Repetitive strain injury

Repetitive strain injury is a class of musculoskeletal disorders in which chronic discomfort, pain and functional impairment may develop as a result of numerous repeated movements. Soft tissue swelling is also sometimes a feature. Many synonyms are used for repetitive strain injury, including "overuse syndrome" and "cumulative trauma disorder."

Several specific disorders fall within this general class of injuries. All have in common the association of repetitive movements, rather than a single initiating event, and a subjective nature of presenting complaints, which may make diagnosis difficult and claims for compensation problematic. [1,2] The major emphasis of this article is repetitive strain injury of the upper extremity.

Occupational Factors

The number of reported cases of repetitive strain injury has increased dramatically in recent years. In Australia, a major epidemic of these injuries, occurring mostly in telephone operators, was documented in the 1980s. [3,4] The cause of this epidemic has never been fully explained. In Japan and the United States, as well, the number of reported cases also appears to be increasing. In a recent series of studies by the National Institute for Occupational Safety and Health, [5] the incidence of repetitive strain injury in newspaper workers was found to be as high as 40 percent.

The sharp increase in cases may be due to a greater awareness of these disorders. However, many authorities in occupational health believe that the rising incidence is the result of an increasing number of jobs that require paced or work-driven execution of a limited number of relatively fine motor movements of the hands and arms, as in keyboarding, assembling small parts, cutting fabric and packaging small items. In the past, many repetitive strain injuries were probably ignored or overlooked. Of unknown importance is the contribution of psychologic stress and tonic or persistent muscle tension during the offending motion.

Occupational factors associated with repetitive strain injury include a sustained and awkward posture, excessive manual force, high rates of repetitive movement and unusual or forceful movement of weaker body parts or parts of the body with a mechanical disadvantage in leverage. Load factors have an important role. Additional occupational hazards, such as a cold working environment and exposure to vibration, may worsen the condition. [1,2] Many of the same types of repetitive strain injuries may also occur as a result of sports participation.

Many specific injuries fall under the rubric of repetitive strain injury. The more common of these injuries are listed by anatomic region in Table 1.

Neck

TENSION NECK SYNDROME

(TENSION MYALGIA)

Tension neck syndrome is a common condition characterized by a persistently stiff, aching neck, often accompanied by a headache. Physical findings include tenderness, decreased range of motion and pain on motion of the neck. It predominantly results from static, sustained muscle contraction, accompanied by local spasm of the trapezius and other neck muscles. The possible association of nodules or trigger points is controversial, although many consider the syndrome to be a form of fibrositis. [6,7]

The syndrome is frequently reported among typists, key-punch operators, cashiers, cyclists (such as couriers), small parts assemblers, packers and other who must maintain a restricted posture with activity of the forearms whiel bracing at the shoulder. [8]

Treatment for the syndrome is conservative. Relaxation exercises, application of heat, fitness training and a soft cervical collar may help relieve symptoms. Making a conscious effort to alter posture, keeping the chin tucked in, avoiding prolonged leaning forward, and stretching exercises are measures that frequently help. [9]

CERVICAL SYNDROME

Cervical syndrome resembles the tension neck syndrome in some patients but may also be associated with pain radiating to one or both arms and numbness or paresthesias in the hands. Range of motion of the neck is usually restricted by pain. Power may be reduced in the deltoid, triceps and biceps, although this may be difficult to document. [10] the syndrome is common among persons who must repeatedly flex or hyperextend the neck an assume awkward positions for long periods, such as painters or decorators, cash register operators, data entry operators and dental surgeons. [8]

Cervical syndrome appears to occur when degenerating discs and weakened vertebral joints are aggravated by exaggerated positions. [9] Overt cervical osteoarthritis may be seen radiographically as spondylosis or osteophytes. However, patients may have all of the symptoms without evidence of bony abnormalities. Patients may also have bony changes without the syndrome, especially as they age.

