Moment arms of the digital flexor tendons at the wrist: role of differential loading in stability of carpal tunnel tendons.

When a flexor digitorum superficialis tendon crossing a flexed or extended wrist has a load applied to it in excess of that applied to adjacent tendons, that tendon may translate across the carpal tunnel. In 6 cadaver specimens, each of the 9 carpal tunnel tendons was loaded with a baseline tension of 85 g and the moment arms of the flexor pollicis longus and the 4 flexor digitorum superficialis tendons were determined. Applying a higher 540-g load to individual flexor digitorum superficialis tendons and the flexor pollicis longus while loading the remaining tendons with the baseline 85-g tension significantly changed the moment arms from those measured under baseline load. The results demonstrated that tendons with applied differential loads in the carpal tunnel shift their positions, as revealed by their changing moment arms.