Abstract:

Objective　To investigate the entry point location and orientation of the supra-acetabular screw as well as its safe corridor size.     Methods    100 (male 50, female 50) CT data of pelvis were collected from our hospital. The three-dimensional model of supra-acetabular corridor (oriented from the anterior inferior iliac spine (AIIS) to posterior superior iliac spine (PSIS) was reconstructed by Mimics software. On the horizontal scan, the screw was placed along the two midpoints of the anterior and posterior narrowing in the corridor, and the relevant parameters of safe corridor were measured from inferior to superior at an interval layer thickness of 2.5 mm. On the middle layer, the orientations of the central virtual screws were measured and the position relation between the entry point and the center apex of AIIS was determined. The safe fixation zone was measured by moving the tip of the screw on the horizontal and sagittal planes.   Results　There were two narrowing in the supra-acetabular corridor. From inferior to superior, the width of the anterior narrowing had the characteristic of narrow-wide-narrow and the posterior narrowing became wider and wider. The width for safe fixation corridor from inferior to superior had the feature of narrow-wide-narrow. The width of the corridor on the middle layer was (10.61±2.10) mm for male and (8.44±2.03) mm for female (t=7.413，P<0.001). On the middle layer, the distances from the entry point to anterior narrowing, greater sciatic notch and posterior narrowing were about 50 mm, 70 mm and 100 mm, respectively. The whole length of the corridor was about 130 mm. The inward inclination angle was (29.50±4.05) degrees for male and (28.00±3.78) degrees for female (t=2.709, P=0.007), and the virtual screw had a safe rang about 5 degrees. The cranial inclination angle was (29.40±5.38) degrees for male and (28.57±6.01) degrees for female (t=1.025, P=0.306), and the safe rang was about 10 degrees. 97% of the entry points were located on the lateral area of the AIIS, and 71% in the lateral-inferior quadrant.   Conclusion    The entry point of the supra-acetabular screw are located on the lateral area of the AIIS. The inward and cranial inclination angles are both about 30 degrees.

Key words: Supra-acetabular fixation;   , Pelvic fracture;   , Anterior inferior iliac spine;   , Imaging study