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, correlating it with the size of the femoral prosthesis and the time since implantation. The age and the weight of the patient was 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. FEA demonstrated changing pressure under the collar. This can be translated into micro-bending, with the degree of movement dependent on the size of the prosthesis, the material of the prosthesis and the weight of the patient.
We postulate the existence of a ‘polyethylene pump’ owing to the bending motion of the collared prosthesis, and that calcar resorption is due to the resultant polyethylene granulomatous lesions .
The abstracts were edited by Prof. M.B.E. Sweet. Correspondence should be addressed to him at the Department of Orthopaedic Surgery, Medical School, University of the Witwatersrand, 7 York Road, Parktown, 2193 South Africa
