Changes in the femoral cortex as related to prosthetic stem.

The need to improve the features of resistance and duration of prosthetic implants, based on the constant increase in the number per year of total hip substitutions has encouraged the study of the causes of aseptic loosening of implants, in particular, any relationship between femoral morphology, features of the implanted prosthesis (size and coating), degree of contact between the latter and the host bone, and the occurrence of changes in bone trophism. The documentation relative to 143 patients, corresponding to 149 primary hip arthroplasties, was evaluated clinically (according to Merle d'Aubigné modified by Charnley) and radiographically, using a computerized radiographic evaluation system devised by our group. In particular, on x-rays (anteroposterior view) obtained in the area corresponding to the upper and lower margins of the smaller trochanter and of the femoral isthmus, measurements relative to femoral diameters, to the distance between them, and to the corresponding flare indexes were obtained; bone thickness, degree of bone-prosthesis correspondence and any changes in bone trophism caused by stress-shielding and stress-concentration were also measured. An analysis of the data was carried out using non-parametric statistical tests, that allowed us to reveal the surgeon's good standardization in preparation of the femur; the tendency for the cortex to thicken for prostheses of the short type, and the narrowing of the standard type prostheses, the influence of the degree of fit of the prosthesis on trophism of the femoral cortex.