To the Editor: In "Work-Related Musculoskeletal Disorders," Drs Silverstein and Franklin1 mention Radecki2 having "profound misclassification" because workers with high-risk jobs3 may be in low-risk industries. In my prospective study, I examined each of 1472 patients. No patient in a "high-risk" job task based on "high-risk" industry3 was classified as being in a low-risk job task. Each clam shucker was classified a clam shucker.
Ergonomic data are not relevant to the causation of median nerve injury at the carpal tunnel if patients with such injury are physically and electrodiagnostically identical regardless of occupation. My study2 found a consistent covariance between median nerve slowing at the carpal tunnel (evidence of injury) and age, body mass index, and the wrist ratio. My formula, "expected" median minus ulnar palmar latency difference = -4.463 + 5.664 (wrist ratio) + 0.023 (body mass index) + 0.011 (age), predicts the degree of median slowing in the dominant hand of any woman undergoing electrodiagnostic testing for hand or forearm complaints. The formula performs well regardless of occupation or illness4 Work is not a factor in the formula; only personal factors are part of this "dose-effect" relationship. Mayo Clinic researchers have said that such personal factors must be considered when interpreting nerve studies.5 A claim of "misclassification" of job task is an irrelevant, misleading distraction.
Drs Silverstein and Franklin1 have presented no reliable formula relating any occupation to median nerve slowing.
Drs Silverstein and Franklin1 said Szabo and Chidgey6 was one of numerous studies demonstrating that forceful, repetitive, and stressful postures contribute to musculoskeletal dysfunction. The six "normal control" patients in the study (no carpal tunnel syndrome) had a mean carpal canal pressure of just 16 mm Hg during passive wrist flexion and extension (critical pressure is approximately 30 mm Hg). Szabo and Chidgey merely show that such wrist movements safely avoid high pressures in six supine control subjects (this safe pressure, 16 mm Hg, is the claimed1 "musculoskeletal dysfunction" of Drs Silverstein and Franklin). Such wrist movements might be considered potentially harmful to the general working population if (1) the control subjects exhibited sustained critically high pressures (they did not), and (2) the general working population works in supine position (they do not). In reality, patients with carpal tunnel syndrome have high carpal tunnel pressures merely with recumbency for sleep, even when wearing splints.7 An explanation for these damaging carpal tunnel pressures merely with recumbency, based on the formula noted above, is available.8
Patrick Radecki, MD
Portland, OR
References
1. Silverstein MA, Silverstein BA, Franklin GM. Evidence for work-related musculoskeletal disorders: a scientific counterargument.
J Occup Environ Med. 1996;38:477-484.
2. Radecki P. Variability in the median and ulnar nerve latencies: implications for diagnosing entrapment.
J Occup Environ Med. 1995;37:1293-1299.
3. Franklin GM, Haug J, Heyer N, Checkoway H, Peck N. Occupational carpal tunnel syndrome in Washington State, 1984-1988.
Am J Public Health. 1991;81:741-746.
4. Radecki P. The predictability of "median slowing" in individual patients.
Muscle Nerve. 1995;19:1057.
5. Dyck PJ, Litchy WJ, Lehman KA, Hokanson BA, Low PA, O'Brien PC. Variables influencing neuropathic endpoints: the Rochester Diabetic Neuropathy Study of healthy subjects.
Neurology. 1995;45:1115-1121.
6. Szabo RM, Chidgey LK. Stress carpal tunnel pressures in patients with carpal tunnel syndrome and normal patients.
J Hand Surg [Am]. 1989;14:624-627.
7. Luchetti R, Schoenhuber R, Alfarano M, Deluca S, De Cicco G, Landi A. Serial overnight recordings of intracarpal canal pressure in carpal tunnel syndrome patients with and without splinting.
J Hand Surg [Br]. 1994;19:35-37.
8. Radecki P. Personal factors and blood volume movement in causation of median neuropathy at the carpal tunnel.
Am J Phys Med Rehabil. 1996;75:235-238.
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Readers are invited to submit letters for publication in this department. Submit them to: The Editor, Journal of Occupational and Environmental Medicine, PO Box 370, Bryn Mawr, PA 19010. Letters should be typewritten and double spaced and should be designated “For Publication.”
