Lateral Roentgenography of the Femoral Neck

Abstract

UNTIL recent years orthopedic surgeons have been content to view the neck of the femur in the anteroposterior or oblique planes roentgenographically. Inability to produce satisfactory lateral roentgenograms of this part has been taken as a matter of fact, and little work along this line has been attempted. In 1932, Clayton Johnson2 described an accurate method whereby the femoral neck might be viewed laterally for judging displacement in fracture of the neck. With the patient in a supine position, he placed a film parallel to the long axis of the femoral shaft and inclined from the horizontal 65 degrees. He then directed the central rays across the patient at an angle 25 degrees below horizontal and across the thigh toward the femoral neck at an angle 25 degrees from the transverse plane of the femoral shaft (Fig. 1). The projection thus obtained was in the plane of anteversion of the femoral neck, commonly called the lateral view, and was undistorted as to relative length of neck to head or shaft. Such a view is readily obtained, can be applied to examination of the femoral head and hip as well as the femoral neck, and is not subject to distortion by curvature of the film. For these reasons the authors have selected this method for use in the investigation of conditions other than fracture, and have elaborated the technic to include a cassette holder to simplify positioning, a Lysholm grid to improve the radiograph, and an exposure technic to insure adequate exposure. The cassette holder, which we obtained commercially although it can readily be constructed, consists of a base on which the patient rests and a side piece tilted 65 degrees from the horizontal. These are of veneer wood, transparent to x-ray, and are held by a metal frame in which two cross bars form a space behind the side piece in which the 8 × 10 film cassette and Lysholm grid may be placed readily and held at the correct angle. A metal triangle with a long wooden pointer indicates the proper centering point for the roentgen tube 25 degrees distal to the transverse plane and 25 degrees inclined from the horizontal. The base of the holder is slipped under the patient's hip, its side piece against the thigh and parallel to the axis of the femoral shaft with the femur in neutral rotation, and the proper positioning is obtained readily and without disturbance by means of the centering triangle. The Lysholm grid, placed between the cassette and cassette holder, is a necessary adjunct in that it greatly diminishes secondary radiation and yields a much more satisfactory radiograph. To determine exposure, measure the transverse diameter of the patient from skin to skin, or piaster surface if a spica has been applied, at the level of the greater trochanters. At 36 inches target-fihn distance, with fast films, screens, and developer, and using 80 milliampere-seconds of current, 3 kilovolts per inch of diameter, plus 30 kilovolts, is adequate exposure.