Safe surgical corridor for iliosacral screw placement in unstable pelvic fractures: a computed-tomography-guided validation study of the “triangulation method”

BACKGROUND: The percutaneous iliosacral screw technique represents a global standard fixation method for unstable fractures of the posterior pelvic ring. However, the inaccurate positioning of iliosacral screws is associated with a significant risk of severe intra-operative complications. Therefore, this study aimed to investigate the relationship between the skin entry point of the transverse iliosacral screw of the first sacral vertebral body and the anterior superior iliac spine and the greater trochanter of the femur using computed-tomography-guided validation. METHODS: Overall, 91 consecutive patients admitted to a tertiary referral center in China for posterior pelvic ring fixation via the “triangulation method” using computed-tomography-guided validation between January 1, 2020, and December 31, 2020, were included in this retrospective observational cohort study. Modeling and simulated iliosacral screw placement were performed using the Mimics software. The distance between the three points of interest was measured, and their relationship in a rectangular coordinate system was determined. Patients were categorized according to gender, body mass index, and femoral rotation angle to investigate the factors affecting the positional relationship between the three points. RESULTS: An equilateral triangular relationship was observed between the positioning points of the transverse iliosacral screw, anterior iliac spine, and greater trochanter. Additionally, 95% of the entry points were within a circle radius centered 12 mm at the apex of an equilateral triangle comprising the anterior superior iliac spine and the greater trochanter as the base. The entry point in the femoral external rotation was more dorsal than that in the internal femoral rotation. Furthermore, the entry point in females was more rostral than that in males, and the entry point in overweight patients was more dorsal than that in normal-weight patients. CONCLUSIONS: The skin entry point of the percutaneous iliosacral screw can be located by drawing an equilateral triangle from the anterior superior iliac spine and the greater trochanter as the base to the dorsum end of the patient’s head. In summary, this retrospective cohort study validated the safety and efficacy of the “triangulation methods” for percutaneous fixation of unstable posterior pelvic ring injuries.