Conservative treatment, including ice or heat applications and massage, may provide marked relief. The use of muscle relaxants and ultrasound may help. A cervical collar, initially soft and then progressing to hard if necessary, can provide substantial symptomatic relief but should not be used for long periods. Surgery is indicated only when a disc is herniated or another serious lesion is present. [11]

Shoulder

THORACIC OUTLET SYNDROME

A neurovascular condition, thoracic outlet syndrome occurs when the nerves

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of the brachial plexus and the brachial artery and its branches are compressed between the muscles of the neck and shoulder. The result is numbness, ischemia and pain in the distal upper extremity, especially when the shoulders are thrown back and the hand is raised. [1]

The syndrome is usually associated with occupations requiring frequent reaching above the shoulder level, prolonged carrying of relatively heavy loads (such as suitcases) at the side of the body, wearing a knapsack or other straps around the shoulder, or bracing with the shoulders while carrying a stretcher or similar load in a fixed position at waist level. Persons at risk include grinders, overhead assembly workers, automobile repair mechanics, cashiers, musicians, operating room personnel, truck drivers, stockroom and shipping workers, and letter carriers. [1,8]

A clinical diagnostic test (Adson's maneuver) for thoracic outlet syndrome is to hyperextend the shoulder, in the manner of a military attention posture, with the chin thrust forward (Figure 1). A weakened pulse and reproduction of symptoms suggest the thoracic outlet syndrome. [12]

Such symptoms may also occur in the presence of atherosclerosis of the brachial artery, in which case the test may not be accurate. A distinguishing feature of thoracic outlet syndrome may be the appearance of pain, numbness and weakness while moving the arms. Similar symptoms may also occur in persons with congenital cervical ribs (visible on radiograph) or abnormal muscle placement and insertion or with edema or hypertrophy at the anterior scalene muscle.

Initial treatment with short-wave diathermy and transcutaneous nerve stimulation may provide symptomatic relief. Merely avoiding the offending motion is often sufficient to manage the problem once it is recognized. In advanced or severe cases, major surgery may be required.

SUPRASPINATUS TENDINITIS

(ROTATOR CUFF TENDINITIS)

The tendon of the supraspinatus is the muscle involved in initial abduction of the humerus. When the arm is in an elevated position, the supraspinatus tendon pushes against the acromion. Pain occurs when the tendon is inflamed. Supraspinatus tendinitis is common among workers who must maintain a position of shoulder abduction with the elbow extended under conditions of load. Examples include welders, painters, aluminum siding and awning installers, riveters and construction workers.

Characteristic pain with elevation of the arm from 70 to 100 degrees is the principal diagnostic feature. This sign is specific because it corresponds to the angle at which the inflamed tendon abuts the acromion as the arm is raised. The effect is often called the "painful arc" or "impingement" syndrome, although the latter term is more specific. [13]

Treatment is often unsatisfactory because the condition waxes and wanes, frequently returning with reuse. Rest, heat application, anti-inflammatory medications and physiotherapy are beneficial. Range-of-motion exercises help prevent the development of frozen shoulder syndrome. Local steroid injections are sometimes used but have not convincingly been shown to be effective. [13-15]

BICIPITAL TENDINITIS

Bicipital tendinitis often occurs concurrently with supraspinatus tendinitis, but it may also occur alone. This condition, which is similar to supraspinatus tendinitis, is associated with pain on movement of the glenohumeral joint and pain over the bicipital tendon as it passes over the bicipital groove and under the acromion. Tendinitis results when the muscle-tendon connection is repeatedly tensed and the tendon begins to fray or tear apart.

Bicipital tendinitis is common among workers who must reach over their heads, such as assembly workers, cleaners and window washers, construction workers, and stockroom and shipping clerks. Treatment for the condition is similar to that for supraspinatus tendinitis. [7,16,17]

ADHESIVE CAPSULITIS

Adhesive capsulitis, or frozen shoulder syndrome, is a condition of contracture in the soft tissues surrounding the glenohumeral joint. It is more often a consequence of shoulder trauma and resultant soft tissue injury than a consequence of repetitive strain injury, but it may be a complication of repetitive strain injury. Thickening of the tendons and bursae result in loss of range of motion. The syndrome is typically caused by prolonged immobilization after injury and disuse of the shoulder to avoid pain. In the early stages, it presents as insidiously progressive shoulder pain and stiffness. Eventually, active and passive range of motion is lost. Forcing passive motion of the shoulder is painful.

Frozen shoulder syndrome is difficult to treat but can be prevented by physiotherapy and range-of-motion exercises during recovery from shoulder injuries. Because of the extent of injury leading to the syndrome, it is often associated with degenerative joint disorders. Management rests on short-term treatment with anti-inflammatory agents and passive range-of-motion exercises. Recovery of function is seldom complete, at least as reported in the literature. [17] However, many rehabilitation specialists believe that most cases resolve over several years, with complete return of function.

