In Vitro Kinetic and Kinematic Analysis of a Recently Designed Total Wrist Implant.

PURPOSE: The purpose of this study was to compare wrist range of motion (ROM) and tendon forces before and after implantation of a recently designed total wrist arthroplasty (TWA). Our hypothesis was that following TWA, the ROM would decrease and the tendon forces increase.

METHODS: Six fresh-frozen cadaver wrists were moved using a wrist joint motion simulator by pulling on five wrist tendons through flexion/extension, radioulnar deviation, and three dart-throw motions arcs before and after TWA implantation. Maximum tendon forces were determined during each cyclic motion. Maximum passive flexion, extension, radial deviation and ulnar deviation were also determined.

RESULTS: Following TWA, the average total flexion/extension arc of motion was found to be 51° (34° flexion, 17° extension), and the total arc of radioulnar deviation was 21° (4° radial and 17° ulnar). When compared to native wrist motion, wrist extension, radial deviation, and ulnar deviation were significantly decreased by 46°, 12°, and 15°, respectively after TWA. Following implantation, during the passive wrist circumduction motion, impingement between the carpal and radial components occurred in four of the six wrists in radial deviation. No consistent large increases in tendon forces were observed; however, small-to-moderate changes cannot be excluded because of limited statistical power.

CONCLUSIONS: We observed an overall decrease in ROM following TWA when compared to the native wrists. Some of the loss in motion may be attributed to increased soft tissue tension following capsular repair, technical issues during implantation, implant orientation, or implant design. Further studies with larger sample sizes are needed to better characterize potential small-to-moderate tendon force changes after implantation.

CLINICAL RELEVANCE: This study provides kinetic and kinematic data for a recently designed total wrist implant that can help improve our understanding of how these implants function and how they may succeed or fail.