Neurological compromise as a result of a tension-extension injury in the cervical spine

Until neurological repair can be successfully achieved, prevention remains the greatest tool for evading the consequences of spinal cord injury (SCI). Current practices for the design of safety devices require an understanding of the threshold for injury; and, in the case of neck injury the threshold has traditionally been failure of the vertebral column. However, SCI may present without catastrophic failure of the column. The relative strain between the vertebral column and the spinal cord, an in vitro histological analysis, and an assessment of neurologic impairment in a tension-extension injury model were performed to enable the investigation of the strain injury threshold for SCI.;Three separate but interrelated studies were conducted to describe the injury threshold of the spinal cord in tension-extension at a loading rate of 350N/s. The first study tested the strain coupling ratio between the cervical vertebral column and spinal cord in ten in vitro Macaca nemestrina specimens. The coupling ratios across the column and across adjacent vertebrae were established. All mean coupling ratios were less than one. Vertebral column failure occurred in the upper cervical spine at a mean of 1951.5 +/- 396N and 16 +/- 5% strain.;The second study also applied tension-extension loading in vitro , but without radiodense spinal cord markers. The spinal cords were removed for histological analysis of mechanical insult upon the tissue. The size properties of the extracellular spaces and their alignment were measured against data from control spinal cords. No differences were observed between groups which could serve as an indicator for injury in future experimental protocols. The length of the vascular endothelium also did not correlate to the applied load or strain.;A final in vivo SCI experiment was performed to assess the relationship between strain and the onset of SCI using evoked potentials. Loads were applied up to 75% of the predicted failure load of the cervical vertebral column. The evoked potential measurements provided no indication of SCI and none were observed in the histology analysis of the spinal cord.;These studies provide a step towards improving our understanding of column-cord interactions and redefining the injury criteria necessary to prevent SCI.