Introduction: Impingement in total hip arthroplasty is an important cause of hip dislocation. Impingement can exist as component-component impingement, component-bone impingement, or bone-bone impingement. Larger bearing diameters and better component positioning through surgical navigation may decrease the incidence of component impingement. The current study investigates the effect of component positioning on bony impingement in total hip arthroplasty. Methods: CT studies of ten patients with osteoarthritis treated by total hip arthroplasty were performed, and three-dimensional reconstructions were created (HipNAV, CASurgica, Inc, Pittsburgh, PA). Hip replacement surgery was then simulated (Meridian stem, Stryker Inc, Rutherford, NJ and Versys cup, Zimmer Inc, Warsaw, Indiana). Each hip model was subjected to four series of total hip replacement simulations. The first three series had the acetabular osteophytes removed as would occur at surgery. Each series started with the center of rotation of the prosthetic acetabulum and femoral head coincident with the native center of rotation. In the first series, the acetabulum was medialized in 2mm increments until the medial wall was perforated. In this series, the femoral offset was not increased to compensate for the medialization. In the second series, the acetabulum was medialized in 2mm increments and the femur was lateralized to maintain constant total offset. In the third series, the issue of component impingement was investigated by positioning the acetabular component 5 cm lateral to the normal center of rotation so that only component impingement occurred. The lateral translation of the hip assured no limitation of motion from bony impingement. Component impingement was calculated in 45 degrees of abduction and both 20 and 30 degrees of anteversion.
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