Tendon Force and Range of Motion Changes After In Vitro Total Wrist Replacement.

Purpose: The purpose of this study was to determine if there were differences in the tendon forces needed to cause wrist motion and in the passive range of wrist motion following total wrist replacement (TWR) using a contemporary arthroplasty design.

Methods: Eight fresh frozen cadaver arms were moved through five different wrist motions using a wrist joint simulator before and after the insertion of a TWR. Changes in the peak tendon forces and wrist range of motion were compared.

Results: During each of the five wrist motions following TWR, there were significant increases in the extensor tendon forces. Most notably, the force in the extensor carpi radialis longus more than doubled in four motions. Also, the range of motion significantly decreased in flexion (average 18 degrees, range of 23 to -5 [one wrist had an increase in flexion]), extension (average 23 degrees, range of 4-32), and radial deviation (average 19 degrees, range of 29 to -2 [one wrist had an increase in radial deviation]) following TWR. The hand and carpus shifted distally following the insertion of a wrist implant (average of 8.5 mm; range of 3.6-18.0).

Conclusions: Wrist tendon forces increased with TWR insertion, even with a fourth-generation design. Positioning of the implant or differences in the biomechanical properties of the implant compared with the intact specimen may have been factors in the reduced range of motion and distal movement of the carpus. The difficulties of implanting a prosthesis that allows normal kinematics may also play a role in these results.

Clinical relevance: Despite the marked improvements in recent TWR designs, additional design and surgical technique modifications are needed to further reduce the tendon forces required to move a wrist following TWR and increase its range of motion.