Prognostic radiological factors affecting clinical outcomes of reverse shoulder arthroplasty in the Korean population

Background: Despite the growing use of reverse shoulder arthroplasty (RSA), it is associated with relatively frequent complications and uncertain clinical outcomes. We investigated radiological factors affecting clinical outcomes of RSA in the Korean population. Methods: We evaluated physical findings, radiographic findings, visual analog scale scores for pain and satisfaction, and several functional scores in 179 consecutive patients who underwent RSA at two centers between 2008 and 2014. Results: In 146 included RSAs, pain and forward flexion improved with deltoid lengthening (average, 23.5 ± 9.1 mm; p = 0.039). External rotation decreased with medialization (average, 16.8 ± 6.0 mm, p = 0.025), whereas internal rotation showed no correlation with humeral retroversion. Scapular notching (n = 44, 30%) significantly decreased with greater inferior glenosphere overhang (average, 2.94 ± 3.0 mm; p = 0.001), greater prosthesis scapular neck angle (average, 104° ± 10.3°; p = 0.001), greater glenoid neck length (average, 9.8 ± 2.54 mm; p = 0.012), lower inferior baseplate tilt angle (average, 105.5° ± 9.2°; p = 0.009), and varus humeral neck-shaft angle (p = 0.046), and it did not affect ranges of motion and pain, satisfaction, and functional scores. At the final followup, medialization was related to improvement in pain and satisfaction, and inferior glenosphere overhang to functional scores. Conclusions: Proper amount of deltoid lengthening (mean, 2.3 cm) and inferior glenosphere overhang (mean, 2.9 mm) should be chosen for the better outcomes, while the center of rotation should be individualized according to patient characteristics in the Korean population.