The Causes of Femoral Head Roughening in Explanted Charnley Hip Prostheses

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Abstract
The effect of particles of first, acrylic bone cement containing either barium sulphate or zirconium dioxide as X-ray contrast media, and secondly, particles of fresh cortical bone, on a surgical grade stainless steel surface against which polyethylene was rubbing, has been investigated. It was found that under physiological loads, particles of acrylic cement which have been embedded in the polyethylene bearing surface caused severe scratching of the stainless steel. Some scratches were found to have pronounced lips similar to those observed on the femoral heads of explanted Charnley hip prostheses. Cortical bone produced only slight damage to the stainless steel. In the case of the acrylic cements, the abrasive constituent was isolated and found to be clusters of particles of the X-ray contrast medium. Particles of acrylic cement are frequently observed embedded in the wear surfaces of explanated Charnley acetabular cups and these particles have also been found to contain clusters of X-ray contrast medium particles. It is therefore concluded that the damage to implanted stainless steel prostheses is predominantly caused by the X-ray contrast medium in the acrylic cement.