Background:The pathogenesis of the central cord syndrome is still unclear. While there is a consensus on hyperextension as the main traumatic mechanism leading to this condition, there is yet to be consensus in studies regarding the pathological features of the spine (intervertebral disc bulging or ligamentum flavum hypertrophy) that could contribute to clinical manifestations. Methods:A comprehensive finite element model of the cervical spine segment and spinal cord was used to simulate high-speed hyperextension. Four stenotic cases were modelled to study the effect of ligamentum flavum hypertrophy and intervertebral disc bulging on the von Mises stress and strain.Findings: During hyperextension, the downward displacement of the ligamentum flavum and a reduction of the spinal canal diameter (up to 17%) led to a dynamic compression of the cord.Ligamentum flavum hypertrophy was associated with stress and strain (peak of 0.011 Mpa and 0.24, respectively) in the lateral corticospinal tracts, which is consistent with the histologic pattern of the central cord syndrome. Linear intervertebral disc bulging alone led to a higher stress in the anterior and posterior funiculi (peak 0.029 Mpa). Combined with hypertrophic ligamentum flavum, it further increased the stress and strain in the corticospinal tracts and in the posterior horn (peak of 0.023 Mpa and 0.35, respectively). Interpretation:The stenotic typology and geometry greatly influence stress and strain distribution resulting from hyperextension. Ligamentum flavum hypertrophy is a main feature leading to central cord syndrome.

Posterior ligamentous complex (PLC) and intervertebral disc (IVD) injuries are common cervical spine flexion-distraction injuries, but the residual stability following their disruption is misknown. The objective of this study was to evaluate the effect of PLC and IVD disruption on post-traumatic cervical spine stability under low flexion moment (2 Nm) using a finite element (FE) model of C2-T1. The PLC was removed first and a progressive disc rupture (one third, two thirds and complete rupture) was modeled to simulate IVD disruption at C2-C3, C4-C5 and C6-C7. At each step, a non-traumatic flexion moment was applied and the change in stability was evaluated. PLC removal had little impact at C2-C3 but increased local range of motion (ROM) at the injured level by 77.2% and 190.7% at C4-C5 and C6-C7 respectively. Complete IVD rupture had the largest impact on C2-C3, increasing C2-C3 ROM by 181 % and creating a large anteroposterior displacement of the C2-C3 segment. The FE analysis showed PLC and disc injuries create spinal instability. However, the PLC played a bigger role in the stability of the middle and lower cervical spine while the IVD was more important at the upper cervical spine. Stabilization appears important when managing patients with soft tissue injuries.