Objective: To study the reaction of tissues in the carpal tunnel after repeated flexion of wrist in order to verify the pathophysiology and pathomechanism of the carpal tunnel syndrome as a cumulative trauma disorder.

Method: Six groups of adult rabbits (5 rabbits were allocated to each groups) were exposed to repeated contractions of the wrist flexors by the median nerve stimulation at the elbow level for different durations; 2 days, 1 week, 2 weeks, 3 weeks, 4 weeks, and 5 weeks. Histological evaluation, morphometric analysis, and electrophysiological studies were carried out after the stimulation.

Results: There were no typical nor consistent findings in the tissues in the carpal tunnel except the median nerve. Inflammatory cell infiltration and edematous changes were noted in the epineurial tissue of median nerve. Decrease of large myelinated fibers and changes of fiber shape were observed in the median nerve. On the morphometric analysis, fiber diameter was smaller in groups of longer exposure duration. Changes were most prominent in 5 weeks group and in the periphery of the nerve fascicle in all the groups. Significant reduction of amplitude and increase of duration of compound muscle action potential were noted on electrophysiological study of the median nerve.

Conclusion: The authors concluded that repeated experimental wrist flexion could give rise to an injury of the median nerve in the carpal tunnel. Accumulation of microtrauma of median nerve by epineurial edema and direct mechanical compression seems to be the pathomechanism of the carpal tunnel syndrome as a cumulative trauma disorder.

Keywords :Carpal tunnel syndrome (CTS), Cumulative trauma disorder (CTD), Experimental investigation, Morphometric analysis