Optimal rotation and screw positioning for initial glenosphere baseplate fixation in reverse shoulder arthroplasty

Abstract

Critical to the longevity of the reverse shoulder arthroplasty is initial rigid fixation of the glenosphere, determined in part by baseplate screw fixation. We studied screw fixation in baseplates placed in several different orientations. Twelve, lightly-embalmed adult scapulae were implanted using a variable-angle and a fixed-angle baseplate. Baseplates were placed in three rotational positions: 1) 12/6 o'clock, 2) 20 degrees rotation toward the coracoid, and 3) 20 degrees rotation toward the scapular spine. Superiorly, perpendicular screws for the variable-angle baseplate in the 12 o'clock (39.7 mm) and coracoid (37.7 mm) position and angled screws in the coracoid position (37.5 mm) were found to be the longest. Inferiorly, screws holes made perpendicular to the baseplate yielded the longest screw lengths (37.4 mm), while inferiorly angled screws were shorter, especially in the anterior-inferior glenoid (16.8 mm). Overall, baseplate rotation toward the spine yielded the lowest mean screw lengths. Proper initial rotation of the baseplate and screw orientation can optimize initial fixation of the glenosphere in reverse shoulder arthroplasty. Level IV, Case Series, Treatment Study.