Use of the Finite Element Method to Study the Mechanism of Spinal Cord Injury Without Radiological Abnormality in the Cervical Spine

Study Design. Three-dimensional C3-C5 and C3-C4 finite element (FE) models were used to analyze biomechanical responses under compression and extension moments. Objective. To validate our models against other published FE models and experimental studies and improve our understanding of the mechanism of spinal cord injury without radiologic abnormality (SCIWORA) in cervical spine. Summary of Background Data. The underlying mechanism for SCIWORA remains unclear. We hypothesized that the incidence of SCIWORA was associated with facet joint morphology and bony pincers mechanism. Methods. FE models were constructed using data from computed tomography scans of the cervical spine of a healthy young man. The C3-C5 FE models consisted of bony vertebra, articulating facets, and intervertebral disc. Facet surfaces were oriented at 30, 45, and 60 from the transverse plane. These models were constrained in all degrees of freedom at the C5 inferior vertebral body and a uniform axial displacement of 1 mm was applied to the superior nodes of C3. Three model versions changed to C3-C4 models with ligaments. The C4 inferior-most bony nodes were constrained, whereas the top of the C3 superior-most bony nodes were left unconstrained. These models were subjected to an axial compression load of 73.6 N with extension moments (1.8 Nm) applied to the upper bony section C3 vertebra. The predicted responses were compared with published results. Results. The response under axial compression was validated and corresponded closely with published results. Under sagittal moment, the C3-C4 FE model with 60 facet was the most flexible in extension (4.22 degrees). Total translation was highest for the model with 60 facet. Conclusion. The load displacement response of C3-C5 FE models was in agreement with published data. We confirmed that the C3-C4 FE model with 60 facet was the most susceptible to SCIWORA and that the bony pincers mechanism was dependent on facet joint inclination.