What are the best trajectories for multiple iliac screw placement in spine surgeries? An anatomical, radiographical and morphometric cadaver analysis.

Abstract

BackgroundConcepts for spinopelvic fixation evolved dramatically over the last decades. Schildhauer et al. described the posterior superior iliac spine (PSIS) – anterior inferior iliac spine (AIIS) trajectory as the optimal bony canal for iliac screw placement. This trajectory has proven to be reliable and valid in terms of effectivity and clinical usefulness. Therefore, this trajectory can be considered as ‘gold standard’ in iliac screw fixation. However, to our knowledge no one described the anatomical considerations in other trajectories to support decision making in patients who need a multiple iliac screw fixation. Our hypothesis is that the trajectory with a starting point between the PSIS and PIIS aimed towards the AIIS might be the second best trajectory for iliac screw placement. MethodsWe performed an anatomical cadaver study to analyze a total of five different trajectories (T1-5) for iliac screw placement. T1: Insertion point (IP) PSIS to AIIS; T2: IP between PSIS&PIIS to AIIS; T3. IP iliac tubercle to AIIS; T4. IP PIIS to AIIS; T5 IP PSIS to Iliac crest (perpendicular to T1). ResultsThe bony canal length was 13.5cm at T1, 12.6cm at T2, 11.8cm at T3, 11.3cm at T4 and 7.8cm at T5. The intercortical width was 1.6cm at T1, 1.5cm at T2, 1.1cm at T3, 2.0cm at T4 and 1.3cm at T5. The longest distances to the next narrow area was 9.4cm at T1, 7.8cm at T2, 8.0cm at T3, 9.3cm at T4 and 5.7cm at T5 (Table 1).The average cortical thickness at the PSIS was 1.97mm (female 1.98mm vs. male 1.96mm) compared to 2.14mm (female 2.2mm vs. 2.1mm) at the starting of T2 (Table 2). ConclusionOur study indicates that the second-best trajectory for iliac screw placement might be the trajectory 3 with a insertion point between the PSIS and PIIS aiming towards the AIIS. These results are in line with the previous reported morphometric studies and might support the surgeon in the decision making to enable optimal multiple iliac screw placement. Biomechanical and clinical are needed to further improve decision making for multiple iliac screw placement.