[The temporal behavior of the anchorage of a cement-free implanted acetabular cup in animal experiments]

The mechanical qualities of the cementless press-fit cup of a hip prosthesis were examined in sheep. Primary anchorage of the cup is achieved by relative oversize of the cup in relation to the acetabulum, causing a press-fit effect. The surface of the cup consists of Sulmesh, a titanium net, which allows bony ingrowth. The quality of the mechanical anchorage in the acetabular bone was tested by measurements of the torque and cranio-caudal tilting moment needed to pull out the cup. It was shown that the secondary biological anchorage of the press-fit cup exceeds the primary mechanical anchorage (measured in previous in vitro experiments) by a factor of three. This improvement of the mechanical fixation of the press-fit cup in the acetabular bone can be explained by bony ingrowth into the Sulmesh and can be confirmed by histological findings.