Carpal kinematics during simulated active and passive motion of the wrist.

PURPOSE: The purpose of this study was to investigate the effect of experimental control mechanisms, simulated active (tendon-driven) and passive (externally assisted), on carpal motion.

METHODS: Kinematics of the carpal bones in five fresh-frozen cadaver upper extremities were studied using an optical motion analysis system. The wrist extensors and flexors were dissected and loaded. For passive motion, the tendons were loaded to simulate muscle tone while the investigator passively moved the wrist using a pin placed in the third metacarpal. To simulate active, patient-driven motion, the tendons were attached directly to guide bars while the investigator used a puppeteer mechanism to move the wrist.

RESULTS: There were no significant differences in carpal motion (flexion-extension motion or radial-ulnar deviation) when the wrist was moved in simulated active motion through the extensor and flexor tendons or in passive motion, with a constant force applied to the tendons. Kinematics for simulated active motion, in general, was more difficult to control and was less smooth than the kinematics for passive motion.

CONCLUSIONS: Carpal bone kinematics (excluding the pisiform) in a healthy normal joint are similar in both simulated active (tendon-driven) and passive (externally assisted) wrist motion because the carpal bones are passively moved during wrist motion (there are no direct tendon-to-muscle attachments to the proximal carpal bones and minimal attachments to the distal carpal bones).