Optimizing iliac screw fixation: a biomechanical study on screw length, trajectory, and diameter

Area of Science:

• Spinal surgery
• Orthopedic biomechanics
• Surgical instrumentation

Background:

• Iliac screw fixation is crucial for spinal fusion.
• Optimizing screw placement enhances stability and reduces complications.
• Understanding factors influencing insertional torque is key to surgical success.

Purpose of the Study:

• To determine the optimal iliac screw size, length, and trajectory for maximal insertional torques.
• To evaluate the impact of screw diameter, trajectory, and depth on fixation strength.
• To correlate insertional torque with specific anatomical landmarks.

Main Methods:

• Ten fresh cadavers were utilized for screw placement.
• 7.5 × 140-mm and 9.5 × 140-mm iliac screws were inserted using 3D image guidance.
• Two trajectories (supraacetabular and AIIS) and insertional torque measurements were recorded.

Main Results:

• Screw diameter significantly impacted insertional torque (9.5mm > 7.5mm).
• Torque increased with screw depth, particularly beyond 80mm.
• Trajectory (supraacetabular vs. AIIS) did not significantly affect torque.

Conclusions:

• Larger diameter and longer iliac screws achieve higher insertional torques.
• Placement near the lateral iliac cortex and superior iliac fossa maximizes fixation.
• Image guidance enables safe and accurate placement of longer iliac screws.