Areas of contact and extent of gaps with implantation of oversized acetabular components in total hip arthroplasty.

Contact between porous surfaces and bone and initial stable fixation of the implant to bone are required to achieve bone ingrowth into prosthetic devices. To avoid the potential problems associated with screws that are often used to obtain initial stability of uncemented acetabular components, oversizing of the component has been recommended. This study investigated the shape of the reamed surface compared with the acetabular reamers used, the areas of bone implant contact obtained with oversizing, and the extent of polar area gaps created by this surgical technique. In embalmed hemipelvises, using surface fitting algorithms, the average departure from sphericity, of the reamed acetabular surface, was 0.56 mm. Using Pressensor film, extensive peripheral cup contact but minimal polar area contact was demonstrated when oversizing the components. In addition, large polar area gaps were demonstrated using polyvinylsiloxane epoxy molds. This study confirms the potential concerns associated with oversizing the acetabular component in relation to the reamed acetabular surface. Although excellent peripheral contact was obtained using this technique, polar area contact was demonstrated to be minimal or nonexistent, and large polar area gaps were observed. In addition, this study demonstrates that a precisely reamed surface can be obtained in the acetabulum when accurately sized reamers are used.