Femoral Anteversion in THA and its Lack of Correlation with Native Acetabular Anteversion

Several studies support the concept that, for optimum range of motion in THA, the combined femoral and acetabular anteversion should be some constant or fall within some "safe zone.'' When using a cementless femoral component, the surgeon has little control of the anteversion of the component since it is dictated by native femoral anteversion. Given this constraint, we asked whether the surgeon should use the native anteversion of the acetabulum as a target for implant position in THA. Forty-six patients scheduled for primary THA underwent CT scanning and preoperative planning using a computer workstation. The native acetabular anteversion and the native femoral anteversion were measured. Prosthetic femoral anteversion was measured on the workstation by three-dimensional templating of a straight-stemmed tapered implant. The mean of the sum of the native acetabular anteversion and native femoral anteversion was 28.9 degrees; however, 17% varied by 10 degrees to 15 degrees and 11% by more than 15 degrees. The mean of native femoral anteversion and prosthetic femoral anteversion was 13.8 degrees (range, -6.1 degrees-32.7 degrees) and 22.5 degrees (range, 1 degrees-39 degrees), respectively. Based on our data, we believe the surgeon should not use the native acetabular anteversion as a target for positioning the acetabular component.