Influence of Rotator Cuff Integrity on Loading and Kinematics Before and After Reverse Shoulder Arthroplasty

TL;DR

This study uses a validated musculoskeletal model to analyze how rotator cuff tears and reverse shoulder arthroplasty affect joint forces and shoulder kinematics, revealing increased compression forces that could impact implant longevity.

Contribution

It introduces a finite-element shoulder model to simulate rotator cuff tears and reverse prosthesis effects, providing detailed insights into joint forces and kinematics.

Findings

Reverse prosthesis increases joint reaction forces, especially with a functional cuff.

Massive rotator cuff tears lead to lower joint reaction forces.

Higher compression forces may elevate wear and fracture risks.

Abstract

Reverse Shoulder Arthroplasty (RSA) has become a very common procedure for shoulder joint replacement, even for scenarios where an anatomical reconstruction would traditionally be used. In this study, we investigate joint reaction forces and scapular kinematics for rotator cuff tears of different tendons with and without a reverse prosthesis. Available motion capture data during anterior flexion was input to a finite-element musculoskeletal shoulder model, and muscle activations were computed using inverse dynamics. The model was validated with respect to in-vivo glenohumeral joint reaction force (JRF) measurements, and also compared to existing clinical and biomechanical data. Simulations were carried out for the intact joint as well as for various tendons involved in a rotator cuff tear: superior (supraspinatus), superior-anterior (supraspinatus and subscapularis), and superior-posterior (supraspinatus, infraspinatus and teres minor). Each rotator cuff tear condition was repeated after shifting the humerus and the glenohumeral joint center of rotation to simulate the effect of a reverse prosthesis. Changes in compressive, shear, and total JRF were analysed, along with scapular upward rotation. The model compared favourably to in-vivo measurements, and existing clinical and biomechanical knowledge. Simulated JRF lie in the ranges of in-vivo JRF measurements and shows a linear increase past 90 degree flexion. Implanting a reverse prosthesis with a functional rotator cuff or with an isolated supraspinatus tear led to over 2 times higher compressive force component than with massive rotator cuff tears (superior-anterior or superior-posterior). Such higher compression forces might increase the risk of wear and implant fracture.