Shoulder joint angles in supine and upright imaging of the preoperative reverse total shoulder arthroplasty patient.

Background: Reverse total shoulder arthroplasty is a common procedure for end-stage glenohumeral arthritis, rotator cuff disease, fracture, or failed arthroplasty. Preoperative planning software allows surgeons to assess implant placement and relies on imported bone models that come from imaging, typically a supine computed tomography (CT) scan. However, daily activities are performed upright. This study quantified the differences in scapulothoracic and glenohumeral joint angles between preoperative supine and upright imaging. Methods: Seven patients underwent preoperative supine CT and upright biplane fluoroscopy imaging. Scapulothoracic and glenohumeral joint angles in supine and upright poses were calculated using Euler angles and compared using 2-sided paired Results: The scapula was 9.3 ± 12.9° more downward rotated in the upright pose than supine ( Conclusion: Patient-specific variation in joint angles between supine and upright poses demonstrates gross changes in both magnitude and direction that exceed common thresholds in implant selection and placement. Thus, preoperative planning using supine CT may inaccurately pose bones, with consequent effects on the surgical plan, the resultant shoulder biomechanics, and clinical outcomes. Preoperative planning software should consider the influence of supine posture when orienting bones for surgical planning.