Yeditepe University Faculty of Medicine 1st Year Anatomy Blog



ANTERIOR ASPECT OF THE

FORERARM

&

CUBITAL FOSSA

26. 12. 2012

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Kaan Yücel

M.D., Ph.D.



The forearm is the part of the upper limb between the elbow wrist joints. Proximally, most major structures pass between the arm and forearm through, or in relation to, the cubital fossa, which is anterior to the elbow joint. The exception is the ulnar nerve, which passes posterior to the medial epicondyle of the humerus.

The bone framework of the forearm consists of two parallel bones, the radius and the ulna which are joined by an interosseous membrane. Although the proximal boundary of the forearm per se is defined by the joint plane of the elbow, functionally the forearm includes the distal humerus. The radius is lateral in position and is small proximally, where it articulates with the humerus, and large distally, where it forms the wrist joint with the carpal bones of the hand.

As in the arm, the forearm is divided into anterior and posterior compartments. In the forearm, these compartments are separated by:

• A lateral intermuscular septum, which passes from the anterior border of the radius to deep fascia surrounding the limb;

• An interosseous membrane, which links adjacent borders of the radius and ulna along most of their length;

• the attachment of deep fascia along the posterior border of the ulna.

The forearm proper is not, in fact, long enough to provide the required length and sufficient area for attachment proximally, so the proximal attachments (origins) of the muscles must occur proximal to the elbow—in the arm—and provided by the humerus. The medial epicondyle and supraepicondylar ridge provide attachment for the forearm flexors, and the lateral formations provide attachment for the forearm extensors. Thus, rather than lying strictly anteriorly and posteriorly, the proximal parts of the “anterior” (flexor-pronator) compartment of the forearm lie anteromedially, and the “posterior” (extensor-supinator) compartment lies posterolaterally.

Spiraling gradually over the length of the forearm, the compartments become truly anterior and posterior in position in the distal forearm and wrist. These fascial compartments, containing the muscles in functional groups, are demarcated by the subcutaneous border of the ulna posteriorly (in the proximal forearm) and then medially (distal forearm) and by the radial artery anteriorly and then laterally. These structures are palpable (the artery by its pulsations) throughout the forearm. Because neither boundary is crossed by motor nerves, they also provide sites for surgical incision.

Muscles in the anterior compartment of the forearm flex the wrist and digits and pronate the hand. Muscles in the posterior compartment extend the wrist and digits and supinate the hand. Major nerves and vessels supply or pass through each compartment.

The flexors and pronators of the forearm in the anterior compartment are served mainly by the median nerve; the one and a half exceptions are innervated by the ulnar nerve. The extensors and supinators of the forearm are in the posterior compartment and are all served by the radial nerve (directly or by its deep branch).

The fascial compartments of the limbs generally end at the joints; therefore, fluids and infections in compartments are usually contained and cannot readily spread to other compartments. The anterior compartment is exceptional in this regard because it communicates with the central compartment of the palm through the carpal tunnel.

Figure 1. Forearm- anterior aspect



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There are 17 muscles crossing the elbow joint, some of which act on the elbow joint exclusively, whereas others act at the wrist and fingers.

The flexor muscles of the forearm are in the anterior (flexor-pronator) compartment of the forearm and are separated from the extensor muscles of the forearm by the radius and ulna and, in the distal two thirds of the forearm, by the interosseous membrane that connects them. The tendons of most flexor muscles are located on the anterior surface of the wrist and are held in place by the palmar carpal ligament and the flexor retinaculum (transverse carpal ligament), thickenings of the antebrachial fascia.

Muscles in the anterior (flexor) compartment of the forearm occur in three layers:

• Superficial layer (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris)

• Intermediate layer (flexor digitorum superficialis)

• Deep layer (flexor digitorum profundus, flexor pollicis longus, and pronator quadratus)

Generally, these muscles are associated with:

➢ movements of the wrist joint;

➢ flexion of the fingers including the thumb; and

➢ pronation.

The five superficial and intermediate muscles cross the elbow joint; the three deep muscles do not. With the exception of the pronator quadratus, the more distally placed a muscle's distal attachment lies, the more distally and deeply placed is its proximal attachment.

All muscles in the anterior compartment of the forearm are innervated by the median nerve, except for the flexor carpi ulnaris muscle and the medial half of the flexor digitorum profundus muscle, which are innervated by the ulnar nerve.

Functionally, the brachioradialis is a flexor of the forearm, but it is located in the posterior (posterolateral) or extensor compartment and is thus supplied by the radial nerve. Therefore, the brachioradialis is a major exception to the rule that (1) the radial nerve supplies only extensor muscles and (2) that all flexors lie in the anterior (flexor) compartment.

SuperfIcIal layer

All four muscles in the superficial layer-flexor carpi ulnaris, palmaris longus, flexor carpi radialis, and pronator teres-have a common origin from the medial epicondyle of the humerus, and, except for the pronator teres, extend distally from the forearm into the hand.

