In vitro biomechanical investigations can help to identify changes in subaxial cervical spine (C3-C7) stability following injury, and determine the efficacy of surgical treatments through controlled joint simulation experiments and kinematic analyses. However, with the large spectrum of cervical spine trauma, a large fraction of the potential injuries have not been examined biomechanically. This includes a lack of studies investigating prevalent flexion-distraction injuries. Therefore, the overall objective of this thesis was to investigate the changes in subaxial cervical spine kinematic stability with simulated flexion-distraction injuries and current surgical instrumentation approaches using both established and novel biomechanical techniques.
Three in vitro experiments were performed with a custom-designed spinal loading simulator. The first evaluated sequential disruption of the posterior ligaments with and without a simulated facet fracture (n=7). In these specimens, posterior lateral mass screw fixation provided more stability than anterior cervical discectomy and fusion with plating (ACDFP). A second study examined a unilateral facet perch injury by reproducing a flexion-distraction injury mechanism with the simulator (n=9). The resulting soft tissue damage was quantified through meticulous dissection of each specimen, which identified the most commonly injured structures across all specimens as both facet capsules, ¾ of the annulus, and ½ of the ligamentum flavum. This information was used to develop and validate a standardized injury model (SIM) in new specimens (n=10). A final study examined the ACDFP surgical factor of graft size height (bony spacer replacing the intervertebral disc to promote fusion) for the SIM and two other injuries (n=7). Results were motion and injury dependent, which suggests that both these factors must be considered in the surgical decision.
Two additional investigations were completed. The first examined mathematical techniques to generate a large number of accurate finite helical axes from six-DOF rigid body tracker output to describe changes in cervical spine kinematic stability. The second explored the effect of boundary conditions and PID control settings on the ability of the current simulator design to reproduce desired loading techniques.
Ultimately, it is hoped that these results, and the protocols developed for future investigations, will provide valuable biomechanical evidence for standardized treatment algorithms
