Clinical Considerations

A. Placement of ligatures

1. A surgical ligature may be placed on the subclavian artery or the axillary artery between the thyrocervical trunk and the subscapular artery, or on the brachial artery distal to the inferior ulnar collateral artery.

2. A surgical ligature may not be placed on the axillary artery just distal to the subscapular artery.

B. The radial artery and the cephalic vein are the vessels most commonly used for access during long-term hemodialysis.

C. Percutaneous arterial catheterization uses the brachial artery if the femoral artery approach is unavailable. The left brachial artery is preferred because approaching from the left side allows access to the descending aorta without crossing the right brachiocephalic trunk and left common carotid arteries, thereby reducing the risk of stroke.

IV. COMPONENTS OF THE BRACHIAL PLEXUS (Figure 18-2) include:

A. Ventral primary rami C5—Tl of the spinal nerves, which are located between the anterior and middle scalene muscles

B. Upper, middle, and lower trunks, which are formed when the rami join. They are located in the posterior triangle of the neck.

C. Three anterior and three posterior divisions, which are formed when the trunks divide into anterior and posterior divisions. They are located deep to the clavicle and are named according to their relation to the axillary artery.

D. Lateral, medial, and posterior cords, which are formed when the anterior and posterior divisions join. They are located in the axilla, deep to the pectoralis minor muscle.

E. The five major terminal branches of the brachial plexus and their spinal cord level of origin are:

1. Musculocutaneous nerve (C5, C6, C7)

F. Clinical consideration: injuries to the brachial plexus

1. Erb-Duchenne (upper trunk) injury involves ventral primary rami C5 and C6. It is caused by a sudden, violent stretch between the head and shoulder (i.e., adduction traction of the arm with hyperextension of the neck). This type of injury damages the musculocutaneous nerve, which innervates the biceps brachii and brachialis muscles; the suprascapular nerve, which innervates the infraspinatus muscle; the axillary nerve, which innervates the teres minor muscle; and the phrenic nerve, which innervates the diaphragm. Clinical signs include: a pronated and medially rotated arm ("waiter's tip" hand) as a result of weakening of the biceps brachii muscle, which is a supinator of the forearm, so that the pronator muscles dominate; weakening of the infraspinous muscle, which is a lateral rotator of the arm, so that the medial rotator muscles dominate; and ipsilateral paralysis of the diaphragm caused by involvement of the C5 component of the phrenic nerve (see Figure 18-2).

2. Klumpke (lower trunk) injury involves ventral primary rami C8 and Tl. It is caused by a sudden upward pull of the arm (i.e., abduction injury). This type of injury damages the median and ulnar nerves, both of which innervate muscles of the forearm and hand, and the sympathetic component of spinal nerve Tl. Clinical signs include: loss of function of the wrist and hand and Horner syndrome, which causes miosis (constriction of the pupil due to paralysis of the dilator pupil-lae muscle), ptosis (drooping of the eyelid due to paralysis of the superior tarsal muscle), and hemianhydrosis (loss of sweating on one side) (see Figure 18-2).

Suprascapular

Suprascapular

Radial Nerve Stretch

Musculocutaneous Axillary Radial Median Ulnar

Injury

Description of injury

Nerves damaged

Clinical sign

Erb-Duchenne (C5 and C6, upper trunk)

Klumpke (C8 and T1, lower trunk)

Violent stretch between the head and shoulder (i.e., adduction traction of the arm and hyper-extension of the neck)

Sudden upward pull of the arm

(i.e., abduction injury)

Musculocutaneous Suprascapular Axillary Phrenic

Violent stretch between the head and shoulder (i.e., adduction traction of the arm and hyper-extension of the neck)

Median Ulnar

Sympathetics of T1 spinal nerve

Pronated and medially rotated arm ("waiter's tip" hand) Ipsilateral paralysis of diaphragm

Loss of function of the wrist and hand Horner syndrome

Figure 18-2. (A) The rami, trunks, divisions (D/V), cords, and five major terminal branches of the brachial plexus, along with their anatomic positions. (B) Erb-Duchenne and Klumpke injuries tc the brachial plexus. (A adapted with permission from April EW: NMS Clinical Anatomy, 3rd ed. Baltimore, Williams & Wilkins, 1997.)

