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
