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Spinal cord injury (SCI) is a global problem that brings a heavy burden to both patients and society. Recent investigations indicated degenerative disease is taking an increasing part in SCI with the growth of the aging population. However, little insight has been gained about the effect of cervical degenerative disease on the spinal cord during dynamic activities. In this work, a dynamic fluid-structure interaction model was developed and validated to investigate the effect of anterior and posterior encroachment caused by degenerative disease on the spinal cord during normal extension and flexion. Maximum von-Mises stress and maximum principal strain were observed at the end of extension and flexion. The abnormal stress distribution caused by degenerative factors was concentrated in the descending tracts of the spinal cord. Our finding indicates that the excessive motion of the cervical spine could potentially exacerbate spinal cord injury and enlarge injury areas. Stress and strain remained low compared to extension during moderate flexion. This suggests that patients with cervical degenerative disease should avoid frequent or excessive flexion and extension which could result in motor function impairment, whereas moderate flexion is safe. Besides, encroachment caused by degenerative factors that are not significant in static imaging could also cause cord compression during normal activities.

This study aims to establish and validate a poroelastic L4-L5 finite element model to evaluate the effect of different sitting postures and their durations on the mechanical responses of the disc. During the sustained loading conditions, the height loss, fluid loss and von-Mises stress gradually increased, but the intradiscal pressure decreased. The varying rates of aforementioned parameters were more significant at the initial loading stage and less so at the end. The predicted values in the flexed sitting posture were significantly greater than other postures. The extended sitting posture caused an obvious von-Mises stress concentration in the posterior region of the inter-lamellar matrix. From the biomechanical perspective, prolonged sitting may pose a high risk of lumbar disc degeneration, and therefore adjusting the posture properly in the early stage of sitting time may be useful to mitigate that. Additionally, upright sitting is a safer posture, while flexed sitting posture is more harmful.

Objective Preexisting severe cervical spinal cord compression is a significant risk factor in cervical hyperextension injury, and the neurological function may deteriorate after a slight force to the forehead. There are few biomechanical studies regarding the influence of pathological factors in hyperextension loading condition. The aim of this study is to analyze the effects of preexisting different types of cervical disc herniation and different degrees of compression on the spinal cord in cervical hyperextension. Method A 3D finite element (FE) model of cervical spinal cord was modeled. Local type with median herniation, local type with lateral herniation, diffuse type with median herniation, and diffuse type with lateral herniation were simulated in neutral and extention positions. The compressions which were equivalent to 10%, 20%, 30%, and 40% of the sagittal diameter of the spinal cord were modeled. Results The results of normal FE model were consistent with those of previous studies. The maximum von Mises stresses appeared in the pia mater for all 32 loading conditions. The maximum von Mises stresses in extension position were much higher than in neutral position. In most cases, the maximum von Mises stresses in diffuse type were higher than in local type. Conclusion Cervical spinal cord with preexisting disc herniation is more likely to be compressed in hyperextension situation than in neutral position. Diffuse type with median herniation may cause more severe compression with higher von Mises stresses concentrated at the anterior horn and the peripheral white matter, resulting in acute central cord syndrome from biomechanical point of view.