Upper Limb 137

V. NERVE LESIONS (Table 18-1)

A. Long thoracic nerve injury

1. The long thoracic nerve may be injured by a stab wound or in the course of removal of lymph nodes during a mastectomy.

2. Paralysis of the serratus anterior muscle occurs so that abduction of the arm past the horizontal position is compromised. In addition, the arm cannot be used to push with.

3. To test the function of the serratus anterior muscle clinically, the patient is asked to face a wall and push against it with both arms. If the nerve is injured, the corresponding medial border and inferior angle of the scapula become prominent (winging of the scapula).

B. Axillary nerve injury

1. The axillary nerve may be injured by a fracture of the surgical neck of the humerus or by anterior dislocation of the shoulder joint.

2. Paralysis of the deltoid muscle occurs so that abduction of the arm to the horizontal position is compromised.

3. Paralysis of the teres minor muscle also occurs so that lateral rotation of the arm is weakened.

4. Sensory loss occurs on the lateral side of the upper arm.

5. To test the function of the deltoid muscle clinically, the patient's arm is abducted to the horizontal position, and the patient is asked to maintain that position against a downward pull.

C. Radial nerve injury

1. The radial nerve may be injured as a result of a midshaft fracture of the humerus, use of a badly fitted crutch, or falling asleep with the arm draped over a chair.

2. Paralysis of the muscles in the extensor compartment of the forearm occurs so that extension of the wrist and digits is lost, and supination is compromised. Extension of the forearm is preserved, however, because innervation to the triceps muscle usually is intact.

3. Sensory loss occurs on the posterior arm, posterior forearm, and lateral aspect of the dorsum of the hand.

4. Clinically, the hand is flexed at the wrist and lies flaccid (wrist drop).

D. Median nerve injury at the elbow or axilla

1. The median nerve may be injured as a result of a supracondylar fracture of the humerus.

2. Paralysis of the muscles in the flexor compartment of the arm occurs so that flexion of the wrist is weakened, and the hand deviates to the ulnar side on flexion. In addition, flexion of the index and middle fingers at the distal (DIP) and proximal (PIP) interphalangeal joints is lost, and pronation is lost.

3. Paralysis of lumbrical muscles 1 and 2 occurs so that flexion of the index and middle fingers at the metacarpophalangeal (MP) joint is lost.

Nerve

Injury

Table 18-1. Nerve Lesions Impairments

Clinical Features

Long thoracic

Stab wound Mastectomy

Abduction of arm past horizontal is compromised

Test: Pushing against a wall causes winging of scapula

Axillary Surgical neck fracture of humerus Anterior dislocation of shoulder joint

Abduction of arm to horizontal is compromised Sensory loss on lateral upper arm

Test: Arm is abducted to horizontal position and patient asked to hold position against a pull

Radial

Median at elbow

Midshaft fracture of humerus

Badly fitted crutch Arm draped over a chair

Supracondylar fracture of humerus

Extension of wrist and digits is lost

Supination is compromised Sensory loss on posterior arm and forearm, and dorsum of hand

Flexion of wrist is weakened Hand deviates to ulnar side when flexed

Flexion of index and middle fingers at DIP, PIP, and MP joints is lost

Abduction, opposition, and flexion of thumb are lost. Sensory loss on palmar and dorsal aspects of index, middle, and half of ring finger and palmar aspect of thumb

Wrist drop

Wrist drop

Ape hand Benediction hand

Median at wrist

Slashing of wrist Carpal tunnel syndrome

Flexion of index and middle fingers at MP joint is weakened

Abduction and opposition of thumb are lost

Sensory loss same as at elbow

Test: Patient makes an "O" with thumb and index finger

Ulnar at Fracture of medial elbow epicondyle of humerus

Hand deviates to radial side when flexed Flexion of ring and little fingers at DIP and MP joints is lost Extension of ring and little fingers at DIP and PIP joints is lost

Adduction and abduction of fingers are lost Adduction of thumb is lost Movement of little finger is lost Sensory loss on pa mar and dorsal aspects of half of ring and little finger

Claw hand

Test: Patient holds a paper between middle and ring fingers

Ulnar nerve at wrist

Slashing of wrist

Flexion of ring and ittle fingers at MP joint is lost Extension of ring and little fingers at DIP and PIP joints is lost Adduction and abduction of fingers are lost Adduction of thumb is lost Movement of little finger is lost Sensory loss same as at elbow

4. Paralysis of the abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis muscles occurs so that abduction, opposition, and flexion of the thumb are lost.

