Determination of acetabular coverage of the femoral head with use of a single anteroposterior radiograph.

We developed a method for the estimation of three-dimensional acetabular coverage of the femoral head with use of only an anteroposterior radiograph of the hip. This technique also allows recalculation of the corrected value for coverage at neutral pelvic tilt. Provided that the acetabulum and femoral head are spherical and congruent, the results are as accurate as those obtained with computerized tomographic reconstruction, the dose of radiation is much lower, and much less time is required for calculation. The hips of 286 normal subjects showed increases with age in both anterior and posterior coverage and backward tilt of the pelvis, along with a decrease in the anterior-posterior ratio of coverage. The proportion of anterior acetabular coverage in female subjects was smaller than that in male subjects. There was more backward tilt of the pelvis and the anterior-posterior ratio of coverage was smaller when the subjects were standing than when they were supine. Acetabular coverage of the femoral head has been evaluated previously on the basis of anteroposterior radiographs of the hip with use of two-dimensional measurements, such as the center-edge angle of Wiberg and the acetabular angle (Sharp angle). Computerized tomographic reconstruction recently has made it possible to measure the three-dimensional coverage of normal and dysp!astic hips’#{176}’3. However, computerized tomography has not been widely used for this purpose because of the greater amounts of radiation and higher costs associated with it. We developed a new method, with the aid of a computer. to evaluate three-dimensional coverage on the basis of an anteroposterior radiograph of the hip. This method appears to be as accurate as that of computerized tomographic reconstruction. The purpose of this report is to introduce the principles of our method of calculation, to document the accu *No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study. tDepartment of Orthopaedics, Aichiken-Saiseikai Hospital, 117 Kamisaradouni, Nishi-ku, Nagoya, 451 Japan. lDepartment of Orthopaedics, Tsushima-City Hospital, 3-73, Tachibana-cho, Tsushima, Aichi, 496 Japan. racy of the method, and to describe our clinical findings relative to the three-dimensional coverage of normal hips that was discovered with use of this technique.