TWELVE YEARS FOLLOW UP EXPERIENCE WITH AN HYDROXYAPATITE COATED HIP ARTHROPLASTY WITH CERAMIC BEARING SURFACES.

Abstract

Hydroxylapatite (HA) is widely employed as coating of cementless hip stems. Nevertheless there is a deficiency of long-term follow-up studies, and none, to our knowledge, with a ceramic on ceramic coupling, that it is important to avoid the effect of polyethylene wear on stem survival.

Between June 1990 and December 1991, 151 prostheses with an anatomic fully HA-coated cobalt-chrome stem, alumina bearing surfaces, and a threaded Ti-6Al-4V cup, were implanted in 147 consecutive patients (57 males, 90 females, average age 58 years). All were primary surgeries, there were no specific exclusions. Ten died for unrelated causes to the surgery, one died from postoperative complications; thirty nine of the surviving patients were lost to follow-up. The Merle D’Aubigné and Postel score was recorded before and after surgery at each review. An anteroposterior view and a frog-lateral view of the involved hip were taken at each follow-up review. The results were analysed by the Kaplan-Meier method to estimate the cumulative probability of revision.

In two cases, the prosthesis was completely removed with Gilderstone’s procedure because of septic loosening. Among the others, 10 cups required revision surgery for aseptic loosening, and 6 stems were revised for thigh pain. The mean Merle D’Aubigné rating improved from 10 before operation to 16.4. Bone stability was recorded in all cases but three in which there was a painfree fibrous stability. The Kaplan-Meier analysis at 12 years predicted asurvival rate for the prosthesis of 86% (95% CI 79 to 92), and for the stem of 93.8% (95% CI 89.7 to 98).

At 12 years the HA-coated stem has shown an overall good outcome while the threaded non HA-coated cup employed had a bad survival that had influenced the survival of the prosthesis. In conclusion we are confident to consider HA a viable and effective coating.