Aseptic loosening of the acetabular component is the main reason for revision hip arthroplasty surgery with loosening rates reported at 25% at 12–15years. The optimum method of acetabular preparation and cementation technique has not been fully evaluated. Clinical follow-up studies suggest multiple keyholes improve survival rates.

Keyholes increase penetration of cement and torsional resistance of the bone-cement interface. Some studies support the traditional three 1/2 inch keyholes other studies have shown multiple smaller holes improve stability. The optimum size and number of holes to provide the strongest fixation has yet to be determined.

Using an established 54mm diameter acetabular model, mahogany, three sizes of keyhole were tested-3x10mm holes, 12x5mm, and 48x2.5mm- the surface area of the defects created were the same in each group. The model acetabulum was filled with cement and a metal central bar inserted through which torque could be applied using an Instron machine. Six specimens from each group were tested. Three 10mm holes produced a significantly stronger resistance to torque when compared to 2.5mm (p≤0.017) and 5mm holes (p≤0.001). There was no significant difference between 2.5mm and 5mm holes (p≤0.139). Each addition of a further 10mm hole significantly increased the torque strength until the model was destroyed at six holes.

In laboratory testing larger key holes provide a stronger cement-acetabular interface.

Radiological assessment of the cement mantle is used routinely to determine the outcome of total hip replacement. We performed a simulated replacement arthroplasty on cadaver femora and took standard postoperative radiographs. The femora were then sectioned into 7 mm slices starting at the calcar, and high-resolution faxitron radiographs were taken of these sections.

Analysis of the faxitron images showed that defects in the cement mantle were observed up to 100 times more frequently than on the standard films. We therefore encourage the search for a better technique in assessing the cement mantle.