Figure 2. Superficial layer muscles of the anterior compartment of the forearm



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The flexor carpi ulnaris muscle is the most medial of the muscles in the superficial layer. having a long linear origin from the olecranon and posterior border of the ulna (ulnar head), in addition to an origin from the medial epicondyle of the humerus (humeral head).

The ulnar nerve enters the anterior compartment of the forearm by passing through the triangular gap between the humeral and ulnar heads of flexor carpi ulnaris. The flexor carpi ulnaris muscle is a powerful flexor and adductor of the wrist and is innervated by the ulnar nerve. The flexor carpi ulnaris simultaneously flexes and adducts the hand at the wrist if acting alone. It flexes the wrist when it acts with the flexor carpi radialis and adducts it when acting with the extensor carpi ulnaris.

This muscle is exceptional among muscles of the anterior compartment, being fully innervated by the ulnar nerve. The tendon of the flexor carpi ulnaris is a guide to the ulnar nerve and artery, which are on its lateral side at the wrist.

To test the flexor carpi ulnaris, the person puts the posterior aspect of the forearm and hand on a flat table and is then asked to flex the wrist against resistance while the examiner palpates the muscle and its tendon.

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The flexor carpi radialis muscle is a long fusiform muscle located medial to the pronator teres and lateral to palmaris longus and has a large and prominent tendon in the distal half of the forearm. Unlike the tendon of the flexor carpi ulnaris, which forms the medial margin of the distal forearm, the tendon of the flexor carpi radialis muscle is positioned just lateral to the midline. In this position, the tendon can be easily palpated, making it an important landmark for finding the pulse in the radial artery, which lies immediately lateral to it. The flexor carpi radialis tendon is a good guide to the radial artery, which lies just lateral to it

The flexor carpi radialis is a powerful flexor of the wrist and can also abduct the wrist. It produces flexion (when acting with the flexor carpi ulnaris) and abduction of the wrist (when acting with the extensors carpi radialis longus and brevis). When acting alone, the flexor carpi radialis produces a combination of flexion and abduction simultaneously at the wrist so that the hand moves anterolaterally.

To test the flexor carpi radialis, the person is asked to flex the wrist against resistance. If acting normally, its tendon can be easily seen and palpated.

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The pronator teres muscle, a fusiform muscle, is the most lateral of the superficial forearm flexors. Its lateral border forms the medial boundary of the cubital fossa. The median nerve often exits the cubital fossa by passing between the humeral and ulnar heads of this muscle. The pronator teres rotates the radius over the ulna during pronation.

To test the pronator teres, the person's forearm is flexed at the elbow and pronated from the supine position against resistance provided by the examiner. If acting normally, the muscle is prominent and can be palpated at the medial margin of the cubital fossa.

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The palmaris longus muscle is absent in about 14-15% of the population on one or both sides (usually the left) in approximately 14% of people, but its actions are not missed. The palmaris longus lies between the flexor carpi ulnaris and the flexor carpi radialis muscles. It is a spindle-shaped muscle with a long tendon, which passes into the hand and attaches to the flexor retinaculum and to a thick layer of deep fascia, the palmar aponeurosis, which underlies and is attached to the skin of the palm and fingers.

In addition to its role as an accessory flexor of the wrist joint, the palmaris longus muscle also opposes shearing forces on the skin of the palm during gripping.

To test the palmaris longus, the wrist is flexed and the pads of the little finger and thumb are tightly pinched together. If present and acting normally, the tendon can be easily seen and palpated.

IntermedIate layer

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The muscle in the intermediate layer of the anterior compartment of forearm is the flexor digitorum superficialis muscle. This large muscle has two heads: humero-ulnar head and radial head.

The median nerve and ulnar artery pass deep to the flexor digitorum superficialis between the two heads.

In the distal forearm, the flexor digitorum superficialis forms four tendons, which pass through the carpal tunnel of the wrist and into the four fingers. The tendons for the ring and middle fingers are superficial to the tendons for the index and little fingers.

In the forearm, carpal tunnel, and proximal regions of the four fingers, the tendons of the flexor digitorum superficialis are anterior to the tendons of the flexor digitorum profundus muscle.

Near the base of the proximal phalanx of each finger, the tendon of the flexor digitorum superficialis splits into two parts to pass dorsally around each side of the tendon of the flexor digitorum profundus and ultimately attach to the margins of the middle phalanx.

The flexor digitorum superficialis flexes the metacarpophalangeal joint and proximal interphalangeal joint of each finger; it also flexes the wrist joint.

To test the flexor digitorum superficialis, one finger is flexed at the proximal interphalangeal joint against resistance and the other three fingers are held in an extended position to inactivate the flexor digitorum profundus.

Figure 3. Intermediate layer muscle of the anterior compartment of the forearm: flexor digitorum superficialis



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Deep layer

There are three deep muscles in the anterior compartment of the forearm: flexor digitorum profundus, flexor pollicis longus, and pronator quadratus.

