Abstract
We have previously reported on early lytic lesions occurring when collared titanium prostheses are used. Previous finite element analysis studies (FEAs) showed that lytic lesions of the calcar were due to concentration of polyethylene wear particles under the collar by a ‘pumping action’. Further follow-up of these calcar lytic lesions showed that their rate of increase in size progressively slowed down. Further FEAs were performed to determine why this was so.
An FEA mesh construct was developed, incorporating the new parameters of no contact between the collar and the calcar bone. A mechanical model to determine displacement parameters was also developed. These FEA studies demonstrated that the pumping action of the collar became less efficient as the size of the lytic lesions increased. This led to less concentration of polyethylene particles under the collar and fewer granulomatous reactions. The change in the proximal prosthesis-cement-bone construct may lead to cement mantle deterioration and earlier failure. We still recommend caution when a collared prosthesis is used, and the material and geometry of the prosthesis remain important.
The abstracts were prepared by Professor M. B. E. Sweet. Correspondence should be addressed to him at PO Box 47363, Parklands, Johannesburg 2121, South Africa.
