Alumina-on-Alumina Coupling with 36 mm Heads

Abstract

According to Charnley, the rationale to have a 22mm head is in reducing the friction torque and the volumetric wear.

This fact is absolutely true for metal-poly coupling and partially true also for ceramic-poly, but if we employ a ceramic-ceramic coupling, a diameter of heads of 36mm doesn’t increase the volumetric wear nor the friction torque, compared with a 22 mm metal-poly coupling.

On the other hand, a bigger diameter leads to more stable artificial joints and to a wider range of motion.

In the last two years we have developed and used an acetabular component, with a 36 mm liner-head alumina-alumina coupling.

We performed a perspective study to investigate the rate of dislocation of the prostheses in the first two month after operation.

We analysed two groups: the first one (225 cases, from March 2001 to December 2002, mean age 64 years and 9 months) in which 36 mm heads were implanted, and the second (151 cases, from January 2001 to December 2002, mean age 66 years and 9 months) in which the surgical technique was the same, but heads of 28 mm were used.

We compared the number of dislocations, 2 (0,88%) in the first group and 7 (4,63%) in the second, and the data confirmed that there is a statistically significant (p=0,020) decrease in dislocations in the group of 36 mm heads.