The Forearm, Wrist, And Hand

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Chapter 7 The Forearm, Wrist, and Hand

The importance of the wrist and hand is evidenced by the fact that the rest of the upper extremity functions primarily to place the hand in a position where it can operate most effectively. Treatment of the wide variety of disorders that occur in the hand requires an understanding of its complicated anatomy and functional physiology.

Anatomy

MUSCLES OF THE HAND

Motions of the wrist and fingers are controlled by groups of muscles that are classified as either intrinsic or extrinsic. Intrinsic muscles arise within the hand and are responsible for the delicate movements of the fingers. Thenar refers to intrinsic muscles of the thumb. Hypothenar refers to those on the ulnar side of the hand. Extrinsic muscles are those that take origin within the forearm.

EXTRINSIC MUSCLES

Motion at the wrist is accomplished by the various wrist flexors and extensors. In addition to providing wrist motion, these muscles stabilize the wrist in slight dorsiflexion, a position that allows maximum function of the extrinsic finger flexors.

Nine finger flexors and the median nerve pass into the hand through the carpal tunnel beneath the transverse carpal ligament (Fig. 7-3). Five deep flexors pass to the distal phalanx of each finger and thumb, and four superficial flexors pass to the middle phalanx of each finger. Each of these finger flexors can be tested individually (Fig. 7-4).

The finger flexors pass beneath a series of ligaments between the distal palmar crease and the distal interphalangeal joint. These annular ligaments, or “pulleys,” prevent the tendon from bowstringing. Tendon repair in this area called “no-man’s land” is often unrewarding because of adhesions that form between the lacerated tendon ends and these ligaments.

The extensor tendons pass dorsally over each finger and thumb and insert into the phalanges. They extend the proximal phalanges and assist the intrinsic muscles in interphalangeal joint extension. The thumb extensors are easily palpated at the anatomic “snuffbox.”

Carpal Tunnel Syndrome

Carpal tunnel syndrome, or compression of the median nerve at the wrist, is the most common entrapment neuropathy in the upper extremity. Compression of the nerve beneath the transverse carpal ligament probably develops as a result of an increase in the volume of the contents in the carpal tunnel. The cause is unknown in most cases. Tenosynovitis of the flexor tendons may be present in some cases, but whether the disorder should be considered an “overuse” condition is controversial. The disorder may be seen in association with hypothyroidism, rheumatoid and gouty arthritis, and aberrant or anomalous muscles in the wrist. A deficiency in vitamin B6 has even been postulated as a cause. Carpal tunnel syndrome is sometimes seen following fractures of the wrist and is not uncommon in the third trimester of pregnancy. (NOTE: When it does occur late in pregnancy, the symptoms of carpal tunney tend to subside after delivery, often quite dramatically within a few days. Thus, treatment is strictly symptomatic, and surgery is generally not recommended in these cases. The disorder often recurs in subsequent pregnancies.) The syndrome is bilateral in up to 50% of cases. Whether occupational and job-related activities are risk factors remains undetermined.

Sometimes, a combination of neck and hand pain can develop, especially in patients who suffer from degenerative cervical disc disease. This is termed the “double-crush syndrome” lesion and results from nerve compression at two separate levels, the neck and the wrist. This suggests that proximal compression may decrease the ability of the nerve to tolerate a second, more distal compression.

CLINICAL FEATURES

The onset is usually spontaneous, with gradually increasing pain and tingling in the hand. Nocturnal pain is common and is frequently the reason the patient seeks medical attention. This may be caused by a slight increase in swelling at the wrist with inactivity or perhaps as a result of wrist flexion at night. Pain may radiate proximally into the forearm and even as high as the shoulder. Numbness and tingling occur along the median nerve distribution, but the sensory impairment rarely involves all 3½ fingers supplied by the median nerve. Often, only the long and index fingers are involved. A sense of weakness and clumsiness in the use of the hand is common. All of these symptoms may be precipitated by various manual activities such as typing or painting. They frequently subside after shaking and moving the hand or allowing it to hang downward. The patient often describes “poor circulation” and “stiffness,” but the hand is usually warm, and the motion is full. These latter symptoms are probably caused by the numbness. Physical examination may reveal some sensory disturbance along the median nerve. Tinel’s sign and Phalen’s maneuver are often positive (Fig. 7-8). Atrophy of the thenar muscles is seen in cases of long-standing duration.