5. Sensory loss occurs on the palmar and dorsal aspects of the index finger, middle finger, and half of the ring finger, and on the palmar aspect of the thumb.

6. Clinically, the thenar eminence is flattened (ape hand), and when the patient is asked to make a fist, the index and middle fingers remain straight while the ring and little fingers flex (benediction hand).

7. To test the motor integrity of the median nerve, the patient is asked to maintain an uO" with the thumb and index finger while the physician attempts to pass a probe between them. This procedure tests the function of the opponens pollicis muscle.

E. Median nerve injury at the wrist

1. The median nerve may be injured by slashing of the wrist (e.g., suicide attempt) or by carpal tunnel syndrome.

2. The muscles in the flexor compartment of the arm are not paralyzed.

3. Paralysis of lumbrical muscles 1 and 2 occurs so that flexion of the index and middle fingers at the MP joint is weakened.

4. Paralysis of the abductor pollicis brevis, opponens pollicis, and flexor pollicis brevis muscles occurs so that abduction and opposition of the thumb are lost. Flexion of the thumb is maintained because the flexor pollicis longus muscle is spared.

5. Sensory loss occurs on the palmar and dorsal aspects of the index finger, middle finger, and half of the ring finger, and on the palmar aspect of the thumb.

6. Clinically, the thenar eminence is flattened (ape hand).

F. Ulnar nerve injury at the elbow or axilla

1. The ulnar nerve may be injured as a result of a fracture of the medial epicondyle of the humerus.

2. Paralysis of the flexor carpi ulnar is muscle occurs so that the hand deviates radially when flexed.

3. Paralysis of the medial part of the flexor digitorum profundus muscle occurs so that flexion of the ring and little fingers at the DIP joint is lost.

4. Paralysis of lumbrical muscles 3 and 4 occurs so that flexion of the ring and little fingers at the MP joint is lost and extension of the ring and little fingers at the DIP and PIP joints is lost.

5. Paralysis of the palmar and dorsal interosseous muscles occurs so that abduction and adduction of the fingers are lost. Flexion of the fingers at the MP joint is lost, and extension of the fingers at the DIP and PIP joints is lost.

6. Paralysis of the adductor pollicis muscle occurs so that adduction of the thumb is lost.

7. Paralysis of the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi muscles occurs so that all movement of the little finger is lost.

8. Sensory loss occurs on the palmar and dorsal aspects of half of the ring finger and the little finger.

9. Clinically a mild clawhand is observed.

10. To test the motor integrity of the ulnar nerve, the patient holds a piece of paper between the middle finger and ring finger as the physician attempts to remove it. This tests the function of the interosseous muscles.

G. Ulnar nerve injury at the wrist

1. The ulnar nerve may be injured by slashing of the wrist (e.g., suicide attempt).

2. This type of injury does not cause paralysis of the flexor carpi ulnaris muscle or the medial part of the flexor digitorum profundus muscle.

3. Paralysis of lumbrical muscles 3 and 4 occurs so that flexion of the ring and little fingers at the MP joint is lost. Extension of the ring and little fingers at the DIP and PIP joints is lost.

4. Paralysis of the palmar and dorsal interosseous muscles occurs so that abduction and adduction of the fingers are lost. Flexion of the fingers at the MP joint is lost. Extension of the fingers at the DIP and PIP joints is lost.

