Flexor tendon forces: in vivo measurements.

S-shaped force transducers were developed for measurement of the forces along intact tendons. After calibration, the transducers were applied to the flexor pollicis longus and flexor digitorum superficialis and profundus tendons of the index finger in five patients operated on for treatment of carpal tunnel syndrome. The tendon forces generated during passive and active motion of the wrist and fingers were recorded. For pinch function, the amount of the applied load was measured with a special pinch meter. Tendon forces in the range of 0.1 to 0.6 kgf were measured during passive mobilization of the wrist. Tendon forces up to 0.9 kgf were present during passive mobilization of the fingers. Tendon forces up to 3.5 kgf were present during active unresisted finger motion. Tendon forces up to 12.0 kgf were recorded during tip pinch, with a mean applied pinch force of 3.5 kgf. These results have potential application in determining the amount of force that a tendon repair would have to resist during passive as well as active postsurgical mobilizations.