Abstract
The reported revision rate of total hip arthroplasties (THAs) due to wear and osteolysis is around 10% at 10 years. However, the actual rate is probably higher: the incidence of osteolysis is reported to be 10% to 45%. Apart from design improvements, improved or new materials and/or and combinations are important in reducing particle-induced osteolysis, especially in young and active patients.
Wear reduction of up to 40% after inert gas sterilisation of polyethylene (PE) has been demonstrated, both in vitro and in vivo. An effective means of providing further increases in wear resistance is to cross-link PE extensively. Early clinical results of non-melt-annealed PE at three years showed wear reduction of up to 85% compared to inert gas radiation-sterilised PE.
In hip joint simulator investigations, bearings with a ceramic ball-head articulating against a composite cup demonstrated wear rates similar to those of ceramic-ceramic bearings. The wear particles are benign. Clinical data collected over two years suggest no disadvantages compared to the standard articulation controls.
The wear resistance of alumina-alumina articulation has been enhanced. In-vitro investigation demonstrated that even with a cup inclination of 60° the wear rate is not increased. The effect of micro-separation of the artificial joint is also minimised. Several prospective multi-centre alumina-alumina studies have shown no additional complications with this articulation. However, alumina is a brittle material with an inherent risk of fracture. The addition of 25% zirconia to alumina (ZTA) in the manufacturing process improves its fracture resistance, increasing its strength by more than 50%, while maintaining its other properties. The wear properties of ZTA are even better than that of alumina, especially in micro-separation articulation mode.
Highly cross-linked and optimised PE and composite technology are promising concepts in address wear particle-induced osteolysis.
The abstracts were prepared by Professor M.B.E. Sweet. Correspondence should be addressed to him at PO Box 47363, Parklands, Johannesburg 2121, South Africa.