5. Paralysis of the adductor pollicis muscle occurs so that adduction of the thumb is lost.

6. Paralysis of the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi muscles occurs so that movement of the little finger is lost. Extension of the fingers at DIP and PIP joints is lost

7. Sensory loss occurs on the palmar and dorsal aspects of half of the ring finger and the little finger.

8. Clinically, a severe clawhand is observed because of the unopposed action of the flexor digitorum profundus.

VI. SHOULDER REGION (Figure 18-3) A. Glenohumeral joint

1. General features. The glenohumeral joint is the articulation of the head of the humerus with the glenoid fossa of the scapula. It has two prominent bursae: the subacromial bursa, which separates the tendon of the supraspinatus muscle from the deltoid muscle, and the subscapular bursa, which separates the scapular fossa from the tendon of the subscapulars muscle. The rotator cuff, along with the tendon of the long head of the biceps brachii muscle, contributes to the stability of the glenohumeral joint by holding the head of the humerus against the glenoid surface of the scapula. The rotator cuff is formed by the tendons of the following muscles, represented by the acronym SITS:

a. Subscapular muscle, which is innervated by the subscapular is nerve b. Infraspinous muscle, which is innervated by the suprascapular nerve c. Teres minor muscle, which is innervated by the axillary nerve d. Supraspinous muscle, which is innervated by the suprascapular nerve

2. Clinical considerations a. Rotator cuff injury. Rotator cuff tendinitis most commonly involves the tendon of the supraspinous muscle and the subacromial bursa. It commonly occurs in middle-aged men and causes pain on lifting the arm above the head. Acute rotator cuff tear causes acute onset of pain and inability to lift the arm above the head after the injury. In most cases, the tendon of the supraspinous muscle is torn.

b. Anterior or inferior dislocation of the humerus is the most common type of shoulder dislocation. The head of the humerus lies anterior and inferior to the coracoid process of the scapula and may damage the axillary nerve or axillary artery. Dislocation occurs because of the shallowness of the glenoid fossa. Clinical signs include: loss of the normal round contour of the shoulder, a palpa-

Upper Limb 141

Anterior Edge Glenoid RimPics Clinical Consideration

^ Figure 18-3. (A) Anteroposterior radiograph of ^^^^^^^^^^ ^^^^^ the shoulder region. (B) Anteroposterior radi ograph of an anterior dislocation of the shoulder. Arrows indicate the edge of the head of the humerus and arrowhead indicate the edge of the glenoid fossa. A Hills-Sachs fracture is associated with an anterior dislocation of the shoulder in which the posterior lateral head of the humerus is fractured as a result of contact with the rim of the glenoid fossa. (C) Anteroposterior radiograph of a separated shoulder. Arrows indicate the coracoclavicular space (CP « ► CL) and acromioclavicular space (AC < > CL). (D) Anteroposterior radiograph of a fracture located in the middle third of the clavicle (arrow A). Note the upward displacement of the proximal fragment (A) and downward displacement of the distal fragment (I). AC = acromion; CL = clavicle; CP = coracoid process; GF= glenoid fossa; H= head of the humerus; P? = first rib; SN= surgical neck of the humerus. (A adapted with permission from Fleckenstein P, Tranum-Jensen J: Anatomy in Diagnostic Imaging. Philadelphia, WB Saunders, 1993, p 58; B adapted with permission from Rosenbaum HD, Hildner JH: Basic Clinical Diagnostic Radiology. Baltimore, University Park Press, 1984, p 46; C adapted with permission from Slaby F, Jacobs ER: Radiographic Anatomy. Media, PA, Harwal, 1990, p 204; D adapted with permission from Levy RC, Hawkins H, Barsan WG: Radiology in Emergency Medicine. St. Louis, CV Mosby, 1986, p 113.)

blc depression under the acromion, and the ability to palpate the head of the humerus in the axilla.

B. Acromioclavicular joint

1. General features. The acromioclavicular joint is the articulation of the lateral end of the clavicle with the acromion of the scapula. It is stabilized by the coracoacro-mial ligament, coracoclavicular ligament (subdivided into the conoid and trapezoid), and acromioclavicular ligament.

