Prediction of sagittal pelvic rotation in plain pelvis x-ray

Abstract

Different methods had been described to estimate the degree of sagittal pelvic rotation in plain pelvic AP XR. Tang measured the obturator foramen ratio, which was defined as the tallest height over the widest width of the right obturator foramen. Katada and Ando measured the pelvic-tilt index, which was defined as the vertical diameter of the obturator foramen divided by the horizontal diameter of the pelvic foramen. Nishihara estimated the pelvic flexion angle by calculating the ratio of the vertical diameter of the pelvic foramen to the horizontal diameter. In our study, 15 sets of plain pelvic AP XR were randomly selected from our XR database for patients having avascular necrosis of hip. Values were then calculated according to methods described by Tang (Mean 0.86, SD 0.11, Range 0.66- 1.14), Katada and Ando (Mean 0.68, SD 0.09, Range 0.47-0.85), and Nishihara (Mean 0.68, SD 0.09, Range 0.47-0.85) respectively for reference. Plain pelvic AP XR were then taken in 13 sets of cadaveric bony pelvis in pre-determined degree of sagittal pelvic rotation (pelvis in neutral sagittal rotation, in 10°, 20°, 30°, 40°, 50° hyperextension, and in 10°, 20°, 30° hyperflexion). The effect of sagittal pelvic rotation on the values calculated by the methods described by Tang, Katada and Ando, and Nishihara were then studied. CONCLUSION: Sagittal Pelvic rotation can be assessed by using Plain Pelvis X-Ray.