Morphological and biomechanical aspects of Al2O3 ceramic joint replacement. Experimental results and design considerations for human endoprostheses

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Abstract
Four different acetabular replacement designs and 2 femoral head replacement designs made out of high density alumina ceramic have been tested in sheep with postoperative survival times of up to 11 months (Frialit 99: Al2O3 99.6%, MgO 0.4%). It can be concluded from these experiments that a cement free implantation technique with alumina requires a primary rigid fixation of the implant to bone, with the possibility for new bone growth along the ceramic and into grooves and macroscopic holes for further interdigitation. Three different solutions for the acetabular component can be recommended for human application. In addition, an all ceramic femoral prosthesis has been tested for bending strength in its neck region. Twenty prostheses have been fractured, all of which showed values for bending strength far higher than the physiological neck fracture level (900 kp/cm2). The present state of development of all ceramic prostheses is discussed. Up to now, the development of fibrous tissue between the bone and the ceramic implant has caused reservations with human implantation. The direct definite anchorage problem has to be resolved first.