The Study Of A New Radiological Measurement Method To Evaluate Adult Acetabular Dysplasia

Objective: Combining with the center edge angle(CEA), acetabular angle(sharp angle) and acetabular head index(AHI) of hip, new index of femoral head center upward and outward displacement were used to the imaging evaluation of adult acetabular dysplasia in Hebei province. Thus we proposed complementary diagnostic method to adult acetabular dysplasia radiologically criteria involving the index of femoral head center upward and outward displacements.Methods:We measured the index of femoral head center upward and outward displacements of all X-ray plain films. We drew a vertical line through point A on the inferior border of the sacroiliac joint to the homolateral anterior sacrum horizontal line which intersected at point B. Meanwhile we drew a vertical line through the femoral head center to line AB which intersected at point C. Then the value of AC/AB*100% was defined as the femoral head center upward displacement index. The smaller the value was, the more the femoral head displaced upward. We saw the middle of pubic symphysis as the body axis, then we drew the parallel lines through the outer edge of the acetabulum, the femoral head center and the lowest point of the anterior sacrum, which intersected at point O, A, B, C respectively. Then the value of OB/OA*100% was defined as the femoral head center outward displacement index. The smaller the value was, the less the femoral head shifted outward. Of which, AB/AC*100% was defined as the femoral head center outward displacement index(tear drop). The smaller the value was, the more the femoral head shifted outward. According to the diagnostic criteria of adult acetabular dysplasia(CEA<20°,sharp angle>45°, AHI<75%), we divided all those cases into abnormal group and normal group. Based on ROC curve, we defined reference values of the femoral head center upward and outward displacements.Results: By the analysis of ROC curve, we found the optimum diagnostic cut-off of femoral head center outward displacement index was 84.45% which had a sensitivity of 92% and specificity of 70.5%. The optimum diagnostic cut-off of femoral head center upward displacement index was 76.25% which showed a sensitivity of 75% and specificity of 69.7%. And, for the femoral head center outward displacement index(tear drop), the optimum diagnostic cut-off was 30.15% which had a sensitivity of 89.8% and specificity of 76.6%.Conclusions: The diagnostic cut-off of femoral head center upward and outward displacement indexes(tear drop) were 76.25% and 30.15%, respectively. The higher of these values than cut-off points, the better acetabular development, and the lower the worse. The diagnostic cut-off of femoral head center outward displacement index was 84.45%. However, the higher of this value than cut-off points, the worse acetabular development, and the lower the better. The sensitivity and specificity of above three indexes showed that they could be used as helpful complementary methods to diagnosis of adult acetabular dysplasia.