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The flexor digitorum profundus muscle is the only muscle that can flex the distal interphalangeal joints of the fingers. This thick muscle “clothes” the anterior aspect of the ulna. The flexor digitorum profundus originates from the anterior and medial surfaces of the ulna and from the adjacent half of the anterior surface of the interosseous membrane. It gives rise to four tendons, which pass through the carpal tunnel into the four medial fingers. Throughout most of their course, the tendons are deep to the tendons of the flexor digitorum superficialis muscle.

Opposite the proximal phalanx of each finger, each tendon of the flexor digitorum profundus passes through a split formed in the overlying tendon of the flexor digitorum superficialis muscle and passes distally to insert into the base of the distal phalanx.

In the palm, the lumbrical muscles originate from the sides of the tendons of the flexor digitorum profundus.

Innervation of the medial and lateral halves of the flexor digitorum profundus varies as follows:

➢ lateral half (associated with the index and middle fingers) is innervated by the anterior interosseous nerve (branch of the median nerve);

➢ medial half (the part associated with the ring and little fingers) is innervated by the ulnar nerve.

The flexor digitorum profundus flexes the distal phalanges of the medial four fingers after the flexor digitorum superficialis has flexed their middle phalanges (i.e., it curls the fingers and assists with flexion of the hand, making a fist). Each tendon is capable of flexing two interphalangeal joints, the metacarpophalangeal joint. Because the tendons cross the wrist, it can flex the wrist joint as well.

To test the flexor digitorum profundus, the proximal interphalangeal joint is held in the extended position while the person attempts to flex the distal interphalangeal joint. The integrity of the median nerve in the proximal forearm can be tested by performing this test using the index finger, and that of the ulnar nerve can be assessed by using the little finger.

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The flexor pollicis longus muscle originates from the anterior surface of the radius and the adjacent half of the anterior surface of the interosseous membrane. It is a powerful muscle and forms a single large tendon, which passes through the carpal tunnel, lateral to the tendons of the flexor digitorum superficialis and flexor digitorum profundus muscles, and into the thumb where it attaches to the base of the distal phalanx.

The flexor pollicis longus flexes the thumb and is innervated by the anterior interosseous nerve (branch of the median nerve).

To test the flexor pollicis longus, the proximal phalanx of the thumb is held and the distal phalanx is flexed against resistance.

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The pronator quadratus, as its name indicates, is quadrangular and pronates the forearm. It originates from a linear ridge on the anterior surface of the lower end of the ulna and passes laterally to insert onto the flat anterior surface of the radius. It lies deep to, and is crossed by, the tendons of the flexor digitorum profundus and flexor pollicis longus muscles. The pronator quadratus clothes the distal fourth of the radius and ulna and the interosseous membrane between them. The pronator quadratus is the only muscle that attaches only to the ulna at one end and only to the radius at the other end.

The pronator quadratus is the prime mover for pronation. The pronator quadratus muscle pulls the distal end of the radius anteriorly over the ulna during pronation. The pronator quadratus initiates pronation; it is assisted by the pronator teres when more speed and power are needed. The pronator quadratus also helps the interosseous membrane hold the radius and ulna together, particularly when upward thrusts are transmitted through the wrist (e.g., during a fall on the hand). The pronator quadratus is innervated by the anterior interosseous nerve (branch of the median nerve).

Figure 4. Muscles of the superficial, intermediate and deep layers of the anterior compartment of the forearm



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ArterIes

The main arteries of the forearm are the ulnar and radial arteries, which usually arise opposite the neck of the radius in the inferior part of the cubital fossa as terminal branches of the brachial artery.

Figure 5. Brachial artery and its two terminal branches: radial and ulnar arteries



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RadIal artery

The radial artery originates from the brachial artery at approximately the neck of the radius and passes along the lateral aspect of the forearm. The radial artery is the smaller of the terminal branches of the brachial artery.

In the distal forearm, the radial artery lies immediately lateral to the large tendon of the flexor carpi radialis muscle and directly anterior to the pronator quadratus muscle and the distal end of the radius. In the distal forearm, the radial artery can be located using the flexor carpi radialis muscle as a landmark. The radial pulse can be felt by gently palpating the radial artery against the underlying muscle and bone. When the brachioradialis is pulled laterally, the entire length of the artery is visible.

Branches of the radial artery originating in the forearm include:

1) radial recurrent artery, which contributes to an anastomotic network around the elbow joint

2) small palmar carpal branch

3) superficial palmar branch enters the hand by passing through, or superficial to, the thenar muscles at the base of the thumb, which anastomoses with the superficial palmar arch formed by the ulnar artery.

Figure 6. Radial artery and its branches



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Ulnar artery

The ulnar artery is larger than the radial artery and passes down the medial side of the forearm. It leaves the cubital fossa by passing deep to the pronator teres muscle, and then passes through the forearm in the fascial plane between the flexor carpi ulnaris and flexor digitorum profundus muscles. In distal regions of the forearm, the ulnar nerve is immediately medial to the ulnar artery.

