A tribological study of retrieved hip prostheses.

One hundred Charnley cemented acetabular cups, 78 of which had the associated femoral stems, were obtained after revision surgery. Patient characteristics, which were obtained from hospital records, and roentgenographs showed that component loosening was the most common cause of failure. Examination of the acetabular cups revealed six categories of damage: socket erosion, rim wear, cement ingress, cratering, discoloration, and articulating surface scoring. Damage to the femoral stems was characterized by stem fracture and roughening of the femoral head. The latter was predominantly caused by the roentgenographic contrast medium within the acrylic cement scratching the articulating surface. The amount of wear, in terms of the penetration of the femoral head into the acetabular cup, could be measured in 87 cases. The mean penetration was 1.69 mm and the mean penetration rate was 0.21 mm per year with a range from less than 0.005 mm to 0.6 mm per year. It was shown that within this group, a high penetration rate precludes a long service life. It is therefore likely that reducing the rate of wear would improve the performance of the artificial hip joint.