Abstract
Resorption of the calcar below the collar of a titanium femoral prosthesis was observed. Biopsies of these lesions showed concentrations of polyethylene. We assessed the size of the resorption and correlated this with the size of the femoral prosthesis and the time since implantation. The age and the weight of the patient were also linked to the size of the prosthesis.
We conducted a finite element analysis (FEA) of the femoral component-femur complex in both the loaded and unloaded situation. The FEA study demonstrated changing pressure under the collar that can be translated into microbending motions, with the degree of the movement dependent on the size of the prosthesis, the material of the prosthesis and the weight of the patient.
We hypothesise that the existence of a ‘polyethylene pump’ due to the bending movements of the collared prosthesis concentrates polyethylene particles under the collar. We therefore postulated that the calcar resorption is due to the polyethylene granulomatous lesions, resulting from the micromotion of the collar of the prosthesis.
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.
