Reliability of and Correlation Between Measurements of Acetabular Morphology

The authors sought to determine the intra- and interrater reliability of contemporary measures of acetabular morphology among a group of hip surgeons and to determine the correlations between measures of acetabular morphology. On 2 separate occasions, 3 hip surgeons independently performed blinded evaluations of anteroposterior pelvic radiographs of 40 patients. The lateral center-edge angle, medial center-edge angle, acetabular arc, extrusion index, acetabular index, Sharp's angle, posterior wall sign, crossover sign, femoro-epiphyseal acetabular roof index, acetabular wall indexes, and delta angle were assessed. A linear mixed model was used for variance estimation, and kappa and intra-class correlation coefficients were assessed for reliability. Pearson correlation coefficients were calculated for all possible pairs of radiographic measures. The acetabular index had the greatest interrater agreement (0.90; 95% confidence interval [CI], 0.84-0.93), whereas the lateral center-edge angle had the higher intrarater agreement (0.96; 95% CI, 0.92-0.98). The acetabular arc angle had the lowest interrater agreement (0.44; 95% CI, 0.29-0.57), and the Sharp's angle had the lowest intrarater agreement (0.66; 95% CI, 0.41-0.84). The posterior wall sign had an interrater agreement of 0.35 (95% CI, 0.11-0.54) and an intrarater agreement of 0.68 (95% CI, 0.49-0.86). The crossover sign had an interrater agreement of 0.66 (95% CI, 0.43-0.84) and an intrarater agreement of 0.85 (95% CI, 0.52-0.89). The acetabular index, lateral center-edge angle, and extrusion index presented with high coefficients of correlation. In addition, acetabular anteversion correlated with severity of dysplasia. Commonly used parameters such as the acetabular index, lateral center-edge angle, and extrusion index are reliable radiographic parameters to assess acetabular morphology. However, correlation between measures suggests that they may be redundant in quantifying acetabular morphology. [Orthopedics. 2018; 41(5):e629-e635.].