Preoperative Planning Software Does Not Accurately Predict Range of Motion in Reverse Total Shoulder Arthroplasty

Background: The purpose of this study was to determine whether preoperative planning software (PPS) accurately predicts clinical range of motion (ROM) in patients with reverse total shoulder arthroplasty 1 year postoperatively with preoperative and postoperative computed tomography (CT) scans. Methods: This was a retrospective study of 16 reverse total shoulder arthroplasty patients with preoperative and postoperative (CT) scans obtained at least 1 year postoperatively. Clinical ROM was measured in abduction, external rotation at resting abduction, extension, and flexion at a minimum of 1 year postoperatively. All clinical measurements were obtained before generation of PPS ROM values. Using postoperative CT scans, the achieved implant component positions were quantified and then replicated in PPS on the preoperative CT scans. The preoperative predicted ROM was then recorded, both with and without osteophyte removal. Bland-Altman plots were generated within each motion comparing the differences between clinically measured motion and software-predicted motion. Results: The variation in clinically measured ROM in abduction, external rotation at resting abduction, extension, and flexion were 118 +/- 27 (65 degrees to 180 degrees), 33 +/- 16 (10 degrees to 75 degrees), 56 +/- 8 (50 degrees to 65 degrees), and 137 +/- 25 (80 degrees to 160 degrees), respectively. Clinically measured motion differed greatly from PPS-predicted ROM, with mean differences of 33 +/- 29 (-32 to 93) for abduction, 44 +/- 25 (-38 to 57) for external rotation, 44 +/- 25 (-35 to 65) for extension, and 54 +/- 50 (-51 to 147) for flexion with no significant correlations between clinically measured and PPS-predicted ROM (P > 0.05). With humeral or humeral and glenoid osteophyte resection, correlations for only flexion became significant (P = 0.002 for both). Conclusion: The passive glenohumeral impingement-free ROM generated from PPS incompletely predicts clinically measured active humerothoracic ROM, possibly because of the unmeasured factors of soft-tissue tension, muscular strength, humeral torsion, resting scapular posture, and, most importantly, scapulothoracic motion. Level of Evidence: IV.