What are the best Trajectories for Multiple Iliac Screw placement in Spine Surgeries? An anatomical, radiographical and morphometric cadaver analysis.

Objectives: A multiple iliac screw fixation can be necessary in cases of osteoporotic bone, communited sacral fractures, en bloc resection of sacral tumors, high grade instabilities and revision surgeries. Protocols or technical recommendation for multiple iliac screws do not exist. The posterior superior iliac spine (PSIS) - anterior inferior iliac spine (AIIS) trajectory has proven to be reliable and valid in terms of effectivity and clinical usefulness. However, to our knowledge no one described anatomical considerations in other trajectories to support the decision making. We therefore, performed an anatomical cadaver study to analyze a total of five different trajectories for iliac screw placement.

Methods: The procedure was performed on two fresh frozen and predissected male pelveses (left and right side) in a surgical training facility. All screws were placed by fellowship trained spine surgeon and an attending spine surgeon. We used five different trajectories as shown in Figure 1.

T1: PSIS -> AIIS

T2: between PSIS&PIIS -> AIIS T3. Iliac tubercle -> AIIS

T4. PIIS -> AIIS

T5. PSIS -> Iliac crest (perpendicular to T1)

A CT-scan was used to confirm screw positioning and measure the trajectory as well as the cortical thickness at the insertion point (T1&T2).

Results and Conclusion: The results for the tested screw trajectories were as follows: (T1) length 13.5 cm, width 1.6 cm; (T2) length 12.5cm, width 1.5 cm; (T3) length 10.8 cm, width 1.1 cm; (T4) length 11.3 cm, width 2.0 cm and (T5) length 8.8 cm, width

1.3 cm. We measured and compared the cortical thickness at the insertion point between T1 and T2 using the CT scans of 30 patients (15m/15f) who underwent a major deformity surgery. The mean age was 62.0 years. The cortical thickness at the PSIS was thinner (1,97 mm) compared to the insertion point of T2.

Our study indicates that the second-best trajectory for iliac screw placement might be the trajectory with a starting point between the PSIS and PIIS. 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.

Stichwörter: iliac screws, trajectories, multiple screws, spine, lumbopelvic fixation

Publication History

Article published online:
15 October 2020