Reverse total shoulder arthroplasty baseplate stability with locking vs. non-locking peripheral screws

Background: There are many options for glenosphere baseplate fixation commercially available, yet there is little biomechanical evidence supporting one type of fixation over another. In this study, we compared the biomechanical fixation of a reverse total shoulder glenoid baseplate secured with locking or non-locking peripheral screws. Methods: Both a non-augmented mini baseplate with full backing support and an augmented baseplate were testing after implantation in solid rigid polyurethane foam. Each baseplate was implanted with a 30 mm central compression screw and four peripheral screws, either locking or non-locking (15 mm anterior/posterior and 30 mm superior/inferior). A 1 Hz cyclic force of 0-750 N was applied at a 60^o angle for 5000 cycles. Throughout the test, the displacement of the baseplate was measured using a 3D Digital Image Correlation System. Findings: The amount of migration measured in the both the non-augmented and augment cases shows no significant differences between locking and non-locking cases at the final cycle count (non-augment: 5.66 +/− 2.29 μm vs. 3.71 +/− 1.23 μm; p = 0.095, augment: 15.43 +/− 8.49 μm vs. 12.46 +/− 3.24 μm; p = 0.314). Additionally, the amount of micromotion measured for both sample types shows the same lack of significant difference (non-augment: 10.79 +/− 5.22 μm vs. 10.16 +/− 7.61 μm; p = 0.388, augment: 55.03 +/− 10.13 μm vs. 54.84 +/− 10.65 μm; p = 0.968). Interpretation: The presence of locking versus non-locking peripheral screws does not make a significant difference on the overall stability of a glenoid baseplate, in both a no defect case with a non-augmented baseplate and a bone defect case with an augmented baseplate.