Adaptation of scapula lateral rotation after reverse anatomy shoulder replacement

Scapula motion is significant for support of the arm and stability of the shoulder. The effect of the humeral elevation on scapular kinematics has been well investigated for normal subjects, but there are limited published studies investigating adaptations after shoulder arthroplasty. Scapula kinematics was measured on 10 shoulders (eight subjects) with a reverse total joint replacement. The measurements were performed using an instrumented palpating technique. Every subject performed three simple tasks: abduction, elevation in scapula plane and forward flexion. Results indicate that, lateral scapula rotation was significantly increased (average of 24.42% over the normal rhythm) but the change was variable. Despite the variability, there is a clear trend correlating humeral performance with increased rotation (R2 0.829). There is clearly an adaptation in lateral scapula rotation in patients with shoulder joint replacement. The reason for this is unclear and may be related to joint pathology or to muscle adaptation following arthroplasty.