The sacral screw placement depending on morphological and anatomical peculiarities

Area of Science:

• Spinal surgery
• Anatomy
• Radiology

Background:

• Lumbosacral fusion (L5/S1) is common for spinal pathologies.
• Sacral screw loosening and pseudarthrosis are significant complications.
• Iliac vessel injury is a risk during S1 screw placement.

Purpose of the Study:

• To identify a "safe zone" for bicortical screw placement at L5/S1.
• To analyze morphological features of the L5/S1 segment to avoid iliac vessel damage.
• To reduce the incidence of pseudarthrosis and screw loosening.

Main Methods:

• Analysis of 100 pelvic CT scans.
• Evaluation of pedicle morphology, iliac vessel and spinal canal positions.
• Assessment of bone density and screw placement angles.

Main Results:

• Iliac vessels average 7° convergence from S1 screw entry point; spinal canal averages 38°.
• Central sacral bone density (276 HU) is higher than the sacral ala.
• Maximal intraosseous screw length achieved at 25° convergence; pedicle dimensions: 20mm width, 13mm height.

Conclusions:

• A safe zone for S1 bicortical screw placement is between 7° and 38° convergence.
• 25° convergence at S1 is recommended for optimal bone density and screw length, reducing loosening.
• Screw diameter is limited by pedicle height, not width.