Keep On Typing

Main Category: Bones / Orthopaedics
Also Included In: Genetics;  Public Health
Article Date: 18 Feb 2007 - 0:00 PDT

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Computer programmers, office workers, college students and Internet addicts everywhere can now breathe a sigh of relief: there is better evidence that genetics rather than hand use is the cause of carpal tunnel syndrome (CTS). A new study presented today at the 74th Annual Meeting of the American Academy of Orthopaedic Surgeons indicates that the causal link between CTS and repetitive use of the hands is much weaker than has been assumed.

"The idea that CTS is related specifically to typing or overuse of the hands in general is pervasive in modern society," said David Ring, MD, senior author of the study. Ring is an assistant professor of orthopaedic surgery and a hand and upper extremity surgeon at Massachusetts General Hospital in Boston. "It is commonly accepted as true, but according to the scientific evidence, the link between hand use and carpal tunnel syndrome is overstated and may be inaccurate. In contrast, there is strong evidence for an inherent, genetic risk for CTS. CTS sufferers are most likely innocent bystanders and should not be blamed for their illness."

Patients with CTS experience hand numbness, and eventually develop weakness and atrophy of some of the small hand muscles that control the thumb. "Another common misconception," said Ring, "is that patients with carpal tunnel syndrome present with complaints of activity-related wrist pain. In fact, the hallmark of CTS is numbness that wakes you at night or is present when you wake in the morning. The numbness can be so intense that it's painful, but pain without numbness is not characteristic of CTS."

Carpal tunnel syndrome remains poorly understood. Pressure in the carpal tunnel (a tunnel formed by the small wrist [carpal] bones and the transverse carpal ligament) is involved in the pathophysiology, and release of the pressure by dividing the transverse carpal ligament stops the process. The cause of the increased pressure, however, remains unknown in the vast majority of patients.

Researchers evaluated data for the cause of CTS by a quantitative scale, based on the Bradford Hill criteria (widely accepted by the scientific establishment), which determines a causal relationship. Average scores for biological factors (genetics, race, age, etc.) were double those of occupational factors (occupation, repetitive hand use, vibration, etc.). In addition, the average strength of causal association (odds ratio) was about three times as strong for biological factors as it was for occupational factors.

"This application of stringent science to theories of causation may affect claims of disability, workers compensation and personal injury," noted Ring. "It should also influence the information that physicians are providing their patients about carpal tunnel syndrome. Physicians have the power to increase or decrease illness and disability with their words. In my opinion, we should provide patients with the most optimistic, positive, practical and enabling illness concepts that are consistent with the best available scientific data."

American Academy of Orthopaedic Surgeons
http://www.aaos.org