Background: Despite the positive results in total shoulder arthroplasties (TSAs), a higher revision rate is documented compared with total hip and knee replacements. Wear is the possible main cause of TSA failure in the long-term. This study investigated the effect of joint kinematics and the influence of the rotator cuff on the polyethylene wear performance in an anatomic TSA.
Methods: Lifting a load of 2 kg with an abduction/adduction of 0° to 90° was simulated for 2 × 106 cycles as a primary motion using a fully kinematic joint simulator. A combined rotation in anteversion-retroversion of ±5° and ±10° was also simulated. The force in the superior-inferior direction and the axial joint compression were applied under force control based on in vivo data of the shoulder. A soft tissue restraint model was used to simulate an intact and an insufficient rotator cuff.
Results: The highest wear rate in the intact rotator cuff group was 58.90 ± 1.20 mg/106 cycles with a combined rotation of ±10°. When an insufficient rotator cuff was simulated, the highest polyethylene wear rate determined was 79.67 ± 4.18 mg/106 cycles.
Conclusions: This study confirms a high dependency of the polyethylene wear behavior and dimension on the joint kinematics in total shoulder replacement. This can be explained by an increasing cross-shear stress on the polyethylene component. The results obtained indicate that additional combined kinematics are an indispensable part of wear tests on anatomic shoulder replacements.
Keywords: Anatomic total shoulder arthroplasty; cross-shear; joint kinematic; rotator cuff; superimposed motion; wear rate.
Copyright © 2018 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Elsevier Inc. All rights reserved.