The ulnar artery leaves the forearm, enters the hand by passing lateral to the pisiform bone and superficial to the flexor retinaculum of the wrist, and arches over the palm. It is often the major blood supply to the medial three and one-half digits.

Pulsations of the ulnar artery can be palpated on the lateral side of the flexor carpi ulnaris tendon, where it lies anterior to the ulnar head.

Figure 7. Ulnar artery and its branches

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VeIns

The superficial veins of the forearm lie in the superficial fascia. The cephalic vein arises from the lateral side of the dorsal venous arch on the back of the hand and winds around the lateral border of the forearm; it then ascends into the cubital fossa and up the front of the arm on the lateral side of the biceps. It terminates in the axillary vein in the deltopectoral triangle. As the cephalic vein passes up the upper limb, it receives a variable number of tributaries from the lateral and posterior surfaces of the limb.

The basilic vein arises from the medial side of the dorsal venous arch on the back of the hand and winds around the medial border of the forearm; it then ascends into the cubital fossa and up the front of the arm on the medial side of the biceps. Its terminates, by joining the venae comitantes of the brachial artery to form the axillary vein. The median cubital vein, a branch of the cephalic vein in the cubital fossa, runs upward and medially and joins the basilic vein. The basilic vein also receives a variable number of tributaries from the medial and posterior surfaces of the upper limb.

Figures 8 & 9. Veins in the anterior compartment of the forearm





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Deep veins accompanying arteries are plentiful in the forearm. These accompanying veins (L. venae comitantes) arise from the anastomosing deep venous palmar arch in the hand. From the lateral side of the arch, paired radial veins arise and accompany the radial artery; from the medial side, paired ulnar veins arise and accompany the ulnar artery. The veins accompanying each artery anastomose freely with each other. The radial and ulnar veins drain the forearm but carry relatively little blood from the hand.

Deep veins of the anterior compartment drain into brachial veins associated with the brachial artery in the cubital fossa.

Nerves

Nerves in the anterior compartment of the forearm are the median and ulnar nerves, and the superficial branch of the radial nerve.

MedIan nerve

The median nerve is the principal nerve of the anterior compartment of the forearm. It supplies muscular branches directly to the muscles of the superficial and intermediate layers of forearm flexors (except the flexor carpi ulnaris), and deep muscles (except for the medial [ulnar] half of the flexor digitorum profundus; ring and little fingers) via its branch, the anterior interosseous nerve.

It leaves the cubital fossa by passing between the two heads of the pronator teres muscle and passing between the humero-ulnar and radial heads of the flexor digitorum superficialis muscle. It leaves the forearm and enters the palm of the hand by passing through the carpal tunnel deep to the flexor retinaculum.

The median nerve has no branches in the arm other than small twigs to the brachial artery. Its major branch in the forearm is the anterior interosseous nerve.

1) Articular branches: These branches pass to the elbow joint as the median nerve passes it.

2) Muscular branches: The nerve to the pronator teres usually arises at the elbow. A broad bundle of nerves pierces the superficial flexor group of muscles and innervates the flexor carpi radialis, palmaris longus, and flexor digitorum superficialis.

3) Anterior interosseous nerve: The largest branch of the median nerve in the forearm is the anterior interosseous nerve innervates the muscles in the deep layer (flexor pollicis longus, the lateral half of flexor digitorum profundus, and pronator quadratus).

4) Palmar cutaneous branch of the median nerve: A small palmar branch passes superficially into the hand and innervates the skin over the base and central palm. This palmar branch is spared in carpal tunnel syndrome because it passes into the hand superficial to the flexor retinaculum of the wrist.

Ulnar nerve

Like the median nerve, the ulnar nerve does not give rise to branches during its passage through the arm. In the forearm it supplies only one and a half muscles, the flexor carpi ulnaris muscle (as it enters the forearm by passing between its two heads of proximal attachment) and the ulnar (medial) part (ring and little fingers) of the flexor digitorum profundus muscle.

The ulnar nerve enters the anterior compartment of the forearm by passing posteriorly around the medial epicondyle of the humerus and between the humeral and ulnar heads of the flexor carpi ulnaris muscle.

In the forearm the ulnar nerve gives rise to:

1) Muscular branches to the flexor carpi ulnaris and to the medial half of the flexor digitorum profundus.

2) Two small cutaneous branches; palmar branch passes into the hand to supply skin on the medial side of the palm; larger dorsal branch innervates skin on the posteromedial side of the back of the hand and most skin on the posterior surfaces of the medial one and one-half digits.

Figure 10. Median nerve



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RadIal nerve

Unlike the medial and ulnar nerves, the radial nerve serves motor and sensory functions in both the arm and the forearm (but only sensory functions in the hand). However, its sensory and motor fibers are distributed in the forearm by two separate branches, the superficial (sensory or cutaneous) and deep radial/posterior interosseous nerve (motor). The radial nerve bifurcates into deep and superficial branches anterior to the lateral epicondyle of the humerus, between the brachialis and the brachioradialis, in the lateral border of the cubital fossa.

