Simulated Automobile and Rotary-Wing Aircraft Impacts: Dynamic Neck Response after Surgical Treatment for Cervical Spondylosis
White, Nicholas Alan
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Degeneration of the cervical spine is part of the normal aging process, usually occurring without clinical symptoms. Symptomatic degeneration most often occurs in the lower cervical spine, presenting as axial neck pain, radiculopathy, myelopathy, or any combination of the three. When conservative treatment does not adequately manage these symptoms, surgical intervention may be required. The longstanding surgical treatment for cervical degeneration is arthrodesis achieved through anterior cervical discectomy and fusion (ACDF). A relatively newer treatment is arthroplasty with a cervical total disc replacement (CTDR), a motion-sparing procedure designed to maintain adjacent-level loading. While literature exists comparing the effects of cervical arthrodesis and cervical arthroplasty on neck kinematics and loading, the vast majority of these studies applied only quasi-static, non-injurious loading conditions. This dissertation research used a state-of-the-art, full body human finite element (FE) model to investigate the effects of these surgical procedures on neck response during simulated dynamic impacts. A method was developed to measure cross-sectional forces and moments at each level of the neck in the FE model. Neck loading was captured during three automobile impact simulations: a frontal impact of a belted driver with airbag deployment, a frontal impact of a belted passenger without airbag deployment, and an unbelted side impact. The measured neck forces and moments were compared to existing injury threshold values and used to calculate injury criteria values. Four additional simulations of the frontal impact with the belted driver were conducted with neck modifications representative of either a fusion or arthroplasty of C5-6. While cross-sectional loading above and below the implants did not vary appreciably, key differences were noted in both the interbody and facet response. However, no neck injury thresholds were exceeded in any of the simulations. With cervical radiculopathy diagnosed in 24,742 active-duty U.S. military personnel between 2000 and 2009, interest in cervical arthroplasty as treatment for symptomatic cervical degeneration in this population has increased. This motion-sparing procedure has the potential to expedite post-operative recovery time, allowing for these highly trained individuals to return to active-duty sooner than with a fusion. Due to the physically demanding nature of the military environment, it is important to ensure that this surgical procedure does not increase the likelihood of a neck injury. An FE simulation environment was developed to investigate aviator head and neck response during a survivable, rotary-wing aircraft impact with the ground using both an anthropomorphic test device (ATD) and a human body model. The head and neck response of the ATD FE simulation was successfully validated against the results of a previously conducted experimental sled test. A more biofidelic head and neck response was produced with the human body model, including realistic changes in neck curvature. Additional simulations were conducted with the human body model to investigate the neck response after cervical arthroplasty of C5-6. While the adjacent-level, cross-sectional loading for the C5-6 segment was not appreciably altered by the CTDRs, the interbody range-of-motion was increased; subsequently altering both the interbody and cervical facet loading. Again, no neck injury thresholds were exceeded in these simulations. Overall, cervical arthroplasty did not appear to have a deleterious effect on the dynamic neck response during a simulated rotary-wing aircraft impact.
- Doctoral Dissertations