Observations on retrieved humeral polyethylene components from reverse total shoulder arthroplasty

Abstract

Analyses of polyethylene components retrieved at revision of total knee, hip, and shoulder replacements have been used to study the effect of design, patient, and surgical factors on initial implant performance, but no studies have reported similar types of findings in retrieved humeral polyethylene components in reverse total shoulder arthroplasty. Our hypothesis is that while the conforming surface of the humeral polyethylene may predispose it to surface wear modalities, as seen in total hip arthroplasty, the presence of clinical instability may also increase the occurrence of focal contact stresses leading to subsurface fatigue failure. Fourteen humeral polyethylene components were retrieved from revision surgery at a single institution. Each polyethylene was analyzed for 9 modes of damage in each of 4 quadrants into which the bearing surface was divided. For each implant, the most recent radiographs before removal were scored using an adapted radiolucency score, and glenosphere positioning was measured. Despite the short mean length of implantation (0.46 ± 0.5 years), scratching and abrasion were seen in 14 and 13 components, respectively, followed by third-body debris and pitting. The modes of damage observed were most severe in the inferior quadrant of the humeral polyethylene. Scapular notching, glenoid, and humeral radiolucencies were prevalent on preoperative radiographs, but their long-term significance has not yet been elucidated. Increased glenosphere inclination was associated with decreased superior and total glenoid radiolucency, along with total polyethylene wear scores. Promising early, functional results with the use of reverse total shoulder arthroplasty has led to the increased expansion of its use, but high complication and revision rates continue to raise concerns regarding implant longevity. The presence of a clinical, adduction deficit may predispose patients to inferior quadrant polyethylene wear. Impingement of the humeral polyethylene at the lateral edge of the scapula leads to inferior quadrant wear and associated polyethylene failure, and implant instability may predispose the components to fatigue wear mechanisms. Analysis of retrieved humeral polyethylene components, along with patient, design, and surgical factors, provide important information on the causes of component failure.