WEAR BEHAVIOR OF AMC CERAMICS ON PE IN HIP PROSTHESES

Abstract

The introduction of ceramics in total hip arthroplasty contributed significantly to the wear reduction of poly-ethylene and in consequence reduced osteolysis and loosening. This great benefit has been demonstrated in several clinical observations. In a recent study from Norway, the wear of a 28mm alumina and a CrCo ball head against Ultra High Molecular Weight Polyethylene (UHMWPE) after 10 years is compared using the RSA method of wear measurement.

It was concluded that the considerable reduced wear for ceramic ball heads in comparison to CrCo ball heads is a great advantage in hip arthroplasty.

A first prospective, randomized study with a 15 years follow up has been presented recently in the EFORT 2009. The comparison of wear of polyethylene between alumina and metal ball head shows a reduction of 44% penetration (linear wear) with the alumina-polyethylene bearing surface. In order to offer improved mechanical resistance and tribological qualities than alumina whilst maintaining structural stability, a new generation of alumina matrix composite (BIOLOX^®delta) has been used in orthopedics since 2001. The topic of this study is to demonstrate the excellent wear performance of the alumina ceramic composite against polyethylene, compared to alumina/PE in vivo.

Methods: The BIOLOX^®delta-PE bearing has been tested on a six station hip simulator (Endolob, Rosenheim) according to ISO/DIS 14242. The newborn calf serum was replaced every 0.5 million cycles and the test was stopped after 5 million cycles. Weight was measured using a high precision balance (Sartorius BP 211D)

Results and Discussion: After 5 million cycles, the insert surface appeared polished with fine scratching on the whole contact area. The wear rates calculated by linear interpolation were 13,52 mg per million cycles. (Standard deviation 0,60). The wear rate measured for BIOLOX^®delta against UHMWPE was 13,52 mg per million cycles.

In general, the wear rate can be regarded as small compared to other hip simulator tests using ceramic against polyethylene couplings. When comparing the results for BIOLOX^®forte on polyethylene with the same 28mm diameter and same testing parameter, we observed 26,57 +/− 3,55mg/million and 16,08+/−2,31 mg/million, respectively. The BIOLOX^®delta on UHMWPE bearing shows improved wear behavior with a much lower wear rate.

Conclusion: This study demonstrates the very low in vitro wear of the Alumina ceramic composite on UHMPE compared to ball heads made of pure alumina. Based on this results and the clinical performance of the alumina-UHMPE bearing from the literature, we can expect a further reduction of wear for the BIOLOX^®delta on UHMWPE in vivo that will increase the survival rate of the total hip arthroplasty.