Cracking and Impingement in Ultra–High-Molecular-Weight Polyethylene Acetabular Liners

The purpose of this study was to determine the prevalence of crack formation in conventional ultra–high-molecular-weight polyethylene cups and its association with rim impingement, oxidation, and time in situ. One hundred twenty acetabular cups were retrieved during revision total hip arthroplasty. In 40% (48/120) of the retrieved specimens, multiple subsurface cracks of several millimeters in length were revealed by transillumination. In 5 specimens, full thickness cracks led to fragmentation of the liner before revision. Thirty-eight (32%) liners had regions of moderate to severe impingement damage to the rim; cracks were initiated at the site of impingement in all but 1 liner (P < .0001). Cracks commonly occur in conventional ultra–high-molecular-weight polyethylene liners, often after neck impingement and almost always in association with oxidation of the polymer.