Comparison of range of motion between 2-year clinical outcomes and predictions of a static scapula preoperative planning software for reverse shoulder arthroplasty

Preoperative planning has gained popularity in the management of reverse shoulder arthroplasty (RSA). Commercially available software provides three-dimensional segmentation of scapula and humerus, as well as providing arc of motion for the implanted articulation and identifying potential areas of bony impingement. However, these software algorithms utilize a fixed scapula model, disregarding the preoperative clinical range of motion of the patient, be it glenohumeral or scapulothoracic, as well as any soft tissue parameters. This study aims to compare the range of motion based on preoperative planning software by using the implant position from postoperative computed tomography (CT) images (P-ROM), with the clinical range of motion (C-ROM) assessed at minimum of 2 years follow-up. Pre- and postoperative CT scans of 46 patients who underwent primary RSA between 2017 and 2021 were analyzed. At the postoperative two-year review, each patient was assessed for active range of motion. Implant size and position based on operative notes and postoperative CT scans were used to replicate the performed surgery in the planning software. Abduction, flexion, and external rotation motion were simulated and recorded. The relationship between C-ROM and P-ROM was investigated using linear regression analysis, Pearson correlation coefficient and paired T-test. P-ROM was significantly lower than C-ROM at two years postoperatively (p <0.001), with an average discrepancy of 78º in abduction, 47º in flexion, and 37º in external rotation (C-ROM: abduction 155º±21º, (80º-180º); flexion 160º±17º, (90º-180º); external rotation 52º±14º, (10º-80º) versus P-ROM: abduction 77º±13º, (53º-107º); flexion 112º±25º, (67º-180º); external rotation 15º±21º, (0º-79º). The linear regression analysis indicated weak agreement between C-ROM and P-ROM (abduction R2=0.03; flexion R2=0.01; external rotation R2=0.04). Pearson's correlation coefficients revealed weak correlations of -0.18, 0.03 and 0.21 for abduction, flexion, and external rotation. P-ROM based on preoperative software in its current form does not allow the prediction of the C-ROM at two-years follow-up for patients undergoing RSA.