Atlantoaxial fixation using C1 posterior arch screws: feasibility study, morphometric data, and biomechanical...

Area of Science:

• Orthopedic Surgery
• Neurosurgery
• Spine Biomechanics

Background:

• The C1-C2 complex presents surgical challenges for achieving biomechanical rigidity and fusion.
• Traditional posterior wiring is largely replaced by segmental constructs, with recent interest in C1 posterior arch fixation.
• C2 laminar screws were developed to reduce surgical morbidity.

Purpose of the Study:

• To perform biomechanical testing of a C1 posterior arch screw (PAS)/C2 pars screw construct.
• To collect morphometric data from CT scans of 150 patients.
• To assess the feasibility of a freehand C1 PAS technique in 45 cadaveric specimens.

Main Methods:

• Cervical spine CT scans (n=150) analyzed for C1 posterior tubercle and arch dimensions.
• Biomechanical comparison of intact, C1 lateral mass/C2 pars, and C1 PAS/C2 pars constructs in 8 cadavers.
• Feasibility and safety assessment of freehand C1 PAS technique in 45 cadavers.

Main Results:

• C1 PAS/C2 pars and C1 lateral mass/C2 pars constructs significantly reduced motion in flexion-extension and axial rotation compared to intact specimens.
• No significant difference in stability between C1 PAS/C2 pars and C1 lateral mass/C2 pars constructs.
• Freehand C1 PAS technique demonstrated high accuracy (91.3% success) with low cortical breach (4.4%).

Conclusions:

• The C1 PAS/C2 pars screw construct provides biomechanical stability equivalent to the C1 lateral mass/C2 pars screw construct.
• Both constructs offer significant rigidity in flexion-extension and axial rotation for C1-C2 fixation.
• The freehand C1 PAS technique is feasible and accurate, with a low incidence of complications.