Introduction: In total hip arthroplasty (THA) polyethylene (PE) wear debris is major cause of osteolysis and aseptic implant loosening. Wear particle volumes must be reduced to increase implant survival. Various ways of crosslinking the molecular chains of PE have been proposed to increase the wear resistance of the bearing material but prospective long-term follow-up studies are scarce.

Materials & Methods A crosslinked PE acetabular insert was developed by gamma irradiating in a nitrogen atmosphere at a dose of 3MRad and subsequent annealing at 50° C for 144 hours to promote further crosslinking (“Duration” process). The Duration PE was compared to a conventionally prepared PE insert (irradiated at 3 MRad in air, no annealing) in a series of small punch tests, a hip wear simulator study and in-vivo as part of a randomized double-blind clinical study at three medical centers the PE-insert being the only variable. A total of 127 patients with 133 inserts (67 conventional, 66 Duration) were followed up between three and five years post-operatively. Wear was measured yearly by using a computer-based image analysis system. Radiographic appearance of potentially wear related phenomena such as osteolysis or loosening was assessed by an independent reviewer.

Results: Higher load at break during the small punch test confirmed the elevated crosslinking levels of Duration PE against the conventional PE. In the joint simulator Duration PE showed significantly lower volumetric wear rates (Mean SD: 21.7 2.3 mm3/10E6 cycles) than conventional PE (39.7 1.5 mm3/10E6 cycles, p< 0.05). A corresponding and significant level of wear reduction for the Duration PE was identified in-vivo (Duration: 43.7 33.6 mm3/year, conventional: 60.4 42.7 mm3/year, p=0.04). Radiographic analysis at the last follow-up gave evidence of femoral osteolytic lesions in five hips with conventional PE inserts and only one hip with a Duration insert.

Conclusions: Acetabular inserts made of crosslinked PE using the Duration process can significantly reduce in-vivo wear rates and the occurrence of potentially wear related osteolytic effects in the long-term follow-up of THA patients. The reduced clinical wear rates corresponded well with the results from the wear simulator measurements. This suggests that a PE with further increased crosslinking which shows even lower wear rates in simulator studies will lead to even lower wear and associated osteolysis in long-term clinical application.