. Flexor digitorum profundus. 5. Ulna. 6. Extensor pollicis longus. 7. Extensor carpi ulnaris. 8. Posterior interosseous neurovascular bundle. 9. Median nerve. 10. Radial artery. 11. Anterior interosseous neurovascular bundle. 12. Abductor pollicis longus. 13. Radius. 14. Extensor carpi radialis brevis. 15. Extensor digitorum.

The posterior interosseous artery accompanies the deep branch of the radial nerve (posterior interosseous nerve) on abductor pollicis longus. Distally it anastomoses with the terminal part of the anterior interosseous artery and the dorsal carpal arch.

Sometimes the posterior interosseous artery disappears halfway down the forearm, in which case the anterior interosseous artery pierces the interosseous membrane more proximally to anastomose with it. Rarely no anastomosis occurs between the anterior and the posterior interosseous arteries.

Posterior interosseous recurrent artery

The posterior interosseous recurrent artery leaves the posterior interosseous artery near its origin and ascends between the lateral epicondyle and olecranon, either on or through supinator, and deep to anconeus. It anastomoses with the middle collateral branch of the profunda brachii artery, posterior ulnar recurrent and ulnar collateral arteries. Occasionally the artery is absent.

Cutaneous branches

The cutaneous perforators of the ulnar artery reach the skin by passing along the fascial septum between flexor carpi ulnaris and flexor digitorum superficialis throughout the length of the forearm. A constant dorso-ulnar perforator vessel is given off distally 2–5 cm proximal to the pisiform and it accompanies the dorsal cutaneous branch of the ulnar nerve. The vessel emerges between flexor carpi ulnaris and extensor carpi ulnaris. A few small musculocutaneous perforators reach the skin via flexor carpi ulnaris and anastomose with their counterparts derived from the radial and the posterior interosseous arteries.

Muscular branches

Muscular branches arise directly from the main vessel and are distributed to the muscles on the ulnar side of the forearm.

Accessory cephalic vein

The accessory cephalic vein may arise either in a dorsal forearm plexus or from the ulnar side of the dorsal venous network in the hand. It joins the cephalic vein distal to the elbow. A large oblique vein often connects the basilic and cephalic veins dorsally in the forearm.

Anterior interosseous nerve syndrome

The anterior interosseous nerve may be affected with the median nerve or by itself in any of the causes of pronator syndrome (p. 836). Median nerve compression is typically caused by pressure from fascial bands on the deep head of the pronator teres or the tendinous radial attachment of flexor digitorum superficialis. Anterior interosseous nerve palsy may be due to external pressure, a form of ‘Saturday night palsy’, and sometimes by tight grip in association with pronation without obvious cause. It may be a manifestation of neuralgic amyotrophy and tends to resolve spontaneously over several months. A variety of aberrant muscles, e.g. an accessory head of flexor pollicis longus, palmaris profundus, or flexor carpi radialis brevis, have all been described as causing entrapment neuropathy of the anterior interosseous nerve.

An anterior interosseous nerve palsy causes weakness of pinch grip due to involvement of flexor pollicis longus and flexor digitorum profundus to the index finger. Innervation of flexor digitorum profundus to the middle finger is rather variable, and therefore this muscle may or may not be weak. The branches to these three muscles may arise separately from the median nerve, so that isolated weakness of the terminal phalanx to the thumb or index finger may occur. Pronator quadratus is also involved but is not clinically significant. Anterior interosseous nerve palsy can be distinguished from pronator syndrome because there are no sensory symptoms. The treatment is exploration of the nerve and surgical decompression.

Radial tunnel syndrome

Radial tunnel syndrome is an entrapment neuropathy of the radial nerve near the elbow, where four structures can potentially cause compression of the nerve. These are fibrous bands (which can tether the radial nerve to the radiohumeral joint); the sharp tendinous medial border of extensor carpi radialis brevis; a leash of vessels from the radial recurrent artery as it passes to supply brachioradialis and extensor carpi radialis longus; the arcade of Frohse, which is the free aponeurotic proximal edge of the superficial part of supinator (see Fig. 48.6).

Usually the only presenting symptom is pain over the extensor mass just distal to the elbow. There is no sensory disturbance or motor loss, but there is frequently tenderness along the course of the radial nerve over the radial head. The pain is exacerbated when the elbow is extended and the wrist is passively flexed and pronated, or extended and supinated against resistance. Extension of the middle finger against resistance when the elbow is fully extended also may lead to increased pain. These manoeuvres tighten the anatomical structures which cause compression.

Radial sensory nerve entrapment (Wartenberg’s disease)

Entrapment of the superficial radial nerve can occur as the nerve emerges from beneath the edge of the brachioradialis tendon about 6 cm proximal to the radial styloid; it is probably pinched by the scissoring effect of brachioradialis and extensor carpi radialis brevis tendons. The condition is frequently associated with previous trauma in this region. The symptoms are pain and paraesthesia over the radial aspect of the dorsum of the wrist and hand.

Posterior interosseous nerve palsy

There are many causes of posterior interosseous nerve palsy. These include trauma and inflammatory swellings, as well as entrapment at the same anatomical sites that can cause radial tunnel syndrome. Pain is similar in nature to that of radial tunnel syndrome and is later accompanied by weakness and paralysis. When fully developed, there is inability to extend the fingers at the metacarpophalangeal joints, weakness of thumb extension and abduction. There is weakness and radial deviation of wrist extension because extensor carpi ulnaris is usually affected, while the radial wrist extensors and brachioradialis are normal (because their nerve supply is given off proximal to the origin of the posterior interosseous nerve). There are no sensory disturbances, because the superficial radial nerve arises above this level.