To Örebro University

Purpose: A biomechanical functional assessment was performed on a newly designed wrist hemiarthroplasty implant with aimed to identifying differences between the native wrist and wrist following the hemiarthroplasty procedure with (Hemi+PRC) and without a proximal row carpectomy (Hemi).

Methods: Six cadaveric wrists were mounted on a custom testing fixture and underwent a series of functional tests to investigate differences in range of motion, muscles moment arms, and axis of rotation between the intact and post-operative wrists. The tested movements included manually-driven flexion-extension, radial-ulnar deviation, dart throwers motion, and circumduction.

Results: The only significant change in range of motion was a decrease in flexion between the intact (77.75±14.40°) and both the Hemi (65.97±17.72°) and Hemi+PRC (60.08±17.18°) conditions. Minor differences in the mean position and variability of the axis of rotation's piercing point were identified. A statistically significant decrease in the flexion moment arm of the flexor carpi radialis was identified between the intact (16.1±2.6mm) and Hemi+PRC (14.0±3.4mm) conditions. Statistically significant decreases were also identified in the radial deviation moment arms of the extensor carpi radialis brevis' between the intact (15.3±7.8mm) and Hemi+PRC (7.3±12.5mm) conditions and the flexor carpi radialis' between the intact (15.3±3.2mm) and Hemi (12.0±5.7mm) conditions as well as in the ulnar deviation moment arm of the extensor carpi ulnaris between the intact (34.9±11.3mm) and Hemi (13.2±21.9mm) conditions.

Conclusions: While some statistically significant functional changes were identified between the native and hemiarthroplasty wrist, the findings suggest that post-operative function is equally acceptable in hemiarthroplasty with and without resection of the proximal carpal row. © 2018 World Scientific Publishing Company.