C1 pedicle screw placement risks in patients with ponticulus posticus: a CTA retrospective simulation study

Area of Science:

• Neurosurgery
• Radiology
• Orthopedic Surgery

Background:

• Ponticulus posticus (POPO) may distort C1 anatomy, increasing risk of vertebral artery compromise (VAC) during C1 pedicle screw (CPS) placement.
• A reliable workflow is needed to identify POPO anatomies suitable for safe CPS placement.

Purpose of the Study:

• To establish a computed tomography angiography (CTA)-based workflow to identify POPO anatomies potentially suitable for CPS placement.
• To evaluate the feasibility and safety of simulated CPS placement in patients with and without POPO.

Main Methods:

• Retrospective CTA simulation study of 141 subjects (46 bilateral POPO, 65 unilateral POPO, 30 non-POPO).
• Simulated CPS trajectories using PedicleScrewSimulator, analyzing morphometric parameters including D3 and D5.
• Evaluated simulated CPS feasibility and VAC for various screw diameters (2.5-4.0 mm).

Main Results:

• Significant differences in D1 and D1-D2 shift among groups; D5 was smaller in bilateral POPO patients.
• Overall simulated CPS feasibility was 96.0% for 3.5 mm screws.
• POPO sides had 93.5% feasibility and 6.5% VAC, versus 99.2% and 0.8% in regular sides.
• An exploratory D3/D5 rule (D3 ≥ 3.4 mm and D5 ≥ 2.0 mm) showed 100% specificity for avoiding simulated 3.5-mm VAC.

Conclusions:

• CTA-based D3 and D5 thresholds can identify POPO anatomies suitable for CPS placement.
• The D3/D5 rule may serve as a conservative screening tool for CPS placement in POPO.
• POPO should not preclude CPS consideration but warrants careful CTA analysis and conservative screw selection.