Accuracy of Planar Anteversion Measurements using Anteroposterior Radiographs

Introduction Several methods have been suggested to measure anteversion of the cup component after total hip arthroplasty using simple anteroposterior (AP) radiographs. Herein, we compared six widely used anteversion measurement methods using two different AP radiographs (conventional pelvis AP vs. hip-centered AP) in order to identify the measurement method and radiograph that provide the highest accuracy and reliability. Methods We developed two custom-made bi-planar anteversion measurement models for the validation. Each model was designed for pelvis AP and hip-centered AP radiographs. The radiographs were acquired with both models’ inclination angle changing from 10° to 70° at 10° increments, and for each inclination angles, anteversion was changed from 0° to 30° at 5° increments. The measurements were obtained independently by two orthopedic surgeons blinded from each other using 6 methods: 1) Pradhan et al., 2) Lewinnek et al., 3) Widmer et al., 4) Liaw et al., 5) Hassan et al., and 6) Ackland et al. The measurements were repeated after 2 months. The accuracy, compared to the reference angle, and intra- and inter-observer reliabilities of each method were calculated. Results The highest accuracy was found when Liaw et al.’s method was used in hip-centered AP radiographs, which showed a difference of 1.37° ± 1.73 from the reference. Moreover, regardless of the type of the radiograph, the methods by Pradhan et al., Lewinnek et al., and Liaw et al. showed excellent correlations with the reference anteversion. However, substantial differences were found when the methods by Widmer et al., Hassan et al., and Ackland et al. were utilized, regardless of the type of radiograph used. When the anteversion was measured in the inclination between 30° and 50°, Pradhan et al.’s method in pelvis AP radiographs showed the highest accuracy (1.23° ± 0.92°). We also found no significant difference when the measured anteversions were compared between pelvis AP and hip-centered AP radiographs. Both inter- and intra-observer reliabilities were high for all measurements tested. Conclusions The methods by Pradhan et al., Liaw et al., and Lewinnek et al. may provide relatively accurate anteversion measurements with high reliability, regardless of the type of radiograph.