By: 25 October 2011

Salineros MJ, Crowninshield RD, Laurent M, Wimmer MA, Jacobs JJ.
Clin Orthop Rel res 2007 (465) 140-149

Approximately one million total hip arthroplasty procedures are performed worldwide each year. Polyethylene is still the main bearing material used. Wear debris from polyethylene has been implicated in aseptic loosening and this has lead to the development of highly cross-linked polyethylene. This study assessed material loss due to clinical wear in highly cross-linked polyethylene and ultra high molecular weight polyethylene sterilised in air or nitrogen. Components retrieved at revision surgery made from three different types of polyethylene were studied.

All had been in vivo for at least 12 months. All had been implanted in the same shell system. Forty six components were analysed with an average implantation of 37 months. Twelve were made from ram-extruded GUR 4150 polyethylene sterilised with gamma irradiation in air, 23 from compression moulded GUR 1050 sterilised with gamma irradiation in nitrogen, 11 were from highly cross-linked polyethylene sterilised with electron beam irradiation.

The average total damage was highest for the gamma in air group and lowest for the highly cross-linked group. Pitting, scratching and burnishing were least severe in the highly cross-linked group and most severe in the gamma in air and gamma in nitrogen groups. Annual wear and creep socket volume change was highest in the gamma in air group and lowest in the highly cross linked group. Overall average wear was lowest for the highly cross-linked group compared to the other two groups (p=0.001).

They conclude that the three generations of polyethylene studied showed progressive improvements in annualised wear and that highly cross-linked polyethylene shows less mechanical damage with similar in vivo use than earlier generation materials.