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The Iliofemoral Line: A Radiographic Sign of Acetabular Dysplasia in the Adult Hip

      Introduction

      Several radiographic parameters utilized for the diagnosis of acetabular dysplasia in adults suffer poor reproducibility and reliability. The purpose of this study was to define and validate a novel radiographic parameter (the ‘iliofemoral line’) for discrimination of hip dysplasia.

      Methods

      A consecutive cohort of 172 adult patients undergoing hip preservation surgery were included. The iliofemoral line was defined as the continuous line extending from the lateral femoral neck through the femoral head-neck junction to the inner cortical lip of the iliac crest. Percent lateralization of the iliofemoral line was calculated as the horizontal distance of the femoral head lying outside of the iliofemoral line relative to the total length of the horizontal femoral head diameter.

      Results

      Percent lateralization of the iliofemoral line was strongly correlated to the lateral center edge angle (LCEA, p<0.001). Values of percent lateralization ranging from 14.5-20.2 predicted the presence of borderline hip dysplasia with a sensitivity of 44.7% and specificity of 94.0%, while values exceeding 20.2 predicted presence of frank acetabular dysplasia with a sensitivity of 81.8% and specificity of 88.5%. By comparison, abnormality of the Shenton line demonstrated a sensitivity of 2.6% and specificity of 94.8% for detection of borderline dysplasia, and a sensitivity of 21.2% and specificity of 99.3% for detection of frank acetabular dysplasia. Compared to the Shenton line, percent lateralization of the iliofemoral line was significantly more sensitive for detection of both borderline and frank acetabular dysplasia (p=0.004 and 0.001, respectively).

      Conclusion

      Percent lateralization of the iliofemoral line is a reliable and accurate radiographic marker of frank acetabular dysplasia, and to a lesser extent, borderline dysplasia. Use of this novel radiographic marker may enable earlier detection of borderline and frank hip dysplasia in young adults presenting with hip pain.