Biomechanical Evaluation of a C1-C2 Posterior Arch Screw Construct

Study DesignIn-vitro biomechanical study.ObjectivesInjuries or degenerative conditions can lead to atlantoaxial instability requiring fixation. We aim to assess and compare the biomechanics of a C1-C2 posterior arch and translaminar screw construct against the Harms procedure for posterior atlantoaxial fixation on a human cadaveric model.MethodsNine human cadaveric cervical specimens from occiput to C3 (C0-C3) were used for range of motion (ROM) testing. Each specimen was tested for 4 configurations: 1. Intact, 2. Destabilized, 3. Harms construct, 4. C1-C2 posterior arch screw (PAS) construct. A pure moment of 1.5 Nm was applied, and ROM of the C1-C2 segment was measured in flexion-extension, lateral bending, and axial rotation.ResultsThe Harms group showed a decrease in ROM in all modes (<i>P</i> < 0.021), and the PAS group showed a decrease in ROM in flexion-extension and lateral bending (<i>P</i> < 0.002), but not in lateral bending (<i>P</i> = 0.176). Compared to the intact condition, Harms showed increased ROM for flexion-extension (<i>P</i> = 0.012), and PAS did not (<i>P</i> = 0.258). In lateral bending, both constructs did not significantly reduce ROM (<i>P</i> > 0.058). In axial rotation, both constructs showed a significant increase in ROM (<i>P</i> < 0.002). There was no significant difference in ROM when comparing Harms with PAS in flexion-extension (<i>P</i> = 1.000), lateral bending (<i>P</i> = 0.163), or axial rotation (<i>P</i> = 1.000).ConclusionsThe study demonstrates that a C1-C2 PAS construct restores or increases biomechanical stability compared to the intact condition. C1-C2 PAS offers similar biomechanical stability compared to the Harms construct.