[Initial stability of press-fit acetabular cups--an in-vitro study].
OBJECTIVE
Mechanical lever-out tests were performed in vitro to investigate the initial stability of press fit acetabular cups.


METHODS
Five different uncemented, hemispherical press-fit cups were implanted in a standardized manner into Sawbones, Polyurethane foam blocks. Each cup was levered-out by using a 250 mm stainless steel rod, which was connected to the acetabular cup. Loads were then applied to the rod causing the cup to be diplaced. Lever-out forces were recorded by a computer.


RESULTS
The results of the lever-out forces ranged between 39,2 and 50,8 Nm. The highest initial stability was achieved by two Titanium cups with a Titanium plasmaspray coating, a flattened pole and a sharp equatorial edge. According to our trials the equatorial rim of the polyurethane cavity is the crucial area for the implant's initial stabilty. There the highest amount of attrition was observed.


CONCLUSIONS
To guarantee a high reproducibilty of the tests it is essential to pay particular attention to the quality of the polyurethane foam blocks, to the exactness of the reaming procedure and to a defined cup insertion. However as our trials were carried out under optimized labaratory conditions one must be careful not to over-interpret its results. Intraoperatively primary stability is also influenced by the quality of the bone.
Wetzel
R
R
Orthopädisch-Unfallchirurgisches Zentrum, Universitätsklinikum Mannheim gGmbH, Theodor Kutzer Ufer 1-3, 68167 Mannheim. ralph.wetzel@karl-olga-krankenhaus.de
Simnacher
M
M
Scheller
G
G
D000077:Acetabulum / Q000503:physiopathology* / Q000601:surgery; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D004548:Elasticity; D019544:Equipment Failure Analysis; D006621:Hip Joint / Q000503:physiopathology* / Q000601:surgery; D006622:Hip Prosthesis; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D009038:Motion; D011312:Pressure; D013314:Stress, Mechanical; D016474:Weight-Bearing