Safe corridor for iliosacral and trans-sacral screw placement in Indian population: A preliminary CT based anatomical study.

Objectives: Nonsurgical management of unstable pelvic ring injuries is associated with poor outcomes. Posterior pelvic ring injuries include sacroiliac joint disruption and sacral fractures or a combination of the two. Morbidity is high in non-operatively managed patients. Screw fixation is being increasingly used to manage unstable posterior pelvic injuries. Limitations include a steep learning curve and potential for neurovascular injury. This is the first study in Indian population to describe the safe corridor for screw placement and check the feasibility of screw in both upper and lower sacral segments.

Methods: This study involved retrospective analysis of 105 pelvic CT scans of patients admitted to the emergency department of a Level 1 trauma centre. Vertical height at the level of constriction (vestibule) of S1 and S2 was measured in coronal sections and anteroposterior width of constrictions was measured in axial sections. We created a trajectory for 7.3 mm cylinder keeping additional 2 mm free bony corridor around it and confirmed that bony limits were not breached in axial, coronal and sagittal sections. Whenever there was breach in bony limit we checked applicability of 6.5 mm screw.

Results: The vertical height and anteroposterior width of vestibule/constriction of S1 was significantly higher in males, whereas S2 vestibule height and width were similar in males and females. Both male and female pelves were amenable to S1 Trans-sacral and S1 Iliosacral screw fixation with a 7.3 mm screw when a safe corridor of 2 mm was kept on all sides. However, when S2 segment was analysed, only 42.9% of male pelves and 25.7% of female pelves were amenable to insertion of trans-sacral 7.3 mm screw.

Conclusion: An individualized approach is necessary and each patient's CT must be carefully studied before embarking on sacroiliac screw fixation in Indian population.