Inertial Flexion-Extension Loading of the Human Neck

The present research was conducted to determine the biomechanics of the cervical spine under de-celerative inertial forces typically encountered in motor vehicle crashes. Using human cadaver head-neck complexes that included the ligamentum nuchae and intact posterior skin, inertial flexion-extension forces were applied using a mini-sled. Retroreflective targets were introduced into the anterior regions of the cervical vertebral bodies, articular facets, and posterior regions of the neck at all levels of the spine. Continuous localized motion analysis techniques coupled with force and acceleration information delineated the overall and segmented spinal component mechanics. The strength and kinematic information were obtained using a highspeed data acquisition system coupled with a frame analyzer and high-speed camera. Increasing decelerative forces resulted in higher motions among the cervical spinal components at all levels. In addition, due to the relative higher mass of the head in contrast to the mass of the human neck, inertial effects played a higher role at higher deceleration levels. Flexion angulation of the neck was associated with a concomitant translation and sagittal rotation of the head. Following attainment of the peak deceleration, an extension signature of the neck occurred as seen on high-speed photography. This study underscores the importance of including the ligamentum nuchae and the posterior soft tissue structures of the human neck in analyzing the overall and localized spinal component motions at every vertebral level under inertially applied flexion-extension. The relative contributions of the distractions occurring in the posterior soft tissues may facilitate in explaining the cervical sprains and strains commonly documented in real-world situations such as whiplash.