It's All in the Wrist: Carpal Tunnel Syndrome

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August/September 2003

By Ellen Rader Smith, MA, OTR, CVE, CPE

Carpal tunnel syndrome (CTS) is one of the more familiar cumulative trauma disorders (CTDs) or repetitive strain injuries. Reported cases of occupational CTS are most common in the manufacturing sector (see Figure 1), but occur throughout industry, in office environments, and among the general population.

But what is carpal tunnel syndrome, and what causes it? CTS is the result of compression or irritation of the median nerve as it passes through the carpal tunnel in the wrist. The median and ulnar nerves and flexor tendons are among the structures that pass through this narrow tunnel. CTS symptoms include pain, numbness (of the thumb and index, middle, and half the ring fingers), a loss of grip or pinch strength, and decreased coordination.

Physicians diagnose CTS based on the patient's subjective complaints (which often begin with those of nocturnal numbness), objective findings based on physical examination and diagnostic tests that can reproduce compression on the median nerve, and electrodiagnostic studies that include nerve conduction velocity tests and electromyograms. At present, the latter is considered to be the most accurate test for nerve compression. Less invasive nerve tests exist and are often used by occupational health clinicians. Epidemiologists who study musculoskeletal injury trends in the workplace, such as those at the National Institute for Occupational Safety and Health (NIOSH), have developed a surveillance case definition for establishing work-related cases of CTS among state-based programs.

What causes compression on the median nerve? Repetitive wrist movements, forceful gripping, contact pressure over the carpal tunnel, maintaining a pinch grip with a flexed wrist, and using vibratory tools, or any combination of these conditions are occupational CTS risk factors. These repeated motions and forceful exertions are very common in the performance of daily work tasks, homemaking, and even child care. Not everyone who performs these movements gets CTS. Some people, such as those who have diabetes or rheumatoid arthritis, are more likely to develop CTS in comparison to persons performing the same work tasks who do not have these medical conditions. Pregnant women may experience a transient CTS that subsides after delivery. However, a new mother who maintains a flexed wrist posture while feeding or holding her baby may be prone to CTS.

Figure 1. Number (thousands) and distribution of repeated trauma disorders in private industry by industry division, 1997 (Source: SOII, 1999).

Early recognition of symptoms is key to helping to control CTS and other overuse, stress, and strain injuries. Obtaining a proper medical diagnosis is important, as many times the various CTDs are misdiagnosed because of overlapping symptoms, poor symptom presentation, or a tendency to simply label persons with CTS when they actually have another cumulative trauma injury. Obtaining the appropriate medical treatment is critical in the case of (or suspected case of) work-related CTS, as is reviewing how the job is designed, the tools or equipment that are used, the work pace, and work methods.

While ergonomists encourage proper medical intervention and would like to know that workers have been properly diagnosed, ergonomists can still conduct their injury prevention work because the so-called risk factors for CTS are also contributors to and exacerbators of many work-related musculoskeletal disorders.

Ergonomic evaluations of the workplace can identify contributory job factors that can result in the recurrence or progression of symptoms, impaired hand usage, and those factors that can minimize the effectiveness of conservative treatment methods (or even postsurgical results). Ergonomic interventions to minimize CTS exposures include the redesign or modification of tools, equipment and workstations; job method modifications; incorporation of rest breaks at regular intervals; the introduction of appropriate stretching exercises; and job rotation so that motion and task diversity is integrated into the day. Employee, supervisor, and management education about CTS causes and aggravating factors is part of a total CTS/CTD injury-prevention program. Employees should also be made aware that working overtime is contraindicated until their symptoms subside.

While CTS can often be managed with conservative measures, early recognition and intervention for work-related CTS are of paramount importance, since without job redesign or reassignment, symptoms are likely to recur when workers resume the precipitating tasks. Failure to eliminate contributory job factors can result in recurrence or progression of symptoms, impaired hand usage, and even the need for surgical treatment. Applying sound ergonomic principles can help contain CTS rates in the workplace. Better surveillance methods will also help in identifying work-related injury trends, so that interventions can be appropriately targeted to these occupational groups.

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August/September 2003