The Anatomical Position of Graf's Standard Plane and Its Relationship With Pelvic Morphology: A Computed Tomography-Based Study.

Objective The Graf method is the most widely used ultrasonographic method for evaluating developmental dysplasia of the hip (DDH), and it relies on a set standard plane. However, no previous reports have discussed the detailed anatomical location of the plane. The aim of this study was to evaluate the exact anatomical position of Graf's standard plane in the pelvis and to ascertain the correlation between this position and pelvic morphology in children without abnormal pelvic morphology. Methods We retrospectively assessed the pelvic CT data of 32 children (64 hips) aged three to five years without abnormal pelvic morphology and measured the pelvic winging and acetabular anteversion and coverage. We defined the coronal plane that passed through the center of the bilateral femoral head as plane A. We determined that Graf's standard plane could be approximated by rotating plane A until the outer wall of the ilium was parallel to the sagittal plane, and we defined this as plane A'. AA' was defined as the angle from plane A to plane A' on the sagittal plane. The anterior rotational angle (clockwise, viewing from the right side) was measured as the positive AA'. Moreover, we measured the pelvic rotation, acetabular anteversion, and acetabular coverage and evaluated the correlation between AA' and these morphological parameters. Results The average AA' was -8.27° and AA' had a significant correlation with acetabular anteversion (Spearman's ρ=0.40**, p<0.01). Conclusions We found that Graf's standard plane, as determined by the CT scan, tilts slightly posteriorly. This information may be useful in improving the ease of ultrasonographic examination of DDH.