Department of Environmental and Industrial Health, University of Michigan, Ann Arbor, Michigan, 1984 Jul; :1-15
Biomechanical aspects of the human carpal tunnel were reviewed, and the relationships between forces inside flexed and extended wrists to wrist size, hand force, and hand position were investigated. Studies have indicated that the major force producing muscles during exertions of the hand are the extrinsic finger flexor muscles. These muscles are connected to the fingers with long tendons passing through the carpal tunnel. Studies have suggested that the force between the extrinsic finger flexor tendons and the trochlea in the flexed wrist compresses the median nerve and is a factor in carpal tunnel syndrome. Direct pressure measurements at the site of the median nerve demonstrated compression of the median nerve. Synovial membranes of the radial and ulnar bursas that surround the extrinsic finger flexor tendons also are compressed by forces in both flexed and extended wrists. Repeated compression may cause synovial inflammation and swelling, compressing the median nerve inside the carpal tunnel. When the wrist is extended, a load distribution on the trochlea of the profundus tendon is about 25 percent greater in females than males. When the wrist is flexed, the load on the trochlea in females is 14 percent greater than in males. Exertions of the hand with a wrist in a greatly deviated position would result in greater total force on the tendons and trochleas than would occur with a nearly straight wrist. For a given hand force, greater forces per unit length and greater resultant forces on the tendons and trochleas would be produced in pinch than in grasp.
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