Wrist Tendon Forces With Respect to Forearm Rotation

Abstract

Early motion therapy protocols are desirable to reduce wrist stiffness after carpal injuries and distal radius fractures. Based on our assumption that a reduction in wrist tendon forces will be associated with a reduction in radioulnar carpal joint reaction force, the goal of this study was to determine the forearm position at which the wrist tendon forces required to initiate wrist motion were the least. We tested 8 fresh-frozen cadaver forearms in a wrist and forearm motion simulator. In each specimen, we generated a wrist flexion-extension motion and a radioulnar deviation motion by pulling on the wrist flexor and extensor tendons with the forearm in supination, pronation, or neutral. We also performed a wrist flexion-extension motion during active forearm rotation. During each motion, we continuously recorded the forces in the 5 wrist tendons. We used repeated-measure analyses of variance to compare tendon forces. During the wrist flexion-extension motion, the summed peak wrist extensor forces were significantly less with the wrist in forearm supination than with the forearm in neutral or during active forearm rotation. For the summed peak wrist flexor forces, flexor tendon forces were significantly less with the forearm in supination compared with active forearm rotation. The extensor carpi radialis longus and flexor carpi ulnaris forces were significantly less in supination than during active forearm motion. During wrist radioulnar deviation motion, peak extensor carpi ulnaris force was significantly less with the forearm in supination than in neutral, and peak flexor carpi radialis force was significantly less with the forearm in supination than in pronation. Peak wrist tendon forces were least in the static forearm supinated position. To reduce deforming forces on a fresh carpal injury or distal radial fracture, active rehabilitation appears to be best initiated with the forearm held in supination.