Musculoskeletal Disorders and the Workplace Low Back and Upper Extremities (2001) / Chapter Skim
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Appendix B: Dissent, Robert M. Szabo
Appendix B: Dissent, Robert M. Szabo
Pages 439-457
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From page 439... ...
The panel agreed and we wrote, "Few high-quality intervention studies related to the primary and secondary prevention of low back pain are available in the literature." No high-quality intervention studies related to the primary and secondary prevention of upper extremity disorders in general and carpal tunnel syndrome in particular are available in the literature. To circumvent the issue of not having reasonable scientific intervention studies available, the panel took a "best practices" approach, which I think is not very scientific.
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From page 440... ...
Another study was misrepresented as demonstrating an association between computer keyboard use and slowed median nerve velocity. Not mentioned in discussing that study was that there were no abnormal median nerve velocities and there were no clinical carpal tunnel syndromes.
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From page 441... ...
One investigation concluding that carpal tunnel syndrome is closely correlated with health habits and life-style49 is supported by an analysis showing that 81.52 percent of the explainable variation in electrophysiologically defined carpal tunnel syndrome was due to body mass index, age, and wrist depth/width ratio, whereas only 8.29 percent was due to job-related factors.24 There may be important interactions between extrinsic and intrinsic risk factors that are yet to be understood. While there is a biologically plausible mechanism to relate forceful grip to compression of the median nerve,6465 there is no such correlate to postulate biological plausibility with regard to repetition.
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From page 442... ...
In female workers, current tobacco, caffeine, and alcohol consumption independently predicted 5 percent of the explainable risk for definite carpal tunnel syndrome. In a case-control study of 600 patients presenting for an independent medical exam, Stallings and colleagues found that obesity was associated with positive findings on nerve conduction exams for median neuropathy with an odds ratio of 3.92 (95 percent confidence interval = 2.65 to 5.79~.59 In a study analyzing the computer records of all personnel on active naval duty in all Navy medical facilities from 1980 to 1988, Garland and colleagues found first hospitalization rates (those patients undergoing surgery)
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From page 443... ...
All three studies were cross-sectional in design. She concluded that when the results of these studies were compared, they provided strong evidence of a causal relationship between repetitive, forceful work and the development of musculoskeletal disorders of the tendons and tendon sheaths in the hands and wrists and nerve entrapment of the median nerve at the carpal tunnel.63 Only two of the studies, however, specifically examined carpal tunnel syndrome; one was the Silverstein study mentioned above.
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From page 444... ...
At first it would seem that the critical issue is whether only studies that use electrodiagnosis should be considered in attempts at resolving the role of job-related risk factors. Comparison of several different median nerve conduction study techniques, however, demonstrates a variety of sensitivities.35 The problem is that no single technique can identify all carpal tunnel syndrome patients without misclassifying an unacceptable number of normals.
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From page 445... ...
proposed a surveillance case definition for work-related carpal tunnel syndrome: the presence of median nerve symptoms; one or more occupational risk factors; and objective evidence by physical examination findings, including the Tinel or Phalen signs or decreased pinprick sensation, or positive diagnostic nerve conduction studies. Using the NIOSH surveillance case definition, if a worker develops classical symptoms and has abnormal electrodiagnostic studies of the median nerve in the face of a work task that is highly forceful and repetitive, then the presumption is that the symptom complex is work related.43 The work by Silverstein and her colleagues58 formed the basis for this case definition; however, the diagnosis in their study was based on reported symptoms not confirmed with electrodiagnosis.
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From page 446... ...
The temporal relationship between physical load factors and the onset of carpal tunnel syndrome has not been demonstrated in either cross-sectional or case-control studies examining prevalence. Armstrong and Chaffin noted that carpal tunnel syndrome subjects used a wrist position that deviated from the straight position more frequently and exerted greater hand forces in all wrist positions than nondiseased subjects; however, they could not establish whether the differences in work methods was a cause or an effect of the disorder.5 The majority of studies to date are prevalence studies in which exposures were measured at the same time that disease status was established.
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From page 447... ...