ACROMIOCLAVICULAR SYNDROME

Acromioclavicular syndrome is an arthritic or post-traumatic condition distinguished by local pain and inflammation of the acromioclavicular joint. It is the result of repeated movement with loaded stress on the joint at waist level, as might occur in grinding, packing, assembly and construction work. The diagnosis can be confirmed by percussing the clavicle as the patient pushes downward against resistance. This maneuver reproduces the pain [12] (Figure 2).

Treatment is conservative. Local injection of steroids may be helpful. Surgical resection of the distal clavicle is required in some cases.

Elbow, Wrist and Hand

EPICONDYLITIS

Epicondylitis involves the origin of tendons leading from the elbow to the hand. The two forms of epicondylitis are commonly named for their sports counterparts: "tennis elbow" (lateral epicondylitis, involving extensors) and "golfer's elbow" (medial epicondylitis, involving flexors). Both conditions arise from repeated and forceful rotation of the forearm with the wrist bent; the different locations reflect different patterns of stress at the elbow. Epicondylitis is common in persons with jobs requiring these types of arm and elbow motions. Examples include small parts assemblers, musicians, construction workers and woodworkers.

The diagnosis of lateral epicondylitis is suggested by pain over the lateral epicondyle on palpation during extension of the fingers and wrist against resistance with the elbow held straight. The diagnosis of medial epicondylitis is suggested by pain over the medial epicondyle on flexion of the fingers and wrist against resistance with the elbow flexed.

Treatment for epicondylitis is conservative and includes local steroid injection and range-of-motion exercises. Epicondylitis often takes months to resolve and frequently recurs. [18] Surgery may help when conservative methods fail.

DE QUERVAIN'S TENOSYNOVITIS

de Quervain's disorder, the most common stenosing tenosynovitis, involves the first dorsal compartment of the extensor tendons of the thumb. The disorder includes both inflammation and effusion of the tendon sheath. It is most common in workers who use hand tools that require repeated radial and ulnar hand motion.

The key diagnostic feature is tenderness over the dorsal compartment (radial styloid process). When the thumb is flexed and adducted, a "trigger" effect or popping sensation may occur as a result of nodules on the tendon surface slipping through fibrosed parts of the tendon sheath. The nodules may be palpable. [19] A clinical maneuver for diagnosis is Finkelstein's test, in which the patient clenches the fist over the flexed thumb while the examiner pushes the base of the thumb toward the ulnar side with force; a positive sign is pain at the radial styloid process, which may radiate down the thumb or up to the elbow [7,12] (Figure 3).

Management is usually conservative, with steroid injection into the sheath if symptoms are present and surgical release if symptoms are severe. Many severe cases are believed to be the result of a congenital anomaly in which the extensor pollicis brevis tendon lies in its own compartment; in this situation, the compartment must be incised for release of compression. [20]

CARPAL TUNNEL SYNDROME

A nerve entrapment condition, carpal tunnel syndrome occurs when the median nerve is compressed along its path in the narrow channel in the wrist defined by the radius, the flexor retinaculum and the tendons of the muscles for flexion of the hand. The result is paresthesias and numbness in the distribution of the nerve, including the volar aspects of the first four digits, the thenar area and the distal dorsal aspects of the second, third and partially the fourth digits. If the condition progresses untreated, atrophy of the thenar muscles may also occur, and fine motor movements may become difficult to execute. The pain and tingling characteristically disturb sleep.

Carpal tunnel syndrome is usually associated with repeated forced hand movements, as performed by cashiers, assembly workers, grinders, typists, key-punch operators, seamstresses and cutter, musicians, packers and bricklayers. [21]

Diagnosis is usually not difficult. Carpal tunnel syndrome is one of the few repetitive strain injuries to have become widely recognized. Tingling paresthesias with percussion over the median nerve at the wrist (Tinel's sign) is strongly suggestive of the diagnosis. Nerve conduction studies showing slowed nerve impulses confirm the diagnosis, [22] although this finding occurs relatively late in the course of entrapment. A relatively specific clinical test is Phalen's maneuver, in which the wrists are passively flexed by pressing the flexed hands together dorsum-to-dorsum for one minute or more in an effort to elicit the pain and paresthesias [12,23] (Figure 4).

