Fig. 3
From: A dataset for quality evaluation of pelvic X-ray and diagnosis of developmental dysplasia of the hip

Radiographic classification systems for DDH. (a) Tönnis classification for DDH in children. The circle marks the femoral head ossification center. The SMA line connects the superior outer acetabular margins. The P line runs perpendicular to the SMA line through the outer acetabular edge. (b) IHDI classification for DDH in children. The circle indicates the proximal femoral metaphysis midpoint. The H line spans the inferior iliac borders above the triradiate cartilage. Line D bisects the inferior lateral quadrant formed by H and P lines.