The Trajectory of Iliac Screw in the Axial Plane in 200 Korean Patients

STUDY DESIGN: A retrospective radiographic analysis. PURPOSE: To estimate the accurate trajectory in the axial plane for iliac screw insertion in 200 Korean patients using radiographic images. OVERVIEW OF LITERATURE: Several complications have been encountered after fusion to the lumbosacral junction, including pseudarthrosis, S1 screw loosening, and sacral fractures. Iliac screw fixation is considered an efficient method for augmenting sacral screw fixation but there are few reports on the trajectory of iliac screw insertion. The trajectory in the sagittal plane can be visualized by intraoperative fluoroscopy. However, there is no method to check the accuracy of the trajectory in the axial plane during surgery. METHODS: Between January 2007 and February 2009, 200 patients (107 men and 93 women) who underwent L-spine computed tomography were enrolled in this study. The mean age of the patients was 55.6 ± 18.3 years (range, 13 to 92 years). The spino-iliac angle (SIA) was measured on the axial image at the S1 level, which was defined as the angle between a vertical line through the center of the spinous process and an oblique line that passed through the center of the outer and inner cortices of the ilium. RESULTS: The group mean SIA was 30.1° ± 7.8°; 30.1° ± 7.7° for men and 29.9° ± 81.1° for women. There was no significant difference according to gender or age (p > 0.05). CONCLUSIONS: The SIA for the axial trajectory of iliac screws is approximately 30° in Korean patients.