• Manohar M Panjabi, Adam M Pearson, Shigeki Ito, Paul C Ivancic, and Jaw-Lin Wang.
• Biomechanics Research Laboratory, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 333 Cedar St., P.O. Box 208071,New Haven, CT 06520-8071, USA. manohar.panjabi@yale.edu
• Clin Biomech (Bristol, Avon). 2004 Jan 1;19(1):1-9.

ObjectiveTo develop a new method to describe cervical spine curvature and evaluate the potential for injury in the upper and lower cervical spine during simulated whiplash.DesignA method was developed to integrate the upper and lower cervical spine rotations and describe the spine curvature.BackgroundIn vivo and in vitro whiplash simulations have documented the development of an S-shape curvature with simultaneous upper cervical spine flexion and lower cervical spine extension immediately following rear-impact. Investigators have hypothesized that the injury potential is highest during the S-shape phase. However, little data exist on the spine curvature during whiplash and its relation to spine injury.MethodsA biofidelic model and a bench-top whiplash apparatus were used in an incremental rear-impact protocol (maximum 8 g) to simulate whiplash of increasing severity. To describe the spine curvature, the upper and lower cervical spine rotations were normalized to corresponding physiological limits.ResultsAverage peak lower cervical spine extension first exceeded the physiological limits (P<0.05) at a horizontal T1 acceleration of 5 g. Average peak upper cervical spine extension exceeded the physiological limit at 8 g, while peak upper cervical spine flexion never exceeded the physiological limit. In the S-shape phase, lower cervical spine extension reached 84% of peak extension during whiplash.ConclusionsBoth the upper and lower cervical spine are at risk for extension injury during rear-impact. Flexion injury is unlikely.

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