Abstract
Purpose
Glenoid component loosening is a common reason for failed total shoulder arthroplasty. Multiple factors have been suggested as causes for component loosening that may be related to cement technique. The purpose of the study was to compare the load transfer across a polyethylene glenoid bone construct with two different cementing techniques.
Method
Eight cadaveric specimens underwent polyethylene glenoid component implantation. Four had cement around the pegs only (CPEG) and four had cement across the entire back (CBACK) of the implant including around the pegs. Step loading was performed with a pneumatic actuator and a non-conforming humeral head construct capable of applying loads at various angles. Strain gauges were placed at the superior and inferior poles of the glenoid and position trackers were applied to the superior and inferior aspects polyethylene component. Micro CT data were obtained before and after the loading protocol.
Results
During compressive loading, greater tension was recorded with the CBACK technique than with the CPEG technique. Compression was recorded superiorly when load was applied at 30 degrees while tension was recorded inferiorly. Greater displacement occurred with the CPEG group. Failure as defined on micro CT occurred more consistently with the CBACK technique than with the CPEG technique.
Conclusion
Tension measurements and upward deflection of the polyethylene with compressive loading at lower angles was unexpected. Early failure of fully cemented glenoids may be due to the fragility of the cement mantle around the periphery of the implant. Tension at the bone cement interface and early cement fracture are unfavorable and this may be a mechanism of implant loosening.