Roentgenograms of the wrist are helpful in ruling out local bony abnormality. Nerve conduction studies may be of benefit but are frequently unnecessary in classic cases. Delayed electrical conduction across the wrist is usually present. Electromyography is generally not required. Some error may exist in electrodiagnostic testing, and it should not be the sole guide to diagnosis and treatment.

Ganglion

Ganglions are soft tissue lesions that are commonly found in the extremities. They are always found adjacent to a joint or tendon sheath. The cause is unknown, but myxoid degeneration of connective tissue and repetitive trauma with chronic irritation are possible causes. The cyst contains a very thick mucinous material and usually has a stalk that can be traced to a tendon sheath or joint.

The ganglion cyst is the most common soft tissue mass in the hand. The usual location is the dorsum of the wrist at the scapholunate ligament, but volar cysts radial to the palmaris longus are not rare. A similar cyst can develop from the flexor tendon sheath near the base of the finger at the metacarpophalangeal (mcp) joint flexion crease. Ganglions are occasionally seen in children but frequently subside spontaneously in this age group in 2 to 3 years.

Degenerative Arthritis

Although osteoarthritis of the wrist and hand is much less common than in the lower extremities, it is sometimes more disabling. In the hand, it is 10 times more common in the females than males, and the most common area of involvement is the trapeziometacarpal or “base joint” of the thumb (Fig. 7-12). Involvement at the base joint of the thumb is particularly bothersome because of the tremendous mobility required by this joint in daily use. Sometimes deformity of this joint even develops the appearance of a “mass” because of osteophyte formation, swelling, and subluxation. The arthritis is considered “primary” in most cases but can also develop secondary to fractures and other joint injuries. When the distal interphalangeal (DIP) joints become involved with arthritis, persistent nodular swellings called Heberden’s nodes may develop. Similar lesions at the proximal interphalangeal (PIP) joints are termed Bouchard’s nodes. Occasionally, mucous cysts also develop at these interphalangeal (IP) joints.

Dupuytren’s Contracture

Dupuytren’s contracture is a disease of the palmar fascia in which progressive contractures of the fascia occur and sometimes lead to a flexion deformity of the distal portion of the palm and fingers. The cause is unknown, but it is often hereditary and bilateral. Predisposing disorders are diabetes, alcoholism, epilepsy, and liver disease. It is seen more often in Scandinavians, and some northern Europeans have a 25% prevalence in patients over the age of 60. Lesions develop more often and earlier in certain families. It is 10 times more common in males, and 5% of patients develop a similar condition elsewhere, such as Peyronie’s disease or Ledderhose disease (involvement of the plantar fascia). Soft tissue “pads “in the knuckles may also be present. Individuals with these additional findings are considered to have Dupuytren’s diathesis, and their disease is generally more severe and recurrent.

Pathologically, the contracture consists of proliferating vascular fibrous tissue that later develops into mature collagen.

Stenosing Tenosynovitis

This common condition of unknown origin may develop from overuse or direct trauma. The resultant inflammation and irritation hinder the normal gliding motion of the tendon. Most cases are primary (idiopathic), although the condition can develop in patients with rheumatoid arthritis. Several distinct syndromes can be described, depending on the site of involvement.

DE QUERVAIN’S DISEASE

Tenosynovitis frequently occurs in the first dorsal extensor compartment of the wrist (Fig. 7-15). The extensor pollicis brevis and abductor pollicis longus occupy this compartment and are involved where they cross over the radial styloid.

