Definition of a quantitative measurement method for acetabular version in a plain radiograph in the healthy adult hip

This study aims to define a quantitative measurement method for acetabular version in a standard anteroposterior hip radiograph, assess the intraobserver and interobserver agreements of this method, and compare it with the gold standard computed tomography (CT).

Anteroposterior standard hip radiographs and simultaneously taken transverse acetabular CT sections of 78 hips of 39 patients (10 males, 29 females; mean age 60 years; range 40 to 81 years) were used in the study. In standard anteroposterior hip radiographs, "acetabular anterior wall line" was identified as the line between the most lateral edge of the acetabulum and the inferolateral edge of the teardrop. "Acetabular posterior wall line" was identified as the line between the most lateral edge of the subchondral sclerosis and the outmost point of acetabulum posterior lunate surface sclerosis. To assess the reliability of this technique, mentioned angles in 78 hips were measured by two authors independently two weeks apart. Direct radiographic values were compared with the acetabular version measurement values in CT examination.

Mean acetabular version angles of 78 hips in plain radiographs and CT were 18.0° (9-25°) and 17.2° (12-25°), respectively. Mean intraobserver measurement differences were 1.3° (0-5°) and 1.5° (0-6°). Mean interobserver measurement difference was 1.4° (0-5°). The mean difference between plain radiography measurements and CT measurements was 2.5° (0-6°). A significant correlation was detected between plain radiographic measurements and CT measurements.

By this quantitative method, acetabular morphology may be measured less invasively, easily, quickly and reliably in plain radiograph in transverse plane.