Abstract
Purpose: The design of the contact surfaces of total knee prostheses is a recognised factor affecting polyethylene wear and thus prosthesis survival. Flat-on-flat prostheses have a limited surface area of contact and are thought to favour polyethylene wear. They are not currently recommended for implantation. Nevertheless, several series have reported similar survival with other more congruent prostheses. We studied a series followed for eight years.
Material and methods: We implanted 223 flat-on-flat design total knee prostheses between 1992 and 1996 (Search®, Aesculap, Chaumont). All patients were followed prospectively and seen at regular intervals for physical examination and x-rays. We noted any intervention for implant revision and recorded time to any such procedures as well as the underlying cause. Kaplan-Meier survival curves were plotted taking revision for any cause other than infection as the endpoint.
Results: Ninety-four percent of the patients were reexamined or questioned by phone for this study conducted during 2001. Six percent of the patients were lost to follow-up after a mean 24 months. Seventy-four percent of the prostheses were still in situ at the time of this study at a mean 78 months follow-up. Ten percent of the patients died with their initial implant in place at a mean 50 months. Ten percent of the patients underwent revision surgery at a mean 37 months, half of them for infection and one quarter for a mechanical cause. The overall rate of revision at eight years was 11%; The rate of revision, infection excluded, at eight years was 6%.
Discussion: Survival of this prosthesis in non-infected patients is similar to that of other more congruent implants. This study confirms earlier clinical findings.The undesirable effect of the linear contact surfaces is proven in the laboratory but must not be considered to be automatically transferable to the clinical level. Polyethylene wear is a multifactorial phenomenon which cannot be reduced to a simple question of prosthesis design.
The abstracts were prepared by Docteur Jean Barthas. Correspondence should be addressed to him at Secrétariat de la Société S.O.F.C.O.T., 56 rue Boissonade, 75014 Paris.
