Proposal for a new trajectory for subaxial cervical lateral mass screws

Area of Science:

• Orthopedic Surgery
• Spine Surgery
• Biomechanical Engineering

Background:

• Posterior cervical spine subaxial fixation commonly uses lateral mass screws and rods.
• Established techniques (Roy Camille, Magerl, Anderson, An) rely on tridimensional angles.
• The reliability of freehand angle estimation in these techniques is not well-understood.

Purpose of the Study:

• To introduce and evaluate a novel posterior cervical spine fixation technique.
• To compare the proposed technique against established methods (Magerl, Anderson, An).
• To assess screw length and potential neurovascular complications associated with each technique.

Main Methods:

• Four lateral mass screw insertion techniques (Magerl, Anderson, An, and the new technique) were applied bilaterally to human spine specimens (C3-C6).
• Screw length was measured after inserting a drill tip guide wire.
• Potential vertebral artery and nerve root injuries were evaluated based on screw exit points.

Main Results:

• The new technique yielded significantly longer screws (17.03 mm) compared to Magerl (14.05 mm), Anderson (13.47 mm), and An (12.8 mm) (p < 0.00001).
• Neurovascular complications were substantially lower with the new technique (2 instances) versus An (13), Anderson (28), and Magerl (37).
• Vertebral artery injury occurred once with Magerl's and 8 times with Anderson's, but never with An's or the new technique.

Conclusions:

• The novel technique facilitates the use of longer lateral mass screws, enhancing purchase and spinal stability.
• This approach significantly reduces the risk of neurovascular complications in posterior cervical spine fixation.