Deformity of the pelvis in developmental dysplasia of the hip: three-dimensional evaluation by means of magnetic resonance image.

Magnetic resonance images of the transverse section of the whole pelvis were obtained in eight infants (two boys and six girls) with unilateral developmental dysplasia of the hip (DDH), and then a three-dimensional image of the pelvis was reconstructed from each slice by using a computerized technique. Based on it, the deformity of the pelvis with DDH was analyzed by measuring bony configuration from the superoinferior, anteroposterior and lateral views. The prime deformity of the pelvis with DDH was not only a simple malrotation but also an increased medial twisting of the whole involved pelvic wing. As a result, the entrance of the socket rotates more anteriorly because of this distortion, which leads to poor anterior acetabular coverage over the femoral head.