The deep branch is predominantly motor and passes between the two heads of the supinator muscle to access and supply muscles in the posterior compartment of the forearm.

The superficial branch of the radial nerve is sensory. It passes down the anterolateral aspect of the forearm deep to the brachioradialis muscle. The nerve continues into the hand where it innervates skin on the posterolateral surface.

Figure 11. Ulnar nerve & Radial nerve



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volar= anterior

Lateral and medıal cutaneous nerves of forearm

The lateral cutaneous nerve of the forearm (lateral antebrachial cutaneous nerve) is the continuation of the musculocutaneous nerve after its motor branches have all been given off to the muscles of the anterior compartment of the arm.

The medial cutaneous nerve of the forearm (medial antebrachial cutaneous nerve) is an independent branch of the medial cord of the brachial plexus. With the posterior cutaneous nerve of the forearm from the radial nerve, each supplying the area of skin indicated by its name, these three nerves provide all the cutaneous innervation of the forearm. There is no “anterior cutaneous nerve of the forearm.” (Memory device: This is similar to the brachial plexus, which has lateral, medial, and posterior cords but no anterior cord.)

Figures 12 & 13. Lateral cutaneous nerve of forearm





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Although the arteries, veins, and nerves of the forearm have been considered separately, it is important to place them into their anatomical context. Except for the superficial veins, which often course independently in the subcutaneous tissue, these neurovascular structures usually exist as components of neurovascular bundles. These bundles are composed of arteries, veins (in the limbs, usually in the form of accompanying veins), and nerves as well as lymphatic vessels, which are usually surrounded by a neurovascular sheath of varying density.

Radial Nerve Injuries

The radial nerve is commonly damaged in the axilla and in the spiral groove.

Injuries to the Median Nerve at the Elbow

Motor

The pronator muscles of the forearm and the long flexor muscles of the wrist and fingers, with the exception of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus, will be paralyzed. As a result, the forearm is kept in the supine position; wrist flexion is weak and is accompanied by adduction. The latter deviation is caused by the paralysis of the flexor carpi radialis and the strength of the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. No flexion is possible at the interphalangeal joints of the index and middle fingers, although weak flexion of the metacarpophalangeal joints of these fingers is attemptedby the interossei. When the patient tries to make fist, the index and to a lesser extent the middle fingers tend to remain straight, whereas the ring and little fingers flex . The latter two fingers are, however, weakened by the loss of the flexor digitorum superficialis. Flexion of the terminal phalanx of the thumb is lost because of paralysis of the flexor pollicis longus. The muscles of the thenar eminence are paralyzed and wasted so that the eminence is flattened. The thumb is laterally rotated and adducted. The hand looks flattened and “ape-like.”

Sensory

Skin sensation is lost on the lateral half or less of the palm of the hand and the palmar aspect of the lateral three and a half fingers. Sensory loss also occurs on the skin of the distal part of the dorsal surfaces of the lateral three and a half fingers. The area of total anesthesia is considerably less because of the overlap of adjacent nerves.

Vasomotor Changes

The skin areas involved in sensory loss are warmer and drier than normal because of the arteriolar dilatation and absence of sweating resulting from loss of sympathetic control.

Trophic Changes

In long-standing cases, changes are found in the hand and fingers. The skin is dry and scaly, the nails crack easily, and atrophy of the pulp of the fingers is present.

Pronator Syndrome

Pronator syndrome, a nerve entrapment syndrome, is caused by compression of the median nerve near the elbow. The nerve may be compressed between the heads of the pronator teres as a result of trauma, muscular hypertrophy, or fibrous bands. Individuals with this syndrome are first seen clinically with pain and tenderness in the proximal aspect of the anterior forearm and hypesthesia of palmar aspects of the radial three and half digits and adjacent palm. Symptoms often follow activities that involve repeated pronation.

Anterior interosseous nerve syndrome

The anterior interosseous nerve ( an entirely motor branch of the median nerve) provides motor innervation to the flexor pollicis longus (FPL), flexor digitorum profundus (FDP) to the index and sometimes middle fingers, and to the pronator quadratus (PQ). Paralysis of these muscles from a complete nerve palsy will result in a pinch deformity, though weakness of pronation may be masked by the concurrent action of the pronator teres (PT). A case report @

Injuries to the Ulnar Nerve at the Elbow

Motor

The flexor carpi ulnaris and the medial half of the flexor digitorum profundus muscles are paralyzed. The paralysis of the flexor carpi ulnaris can be observed by asking the patient to make a tightly clenched fist. Normally, the synergistic action of the flexor carpi ulnaris tendon can be observed as it passes to the pisiform bone; the tightening of the tendon will be absent if the muscle is paralyzed. The profundus tendons to the ring and little fingers will be functionless, and the terminal phalanges of these fingers are therefore not capable of

being markedly flexed. Flexion of the wrist joint will result in abduction, owing to paralysis of the flexor carpi ulnaris.

