A Biomechanical Comparison of Distraction Methods for Treatment of Basilar Invagination

Introduction: Treatment of basilar invagination aims to reduce the deformity, realign the craniovertebral junction, and relieve compression of the spinal cord and brainstem through C1-2 distraction. Due to the distractive forces required and risk of vertebral artery damage, the latter may be technically challenging. This study compares the biomechanical stability of two different BI treatment techniques: joint distraction using screw-rod constructs alone and intra-articular spacers with screw-rod constructs.

Methods: Polyaxial screws were inserted in the bilateral C1 lateral mass and bilateral C2 vertebrae of twelve fresh frozen human cadavers. C2 screw techniques included pedicle, pars, medial in-out-in, and subfacetal, and translaminar. C1-2 range of motion (ROM) was tested using a six-degrees-of-freedom motion simulator in flexion/extension (FE), lateral bending (LB), and axial rotation (AR) with motion analysis software. Each specimen underwent four ROM tests: intact, no distraction, distraction with spacers, distraction without spacers. All constructs had screw and rod fixation except intact.

Results: Average ROM for intact specimens was 11.04° in FE, 3.21° in LB, and 59.43° in AR. A two-way mixed ANOVA showed a significant difference (p <.001) between intact and all other constructs: screw-rods, spacers, and distraction. There was a significant difference between distraction with spacer constructs and distraction without spacer constructs on FE (p = .001), LB (p < .001), and AR (p = .001) motion. Compared to the spacer construct, ROM increased by 137.7% ± 132.47% in FE, 308.6% ± 255.2% in LB, and 132.4% ± 84.3% in AR for the distraction without spacer construct.

Conclusion : Distraction of C1-2 for basilar invagination using intra-articular spacers provided more stability compared to distraction without spacers. Further studies may involve a dynamic model to show distraction without spacers may increase stress and strain on screw-rod constructs alone.