Study finds, Biomechanical effect of preexisting different t
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. 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.

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.

--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.

In conclusion, in hyperextension, the cervical spinal cord with a previous disc herniation is more likely to be crushed than in neutral. From a biomechanical standpoint, the diffuse form with median herniation may induce more severe compression with larger von Mises stresses focused at the anterior horn and peripheral white matter, leading to acute central cord syndrome.