Polyethylene wear in retrieved reverse total shoulder components

Background Reverse total shoulder arthroplasty has been used to treat rotator cuff tear arthropathy and proximal humerus fractures, as well as for failed conventional total shoulder prostheses. It has been suggested that polyethylene wear is potentially higher in reverse shoulder replacements than in conventional shoulder replacements. The modes and degree of polyethylene wear have not been completely elucidated. The purpose of this study was to evaluate polyethylene wear patterns in 7 specimens retrieved at revision arthroplasty and identify factors that may be associated with increased wear. Methods Reverse total shoulder components were retrieved from 7 patients during revision arthroplasty for loosening and/or pain. Preoperative glenoid tilt and placement and scapular notching were evaluated by use of preoperative radiographs. Polyethylene wear was evaluated via micro–computed tomography and optical microscopy. Results Wear on the rim of the polyethylene humeral cup was identified on all retrieved components. The extent of rim wear varied from a penetration depth of 0.1 to 4.7 mm. We could not show a correlation between scapular notching and rim wear. However, rim wear was more extensive when the inferior screw had made contact with the liner. Metal-on-metal wear between the humeral component and the inferior screw of 1 component was also observed. Wear of the intended bearing surface was minimal. Discussion Rim damage was the predominant cause of polyethylene wear in our retrieved specimens. Direct contact between the humeral component and inferior metaglene screws is concerning because this could lead to accelerated ultra-highmolecular weight polyethylene wear and also induce mechanical loosening of the glenoid component.