Wrist Kinematics and Function: Comparison of Normal and Wrist Joint Replacement

Purpose: The purpose of this study was to measure biomechanical differences between normal wrist function and wrist function following partial and complete total wrist joint replacement. For a comparison, proximal row carpectomy (PRC) was performed as a common wrist reconstructive salvage procedure.

Materials and Methods: This study utilized cadaveric wrist specimens in a within-specimen analysis. Wrist function was assessed using two measures: (1) kinematic function was quantified using wrist range of motion and axis of rotation measurements and (2) changes in extrinsic flexor and extensor muscle moment arms were quantified using measurements of tendon excursion relative to angular position. All of these measurements were performed for four functional motions: wrist flexion/extension, radial/ulnar deviation, dart thrower's motion (wrist extension, radial deviation to wrist flexion with ulnar deviation), and circumduction. Three treatments were studied: (1) PRC, distal radius hemiarthroplasty (RHA), and (3) total wrist arthroplasty (TWA) (Fig. 1 and Fig. 2).

Results: Results of this study demonstrated that following PRC there is a significant increase in wrist extension (9.3 ± 5.3°, p = 0.018) during the flexion/extension task without changes in wrist flexion or radioulnar deviation. Following the RHA, there were significant measurable changes in wrist motion. Following TWA, there was a significant decrease in flexion of the wrist (12.2 ± 7.0°, p = 0.018) compared with the native wrist, with no other significant changes in range motion.

With respect to muscle-tendon unit moment arms, there were no significant changes in muscle moment arms for the major wrist flexor and extensor muscles, suggesting that the center(s) of rotation of the wrist did not change following reconstruction motion procedures in comparison to the normal wrist. The reconstructive procedures were unable to duplicate normal-wrist dart thrower's motion or circumduction (Fig. 3).

Conclusion: The conclusion of this study is that none of the reconstructive wrist procedures are able to duplicate the normal kinematics of the wrist. However, TWA had the least variability in comparison between specimens tested, and the center(s) of wrist range of motion changed the greatest (distal to proximal location) after PRC.

Fig. 1 Example of experimental set up.

Fig. 2 Schematic of wrist motions to be tested. (A) Abduction/Adduction (B) Flexion/Extension (C) Circumduction (D) Dart thrower's motion (18,19).

Fig. 3 Example specimen of instantaneous helical axis computation during radial/ulnar deviation. Solid blue line = trajectory of intact hand. Solid red line = trajectory of hand with TWA. Blue/Green gradient = instantaneous helical axis transition from radial to ulnar deviation. Red/Yellow gradient = instantaneous helical axis transition from radial to ulnar deviation. (A) Dorsal View, PRC (B) Lateral View, PRC (C) Dorsal View, RHA (D) Lateral View, RHA (E) Dorsal View, TWA (F) Lateral View, TWA.