The line that signifies acetabular dysplasia
Currently, there are several radiographic parameters in use for the diagnosis of acetabular dysplasia in adults. However, say researchers at the University of Colorado School of Medicine, these parameters are far from ideal, showing only poor reproducibility and reliability. In the present study, the authors aimed to define and validate a novel radiographic parameter called the iliofemoral line (IFL) for the detection of frank and borderline hip dysplasia. The IFL extends from the lateral femoral neck through the inner cortical lip of the iliac crest, and intersects the femoral head in cases of dysplasia. The positive study results: IFL was found to be a reliable and accurate radiographic marker of frank acetabular dysplasia and to a lesser extent for borderline dysplasia.
The cohort study included 222 adult patients (436 hips) who underwent hip preservation surgery. The authors defined percent medialization of the IFL as the horizontal distance of the exposed femoral head lateral to the IFL, relative to the horizontal femoral head width at the center of the femoral head.
There was a strong correlation between percent medialization of the IFL and the lateral center edge angle (P < 0.0001). Values of percent medialization of 15-22 % predicted the presence of borderline hip dysplasia with a sensitivity of 62 % and specificity of 89 %; values > 22 % predicted the presence of frank acetabular dysplasia with a sensitivity of 77 % and specificity of 94 %. Compared to previously validated parameters such as the Shenton line, percent medialization of the IFL was significantly more sensitive for the detection of both borderline and frank acetabular dysplasia (both P < 0.0001). The intraobserver and interobserver reproducibility of the horizontal difference outside the IFL were 0.99 and 0.96, respectively.
Percent medialization of the IFL is a reliable and accurate radiographic marker of frank acetabular dysplasia and borderline dysplasia. The authors hope that the use of this radiographic parameter as an additional tool could lead to an earlier detection of borderline and frank hip dysplasia in young adults presenting with hip pain.