Early Failure of a Cross-Linked Polyethylene Acetabular Liner

The use of highly cross-linked ultra-high molecular weight polyethylene in total hip arthroplasty has become a popular alternative to the use of conventional polyethylene. Evaluations with use of hip simulator tests1-4 and clinical evaluations of total hip replacements5-10 have independently shown that polyethylene materials processed with gamma irradiation followed by melting or annealing have extremely low wear rates. However, it also has been demonstrated that such cross-linking processes may reduce the fracture toughness and resistance to fatigue crack propagation of polyethylene11-16. Bradford et al.14 found that retrieved cross-linked polyethylene acetabular liners exhibited surface cracking that had not been predicted by in vitro hip simulator studies. Tower et al.17 observed fatigue failure at the superior aspect of the rim of four retrieved highly cross-linked acetabular bearings. They concluded that the factors contributing to these failures included thin polyethylene at the cup rim, a relatively vertical cup alignment, and compromised material properties of the cross-linked polyethylene in comparison with conventional polyethylene. In the current case report, we describe the failure of a highly cross-linked polyethylene acetabular liner less than three years after implantation. We believe that the mechanisms of failure were fracture of the cross-linked polyethylene where it was thin along the locking groove and abnormal loading of the cup because of improper seating of the liner in the shell at the time of the original procedure. This study was conducted with institutional review board approval and in compliance with HIPAA (Health Insurance Portability and Accountability Act) requirements at our institution.