Implant wear and osteolysis with a hydroxylapatite-coated screw cup.

Radiographs of 72 uncemented hip implants with a mean follow-up of 6.5 years were analysed to measure wear of the implant. The wear rate was measured using the modified technique of Livermore and was found to be 0.13 mm per year (CI 95% 0.080-0.18). There was no statistical correlation between wear and age, gender and cup angle, but there was a correlation between wear and the number and size of cysts. This has not been previously published. In view of the risk of loosening and of a dramatic increase in the rate of wear when the femoral head articulates with the metal backing, it is important to plan revision of these cups in good time and to ensure regular radiographic surveillance of these patients.