The medial border of the front of the forearm will show flattening, owing to the wasting of the underlying ulnaris and profundus muscles. The small muscles of the hand will be paralyzed, except the muscles of the thenar eminence and the first two lumbricals,which are supplied by the median nerve. The patient is unable to adduct and abduct the fingers and consequently is unable to grip a piece of paper placed between the fingers. Remember that the extensor digitorum can abduct the fingers to a small extent, but only when the metacarpophalangeal joints are hyperextended.It is impossible to adduct the thumb because the adductor pollicis muscle is paralyzed. If the patient is asked to grip a piece of paper between the thumb and the

index finger, he or she does so by strongly contracting the flexor pollicis longus and flexing the terminal phalanx (Froment’s sign).

The metacarpophalangeal joints become hyperextended because of the paralysis of the lumbrical and

interosseous muscles, which normally flex these joints. Because the first and second lumbricals are not paralyzed (they are supplied by the median nerve), the hyperextension of the metacarpophalangeal joints is most prominent in the fourth and fifth fingers. The interphalangeal joints are flexed, owing again to the paralysis of the lumbrical and interosseous muscles, which normally extend these joints through the extensor expansion. The flexion deformity at the interphalangeal joints of the fourth and fifth fingers is obvious because the first and second lumbrical muscles of the index and middle fingers are not paralyzed. In longstanding

cases the hand assumes the characteristic “claw” deformity (main en griffe). Wasting of the paralyzed muscles

results in flattening of the hypothenar eminence and loss of the convex curve to the medial border of the hand.

Examination of the dorsum of the hand will show hollowing between the metacarpal bones caused by wasting of the dorsal interosseous muscles.

Sensory

Loss of skin sensation will be observed over the anterior and posterior surfaces of the medial third of the hand and the medial one and a half fingers.

Vasomotor Changes

The skin areas involved in sensory loss are warmer and drier than normal because of the arteriolar dilatation and absence of sweating resulting from loss of sympathetic control.

Communications Between Median and Ulnar Nerves

[pic] Occasionally, communications occur between the median and the ulnar nerves in the forearm. These branches are usually represented by slender nerves, but the communications are important clinically because even with a complete lesion of the median nerve, some muscles may not be paralyzed. This may lead to an erroneous conclusion that the median nerve has not been damaged.

Measuring Pulse Rate

The common place for measuring the pulse rate is where the radial artery lies on the anterior surface of the distal end of the radius, proximal to the wrist, between the tendons of the flexor carpi radialis and brachioradialis. Here the artery is covered by only fascia and skin. The artery can be compressed against the distal end of the radius, where it lies between the tendons of the flexor carpi radialis and abductor pollicis longus. When measuring the radial pulse rate, the pulp of the thumb should not be used because it has its own pulse, which could obscure the patient's pulse. If a pulse cannot be felt, try the other wrist because an aberrant radial artery on one side may make the pulse difficult to palpate. A radial pulse may also be felt by pressing lightly in the anatomical snuff box between the extensor pollicus longus and brevis muscles.

The cubital fossa is an important area of transition between the arm and the forearm. The cubital fossa is seen superficially as a depression on the anterior aspect of the elbow. Deeply, it is a space filled with a variable amount of fat anterior to the most distal part of the humerus and the elbow joint.

• Superiorly, an imaginary line connecting the medial and lateral epicondyles.

• Medially, the mass of flexor muscles of the forearm arising from the common flexor attachment on the medial epicondyle; most specifically, the pronator teres.

• Laterally, the mass of extensor muscles of the forearm arising from the lateral epicondyle and supraepicondylar ridge; most specifically, the brachioradialis.

As a summary, the pronator teres makes the medial border, whereas the brachioradialis makes the lateral one.

The floor of the cubital fossa is formed by the brachialis and supinator muscles of the arm and forearm, respectively. The roof of the cubital fossa is formed by the continuity of brachial and antebrachial (deep) fascia reinforced by the bicipital aponeurosis, subcutaneous tissue, and skin.

The contents of the cubital fossa are the:

• Terminal part of the brachial artery and the commencement of its terminal branches, the radial and ulnar arteries. The brachial artery lies between the biceps tendon and the median nerve.

• (Deep) accompanying veins of the arteries

• Biceps brachii tendon

• Median nerve

• Radial nerve

Superficially, in the subcutaneous tissue overlying the fossa are the median cubital vein, lying anterior to the brachial artery, and the medial and lateral antebrachial cutaneous nerves, related to the basilic and cephalic veins.

The supratrochlear lymph node lies in the superficial fascia over the upper part of the fossa, above the trochlea. It receives afferent lymph vessels from the third, fourth, and fifth fingers; the medial part of the hand; and the medial side of the forearm. The efferent lymph vessels pass up to the axilla and enter the lateral axillary nodes (The superficial lymph vessels from the thumb and lateral fingers and the lateral areas of the hand and forearm follow the cephalic vein to the infraclavicular group of nodes. Those from the medial fingers and the medial areas of the hand and forearm follow the basilic vein to the cubital fossa).

