Design of intramedullary femoral stems using computer graphics.

This study describes a method for maximizing the size of an intramedullary stem which can physically be inserted into the canal of the femur. The potential applications of this are for ‘press-fit’ stems where maximizing the area of contact with the endosteal surface is likely to be important, and for cemented stems where a uniform cement layer is desirable. The 3-dimensional shape of a femur is described by using CT data of transverse sections. The computer program uses an algorithm which minimizes the amount of material removed from the stem sections, with preference being given to areas of maximum load transmission. Different parameters are investigated, such as the level and angle of the neck cut, and the length of the stem. Comparisons of percentage of the canal filled are made with standard symmetrical stems. It is shown that computer-generated stems filled substantially more than available symmetrical stems.