Modified False-Profile Radiograph of the Hip Provides Better Visualization of the Anterosuperior Femoral Head-Neck Junction

Abstract

The purpose of this study was to quantify the amount of internal femur rotation required to visualize the 12 to 3 o'clock positions of the femoral head-neck junction as seen on the false-profile radiograph. Computed tomography (CT) images of the femur were retrospectively reviewed from control subjects and cam femoroacetabular impingement (FAI) patients. Using an automatically determined clockface, the positions between 12 and 3 o'clock were determined. The optimal femoral rotation angle to visualize each clockface position on the femoral head-neck junction was calculated based on the CT surface data. Fifty-nine control subjects and 38 cam FAI patients were evaluated for this study. The mean (95% confidence interval) internal femur rotation needed to optimally visualize the clockface positions of the femoral head-neck junction on the modified false-profile radiograph were 0.9° (0.8°-1.0°) for 3:00, 10.3° (10.0°-10.6°) for 2:30, 21.6° (21.0°-22.1°) for 2:00, 34.3° (33.6°-35.1°) for 1:30, 49.6° (48.6°-50.4°) for 1:00, 68.4° (67.7°-69.0°) for 12:30, and 90.1° (89.9°-90.4°) for 12:00. Internal femur rotation of 35° during the false-profile radiograph may better visualize the femoral head-neck junction in the anterosuperior (1 to 2 o'clock) region commonly associated with the cam lesion. From this view, rotation angles between 0° and 90° can be used to visualize other regions of the anterosuperior femoral head-neck junction. The internal rotation of the affected femur for a modified false-profile radiograph may provide a new radiographic view that can be used to quantify anterosuperior femoral head-neck morphology.