The brachial artery normally bifurcates into the radial and ulnar arteries in the apex of the fossa, although this bifurcation may occur much higher in the arm, even in the axilla. When taking a blood pressure reading from a patient, the clinician places the stethoscope over the brachial artery in the cubital fossa.

The median nerve lies immediately medial to the brachial artery and leaves the fossa by passing between the ulnar and humeral heads of the pronator teres muscle.

The brachial artery and the median nerve are covered and protected anteriorly in the distal part of the cubital fossa by the bicipital aponeurosis. This flat connective tissue membrane passes between the medial side of the tendon of the biceps brachii muscle and deep fascia of the forearm. The sharp medial margin of the bicipital aponeurosis can often be felt.

The radial nerve lies just under the lip of the brachioradialis muscle, which forms the lateral margin of the fossa. In the cubital fossa the radial nerve gives off the deep branch of the radial nerve and continues as the superficial radial nerve. The deep branch supplies the extensor carpi radialis brevis and the supinator in the cubital fossa and all the extensor muscles in the posterior compartment of the forearm.

The ulnar nerve does not pass through the cubital fossa. Instead, it passes posterior to the medial epicondyle.

The roof of the cubital fossa is formed by superficial fascia and skin. The most important structure within the roof is the median cubital vein, which passes diagonally across the roof and connects the cephalic vein on the lateral side of the upper limb with the basilic vein on the medial side. The bicipital aponeurosis separates the median cubital vein from the brachial artery and median nerve. Other structures within the roof are cutaneous nerves;-the medial cutaneous and lateral cutaneous nerves of the forearm.

Figure 14. Cubital fossa



[pic]

Table 1. Muscles of the anterior compartment of the forearm (superficial and intermediate layers)

|Superficial (first) layer |

|Pronator teres | | |Median nerve |Pronates and flexes forearm (at |

| | | | |elbow) |

|Ulnar head |Coronoid process |Lateral surface of radius | | |

|Humeral head |Medial epicondyle and adjacent | | | |

| |supraepicondylar ridge | | | |

|Flexor carpi radialis (FCR) |Medial epicondyle of humerus |Base of metacarpals II and III | |Flexes and abducts hand (at |

| | | | |wrist) |

|Palmaris longus |Medial epicondyle of humerus |Flexor retinaculum and palmar | |Flexes hand (at wrist) and |

| |(common flexor origin) |aponeurosis | |tenses palmar aponeurosis |

|Flexor carpi ulnaris (FCU) | | | | |

|Humeral head |Medial epicondyle of humerus |Pisiform & hamate |Ulnar nerve |Flexes and adducts the wrist |

| | |5th metacarpal | |joint |

|Ulnar head |Olecranon | | | |

| |Posterior border of ulna | | | |

|Intermediate (second) layer |

|Flexor digitorum superficialis (FDS) |

|Humeroulnar head |Medial epicondyle of humerus |Shafts of middle phalanges of |Median nerve |Flexes proximal interphalangeal |

| |Adjacent margin of coronoid |medial four digits | |joints of the index, middle, |

| |process | | |ring, and little fingers; can |

| | | | |also flex metacarpophalangeal |

| | | | |joints of the same fingers and |

| | | | |the wrist joint |

|Radial head |Superior half of anterior border| | | |

|Muscle |Proximal Attachment |Distal Attachment |Innervation |Main Action |

Table 2. Muscles of the anterior compartment of the forearm (deep layer)

|Muscle |Proximal Attachment |Distal Attachment |Innervation |Main Action |

|Flexor digitorum profundus (FDP) |

|Medial part |Proximal three quarters of |Bases of distal phalanges of 4th|Ulnar nerve |Flexes distal phalanges 4 and 5 |

| |medial and anterior surfaces of |and 5th digits | |at distal interphalangeal joints|

| |ulna and interosseous membrane | | | |

|Lateral part | |Bases of distal phalanges of 2nd|Anterior interosseous nerve, |Flexes distal phalanges 2 and 3 |

| | |and 3rd digits |from median nerve |at distal interphalangeal joints|

|Flexor pollicis longus (FPL) |Anterior surface of radius and |Base of distal phalanx of thumb | |Flexes phalanges of 1st digit |

| |adjacent interosseous membrane | | |(thumb) |

|Pronator quadratus |Distal quarter of anterior |Distal quarter of anterior | |Pronates forearm; deep fibers |

| |surface of ulna |surface of radius | |bind radius and ulna together |

[pic][pic][pic]

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A TOTAL OF 14 FIGURES IN THE TEXT

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The forearm is the part of the upper limb between the elbow wrist joints. Proximally, most major structures pass between the arm and forearm through, or in relation to, the cubital fossa, which is anterior to the elbow joint. The exception is the ulnar nerve, which passes posterior to the medial epicondyle of the humerus.

