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CTS not connected to keyboard use, sedentary work, but could have genetic link

Associations exist between carpal tunnel syndrome and high-force repetitivejobs, some diseases.

Issue: July 2006

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In the half-century since surgical treatment for carpal tunnel syndrome became popularized, the thousands of studies about this condition published in the hand surgery, plastic surgery, orthopedic surgery, and occupational and industrial medicine literature identified little about its etiology.

“We do not have, in most cases, a good explanation why people get carpal tunnel syndrome (CTS),” said Kevin Chung, MD, MS, associate professor of surgery, section of plastic surgery, University of Michigan.

Some recent worldwide CTS research has helped shed a little more light on those activities and health-related issues associated with the condition.

In CTS, the carpal tunnel becomes overly narrow, which compresses the median nerve that lies within it, according to Chung. The result: the nerve stops functioning well. That can lead to tingling or numbness in the fingers and a reduction in the sensory and motor function in the hand.

In terms of etiology, certain activities or health conditions may place increased pressure on the median nerve and, therefore, may be more highly associated with CTS. Fortunately, releasing the transverse carpal ligament can reduce that pressure build-up, as can some conservative treatments.

“Most patients get better after carpal tunnel release, indicating that by giving the nerve more room it tends to function better,” Chung said.

Situations that cause increased pressure in the carpal tunnel continue to be investigated, but “etiology-wise we do not know what causes most of the CTS.”

Risk factors

Diseases and certain medical conditions, like obesity and pregnancy, have been shown to be strongly associated with CTS, particularly those that cause neuropathy, like diabetes and hypothyroidism.

Others, like rheumatoid arthritis, gout, tuberculosis and being in the third-trimester of pregnancy, may be risk factors for CTS because increased synovial tissue and fluid in the carpal tunnel causes median nerve compression.

Changes within the tunnel from fractures or bleeding can also induce acute CTS.

Just performing activities with the hands in extreme flexed or extended positions, such as using crutches, a walker or cane for a long time, may increase carpal tunnel pressure, putting patients at risk for CTS, said Robert M. Szabo, MD, MPH.

Work force

“We’ve been trying to find an association between CTS and work. But this association is difficult to study because for variability in working conditions that place different amount of stresses on the hand. Additionally, other nonwork-related activities are difficult to quantify,” Chung explained.

But, experts agree that sedentary, low-force work activities have a weak association with CTS. “When it comes down to the work place … force and repetition alone have not been statistically shown to increase the risks of CTS,” said Szabo, professor of orthopedic surgery and chief of the hand and upper extremity service, University of California-Davis, School of Medicine, Sacramento.

But in combination, force and repetition lead to problems.

Heavy keyboarding’s previous association with CTS has been ruled out because although it is repetitive, it lacks sufficient force to cause the problem and it is done with the wrists extended normally, not flexed, Szabo said.

Keyboard theory nixed

In 2001, Mayo Clinic investigators, Phoenix, published results of a small study of workers who used computers up to seven hours a day. Their unexpected findings: “Only 10.5% of the study participants, all of whom used computers extensively, met clinical criteria for CTS. This incidence is similar to that found in the general population,” according to a press release.

A Danish study of more than 6000 workers published in 2003 also ended much speculation about the keyboarding connection. Of those who had baseline signs of CTS, including pain in the median nerve of the right hand, researcher found a low incidence of right-hand CTS at the one-year follow-up. Computer use does not appear to be an occupation that leads to CTS symptoms, the authors concluded.

“That doesn’t mean that there aren’t work-related CTS [cases], but computer keyboard is not one of them,” said Barry P. Simmons, MD, hand and upper extremity section editor of the Orthopedics Today editorial board.

Work-related CTS

Simmons cited reports of computer-related keyboard disorders — work-related musculoskeletal disorders (WRMSDs) — that were not CTS. They include ulnar neuropathy, shoulder and neck problems, hand symptoms related to neck arthritis, even fatigue.

Highly industrial, repetitive work in the fishery and meat packing industries, or carpentry, has a higher association with CTS, Chung said.

Environments with a lot of vibration or cold temperatures are not necessarily associated with CTS, but perhaps affect nerve vascularity, Szabo said.

CTS challenges

Physicians who spoke to Orthopedics Today said preventing CTS is impossible without knowing its causes. They agreed that modifying the work place environment may not necessarily help. Szabo said it could affect patients more on a psychosocial level than physically.

“If your job is to get a patient back to … work and cured, you want to do that in the fastest way possible. There’s no advantage to encourage them it’s work-related,” he told Orthopedics Today.

When Szabo initially sees CTS patients, he tells them where he stands on causes and treatments.

“I also see a lot of psychosomatic problems, where I don’t think there’s anything physically wrong.” Szabo said.

Recent CTS etiology work has explored the genetic connection for women under 30 years old. “That’s probably going to explain a lot of CTS in time,” he said.

Chung urged primary care physicians, ergonomic specialists, and others groups to unite and work for the benefit of the patient for a comprehensive evaluation and to develop an overriding strategy.

For more information:

• Andersen JH, Thomsen JF, Overgaard E, et al. Computer use and carpal tunnel syndrome. JAMA. 2003;289:2963-69.
• Hakim AJ, Cherkas L, El Zayat S, et al. The genetic contribution to carpal tunnel syndrome in women: a twin study. Arthritis Rheum. 2002;47(3):275-9.
• Szabo RM. Determining causation of work-related upper extremity disorders. Clin Occup Environ Med. 2006;5:225-234.