© 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.