TRIGGER FINGER AND THUMB

If swelling of the flexor tendon and sheath occurs, passage of the tendon through the constricted sheath may become difficult (Fig. 7-17). This may result in snapping or “triggering” of the affected finger at the MP joint as the swollen, nodular tendon passes through the constricted sheath. The symptoms are frequently worse after rest and improve with active use of the finger. The effect of the triggering itself is transmitted distally to the DIP joint. The finger may even lock completely in either flexion or extension. If the digit locks in flexion, manipulation may be required to extend the finger, a maneuver usually accompanied by a palpable snap. In mild cases, however, the triggering effect may be subtle. Examination usually reveals tenderness and a firm swelling at the proximal flexor pulley. If multiple fingers are involved, rheumatoid disease should be suspected. A congenital form is occasionally seen in the thumb of children.

The treatment is the same as that for de Quervain’s disease. Sometimes splinting only the DIP joint is needed. Surgical release is frequently necessary, but many patients, especially children, recover spontaneously.

Repetitive Motion Syndrome

This syndrome is a controversial diagnosis, in which pain develops in the forearm and hand during the course of normal activities, usually in the workplace. Among the other names used are cumulative trauma disorder and repetitive strain injury. Because of the inability to establish any clear source for the problem, the term idiopathic arm pain is commonly used. A similar chronic pain syndrome may be seen in the neck and shoulder area as well as the lower part of the back. The disorder has been the subject of much media attention and has even set labor against management in many large industries. It has also been the source of a great deal of litigation, mainly directed at workers’ compensation carriers. The condition appears to reflect a complicated mixture of physical and psychosocial factors.

Some reasons for the controversial nature of the disorder are as follows:

Clinical Features

Minimal pressure against the elbow may lead to paresthesias and numbness along the distribution of the ulnar nerve in the forearm and hand, mainly the small finger (Table 7-1). Tinel’s sign is often positive. The elbow flexion test may be abnormal. This test is performed by having the patient flex the elbow for 30 to 60 seconds with the wrist extended. This maneuver increases the volume and pressure in the cubital tunnel and may reproduce symptoms. The test is not diagnostic, however, because it may be positive in asymptomatic individuals.

Table 7-1 Differential Diagnosis of Common Causes of Forearm and Hand Pain*

Disorder Findings Present Findings Absent
Carpal tunnel syndrome Painful paresthesias along portions of median nerve (i.e., palm side of hand). Index and long often only fingers involved. May have night pain in long-standing cases. Pain may radiate as high as shoulder. Tinel’s sign may be positive at wrist. Pain not worsened by resisted motion or stretching. No symptoms on dorsum of hand. Full range of motion.
Tenosynovitis Pain and tenderness usually well localized to site of involvement. Pain may be reproduced by passive stretch or resistance against movement of affected tendon. May be local swelling. No paresthesias. Full range of motion. No night pain.
Tennis elbow (most common lateral) Pain may radiate from elbow to forearm and hand. Localized tenderness at epicondyle. Pain aggravated by resisted dorsiflexion of wrist (if lateral). Pain with gripping activities. Full range of motion, no paresthesias or night pain.
Osteoarthritis Local tenderness, sometimes with swelling of affected joint. Pain with motion. Decreased motion. No paresthesias. Tinel’s sign negative.
Cubital tunnel syndrome Painful paresthesias along ulnar nerve distribution in forearm and hand. Tinel’s sign may be positive behind medial epicondyle. Full range of motion. Pain not worsened by resisted motion. No night pain.*

* Notes: Treatment and workup: 1. NSAID, moist heat, splint, and modification of activities as indicated for 2 to 4 weeks. 2. Roentgenogram, inject (if appropriate), change NSAID for 2 to 4 weeks. 3. Nerve conduction studies, referral as indicated.

In contrast to ulnar tunnel syndrome at the wrist, symptoms are also present on the dorsum of the hand and ulnar forearm. More severe involvement leads to progressive forearm, hypothenar, and intrinsic motor weakness (weak fanning of the fingers) and atrophy, especially the first dorsal interosseous muscle (Fig 7-19). If the nerve subluxes, the subluxation is usually palpable with elbow flexion and extension. Nerve conduction studies usually reveal delayed conduction at the elbow.

TREATMENT

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