NEW ALUMINA ON ALUMINA BEARING SURFACES: DIAMETER OF 36 MM

Abstract

On a theorethical basis a larger head diameter permit ewider range of motion and enhance the stability of the implant, reducing the risk of dislocation but increasing the level of friction and the production of debris. The need for a small head diameter (22 or 28 mm) was thus storically connected to the behaviour of the metal-polyethilene interface and the problem of PE debris. After the introduction of ceramics the production of debris diminished but the technology didn’t permit diameter-wider than 28 – 32 mm. The development of new ceramics with improved mechanical properties permit now to obtain thinner acetabular inserts and thus a larger head diameter, without increases the production of debris.

From september 2003 to jenuary 2004 we have implanted 20 uncemented alumina on alumina THR with an head diameter of 36mm. The diagnosis was: hip fracture (14 cases) and hip osteoarthritis in 6cases. The mean age at operation was 73 years (52–88).. The mean follow-uptime was 5 months (3–8) The study is focused on preliminary observation about early complication.

All the patients at the last follow-up have regained complete authonomy during the normal day life activity We have had only one early dislocation, occurred in the 5th post-op day, with the patient in sitting position. After reduction (under anesthesia) and partial immobilization for3 weeks in hip-spica cast there was not recurrence of the dislocation. No other complications were noted.

One of the major problem regarding theutilization af alumina in hip arthroplasty is an higher risk of dislocation of the implant. The introduction of a new ceramic with improved mechanical properties that permit larger head size should minimize this risk. This fact, associated to the low production of debris of the alumina bearing-surfaces open new prospective in performing THR.