Canal geometry changes associated with axial compressive cervical spine fracture

Study Design. A laboratory study using isolated ligamentous human cadaveric cervical spines to investigate canal occlusion during (transient) and afte r (steady-state) axial compressive fracture. Objectives. To determine whether differences exist between transient and po stinjury canal occlusion under axial compressive loading, and to examine th e effect of loading rate on canal occlusion. Summary of Background Data. Prior studies have shown no correlation between neurologic deficit and canal occlusion measurements made on radiographs an d computed tomography scans. The authors hypothesized that postinjury radio graphic assessment does not provide an appreciation for the transient occlu sion that occurs during the traumatic fracture event, which may significant ly affect the neurologic outcome. Methods. Twelve human cervical spines were instrumented with a specially de signed canal occlusion transducer, which dynamically monitored canal occlus ion during axial compressive impact. Six specimens were Subjected to a fast -loading rate (time to peak load, similar to 20 msec) and the other six wer e subjected to a slow-loading rate (time to peak load, similar to 250 msec) . After impact, two different postinjury canal occlusion measurements were performed. Results. Each of the six specimens subjected to the fast-loading rate incur red burst fractures, whereas the Slow-loading rate produced six wedge-compr ession fractures. For the fast-rate group, the postinjury occlusion-measure ments were significantly smaller than the transient occlusion. In contrast, transient occlusion was not found to be significantly different from posti njury occlusion in the slow-rate group. All of the comparisons between load ing rate groups showed significant differences, with the fast-rate fracture s producing larger amounts of canal occlusion in every category. Conclusions. The findings indicate that even if canal occlusion could be me asured immediately after axial compressive trauma; the measurement would un derestimate the maximal amount of transient canal occlusion. Therefore, pos tinjury measurement of canal occlusion may indicate a smaller degree of neu rologic deficit than what might be expected if the transient occlusion coul d be measured.