The neutral posture of the cervical spine is not unique in human subjects |
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| Institution: | 1. University of British Columbia, School of Biomedical Engineering, Vancouver, British Columbia, Canada;2. University of British Columbia, Department of Mechanical Engineering, Vancouver, British Columbia, Canada;3. University of British Columbia, School of Kinesiology, Vancouver, British Columbia, Canada;4. University of British Columbia, Brain Research Center, Vancouver, British Columbia, Canada;5. University of British Columbia, Institute for Computing, Information and Cognitive Systems, Vancouver, British Columbia, Canada;6. University of British Columbia, Combined Neurosurgical and Orthopaedic Spine Program, Vancouver, British Columbia, Canada;7. University of British Columbia, International Collaboration on Repair Discoveries, Vancouver, British Columbia, Canada;8. Department of Orthopaedics, University of British Columbia, Vancouver, British Columbia, Canada;9. University of British Columbia, Orthopaedic and Injury Biomechanics Group, Departments of Mechanical Engineering and Orthopaedics, Vancouver, British Columbia, Canada;10. MEA Forensic Engineers & Scientists, Richmond, British Columbia, Canada;1. Department of Neurosurgery, Emory University, Atlanta, Georgia, USA;2. Department of Neurosurgery, University of Florida, Gainesville, Florida, USA;1. Materials Science and Engineering Graduate Program, University of California, San Diego, La Jolla, CA, USA;2. Department of Bioengineering, University of California, San Diego, La Jolla, CA, USA;3. Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA, USA;4. Department of Orthopaedic Surgery, University of California, San Diego, La Jolla, CA, USA;5. Center for Musculoskeletal Research, Institute of Engineering in Medicine, University of California, San Diego, La Jolla, CA, USA;6. Department of Orthopaedic Surgery, Scripps Clinic, La Jolla, CA, USA;1. Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States;2. Mechanical Engineering and Materials Science, Washington University in St. Louis, St. Louis, MO, United States;3. Biomedical Engineering, University of Delaware, Newark, DE, United States |
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| Abstract: | Cervical spine injuries often happen in dynamic environments (e.g., sports and motor vehicle crashes) where individuals may be moving their head and neck immediately prior to impact. This motion may reposition the cervical vertebrae in a way that is dissimilar to the upright resting posture that is often used as the initial position in cadaveric studies of catastrophic neck injury. Therefore our aim was to compare the “neutral” cervical alignment measured using fluoroscopy of 11 human subjects while resting in a neutral posture and as their neck passed through neutral during the four combinations of active flexion and extension movements in both an upright and inverted posture. Muscle activation patterns were also measured unilaterally using surface and indwelling electromyography in 8 muscles and then compared between the different conditions. Overall, the head posture, cervical spine alignment and muscle activation levels were significantly different while moving compared to resting upright. Compared to the resting upright condition, average head postures were 6–13° more extended, average vertebral angles varied from 11° more extended to 10° more flexed, and average muscle activation levels varied from unchanged to 10% MVC more active, although the exact differences varied with both direction of motion and orientation. These findings are important for ex vivo testing where the head and neck are statically positioned prior to impact – often in an upright neutral posture with negligible muscle forces – and suggest that current cadaveric head-first impact tests may not reflect many dynamic injury environments. |
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| Keywords: | Neck injury Upside down Muscles Posture Motion |
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