The effect of glenoid bone loss on reverse shoulder arthroplasty baseplate fixation

Background Glenoid bone loss is commonly observed during primary and revision reverse shoulder arthroplasty. Glenoid baseplates are often implanted with incomplete glenoid bone support. The purpose of this study was to evaluate the glenoid component fixation of the glenoid baseplate with variable amounts of incomplete coverage. Methods Twenty-eight polyurethane trabecular bone surrogates were instrumented with the same center screw–type glenoid baseplate with 4 peripheral 5.0-mm locking screws in a glenoid bone loss model consisting of 25%, 50%, 75%, and 100% coverage. Each construct was tested through a 55° arc of motion with both compressive and shear forces across the glenosphere. Baseplate micromotion was recorded throughout 10,000 cycles for each model. Results There was no significant difference in baseline micromotion between the 4 experimental groups ( P = .099). In the 25% baseplate coverage group, 3 of 7 exhibited micromotion above the 150-μm threshold (624.5, 469.1, and 712.1 μm) during cyclic loading. After 10,000 cycles of loading, the 25% coverage group exhibited significantly more micromotion than the 50% ( P = .049), 75% ( P = .026), and 100% ( P = .040) coverage groups. There was no significant difference between the 100%, 75%, and 50% coverage groups ( P = 1.00). Conclusions Glenoid baseplate fixation in the setting of glenoid bone loss is no different when 50%, 75%, or 100% of the baseplate is supported by glenoid bone. Bone loss resulting in only 25% coverage results in significantly greater micromotion, often above the 150-μm threshold.