Carpal tunnel syndrome: contribution of flexor tendons.

Tension in flexor tendons during wrist flexion may play a role in otherwise unexplained instances of the carpal tunnel syndrome. As the wrist is flexed, the median nerve in the tunnel bends around the taut flexor retinaculum. At the same time, the nerve is subject to compression against this ligament by tensed overlying flexor tendons that also bend around the ligament. Experimental data to support this possibility have been collected from cadaver hands. A pressure transducer has been substituted for the median nerve in the tunnel and registered sizable pressures when tension was applied to the flexor digitorum profundus tendons of the second and third digits during varying degrees of wrist flexion. If the profundus tendons are not tensed, pressure in the tunnel remains negligible until wrist flexion reaches its extreme. Thus, repetitive hand activities involving pinch or grasp during wrist flexion may be a contributing factor in some instances of the carpal tunnel syndrome.