ALUMINA/ALUMINA ARTICULATION: MIXING MATERIALS

Abstract

Introduction: Ceramic/ceramic articulation has a long history and is accepted as a low wear couple for total hip joint application. Due to the requirements for strength of the ball-head it may be necessary to combine products from different Alumina manufacturers.

Material and methods: Alumina components according to ISO 6474 for commercial hip joint prosthesis were obtained from 3 sources and subjected to a series of simulator tests up to 5 million cycles. Variations were the type of testing and the quality and type of the Alumina. Wear tests were performed with two different types of simulators and different protocols also including micro-separation testing. Wear was characterised by weight loss, change in surface appearance and particle analysis.

Results: Standard wear testing yielded very low wear rates below 0.5 mm3 per million cycles for the Alumina combinations of the third generation with a running in period and a steady state wear after 1 million cycles. Increasing the inclination of the cup up to 60° did not increase the wear rate. Mixing the components from various sources did not affect the wear rate significantly. Micro-separation testing increased the overall wear rate significantly and showed clinical relevant patterns with grain pullout and grain relieve. After a running in period a steady state without “avalanche” effect was observed again. The particle analysis compared favourably with retrieval studies. Although the wear rate was lower for the mixed couples it was statistically not significant.

Conclusion: An improved test method for ceramics demonstrates clinically relevant wear in respect of amount, appearance and particle size. The new generation Alumina is more wear resistant and less sensitive to cup position and to micro-separation. Mixing of Alumina components from a single implant manufacturer does not change the low wear rates of ceramic/ceramic articulation and can, therefore, be applied.