The effects of glenoid component alignment variations on cement mantle stresses in total shoulder arthroplasty.

Loosening of the glenoid component has been cited as the most frequent cause of patient dissatisfaction with total shoulder arthroplasty, and it has been demonstrated in clinical studies that misalignment of the prostheses can be a causative factor. Finite element analyses of five different glenoid component alignments (central, anteverted, retroverted, inferiorly inclined, and superiorly inclined) were conducted in order to predict changes in the survivability of the cement mantle surrounding the glenoid component. The potential for mechanical failure of the mantle in the centrally aligned implant, during unloaded abduction, was seen to be lower than for any other alignment. Normal bone outperformed simulated rheumatoid models in all cases. Retroversion was worse than anteversion, and superoinferior misalignment was worse than anteroposterior. The quality of the supporting bone stock was found to be particularly significant to cement survivability, more so than the occurrence of eccentric loading of the joint. Shear forces acting on the glenoid component were found to be more detrimental than axial forces, resulting in a greater likelihood of failure toward the extremes of motion. The study suggests that significant efforts should be made to align the glenoid component correctly and also to ensure suitably consistent support of the prosthesis within the bone.