Imaging study of second sacral alar-iliac screw placement in adult degenerative scoliosis

Abstract

Objective To discuss the imagingcharacteristics of S2AI screw trajectory in ADS patients. Methods Forty patients with degenerative scoliosis were scanned with Simens Sliding 40-slice spiral CT scanner. Three-dimensional scanning and reconstruction were performed in these patients with the scanning range including thoracolumbar spine, lumbar spine, lumbosacral region, pelvis and bilateral hip joints. The base of the lateral sacral crest on the midline between the lower edge of S1 dorsal foramina and the upper edge of S2 dorsal foramina was the starting point. The placement plane of S2AI screw trajectory was determined from the starting point to the lower margin of anterior inferior iliac spine. A 10mm diameter screw was the design template. A circle with a diameter of 5 mm as the center of the lowest point of the ilium inner cortex was made, and a tangent line from the starting point to the outer diameter of the circle (the inner part of the ilium) was selected as the axis of the screw trajectory. The lateral angle and the length of the axis of the screw trajectory and iliac width were measured in transverse plane. The caudal angle, the distance from the axis of the screw trajectory to iliosciatic notch, and the caudal angle, the distance from the axis of the screw trajectory to the upper edge of the acetabulum were measured in sagittal plane. These parameters were recorded and analyzed. Results The trajectory length of S2AI screw in ADS patients was 12.00±0.99 cm, the lateral angle was 41.24°±3.92°, the caudal angle was 27.73°±6.45°, and the distance from the axis of the screw trajectory to iliosciatic notch was 1.05±0.81 cm, the distance from the axis of the screw trajectory to the upper edge of the acetabulum was 1.85 ± 0.33 cm, and the iliac width was 2.12±1.65 cm. The trajectory length, lateral angle, caudal angle, distance from the axis of the screw trajectory to iliosciatic notch, distance from the axis of the screw trajectory to the upper edge of the acetabulum and iliac width of S2AI screw was respectively 12.40±0.83 cm, 39.47°±1.76°, 28.00°±6.39°, 1.08±0.32 cm, 1.76±0.34 cm, 2.26±0.25 cm in male patients, and was respectively 11.75±1.01 cm, 42.30°±4.48°, 27.56°±6.61°, 1.21±1.00 cm, 1.90±0.32 cm, 2.04±0.18 cm in female patients. The screw length and lateral angle had statistically difference between male and female patients(P<0.05). Compared with non-ADS patients in previous studies, female patients with ADS had significant differences in increased lateral angle and decreased caudal angle of S2AI screw. Conclusion There is ideal trajectory of S2AI screws in ADS patients. There was no significant difference of the length of S2AI screws between ADS patients and non-ADS population. Different direction was noticed in the placement of S2AI screws, especially in female patients. Increased lateral angle and decreased caudal angle would be obtained in the procedure of placing S2AI screws in female ADS patients during operation. Key words: Adult; Lumbar vertebrae; Intervertebral disc degeneration; Scoliosis; Spinal fusion; Pelvis; Tomography scanners, X-ray computed