INITIAL MECHANICAL STABILITY OF ACETABULAR PROSTHESES

Secure initial stability is crucial for prostheses designed for biolog ical ingrowth without it, subsequent tissue ingrowth is impossible. Me chanical testing was performed in vitro to measure the interface shear stability of acetabular cup prostheses. Cemented, threaded, finned, a nd press-fit cups, both with and without supplemental screw fixation, were tested. A mechanically consistent polyethylene foam was used as a substrate to obviate the variations inherent in cadaver bones. Ramped , eccentric rim loads were applied using a servohydraulic materials te sting system. Reaming, insertion, and loading variables were carefully controlled. Cups with external threads were significantly more stable than those fixed by fins or screws. Press-fit cups were significantly looser than all other tested designs. None of the uncemented prosthes es approached the initial stability of cups secured with acrylic bone cement.