ANTERIOR ASPECT OF FOREARM

Muscles in the anterior compartment of the forearm flex the wrist and digits and pronate the hand. Muscles in the posterior compartment extend the wrist and digits and supinate the hand. Major nerves and vessels supply or pass through each compartment.

The flexors and pronators of the forearm in the anterior compartment are served mainly by the median nerve; the one and a half exceptions are innervated by the ulnar nerve. The extensors and supinators of the forearm are in the posterior compartment and are all served by the radial nerve (directly or by its deep branch).

Muscles in the anterior (flexor) compartment of the forearm occur in three layers:

• Superficial layer (pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris)

• Intermediate layer (flexor digitorum superficialis)

• Deep layer (flexor digitorum profundus, flexor pollicis longus, and pronator quadratus)

Generally, these muscles are associated with: movements of the wrist joint; flexion of the fingers including the thumb; andpronation.

The main arteries of the forearm are the ulnar and radial arteries, which usually arise opposite the neck of the radius in the inferior part of the cubital fossa as terminal branches of the brachial artery.

The superficial veins of the forearm lie in the superficial fascia. The cephalic vein arises from the lateral side of the dorsal venous arch on the back of the hand and winds around the lateral border of the forearm; it then ascends into the cubital fossa and up the front of the arm on the lateral side of the biceps. It terminates in the axillary vein in the deltopectoral triangle. The basilic vein arises from the medial side of the dorsal venous arch on the back of the hand and winds around the medial border of the forearm; it then ascends into the cubital fossa and up the front of the arm on the medial side of the biceps. Its terminates, by joining the venae comitantes of the brachial artery to form the axillary vein.

Nerves in the anterior compartment of the forearm are the median and ulnar nerves, and the superficial branch of the radial nerve.

The median nerve is the principal nerve of the anterior compartment of the forearm. It supplies muscular branches directly to the muscles of the superficial and intermediate layers of forearm flexors (except the flexor carpi ulnaris), and deep muscles (except for the medial [ulnar] half of the flexor digitorum profundus; ring and little fingers) via its branch, the anterior interosseous nerve. The median nerve has no branches in the arm other than small twigs to the brachial artery. Its major branch in the forearm is the anterior interosseous nerve.

Like the median nerve, the ulnar nerve does not give rise to branches during its passage through the arm. In the forearm it supplies only one and a half muscles, the flexor carpi ulnaris muscle (as it enters the forearm by passing between its two heads of proximal attachment) and the ulnar (medial) part (ring and little fingers) of the flexor digitorum profundus muscle.

Unlike the medial and ulnar nerves, the radial nerve serves motor and sensory functions in both the arm and the forearm (but only sensory functions in the hand). However, its sensory and motor fibers are distributed in the forearm by two separate branches, the superficial (sensory or cutaneous) and deep radial/posterior interosseous nerve (motor).

The lateral cutaneous nerve of the forearm (lateral antebrachial cutaneous nerve) is the continuation of the musculocutaneous nerve after its motor branches have all been given off to the muscles of the anterior compartment of the arm.

CUBITAL FOSSA

The pronator teres makes the medial border, whereas the brachioradialis makes the lateral border of the cubital fossa.

The contents of the cubital fossa are the:

• Terminal part of the brachial artery and the commencement of its terminal branches, the radial and ulnar arteries. The brachial artery lies between the biceps tendon and the median nerve.

• (Deep) accompanying veins of the arteries

• Biceps brachii tendon

• Median nerve

• Radial nerve

1. FOREARM

2. muscles

Branches of the ulnar artery that arise in the forearm include:

1) ulnar recurrent artery with anterior and posterior branches, which contribute to an anastomotic network of vessels around the elbow joint (The anterior and posterior ulnar recurrent arteries anastomose with the inferior and superior ulnar collateral arteries, respectively, thereby participating in the periarticular arterial anastomoses of the elbow)

2) numerous muscular arteries, which supply surrounding muscles

3) common interosseous artery, which divides into anterior and posterior interosseous arteries

4) two small carpal arteries (dorsal carpal branch and [pic][?] |12345789;>?@ABðàÑÂѳ¨???v??hZO?-jh-Ö5?OJQJU[pic]^Jh[¤5?OJQJ^JhÛ`h[¤5?OJQJ^JhÛ`hn\ó5?OJQJ^JhÔ

F5?OJQJ^JhÛ`h³½5?OJQJ^JhÛ`h | Æ5?OJQJ^Jh•&\5?OJQJ^Jh305?OJQJ^JhŸf§5?CJ8OJQJ^JaJ8h"“5?CJ8OJQJ^JaJ8h305?CJ8OJQJ^JaJ8-hÛ`hŸf§5?;?Opalmar carpal branch)

Perforating the interosseous membrane in the distal forearm, the anterior interosseous artery terminates by joining the posterior interosseous artery.

CLINICAL ANATOMY

3. CUBITAL FOSSA

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