Do Iliac Screws Placed Close to the Sciatic Notch Have Greater Pullout Strength?

Area of Science:

• Spinal surgery
• Orthopedic biomechanics
• Surgical anatomy

Background:

• Optimal placement of S2 alar-iliac (S2AI) screws relative to the sciatic notch is not well-defined.
• Understanding screw positioning is crucial for spinal fusion procedures.

Purpose of the Study:

• To compare the biomechanical pullout strength of S2AI screws placed within 5 mm versus greater than 5 mm from the sciatic notch.
• To evaluate fixation strength and stability in relation to sciatic notch proximity.

Main Methods:

• A biomechanical study using 12 cadavers with bilateral S2AI screw insertion.
• Screws were dichotomized as ≤5 mm (right) or >5 mm (left) from the sciatic notch, confirmed via fluoroscopy.
• Pullout strength, stiffness, yield force, and work to failure were measured using a load cell and analyzed with the Mann-Whitney test.

Main Results:

• No statistically significant difference in screw pullout strength between screws close to and far from the sciatic notch (861.8 ± 340.7 N vs 778.7 ± 350.8 N, P=.859).
• Trends for higher stiffness and yield force were observed for screws closer to the notch, but these were also not statistically significant.
• Work to failure was higher for screws farther from the notch, though this difference was not significant.

Conclusions:

• Placing S2AI screws ≤5 mm from the sciatic notch did not yield statistically stronger fixation compared to screws placed farther away.
• The proximity of S2AI screws to the sciatic notch does not significantly impact biomechanical fixation strength in this cadaveric model.