Fig. 1

a: The axial observation perspective was parallel to the quadrilateral surface (green dotted line) and perpendicular to the arcuate line (red dotted line). The region surrounded by the green line was commonly used for screw placement through the middle window of the ilioinguinal approach. Insertion point O was 5 mm away from the quadrilateral surface. The blue line represents the distance from eminelntia iliopectinea to the quadrilateral surface. OO’ represents the distance from point O to the blue line. b: The distance (blue dotted line) from point A and point B to point O was 10 mm. Points A, O and B were on the same line, which was parallel to the quadrilateral surface