True or False? The most common cause of carpal tunnel syndrome is job-related overuse of the hands and wrists, such as when typing on computer keyboards for hours at a time.


False. The issue of whether occupation and job-related hand or wrist overuse are risk factors for developing CTS is highly controversial. Several investigators have listed occupation and heavy manual labor as causal factors for the disorder.[1-4] But the opposite view has been argued for as long.[5-8] Nathan and colleagues[9] reported that results of nerve conduction studies of large numbers of industrial employees showed no consistent association between the prevalence of CTS (detected by decreased sensory nerve conduction) and the type and level of occupational hand activity, length of employment, or bilateral versus unilateral activity. Anything that compromises the space available for the median nerve in the carpal tunnel can cause CTS. Local structural changes and masses at the wrist are known causes, including distal radius fractures, blunt trauma with associated hemorrhage and swelling, and tumors such as lipomas and ganglion cysts. A wide variety of systemic illnesses, metabolic diseases, overuse syndromes, and aberrant anatomic structures also have been described as causes of CTS. 

Source: Slater RR.: Carpal Tunnel Syndrome: Current Concepts.J South Orthop Assoc. 1999;8(3).

 References

  1. Armstrong TJ, Chaffin DB: Carpal tunnel syndrome and selected personal attributes. J Occup Environ Med. 1979;21:481-486. 
  2. Birkbeck MQ, Beer TC: Occupation in relation to the carpal tunnel syndrome. Rheumatol Rehab. 1975;14:218-221. 
  3. Cannon LJ, Bernacki EJ, Walter SD. Personal and occupational factors associated with carpal tunnel syndrome. J Occup Med. 1981;23:255-258.
  4. Posch JL, Marcotte DR. Carpal tunnel syndrome: an analysis of 1,201 cases. Orthop Rev. 1976;5:25-35. 
  5. Hadler NM: Illness in the workplace: the challenge of musculoskeletal symptoms. J Hand Surg Am 10:451-456, 1985 
  6. Phalen GS. Neuropathy of the median nerve due to compression beneath the transverse carpal ligament. J Bone Joint Surg Am. 1950;32:109-112. 
  7. Phalen GS. The carpal tunnel syndrome. Seventeen years' experience in diagnosis and treatment of 654 hands. J Bone Joint Surg Am. 1966;48:211-228. 
  8. Phalen GS. The carpal-tunnel syndrome. Clinical evaluation of 598 hands. Clin Orthop. 1972;83:29-40. 
  9. Hadler NM. Illness in the workplace: the challenge of musculoskeletal symptoms. J Hand Surg Am. 1985;10:451-456. 

    10. Nathan PA, Meadows KD, Doyle LS. Occupation as a risk factor for impaired sensory conduction of the median nerve at the carpal tunnel. J Hand Surg Br. 1988;13:167-170.

Now, this flies in the face of the opinions of many organizations including the US Government Occupational Safety and Health Administration. Unfortunately, even that body can not be expected to produce an unbiased opinion. The government represents the interests of those influencing the government - good or bad, right or wrong, and truth has no independent representation. The OSHA guidelines do not take into account any factors other than occupation (including age, sex, and activities outside the workplace), and do not at all address the possibility that activities may exacerbate symptoms of carpal tunnel syndrome without actually causing it. By the same logic, one could conclude that a job which involved walking up stairs caused lung disease, because people develop symptoms (shortness of breath) while performing that activity.

Carpal tunnel syndrome is very common in the general population, and does not always cause symptoms:

 
1: Am J Ind Med 1996 Sep;30(3):355-61

Prevalence of abnormal median nerve conduction in applicants for industrial jobs.

Bingham RC, Rosecrance JC, Cook TM

Department of Preventive Medicine, University of Iowa, Iowa City 52242-5000, USA.

There has been much debate regarding the work relatedness of carpal tunnel syndrome (CTS) and whether workers diagnosed with CTS had pre-existing disease at the time they were hired. To elucidate the latter issue, we examined the prevalence of abnormal median nerve conduction within the carpal tunnel in applicants for industrial jobs. Nerve conduction studies (NCS) were performed on both hands of 1,021 applicants following a conditional offer of employment. Each applicant completed a self-administered symptom survey specific to the upper extremity. Applicants had worked previously for an average of 4.4 (range 0-33) years and had a mean age of 30.1 (S.D. 8.9) years. Nerve conduction studies were performed in a private medical clinic. Sensory palmar latencies were determined over an 8 cm segment for the median and ulnar nerves. The difference between the median and ulnar sensory latencies was the primary electrophysiologic measurement used to determine median neuropathy. Using a very conservative criterion for abnormal median nerve conduction, 17.5% of the applicants were classified with neuropathy in at least one hand. Despite the relatively high prevalence of median neuropathy, relatively few (10%) with positive NCS acknowledged symptoms associated with CTS. Males had a higher percentage of median neuropathy than did females. We conclude that a large percentage of industrial workers have objective evidence of abnormal median nerve conduction within the carpal tunnel when hired. The high prevalence of abnormal median nerve conduction without corresponding symptoms may suggest a subclinical entity associated with CTS.

PMID: 8876806, UI: 97030865

The incidence of carpal tunnel syndrome relates to age and sex, not type of employment:

 
J Hand Surg [Br] 1988 May;13(2):167-70

Occupation as a risk factor for impaired sensory conduction of the median nerve at the carpal tunnel.

Nathan PA, Meadows KD, Doyle LS

Portland Hand Surgery and Rehabilitation Center, Oregon 97210.

471 industrial employees from 27 occupations in four industries were surveyed to evaluate the role of occupational hand activity as a risk factor for slowing of sensory conduction of the median nerve at the carpal tunnel. After age-adjusting the latency values, slowing of the sensory fibres of the median nerve was found in 39% of the subjects and in 26% of the hands. No consistent association was found between the type and the level of occupational hand activity and the prevalence or the severity of slowing. In addition, the prevalence of bilateral slowing of conduction of the median nerve was not associated with bimanual occupational hand activity, and the length of employment of the subjects in the current industry did not influence the occurrence of impaired sensory conduction of the median nerve at the carpal tunnel.

PMID: 3385295, UI: 88258259

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