Observations on retrieved glenoid components from total shoulder arthroplasty

Hypothesis: Polyethylene components retrieved at revision of total knee and hip replacements have been analyzed to study the effect of design, patient, and surgical factors on initial implant performance, but few studies have reported similar types of findings in retrieved glenoids. Materials and methods: From 1979 to 2006, 78 glenoid components were retrieved from revision surgery in 73 patients at a single institution. Each glenoid component was analyzed for 9 modes of damage in each of 4 quadrants into which the bearing surface was divided. For each glenoid, the most recent radiographs before removal were scored using an adapted radiolucency score. Results: Scratching, pitting, and burnishing were the most common and most severe types of polyethylene wear. In addition, the modes of damage observed were not uniformly distributed across the bearing surface, but commonly focused in the inferior quadrant of the glenoid, suggesting a propensity for a humeral impingement mechanism leading to glenoid loosening. The radiographic analysis performed was found to severely underestimate the presence of clinical glenoid loosening. Conclusion: Impingement of the glenoid with bone at the edge of the humeral component and edge deformation secondary to eccentric forces of the humeral head on the glenoid rim are highly associated with glenoid loosening. Analysis of retrieved glenoid components, along with patient, design, and surgical factors, provide important information on the causes of component failure. Level of evidence: Basic science study.