1. Axial view – Left Iliosacral at S1
Coronal view – Left Iliosacral at S1 B
Axial view - TSTI at S1 C
Coronal view - TSTI at S1 D
Axial view - TSTI at S2 E
Coronal view - TSTI at S2 F
Figure, Supplemental Digital Content 1A-F. This figure shows the measurement technique used to measure “safe” radiologic pathways. For the trans-sacral trans-iliac (TSTI) screw measurements, the anterior white line is defined as the most posterior (or caudal) margin of either the iliac cortical density or the anterior sacral slope at either S1 or S2. The posterior white line is defined as the most anterior border of either the S1 neural foramen or S2 neural foramen for S1 and S2, respectively. For the ilio-sacral screw measurements, the white line represents the path taken by an iliosacral screw. In either TSTI or ilio-sacral screw measurements, the red arrow represents the measurement taken. Note for ilio-sacral screws, measurements were done bilaterally but only the left is shown for demonstration. Measurement techniques are shown for a(n) (a) axial view for width measurement for a left ilio-sacral screw at S1, (b) coronal view for height measurement for a left ilio-sacral at S1, (c) axial view for width measurement for a TSTI screw at S1, (d) coronal view for height measurement for a TSTI screw at S1, (e) axial view for width measurement for a TSTI screw at S2, and (f) coronal view for height measurement for a TSTI screw at S2.