[Bone Stress and Reconstruction of the Bone at the Alloarthroplasty of the Upper End of the Femur with Cement Bonding (author's Transl)]

Structure and shape of the upper end of the femur are determined by direction and height according to their strain. Forces which flow from pelvis into femoral head have at first an unfavourable direction that means a non-axial direction of the femoral shaft. The mechanic task of the proximal femur (epi- and metaphysis) is to divert the forces in a way that they disperse in axial direction to the shaft (tension and pressure forces of the upper end of the femur). By replacement of the endoprosthesis, the epiphysis and a large part of the metaphysis is removed and will be replaced by metal- or bone cement. This leads to a thorough change of the mechanical stress. According to Wolff's transformation law the bone tends to adopt the changes stress throught reconstructing processes. Static and morphologic researches of the normal and endoprosthetic femur could demonstrate a conformity of bone reconstruction and changed bone stress. The spongiosa remaining after resection is not sufficient to distribute the influenced forces of the shaft of the bone. Result is a cancellous bone of the upper end of the shaft. We call this reaction "Metaphysierung". According to the unphysiologic high bending stress of the shaft in level of the lower half of the haft of the prosthesis, a hypertrophy of cortex and vault occurs. The large stress of this part of the bone can be the cause of non-infectious late loosenings of the prosthesis.