Cervical stability with lateral mass plating: unicortical versus bicortical screw purchase

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Spinal Fusion Techniques

Background:

• Traditional cervical lateral mass fixation uses bicortical screws, risking injury to vertebral vessels and nerve roots.
• Unicortical fixation offers a potentially safer alternative by avoiding these complications.
• Previous studies suggest comparable stability, but comprehensive biomechanical data is lacking.

Purpose of the Study:

• To biomechanically compare the cervical stability of lateral mass fixation using unicortical versus bicortical screw purchase.
• To evaluate the influence of screw length and laminectomy on fixation stability.

Main Methods:

• Human cadaveric cervical spine sections (C3-C5) were tested under flexion-extension, torsion, and lateral bending.
• Fixation constructs included bicortical screws, long unicortical screws (14mm), and short unicortical screws (10mm).
• Testing was performed with and without laminectomy using an MTS machine, with displacement measured under applied torque.

Main Results:

• Bicortical constructs were generally stiffer than unicortical constructs in most bending modes.
• No significant differences in stability were observed between bicortical and long unicortical constructs without laminectomy.
• Significant differences emerged in the lateral bending mode with laminectomy, and between bicortical and short unicortical constructs.

Conclusions:

• Long unicortical Magerl screws may serve as an acceptable and safe alternative to bicortical screw fixation for cervical lateral mass fixation.
• This approach could mitigate the risks associated with bicortical screw placement.