Reliability of the sourcil method of acetabular index measurement in developmental dysplasia of the hip

Purpose The ability to monitor and study developmental dysplasia of the hip (DDH) requires validated radiographic outcome measures. The sourcil method of acetabular index measurement (AI-S) has not yet been shown to be a reliable measure of acetabular dysplasia in a DDH population, despite its widespread use. The aims of this study were to test the reliability of the AI-S method in a DDH population, and to compare the reliability of the AI-S method with that of the classic lateral edge method (AI-L). Methods From an institutional database, standardized anteroposterior hip radiographs were obtained from a cohort of 35 female patients (70 hips) at two and five years of age who had been treated nonoperatively for DDH. Three observers independently measured the acetabular index using the AI-L and AI-S methods on all 70 hips at two time points, four weeks apart. Results The inter-rater reliability intraclass correlation coefficient (ICC) for the AI-L and AI-S methods was between good and excellent at 0.94 (confidence interval (CI) 0.89 to 0.96) and 0.91 (CI 0.87 to 0.94), respectively. The ICCs for intra-rater reliability for the AI-L method were excellent at 0.93 (CI 0.90 to 0.95), 0.95 (CI 0.93 to 0.97) and 0.95 (CI 0.94 to 0.97) for raters 1, 2 and 3, respectively. The ICCs for intra-rater reliability for the AI-S method were between good and excellent at 0.91 (CI 0.87 to 0.93), 0.93 (CI 0.90 to 0.95) and 0.90 (CI 0.86 to 0.93) for raters 1, 2 and 3 respectively. Conclusion Both AI-S and AI-L methods are equally reliable radiographic measures of DDH.