2. Clinical considerations a. Acromioclavicular subluxation (shoulder separation) is a common injury that is caused by a downward blow at the tip of the shoulder. There are three grades of shoulder separation:

(1) Grade I (minor sprain). No ligament tearing and no abnormal joint spaces

(2) Grade II. Tearing of the acromioclavicular ligament so that the acromioclavicular space is 50% wider than in the uninjured (contralateral) shoulder

(3) Grade III. Tearing of the coracoclavicular and acromioclavicular ligaments so that the coracoclavicular and acromioclavicular spaces are 50% wider than in the normal contralateral shoulder. Clinical signs include: injured arm that hangs noticeably lower than the normal (contralateral) arm and a noticeable bulge at the tip of the shoulder as a result of upward displacement of the clavicle. Depressing and then releasing the lateral end of the clavicle causes a rebound ("piano key sign"). A radiograph taken with the patient holding a 10-pound weight on the injured side shows marked separation of the acromion from the clavicle in grade II and III separations.

b. Fracture of the clavicle occurs most commonly at the middle third of the clavicle. This type of fracture causes upward displacement of the proximal fragment as a result of the pull of the sternocleidomastoid muscle and downward displacement of the distal fragment as a result of gravity and the pull of the deltoid muscle. The subclavian artery and vein and the divisions of the brachial plexus that are located deep to the clavicle may be at increased risk for injury.

VII. ELBOW REGION (Figure 18-4)

A. The elbow consists of three articulations among the humerus, ulnar, and radial bones:

1. The humeroulnar joint, where flexion and extension of the forearm occur, is reinforced by the ulnar collateral ligament. A tear of this ligament permits abnormal abduction of the forearm.

2. The humeroradial joint, where flexion and extension of the forearm occur, is reinforced by the radial collateral ligament. A tear of this ligament permits abnormal adduction of the forearm.

3. The radioulnar joint, where pronation and supination of the forearm occur, is reinforced by the annular ligament.

B. Clinical considerations

1. Nursemaid elbow is a severe distal traction of the radius (e.g., caused by a parent yanking a child's arm). It can cause subluxation of the head of the radius from its encirclement by the annular ligament. Reduction involves applying direct pressure posteriorly on the head of the radius while simultaneously supinating and extending the forearm. This manipulation effectively "screws" the head of the radius

Pics Clinical Consideration

Figure 18-4. (A) The elbow region. Note the location of the ligaments that support the elbow joint. Anteroposterior (B) and lateral (C) radiographs of the right elbow joint. (D) Lateral radiograph of a supracondylar fracture (B arrows) of the humerus. Displacement of the humerus jeopardizes the contents of the cubital fossa, specifically, the median nerve and brachial artery. AN = annular ligament; C = capitulum; H = humerus; HR = head of the radius; L = lateral epicondyle; M = medial epicondyle; OP = olecranon process; R = radius; RC = radial collateral ligament; RT = radial tuberosity; T= trochlea; U= ulna; UC= ulnar collateral ligament. (A adapted with permission from April EW: Anatomy, 3rd ed. Baltimore, Williams & Wilkins, 1997, p 74; B and C adapted with permission from Slaby F, Jacobs ER: Radiographic Anatomy Media, PA, Harwal, 1990, pp 10, 12; D adapted with permission from Levy RC, Hawkins H, Barsan WG: Radiology in Emergency Medicine. St. Louis, CV Mosby, 1986, p 341.)

Figure 18-4. (A) The elbow region. Note the location of the ligaments that support the elbow joint. Anteroposterior (B) and lateral (C) radiographs of the right elbow joint. (D) Lateral radiograph of a supracondylar fracture (B arrows) of the humerus. Displacement of the humerus jeopardizes the contents of the cubital fossa, specifically, the median nerve and brachial artery. AN = annular ligament; C = capitulum; H = humerus; HR = head of the radius; L = lateral epicondyle; M = medial epicondyle; OP = olecranon process; R = radius; RC = radial collateral ligament; RT = radial tuberosity; T= trochlea; U= ulna; UC= ulnar collateral ligament. (A adapted with permission from April EW: Anatomy, 3rd ed. Baltimore, Williams & Wilkins, 1997, p 74; B and C adapted with permission from Slaby F, Jacobs ER: Radiographic Anatomy Media, PA, Harwal, 1990, pp 10, 12; D adapted with permission from Levy RC, Hawkins H, Barsan WG: Radiology in Emergency Medicine. St. Louis, CV Mosby, 1986, p 341.)

into the annular ligament. Clinical signs include: a flexed, pronated forearm held close to the body.

2. Lateral epicondylitis (tennis elbow) is inflammation of the common extensor tendon of the wrist where it originates on the lateral epicondyle of the humerus.

