The optimal pathway for S1 sacroiliac screwing: 3D imaging study and clinical application

Abstract

Objective To determine the optimal pathway for S1 sacroiliac screwing based on the largest safe zone in Chinese population using 3D imaging models and observe its clinical application in patients with sacroiliac joint fracture or dislocation. Methods Pelvic CT scans of 54 Chinese adults were obtained to create reconstruction 3D models of the right hemi-pelvis. After the models were transparentized and rotated to the axial view of the S1 pedicle, the angle was slightly adjusted to maximize the translucent safe zone. Next, simulative insertion into the center of this zone was conducted with one virtual screw, as large as possible and tangent to the boundary. Measured were the diameter and length of the screw, the vertical distances from the entry point to the horizontal tangent line of the greater sciatic notch and to the vertical tangent line of the posterior superior iliac spine, and from the exit point to the S1 superior endplate and to the anterior cortex. The differences between males and females were analyzed. The above parameters of the optimal pathway for S1 sacroiliac screwing were used in insertion of 16 screws in the 12 patients with sacroiliac joint fracture or dislocation from January 2014 to January 2016 at Department of Orthopaedics and Traumatology, Nanfang Hospital. They were 8 males and 4 females, from 16 to 47 years of age (average, 34 years). According to the Tile classification, 6 cases belonged to Type Ⅱ and 6 ones to Type Ⅲ. The efficacy of S1 sacroiliac screwing was observed. Results In all the pelvic 3D imaging models, an oval translucent area for safe screw insertion could be easily identified from the S1 pedicle axial view. The maximum diameter and length of the optimal intraosseous pathway were 13.66±2.04 mm and 77.66±4.25 mm; the vertical distances from the entry point to the horizontal tangent line of the greater sciatic notch and to the vertical tangent line of the posterior superior iliac spine were 32.77±4.55 mm and 49.57±5.24 mm; the vertical distances from the exit point to the S1 superior endplate and to the anterior cortex were 9.30±1.54 mm and 15.85±2.12 mm. The differences were of statistical significance between males and females regarding the maximum diameter, the distance from the entry point to the vertical axis, and the distance from the exit point to the anterior cortex (P<0.05). All the 16 screws were safely implanted in the 12 patients. Conclusion The optimal screw pathway can be easily identified and its parameters can be measured in pelvic 3D imaging models using computer virtual technology. The clinical application has proved that the parameters can serve as a theoretical basis for safe placement of S1 sacroiliac screws. Key words: Sacroiliac joint; Bone nails; Fracture fixation, internal; Computer virtual technology; Anatomy