The scapulothoracic conundrum in reverse shoulder arthroplasty: where do we stand and what is yet to expand?

Abstract

The normal functioning of the shoulder is characterized by the harmonious coordination between the glenohumeral joint and the scapulothoracic complex, a phenomenon commonly referred to as scapulohumeral rhythm (SHR). Reverse total shoulder arthroplasty (rTSA) shoulders exhibit distinct kinematics compared to normal shoulders. Reduced scapulohumeral rhythm (SHR) in rTSA shoulders implies a greater reliance on scapulothoracic motion over glenohumeral motion for arm elevation. Dynamic analyses suggest heightened scapulothoracic movement after rTSA, implying alterations in rotational movements across various planes. Utilization of reliable tools to measure preoperative scapulothoracic motion and forecast postoperative SHR in rTSA may improve functional results. Posture types and scapulothoracic orientation play an important role in optimal implant configuration and positioning, as well as clinical outcome, and should therefore be considered during patient selection, preoperative planning, and implantation of an rTSA. Recognizing the static position and kinematic changes of the scapulothoracic joint is vital for postoperative rehabilitation and optimizing outcomes in rTSA patients.

Keywords: arthroplasty; kinematics; reverse shoulder; scapulothoracic biomechanics.

Figure 1

Illustration of scapular and glenohumeral elevation following reverse total shoulder arthroplasty, demonstrating the contribution of the scapulothoracic complex to postoperative joint kinematics.

Figure 2

(A) Illustrations and (B) three-dimensional CT images of patients with types A, B, and C posture show increasing scapular internal rotation, anterior tilt, protraction, and drooping, as well as kyphosis and a barrel-shaped chest. (Reproduced with permission from Moroder et al. (47)).