3. Medial epicondylitis (golfer elbow) is inflammation of the common flexor tendon of the wrist where it originates on the medial epicondyle of the humerus.

4. Supracondylar fracture of the humerus jeopardizes the contents of the cubital fossa, specifically the median nerve (see Table 18-1) and brachial artery. The cubital fossa contains the median nerve, brachial artery, biceps brachii tendon, median cubital vein (superficial to the bicipital aponeurosis), and radial nerve (deep to the brachioradialis muscle).

VIII. WRIST AND HAND REGION (Figure 18-5)

A. The wrist (radiocarpal) joint is the articulation of the concave distal end of the radius with the scaphoid and lunate carpal bones. Flexion/extension and abduction/ adduction of the hand occur at the wrist. The ulnar bone plays a minor role at this joint.

B. The metacarpophalangeal (MP) joint is located between the metacarpals and the proximal phalanx. Flexion at this joint is accomplished by the flexor digitorum superfi-cialis, flexor digitorum profundus, and lumbrical muscles. Adduction at this joint is accomplished by the palmar interosseous muscles (hence, the acronym PAD), and abduction is accomplished by the dorsal interosseous muscles (DAB).

C. The proximal inter phalangeal (PIP) joint is located between the proximal and middle phalanges. Flexion at this joint is accomplished primarily by the flexor digitorum superficialis muscle.

D. The distal interphalangeal (DIP) joint is located between the middle and distal phalanges. Flexion at this joint is accomplished primarily by the flexor digitorum profundus muscle.

E. Clinical considerations

1. Carpal tunnel syndrome is tendosynovitis caused by repetitive hand movements (e.g., data entry) that compress the median nerve within the carpal tunnel. The flexor retinaculum (composed of the volar carpal ligament and transverse carpal ligament) is attached to the palmar surface of the carpal bones and forms the carpal tunnel. The following structures pass through the carpal tunnel: the flexor digitorum superficialis tendons, flexor digitorum profundus tendons, flexor pollicis longus tendon, and the median nerve. No arteries pass through this tunnel. Clinical signs include: sensory loss on the palmar and dorsal aspects of the index finger, middle finger, and half of the ring finger, and on the palmar aspect of the thumb; flattening of the thenar eminence (ape hand); a tingling sensation produced by tapping the palmaris longus tendon (Tinel test); and the ability to elicit symptoms by forced flexion of the wrist and to alleviate them by extension of the wrist (Phalen test).

2. Slashing of the wrist ("suicide cuts"). A deep laceration on the radial side of the wrist may cut the radial artery, median nerve, flexor carpi radialis tendon,

Second Middle Phalanx Fracture Pip Joint

Figure 18-5. (>4) Posteroanterior radiograph of the hand and wrist. C = capitate; DIP = distal inter-phalangeal joint; DP = distal phalanx; H = hamate; L = lunate; MP = middle phalanx; MPJ = metacarpophalangeal joint; P = pisiform; PIP= proximal interphalangeal joint; PP = proximal phalanx; R = radius; RCJ= radiocarpal joint; S= scaphoid; T= trapezoid; TO = triquetrum; TZ = trapezium; U = ulna; / = first metacarpal; 11 = second metacarpal; 111 = third metacarpal; IV = fourth metacarpal; V = fifth metacarpal. (B) Radiograph of a scaphoid fracture (arrows). The proximal part of the scaphoid is susceptible to osteonecrosis. (C) Lateral radiograph of a Colles fracture (arrow A). The distal fragment of the radius (DR) is displaced posteriorly (arrow) in the "dinner fork" deformity. (D) Radiograph of the hand shows a boxer fracture (arrows) at the head of the fifth metacarpal (V).The location of a "gamekeeper thumb," in which the ulnar collateral ligament of the metacarpophalangeal joint of the thumb becomes disrupted (dotted line), is shown. (A adapted with permission from Slaby F, Jacobs ER: Radiographic Anatomy. Media, PA, Harwal, 1990, p 22; B reprinted and D adapted with permission from Rosenbaum HD, Hildner JH: Basic Clinical Diagnostic Radiology Baltimore, University Park Press, 1984, p 41; C adapted with permission from Levy RC, Hawkins H, Barsan WG: Radiology in Emergency Medicine. St. Louis, CV Mosby. 1986, p 353.)

and palmaris longus tendon. A deep laceration on the ulnar side of the wrist may cut the ulnar artery, ulnar nerve, and flexor carpi ulnaris tendon.