Conservative treatment, including a splint, often fails to provide relief. Surgery to release the entrapped nerve is usually effective. [7]

ULNAR NERVE ENTRAPMENT

The ulnar nerve passes behind the medial epicondyle and the elbow. In this position, it is vulnerable to repeated minor trauma. In time, the injured nerve may become entrapped by local swelling and tissue hypertrophy and become even more susceptible to minor trauma. Signs are similar to those of carpal tunnel syndrome, although the paresthesias are felt over the ulnar side of the hand and over the fifth digit.

The diagnosis of ulnar nerve entrapment is established in a similar manner as diagnosis of carpal tunnel syndrome, with the exception that Tinel's sign is demonstrated over the epicondyle. The treatment is also similar.[24]

Evaluation and Treatment

Repetitive strain injury must be distinguished from nonoccupational rheumatologic conditions, temporary pain from sprains or muscle strain, joint or tendon infections, psychologic disorders (including compensation neurosis), abnormalities of bony structure and single-event injuries. In the United Kingdom, the Industrial Survey Unit of the Arthritis and Rheumatism Council [25] concluded that the diagnosis of repetitive strain injury is suggested by persistent or recurrent musculoskeletal pain without immediate traumatic cause within the previous six weeks.

Repetitive strain injury is often considered to develop through three stages [26]:

1. Stage 1 is a condition of fatigue characterized by increased aching and tiredness during the work shift. The symptoms usually subside with overnight rest. Stage 1, when it is recognized, should be construed as a warning to protect the affected body part.

2. Stage 2 is persistence of the discomfort into the next day, with earlier onset of fatigue during the workday. Stage 2 is a sign that the injury is developing and that steps should be taken immediately to reduce the strain on the affected part, to rest the affected part more frequently or to redesign the work process to avoid the offending motion.

3. Stage 3 is chronic aching, fatigue and weakness that persist despite rest of the affected part.

These three stages are, of course, generalizations, with each disorder having its own natural history. However, some observations can be made. Because the symptoms of repetitive strain injury are mostly subjective and gradual in onset, obtaining a satisfactory history for these conditions can be difficult. A helpful diagnostic maneuver is to have the patient reenact work activities to see what parts of the body are subjected to repetitive strain. Initial treatment is usually conservative, involving rest, initial cooling with ice followed later by local heat, and anti-inflammatory medications, as appropriate to the condition. Surgery is indicated in some cases that do not respond to treatment.

Patients with a repetitive strain injury typically require weeks or months to recover. These conditions often worsen or improve without obvious reason. Many patients have prolonged and difficult recoveries. Some cannot return to their previous occupations. In all cases, patients must be careful not to reinjure themselves or to overuse the affected body part after they return to work. A "work-hardening" program conducted by a qualified physiotherapist may facilitate return to work with less risk. Attention should also be given to adequate pain control, emotional support and stress management during convalescence, since these injuries are frustrating and may be financially threatening. [1]

Prevention is more effective than treatment in controlling the problem. Changing the nature of the operation, the tools or the layout of the workplace can modify or eliminate the offending action. These measures are relatively simple but may require the services of a consulting ergonomist. A useful resource for identifying simple solutions to these problems is the Job Accommodation Network (800-526-7234), a federally sponsored program to facilitate cost-effective workplace modifications.

REFERENCES

[1] Putz-Anderson V, ed. Cumulative trauma disorders: a manual for musculoskeletal diseases of the upper limbs. New York: Taylor & Francis, 1988.

[2] Chatterjee DS. Repetition strain injury--a recent review. J Soc Occup Med 1987; 37:100-5.

[3] Miller MH, Topliss DJ. Chronic upper limb pain syndrome (repetitive strain injury) in the Australian workforce: a systematic cross sectional rheumatological study of 229 patients. J Rheumatol 1988; 15:1705-12.

[4] Hocking B. Epidemiological aspects of "repetition strain injury" in Telecom Australia. Med J Aust 1987;147:218-22.

[5] U.S. National Institute for Occupational Safety and Health. Health hazard evaluation report: Newsday, Inc. NIOSH HETA A9-250, 1990.

[6] Maeda K. Regional myofascial pain syndromes. Rheum Dis Clin North Am 1989; 15:31-60.

