[Mechanical tests with polymethylmethacrylate in fresh specimens and specimens obtained from loosened prosthesis (author's transl)].

Mechanical testing of specimen from fresh acrylic cement and from lossened prostheses between one and two years after implantation shows difference in compressive strength. Air bubbles, blood particles, and folds distinctly influence mechanical properties. Therefore, care should be taken to avoid these enclosures during implantation. But it is not the aging of the acrylic cement which presents the main problem in endoprosthetic fixation, but the cement-bone interface. Clinical experience and this mechanical study show that fracture of the acrylic cement is not due to primary fatigue of the material, but occurs secondarily after loosening of the bonding between bone and cement.