Reproducibility of radiographic hip measurements in adults

Hip dysplasia may cause pain and premature hip osteoarthritis. Here, our objective was to assess the inter- and intraobserver reproducibility of radiographic hip parameter measurement in adults.

We used anteroposterior pelvic radiographs and false-profile lateral hip radiographs from 30 individuals (60 hips) enrolled in a prevalence study of hip osteoarthritis. For each hip, two independent observers recorded five parameters twice, at an interval of 1 month. The five parameters were the vertical-center-edge angle (VCE), the anterior center-edge angle (vertical-center-anterior angle, VCA), the acetabular roof angle (HTE), the neck-shaft angle (CC'D), and acetabulum depth (AD). Reproducibility was assessed using Bland-Altman plots, intraclass correlation coefficients (ICCs), and kappa coefficients for the radiographic diagnosis of hip dysplasia using widely accepted cutoffs.

Of the 60 hips, 51 were assessable. Intraobserver ICC values ranged from 0.72 to 0.94 and interobserver ICC values from 0.68 to 0.84. Kappa coefficients were between 0.60 and 1.00, except for the VCA angle (κ=0.41).

In this study, reproducibility of the main radiographic hip parameters was good according to all evaluation methods used. However, CC'D and, to an even greater extent, the VCA angle seemed challenging to measure.