LAUSR

BACKGROUND While reverse shoulder arthroplasty (RTSA) has excellent reported outcomes and satisfaction, patients often have postoperative limitations in range of motion (ROM), specifically internal rotation. Increased lateralization is thought to improve ROM following RTSA. The purpose of this study was to evaluate the association between radiographic measurements of lateralization and postoperative ROM and clinical outcome scores following RTSA. The authors hypothesized that increased radiographic lateralization would be associated with improved postoperative ROM, specifically internal rotation, but have no significant association with clinical outcome scores. METHODS Patients who underwent RTSA with a 135° neck shaft angle prosthesis and minimum 2 year clinical and radiographic follow-up were included and retrospectively reviewed. Postoperative radiographs were evaluated for several lateralization measurements including the lateralization shoulder angle (LSA), distance from lateral border of acromion to lateral portion of glenosphere, distance from the glenoid to the most lateral aspect of the greater tuberosity and the distance from the lateral aspect of acromion to the most lateral aspect of the greater tuberosity. Linear regression analyses were utilized to evaluate the independent association of each radiographic measurement of lateralization on forward flexion (FF), external rotation (ER), internal rotation (IR) and the American Shoulder and Elbow Surgeons (ASES) index score at 2 years postoperative. Receiver operator curves (ROC) were constructed to identify and significant thresholds of each radiographic lateralization measurement. RESULTS 203 patients were included. For internal rotation, a greater LSA (p=0.007), shorter acromion to glenosphere distance (meaning more glenoid lateralization) (p=0.005) and a greater acromion to greater tuberosity distance (with the tuberosity more lateral to the acromion) (p=0.021) were associated with improved IR. Overall, ROC analysis demonstrated very little significant data, the most notable of which was the LSA, which had a significant cutoff of 82 degrees (sensitivity 57%, specificity 68%, p = 0.012). CONCLUSION Of the numerous radiographic measures of lateralization after RTSA, the LSA is the most significantly associated with outcomes, including improved internal rotation, and a decrease in forward flexion and ASES score. The clinical significance of these statistically significant findings requires further study, as the observed associations were for very small changes that may not represent clinical significance.