It has become a forgone conclusion that if you use a computer frequently, you are at risk of developing carpal tunnel syndrome. Alternatively, it is assumed that if you already have carpal tunnel syndrome, the cause is overuse of your hands, with the most common culprit being the regular use of a keyboard and computer. Although there is some relationship between the two, we now know that developing carpal tunnel syndrome is a multi-factorial problem and using a keyboard can worsen it but does not typically cause it.
Carpal tunnel syndrome is a very specific condition where there is increased pressure on the median nerve as it crosses the wrist resulting in numbness and tingling of the thumb, index, middle, and part of the ring finger. Advanced cases may also identify atrophy and weakness of the thumb.
The assumed relationship between keyboarding and carpal tunnel syndrome is a product of the computer boom of the 1980s and ‘90s, when the use of computers in the workplace grew exponentially. During that time there was also an increase in workers compensation claims
for carpal tunnel syndrome. This was exacerbated by a number of early studies that substantiated the perceived relationship. However, since then a number of more organized studies have found this to not be entirely true. Although heavy keyboard use may aggravate carpal tunnel syndrome, the actual cause is more strongly correlated to age, gender, weight, medical conditions such as diabetes and hypothyroidism, and injuries to the wrist. Occupational exposures that can cause carpal tunnel syndrome involve excessive and/or sustained exposure to vibration or prolonged flexed or extended posturing of the wrist.
The diagnosis of carpal tunnel syndrome can be readily made by hand surgeons and orthopaedic surgeons through a careful look at patient history and physical examination. Additional diagnostic studies in the form of a nerve conduction study and electromyogram (EMG) can confirm and grade the extent of carpal tunnel syndrome. Its management is subsequently based upon that grade and can include splints, injections, and surgery (either open or endoscopic).
Asif M. Ilyas, MD
© Risk & Insurance 2006
A 47-year-old, sedentary, overweight customer service representative began to wake up with numbness, first in one hand and then in both. She soon found herself shaking her hands out at work, where she typed all day while on the phone with a headset talking to customers. Her company had changed each workstation two years before for ergonomic reasons. Though Mary had been in this job for seven years, there had hardly been any change in the job in the past four years. Mary incurred no overtime. She had no hobbies that placed extra demands on her hands.
So was her condition work-related? Don’t jump to that conclusion, says Verne Backus, an occupational-medicine physician in Vermont and the person who presented Mary’s case to me.
She woke several times a night, but didn’t feel rested even after seven hours’ sleep. Then one day while driving to work, her hands became so numb she had trouble holding the wheel. Her doctor gave her wrist splints to wear at night. After initial relief, the symptoms returned.
A neurologist studied her nerves and diagnosed bilateral moderate carpal tunnel syndrome. She was referred to a hand surgeon, who opined that because her hands bothered her when she was typing, work had caused the condition. Mary filed a workers’ compensation claim.
Her insurance adjuster hired a physical therapist to perform a work-site assessment. The therapist interviewed the worker and her supervisor, and observed Mary as she worked. To determine causality, the therapist then applied four assessment tools that allow the examiner to assign probability scores based upon the known work factors contributing to carpal tunnel syndrome. The factors include forceful gripping, awkward postures, sustained gripping, cold and repetition. The focal point for repetition was not her fingers tapping the keyboard, but muscle groups in the wrist.
The therapist reported that the scores weren’t indicative of work causality. The insurer successfully denied the workers’ comp claim. So what caused Mary’s CTS?
Mary’s primary care provider had ruled out metabolic causes associated with carpal tunnel, such as diabetes and hypothyroidism. Her case may have arisen from a congenitally small carpal canal, age-related changes in structures in the canal or an increase in body fat. Deconditioning may have been a factor. But many conditions are idiopathic, which means that we cannot determine their cause.
Backus’ main point is this: It is a mistake to assume that if there is no other plausible explanation, the cause has to be work.
David Rempel, a physician and expert on carpal tunnel syndrome in the San Francisco area, has studied the condition for 20 years. Mary being overweight, he tells me, is a risk factor for carpal tunnel. So is full-time work at the keyboard. But Mary is not engaging in the primary workplace risk factor: repetitive forceful gripping. Rempel questions if deconditioning can increase the odds of acquiring carpal tunnel.
He has seen work-site prevalence rates as high as 15 percent in high-injury-risk jobs such as meatpacking and lumber mills. But many people in retirement acquire the condition as well. A large-scale workplace study to get a clearer picture hasn’t been done.
We should double-check our attempts to resolve carpal tunnel as a workplace risk. There are useful but inclusive research reports, case evaluations of varying quality, administrative law judges tilting to one or more contradictory biases, and many individuals left with discomfort or pain. I think we need that large-scale study.