Hales and Bernard concluded that 16 of 22 studies reported a positive association between occupational factors (repetition being only one) and carpal tunnel syndrome, but not a single one of these studies had quantified both exposure and disease ascertainment.28 Confounding can result in incorrectly attributing the etiology of carpal tunnel syndrome to the wrong risk factor.
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From page 448... ...
To test the hypothesis that carpal tunnel syndrome is associated with occupational risk factors, a study incorporating electrophysiological tests, physical examinations, and questionnaires was performed at a ski assembly plant where jobs were classified as repetitive and nonrepetitive.7 Repetitive jobs were defined as activities that required repetitive or sustained flexion, extension, or ulnar deviation of the wrist or use of a pinch-type grip. The conclusion drawn, based on a crude prevalence ratio of 4.92 (95 percent confidence interval = 1.17- 20.7)
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From page 449... ...
"Teaching 25 years ago regarded carpal tunnel syndrome as a problem that would resolve following surgery when it was indicated."43 When patients with carpal tunnel syndrome appear to have some relationship between their symptoms and their work, the problem is different. In one study of workers' compensation patients, individuals with less abnormal nerve conduction velocities were more likely to have persistent symptoms and more often changed jobs based on those symptoms than those with more prominent nerve conduction abnormalities.3~ Higgs found that those workers undergoing carpal tunnel release in his study who had legal representation were twice as likely to have poor outcomes.
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From page 450... ...
The authors concluded that disability following carpal tunnel syndrome surgery may be related to other medical, psychosocial, administrative, legal, or work-related factors. Franklin similarly concluded that a number of factors need to be considered when interpreting outcome studies in workers' compensation patients: factors that predict good or poor outcome may not be the same as in the general population; comparable procedures have worse outcomes in the workers' compensation patients; outcomes after surgery are strongly correlated with the duration of preoperative disability but not the biological severity of the initial injury.2~ Both people involved with repetitive activities and those who are not develop carpal tunnel syndrome.
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From page 451... ...
Since wrist flexion/extension increases carpal tunnel pressure, which in turn inhibits median nerve function, it seems reasonable to use a splint that maintains the wrist in neutral position; however, one study demonstrated that carpal tunnel pressures were higher with splint use at baseline and during repetitive hand activity, perhaps suggesting some external compression.55 Epidemiological studies of occupational carpal tunnel syndrome have usually not isolated the issue of wrist or finger position from grip force and repetition. Motion analysis studies of sign language interpreters for the deaf and grocery checkers 29 have shown that workers with symptomatic hands had more frequent and more extensive flexion and extension than nonsymptomatic workers, suggesting that extreme flexion or extension may be an extrinsic risk factor.
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From page 452... ...
Some have asserted that there is little substantive evidence that these methods are either valid or reliable.60 Others have found that ergonomics have resulted in substantial improvements in the workplace.52 There is little doubt that most ergonomic interventions increase comfort in the work environment, which is of great benefit to the worker. While ergonomists may create a more comfortable environment, they have not lowered the incidence of well-documented medical conditions, such as carpal tunnel syndrome.
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From page 453... ...
In a time of relative prosperity, with technological changes and computerization of clerical tasks that threatened those less adaptable to change, and in a country with as many physicians and pharmacists per capita as any industrialized nation, the inability to work because of a physical ailment became more socially acceptable.33 34 Kiesler and Finholt concluded that the repetitive stress injury epidemic in Australia was more indicative of social problems than of workplace factors, and dissatisfaction was a major contributor, as was social legitimization of complaints related to repetitive stress injury.40 Political and social factors can act in both directions. The single factor that had the greatest influence on the decline of repetitive stress injury in Australia was a judicial decision in the case Cooper v.
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From page 454... ...
G.; and Spaans, F.: Risk factors for carpal tunnel syndrome. Am J Epidemiol, 132~6~: 1102-1110, 1990.
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From page 455... ...
24. Gerr, F., and Letz, R.: Risk factors for carpal tunnel syndrome in industry: blaming the victim?
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From page 456... ...
D.; and Lockwood, R S.: Slowing of sensory conduction of the median nerve and carpal tunnel syndrome in Japanese and American industrial workers.
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From page 457... ...
J.: The relationship between body mass index and the diagnosis of carpal tunnel syndrome. Muscle Nerve, 17~6~: 632-6,1994.
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