Shearing injuries to subsynovial connective tissue possible cause of carpal tunnel syndrome

Pathologic tissue changes were most severe closer to the tendon and progressively decreased among more superficial layers.

Carpal tunnel syndrome may result from a shearing injury to tissues lining tendons within the carpal tunnel, suggest the results of a study by researchers at the Mayo Clinic in Rochester, Minn.

Peter Amadio, MD, chair of orthopedic surgery at the Mayo Clinic College of Medicine, and colleagues used light and scanning electron microscopy to evaluate the ultrastructural morphology of subsynovial connective tissue. The researchers examined biopsy specimens for 12 hands of 11 patients with idiopathic carpal tunnel syndrome and for two cadavers that had a history of carpal tunnel syndrome. Another 14 cadavers served as a control group, according to the study, published in the November issue of Plastic and Reconstructive Surgery.

Amadio and colleagues found that patients with idiopathic carpal tunnel syndrome had lost the small layers of fibrous tissue that interconnect between the subsynovial connective tissue and adhere to the synovial membrane and flexor tendons, according to the study.

"During tendon motion, the loose fibers between adjacent layers are stretched. The control tissue showed interconnections between all the parallel layers, whereas in patients with idiopathic carpal tunnel syndrome, these interconnections were absent, replaced with thicker parallel fibrous bundles," the authors said in the study.

The researchers saw similar changes in specimens taken from the two cadavers with a history of carpal tunnel syndrome, they added.

The observed pathologic changes were most apparent close to the tendon and progressively decreased in severity among more superficial layers, according to the study. This finding suggests that the changes may have resulted from a shearing injury, the authors said.

As such injuries heal, resulting scar tissue impedes the sliding motion of the tendon, compresses the median nerve, cuts off the nerve's blood supply and eventually leads to the pressure buildup characteristic of carpal tunnel syndrome, according to a press release from the Mayo Clinic.

The researchers did not specifically probe the possible causes of such shearing injuries, but Amadio and colleagues are looking into the possible role of trauma or stress to the tissue lining caused by repeated finger movements. "Such shearing injuries could be the result of marked or repetitive differential motion of adjacent digits and may support the hypothesis of a traumatic cause for carpal tunnel syndrome," Amadio said in the press release.

The study was funded by the National Institutes of Health and the Mayo Clinic.

For more information:
Ettema A, Amadio PC, Zhao C, et al. Changes in the functional structure of the tenosynovium in idiopathic carpal tunnel syndrome: A scanning electron microscope study. Plast Reconstr Surg. 2006;118:1413-1422.