Optimization of glenoid fixation in reverse shoulder arthroplasty using 3-dimensional modeling

BackgroundReverse shoulder fixation complications may be related to how much glenoid bone is removed and how the fixation screws are located in the glenoid. The purpose of this study was to determine how much bone volume and surface area are lost with incremental reaming and to evaluate screw fixation.MethodsA contemporary reverse shoulder implant was virtually implanted into models of 6 different shoulders following initial and then after additional incremental reaming was performed. Changes in the glenoid bone surface area and volume available for fixation were statistically evaluated using repeated measures ANOVAs.ResultsThe total bone volume, the amount of reamed glenoid surface area available for an implant baseplate, and the actual amount of the glenoid in contact with a baseplate decreased with increasing amounts of reaming. With 5 mm of reaming, the total volume decreased by 2810 mm3, the reamed glenoid surface area decreased by 28%, and the amount of the glenoid in contact with the baseplate decreased by 27%. The amount of engagement of anterior and posterior screws was much less than that of the superior and inferior screws.ConclusionCareful reaming of the glenoid surface is critical, because as little as 1 extra millimeter of bone removal decreases the amount of bone available for implant fixation. After reaming there may not be enough bone to accommodate anterior and posterior screws with the design used in this study.