Association between dislocation, impingement, and articular geometry in retrieved acetabular polyethylene cups

We used a novel analysis technique and retrieved acetabular polyethylene liners to investigate relationships between impingement damage, dislocation history, and polyethylene liner geometry. Forty‐eight polyethylene liners with neutral rim elevation were visually assessed for peripheral rim damage consistent with impingement between the liner rim and femoral component. Liner articular geometry was measured using a digital stylus, and the geometric relationships between the liner rim and center of the femoral head were characterized by lip height, head center inset, and head penetration into the polyethylene liner. Thirteen (27%) retrieved liners had rim impingement damage and 12 (25%) had a history of dislocation. The proportion of liners with impingement was not significantly different among dislocated and stable liners. Lip height, head center inset, and head penetration were not significantly different between liners with and without impingement damage. Dislocated liners had a significantly shorter head center inset, with significantly less head penetration because of shorter functional duration. Designing polyethylene liners with a sufficiently deep articular surface that exceeds 0.95 mm may prove beneficial for decreasing the prevalence of early dislocation, independent of impingement damage.