Fixation of the acetabular cup in cemented total hip replacement: improving the anchorage hole profile using finite element method.

Long-term studies have shown that failure of the acetabular component in total hip replacement increases exponentially ten years following surgery and occurs mostly at the bone-cement interface. During the cemented fixation of the acetabular cup, straight anchorage holes, 3-15 mm diameter and 3-20 mm deep, are drilled in the acetabulum in order to increase torsional resistance at the bone-cement interface. The aim of this paper is to provide guidelines for improving the profile of anchorage holes. Results from our finite element models show that the efficiency of anchorage holes may be improved if they are drilled perpendicularly to the acetabulum floor and if they have chamfered necks. A 10 degree inclination of the anchorage hole increases Von Mises stress in the cement mantle by 6% while creating chamfered anchorage holes, instead of straight holes, decreases it by 14%. Increasing depth of anchorage holes does not improve efficiency.