3. Fracture of the scaphoid (see Figure 18-5B). The scaphoid is the most commonly fractured carpal bone. It articulates with the distal end of the radius at the radiocarpal joint. Fracture of the scaphoid is associated with osteonecrosis of the scaphoid bone (proximal fragment) because the blood supply flows from distal to proximal. Clinical signs include: tenderness in the "anatomic snuffbox" (formed by the extensor pollicis longus, extensor pollicis brevis, and abductor pollicis longus tendons), because the scaphoid lies in the floor of the snuffbox. A radiograph may appear normal for several weeks until bone resorption occurs.

4. Colles fracture is posterior displacement of the distal portion of the radius ("dinner fork" deformity) [see Figure 18-5CJ. Typically, it occurs when a person falls on an outstretched hand with the wrist extended, and it often is accompanied by a fracture of the ulnar styloid process.

5. Boxer fracture is a fracture at the head of the fifth metacarpal (little finger) (see Figure 18-5D|. It occurs when a closed fist is used to hit a hard or inflexible object. Clinical signs include: pain on the ulnar side of the hand, depression of the head of the fifth metacarpal, and pain elicited by attempts to flex the little finger.

6. Gamekeeper thumb is a disruption of the ulnar collateral ligament of the MP joint of the thumb. It commonly occurs when a skier's thumb becomes entangled with the ski pole during a fall. It often is associated with an avulsion fracture at the base of the proximal phalanx of the thumb (see Figure 18-5D).

7. Volkmann ischemic contracture causes contraction of the muscles of the forearm. It is often associated with a supracondylar fracture of the humerus in which the brachial artery goes into spasm, reducing blood flow. It also may be caused by a cast that is too tight or by compartment syndrome (see Chapter 19 I F 4), in which muscles are subjected to increased pressure because of edema or hemorrhage.

8. Dupuytren contracture is thickening and contracture of the palmar aponeurosis that causes progressive flexion of the fingers. It usually is more pronounced in the ring and little fingers. It is highly correlated with coronary artery disease, possibly because of vasospasm caused by sympathetic innervation of the vasculature within the T1 component of the ulnar nerve.

IX. CROSS-SECTIONAL ANATOMY OF THE RIGHT ARM AND FOREARM (Figure 18-6)

Compartment Syndrome Forearm

Figure 18-6. (/A) Cross-section through the right brachium (arm). The horizontal line divides the flexor (anterior) compartment from the extensor (posterior) compartment. The radial nerve (RN) travels with the deep brachial artery (DB) within the extensor compartment. The median nerve (MN) travels with the brachial artery (BA). The ulnar nerve (UN) is seen near the basilic vein (BV). B= biceps brachii; BR= brachioradialis; CV= cephalic vein; H= humerus; LAH= lateral head of the triceps; LH = long head of the triceps; MCN = musculocutaneous nerve; MH = medial head of the triceps. (B) Cross-section through the right antebrachium (forearm). The horizontal line divides the flexor (anterior) compartment from the extensor (posterior) compartment. Note the location of the ulnar artery (UA), ulnar nerve (UN), median nerve (MN), radial artery (RA), and superficial branch of the radial nerve (SRN) within the flexor compartment. APL = abductor pol-licis longus; BR = brachioradialis; ECB = extensor carpi radialis brevis; ECL = extensor carpi radi-alis longus; ECU - extensor carpi ulnaris; ED - extensor digitorum; EDM = extensor digiti minimi; EPL = extensor pollicis longus; FCR = flexor carpi radialis; ECU = flexor carpi ulnaris; FDP = flexor digitorum profundus; FDS = flexor digitorum superficial; FPL = flexor pollicis longus; PL = palmaris longus; R= radius; U= ulna. (Adapted with permission from Barrett CP, Poliakoff SJ, Holder LE, et al: Primer of Sectional Anatomy with MRI and CT Correlation, 2nd ed. Baltimore, Williams & Wilkins, 1994.)

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