Ceramic–ceramic coupling with big heads: clinical outcome

摘要

The wear and the friction torque are proportional to the head diameter in THA. That is the reason why, in the past, according to Charnley’s “low friction arthroplasty”, the head diameter was as small as possible employing metal–polyethylene coupling. On the contrary with ceramic–ceramic, the head diameter raise does not increase in a considerable way neither the wear rate nor the friction torque. A bigger diameter head leads to a more stable artificial joint and to a wider range of motion. An acetabular component with a 36 mm liner-head ceramic–ceramic coupling has been developed and implanted since 2001. We performed a prospective study to investigate the dislocation rate of this new prosthesis in the first 2 years after the operation. We matched two groups of patients, comparable in diagnosis and age: the first one (370 cases, from March 2001 to March 2004) in which 36 mm heads were implanted, and the second one (223 cases, from January 2001 to March 2004) in which 28 mm heads were used. The surgical technique (postero–lateral approach), the surgeons and the stems (cemented and uncemented) were the same. We compared the number of dislocations in the two groups. There were four dislocations (1.08%) in the first group and 10 (4.48%) in the second. The data confirmed that there was a statistically significant (P = 0.011) decrease of the dislocations in the group of 36 mm heads. Moreover, we are able now to evaluate the recurrent dislocations that needed a revision: one in the group of 36 mm head (0.27%) and three in the group of 28 mm (1.34%), confirming the lower rate in the bigger heads.