Carpal tunnel syndrome -- a disabling disorder of the wrists and arms -- is thought to be due to repetitive motions such as those performed using a computer keyboard or a factory machine. But how these movements lead to the disorder is not known. US researchers may have found a clue -- people with carpal tunnel syndrome appear to have abnormal collagen levels that may make their wrists stiffer than normal.

"My lab is the first lab to culture these cells and also try to figure out the physiological mechanism," said Dr. Joana Chakraborty of the Medical College of Ohio in Toledo, in an interview with Reuters Health.

The carpal tunnel is an anatomical structure formed by a strong fibrous band called the flexor retinaculum (FR) as it stretches over the surfaces of the wrist bones. A small reduction in the space of this tunnel -- such as that caused by swelling -- may exert enough pressure on a nerve in the wrist to cause carpal tunnel syndrome, said the researchers led by Chakraborty and Dr. John Robinson, also of the Medical College of Ohio.

The researchers removed cells from the flexor retinaculum from five patients, four of whom had carpal tunnel syndrome. The team examined these cells to determine their growth rate in the absence of various factors. The investigators found several differences between people with and without carpal tunnel syndrome (CTS).

When the CTS cells were exposed to growth factors and ascorbic acid (vitamin C), they reproduced more rapidly and produced more collagen, a type of connective tissue, than the cells from the patient without CTS. In addition, the researchers found that the CTS cells produced more of a certain type of collagen (type III) that could produce increased stiffness and lead to the development of CTS.

"We have seen that people with carpal tunnel syndrome have a different physiology activity of the cells of the flexor retinaculum," said Chakraborty.

The authors note that previous studies have shown that vitamin C is essential for normal collagen formation and in humans, it increases collagen synthesis up to eightfold. But the study did not show if the vitamin can help CTS patients.

More genetic studies are needed to study the role of collagen in CTS, said Chakraborty. In addition, further research is needed to determine the effects of strain and vibration on collagen production in patients with the disorder. "It doesn't happen to everybody, it only happens with some people," said Chakraborty. "We really want to get to the bottom of this thing so people can be helped.

Journal of Occupational and Environmental Medicine March 2000;42:251-259.