[Comparative analysis of shaft geometry in frequently used endophrostheses of the hip joint].

The static behavior of various types of endoprostheses in partial or total hip replacements were tested by means of geometrical analysis in order to examine the loosening phenomena. -- The 3 heterogenous structural materials with highly differing elastic modules such as methylmetacrylate, steel, and bone, which are presently still necessary for the firm embedding of hip prosthesis, are the decisive factors in the observed loosening and migrating of hip arthroplastics. Deformation and fracture of methylmetacrylate alter the primary stabilization of femoral components, changing a two-point fixational system (a two-armed handle) into a device firmly fixed only at one side, thereby increasing the bending and stretching moments so that loosening, varus migration, and metal fatique may occur. -- Prostheses with long-shaft femoral components, with a great surface pressure, and a great momentum of resistance in the upper, endangered third part as well as prosthesis collars up to 65 degrees, are therefore preferable in order to avoid implant complications.