Second Sacral Alar Screw Fixation: Anatomic Study of Three-Dimensional Computed Tomography and Case Report

Area of Science:

• Spinal surgery
• Orthopedic biomechanics
• Radiographic anatomy

Background:

• Posterior S2 alar screws are a potential alternative for sacral fixation in lumbosacral instrumentation and fusion.
• Optimal placement requires understanding specific radiographic parameters to avoid sacroiliac joint disruption.

Observation:

• A morphometric study utilized 3D CT scans of 60 adult pelves to map S2 alar screw trajectories.
• Entry points were typically superior and lateral to the S2 dorsal foramen.
• Ideal trajectories were identified by maximizing length and width in the transverse and sagittal planes.

Findings:

• Optimal S2 alar screw trajectories were identified, with significant differences in lateral angulation between sexes (females more lateral).
• Male patients demonstrated significantly longer maximal trajectory lengths compared to female patients.
• Clinical application in 7 patients with complex spinal conditions showed no intraoperative complications, with one screw failure due to osteoporosis.

Implications:

• S2 alar screws provide a viable option for enhancing biomechanical stability in lumbosacral constructs.
• 3D CT analysis enables precise determination of S2 alar screw trajectories for safe and effective surgical planning.
• This morphometric data aids surgeons in selecting optimal screw placement for improved patient outcomes.