How Reliable Is the Measurement of the Lateral Center Edge Angle on Scoliosis Radiographs for Detecting Acetabular Dysplasia?

Purpose: Hip dysplasia reportedly occurs in up to 12% of the general population and may be higher in patients with adolescent idiopathic scoliosis (AIS). When using lateral center edge angle (LCEA) measurements to help identify hip dysplasia, it is uncertain if this measurement can be performed reliably on scoliosis radiographs due to parallax. The purpose of this study is to evaluate the reliability of measuring LCEA on scoliosis radiographs compared with standard pelvis radiographs. Methods: This study evaluated 40 hips on 20 patients (mean age 12.5 years ± 3.1; 50% Female) who received PA scoliosis radiographs and AP pelvis radiographs within 1 year of each other. Review was performed by 4 pediatric radiologists (2 general, 2 MSK), 2 pediatric orthopaedic surgeons, and 1 research fellow. Radiographic measurement of the LCEA for each hip was first performed on the scoliosis radiograph. After a minimum of 3 days, the LCEA was measured on a pelvis radiograph of the same individual obtained within 1 year of the scoliosis radiograph. Pearson coefficient was used to measure agreement between scoliosis and pelvis radiograph measurements. Intraclass correlation coefficient (ICC) was used to evaluate intraobserver and interobserver agreement. ICC values <0.5 were classified as poor reliability, 0.5 to 0.75 were classified moderate, 0.75 to 0.90 were classified good, and >0.9 indicated excellent reliability. Results: The mean difference between scoliosis and pelvis radiographs was 54 ± 79 days. There was good-to-excellent interobserver agreement on LCEA measurements made between readers on scoliosis radiographs (ICC: 0.94, 95% CI: 0.90-0.96, P <0.001) and pelvis radiographs (ICC: 0.91, 95% CI: 0.83-0.95, P <0.001), and moderate-to-excellent intraobserver agreement for scoliosis radiographs (ICC range: 0.68 to 0.98; P <0.001) and pelvis radiographs (ICC range: 0.62 to 0.96; P <0.001). There was a strong correlation between LCEA measurements made on scoliosis and pelvis radiographs ( r 2 =0.66, P <0.001), and the intermodality agreement between scoliosis and pelvis radiograph LCEA measurements were moderate to good (ICC range: 0.68 to 0.89, P <0.001). Conclusions: Overall, there was good-to-excellent agreement between readers on scoliosis and pelvis radiographs, respectively, and moderate-to-excellent intraobserver agreement between LCEA measurements made on scoliosis radiographs and pelvis radiographs, respectively. LCEA measurements made on scoliosis radiographs strongly correlated to the measurements made on pelvis radiographs, and the intermodality ICC was also considered moderate to good. Dedicated pelvis radiographs may not be necessary during scoliosis workup and follow-up surveillance, thereby decreasing radiation exposure, cost, and improving patient care workflow. Level of Evidence: Level IV—diagnostic study.