[7] Malamet RL, Kelly GB. Nonarticular rheumatism: bursitis, tenosynovitis, trigger finger, Dupuytren's contracture, Raynaud's phenomenon, and fibrositis. In: Barker LR, Burton JR, Zieve PD, eds. Principles of ambulatory medicine. 2d 3e. Baltimore: Williams & Wilkins, 1986:864-74.

[8] Hagberg M, Wegman DH. Prevalence rates and odds ratios of shoulder-neck diseases in different occupational groups. Br J Ind Med 1987; 44:602-10.

[9] Hagberg M. Occupational musculoskeletal stress and disorders of the neck and shoulder: a review of possible pathophysiology. Int Arch Occup Environ Health 1984; 53:269-78.

[10] Anderson JA. Shoulder pain and tension neck and their relation to work. Scand J Work Environ Health 1984; 10(6 spec. no.): 435-42.

[11] Heberts P, Kadefors R, Petersen I. Shoulder pain in industry: an epidomiological study. Orthop Scan 1981; 52:299-306.

[12] Hoppenfeld S, Hutton R. Physical examination of the spine and extremities. New York: Appleton-Century-Crofts, 1976:7,23-4,76-7, 83,127.

[13] Tola S, Riihimaki H, Videman T, Viikari-Juntura E, Hanninen K. Neck and shoulder symptoms among men in machine operating, dynamic physical work and sedentary work. Scand J Work Environ Health 1988; 14:299-305.

[14] Engel H. Occupationally related musculoskeletal disorders of the upper limb in industry. J R Soc Med 1988; 81:52-3.

[15] Archibald RM, Remp HB, Marks LJ, Wynn Parry CB. Orthopaedics. In: Edwards FC, McCallum RI, Taylor PJ, eds. Fitness for work: the medical aspects. New York: Oxford University Press, 1988: 126-41.

[16] Curwin S, Stanish WD. Tendinitis, its etiology and treatment. Lexington, Mass.: Collamore Press, 1984:36.

[17] Hansen NM, Burton JR. Shoulder pain. In: Barker LR, Burton JR, Zieve PD, eds. Principles of ambulatory medicine. 2d ed. Baltimore: Williams & Wilkins, 1986; 835-40.

[18] Thorson EP, Szabo RM. Tendonitis of the wrist and elbow. State Art Rev Occup Med 1989; 4:419-31.

[19] Witczak JW, Masear VR, Meyer RD. Triggering of the thumb with de Quervain's stenosing tendovaginitis. J Hand Surg [St. Louis] 1990; 15:265-8.

[20] Harvey FJ, Harvey PM, Horsley MW. De Quervain's disease: surgical or nonsurgical treatment. J Hand Surg [St. Louis] 1990;15: 83-7.

[21] Wieslander G, Norback D, Gothe CJ, Juhlin L. Carpal tunnel syndrome (CTS) and exposure to vibration, repetitive wrist movements, and heavy manual work: a case-referent study. Br J Ind Med 1989;46:43-7.

[22] Bleecker ML, Agnew J. New techniques for the diagnosis of carpal tunnel syndrome. Scand J Work Environ Health 1987;13:385-8.

[23] Phalen GS. The carpal-tunnel syndrome. Clinical evaluation of 598 hands. Clin Orthop 1972;83:29-40.

[24] Josifek LF, Bleecker ML. Peripheral neuropathy. In: Barker LR, Burton JR, Zieve PD, eds. Principles of ambulatory medicine. 2d ed. Baltimore: Williams & Wilkins, 1986.

[25] Anderson JA. Rheumatism in industry: a review. Br J Ind Med 1971;28:103-21.

[26] Browne CD, Nolan BM, Faithfull DK. Occupational repetition strain injuries. Guidelines for diagnosis and management. Med J Aust 1984;140:329-32.

TEE L. GUIDOTTI, M.D., M.P.H. is professor of occupational medicine at the University of Alberta Faculty of Medicine, Edmonton, Canada. Dr. Guidotti is a graduate of the University of California-San Diego School of Medicine and the Johns Hopkins University School of Hygiene and Public Health, Baltimore. His postgraduate training included a residency in internal medicine and fellowships in pulmonary medicine and occupational medicine, all at the Johns Hopkins Hospital. Dr. Guidotti is a member of AFP's Editorial Advisory Board.

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