Glenosphere baseplate stability with superior glenoid bone loss
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Superior glenoid wear is common in rotator cuff tear arthroplasty and can be a treatment challenge in reverse total shoulder arthroplasty (RSA). The purpose of this study was to characterize the migration and micromotion of glenosphere baseplates in response to physiologic loads with different size superior glenoid defects. The secondary goal was to assess the effectiveness of an augmented baseplate, designed with a backside wedge, to provide supplemental support and motion restraint within the glenoid bone defect condition. Solid rigid polyurethane foam was machined to a 33mm diameter cylinder to model the glenoid, and a superior wedge defect was created resulting in variable percentage of baseplate contact (100%, 90%, 75% and 50%) with the bone foam. Ten implanted glenosphere baseplate samples were tested with full baseplate contact and each of the bone loss models. The motion of the inferior and superior baseplate edges were monitored during testing via an array of three linear variable differential transformers (LVDTs). The migration and micromotion in both the superior/inferior (S/I) and medial/lateral (M/L) directions for the baseplate edges were calculated. In the second part of the study, an augmented baseplate was implanted in the 50% defect case and was tested using the same protocol. Analysis revealed that there was no statistical difference in any of the implant migrations. Additionally, there was no statistical difference in the M/L micromotion at the inferior baseplate edge in any of the testing scenarios. The M/L micromotion at the superior baseplate edge and the S/I micromotion of the baseplate were significantly higher in the 50% defect compared to all other groups at 5000 cycles. There were no statistical differences noted between any other groups. The augmented baseplate significantly reduced both M/L micromotion at the superior baseplate edge and S/I micromotion of the baseplate at cycle 5000 compared to the standard baseplate with 50% defect making it comparable to the motion of the baseplate with the full substrate contact. The presence of glenoid bone defects approaching 50% loss of baseplate contact has been shown here to significantly increase the baseplate micromotion. The use of an augmented baseplate for 50% defects decreased micromotion compared to the non-augmented baseplate restoring motion restraint similar to the fully supported non-augmented baseplate.