Can EOS imaging substitute traditional AP pelvis radiographs? A Comparative study

INTRODUCTION: Young patients followed for hip disorders often require serial imaging and incur significant radiation to the abdomen and pelvis. The EOS imaging system offers a low-radiation alternative. However, consistency with radiographic parameters from conventional radiographs (CR) have not been studied. We evaluated the reliability and validity of EOS imaging in comparison to CR in evaluating acetabular morphology. METHODS: 48 hips (27 patients, 66.67% female, 14.4 ± 3.6 years old), indicated for open hip preservation procedure between 2015-2017, which had both EOS imaging and AP pelvis CR taken pre-operatively were examined. Both symptomatic and contralateral hips were measured, excluding hips with prior osteotomies. Three orthopaedic surgeons measured Tonnis angle, lateral center edge angle (LCEA), acetabular depth ratio (ADR), and extrusion index (EI) in both imaging modalities. Images were measured twice, two weeks apart. Reliability was assessed using intraclass correlation coefficients (ICC). Bland-Altman analysis was used to evaluate test-retest agreement and inter-modality agreement. RESULTS: Test-retest reliability was excellent for all raters on all tests (ICC range 0.8047 to 0.9714). Inter-rater reliability was also excellent for all measures on both modalities (ICC range 0.8593 to 0.9547). ICC values were consistent across EOS and CR. By Bland-Altman analysis, test-retest agreement was high, with no statistically significant mean differences in any test or modality (p > 0.6) except LCEA measured on EOS images (p = 0.02), which was 1.16° lower. Tonnis angle (p < 0.005) and ADR (p < 0.001) were statistically different from EOS to CR. Bias was also not uni-directional across tests: LCEA and ADR were, on average, higher on CR while Tonnis angle and EI were, on average, higher on EOS images. Reliability between the EOS and CR images was excellent for all raters on all tests (ICC range 0.8402 to 0.9458). DISCUSSION AND CONCLUSION: LCEA, ADR, EI, and Tonnis angle have consistently high test-retest reliability, test-retest agreement, and inter-observer reliability in both EOS imaging and CR to evaluate acetabular morphology. Inter-modality disagreement was observed between EOS and CR, but the difference was small and likely not clinically significant. When establishing acetabular morphology, these results suggest that EOS may provide an opportunity to minimize radiation exposure for patients followed long-term for hip pathology while maintaining the accuracy of diagnostic measures.