A comparison of glenoid components cemented in two different materials using real-time tracking of rocking-horse loosening after total shoulder arthroplasty
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The loosening of the glenoid component after total shoulder arthroplasty is believed to be related to the cyclic off-center loading of the humeral head on the glenoid (rocking-horse effect). The goal of this study was to biomechanically test rocking-horse loosening of glenoid components cemented into Sawbone material and compare the results to previously obtained data of glenoid components cemented into cadaver scapulae. The data from both materials was delivered using the same test system that tracked both micromotion and subsidence of the glenoid component in real-time throughout testing, based off the ASTM F2028 testing apparatus. A comparison of the subsidence data from the Sawbone constructs to that of the cadaver constructs indicated that there is no significant difference in subsidence between the two materials. After 50,000 cycles, the average subsidence of the glenoid in the cadaver bone was not significantly different to the subsidence of the glenoid in the Sawbone constructs. When comparing the micromotion of the glenoid in the Sawbone constructs to the cadaver constructs there was only a significant difference in the distraction of the inferior edge of the glenoid when the humeral head is in the max superior position after 10,000 cycles. In all cases there was an abrupt initial increase in the compression and distraction displacements of the glenoid, followed by slower increase that reaches a plateau as the cycle count increased. The post hoc statistical analysis also showed that after 1,000 cycles there is no significant difference in the compression and distraction displacements of the glenoid as the cycle count reaches 50,000 cycles. After 1,000 cycles the displacement of the glenoid in both the Sawbone and cadaver constructs reaches its plateau.