Fig. 4From: The safe screw path along inferior border of the arcuate line at acetabular area: an anatomical study based on CT scansFor section 2, 3 and 4, a line through the screw entry point and tangent to the lower margin of the arc was defined as the screw-placement direction. The angle between this tangent line and the normal plane was marked as θ. Due to the similar shaping, the measurement for section 2 and section 3 was represented with the same modelBack to article page