[Computer-assisted design and production of a femoral hip prosthesis]

The authors believe that a better design of prosthetic femoral stem might reduce the incidence of loosening. They have developed a method to make a prosthesis precisely adapted to a patient. Two X-Rays, one antero-posterior and one lateral view are taken. Several bony points are precisely determined. The magnification of the X-Rays is calculated, using a metallic circular collar placed around the thigh. A computer analyses the X-Rays, bony points are numerated and the prostheses have a length, thickness and shape adapted to the patient's hip. A study of the pressures transmitted by the prostheses to the bone was made using geometrical models. Compared to conventional prostheses, a prosthesis made as an exact fit to the hip of the patient reduces the pressure applied on femoral cortex by two thirds. A prosthesis with a collar also allows reduction of pressure on the cortex by a degree of three to one. The personalized prosthesis obtained by the use of a computer appears to be a stage in progress towards a better fitting and more reliable prosthesis. Twenty five patients have been operated on with good short-term results.