DYNAMIC-RESPONSES OF THE HEAD AND CERVICAL-SPINE TO AXIAL IMPACT LOADING

This study explores the inertial effects of the head and torso on cerv ical spine dynamics with the specific goal of determining whether the head mass can provide a constraining cervical spine end condition. The hypothesis was tested using a low friction impact surface and a pocke ting foam impact surface. Impact orientation was also varied. Tests we re conducted on whole unembalmed heads and cervical spines using a dro p track system to produce impact velocities on the order of 3.2 ms(-1) . Data for the head impact forces and the reactions at T1 were recorde d and the tests were also imaged at 1000 frames s(-1). Injuries occurr ed 2-19 ms following head impact and prior to significant head motion. Average compressive load a failure was 1727 +/- 387 N. Decoupling was observed between the head and T1. Cervical spine loading due to head rebound constituted up to 54 +/- 16% of the total axial neck load for padded impacts and up to 38 +/- 30% of the total axial neck load for r igid impacts. Dynamic buckling was also observed; including first-orde r modes and transient higher-order modes which shifted the structure f rom a primarily compressive mode of deformation to various bending mod es. These experiments demonstrate that in the absence of head pocketin g, the head mass can provide sufficient constraint to cause cervical s pine injury. The results also show that cervical spinal injury dynamic s are complex, and that a large sample size of experimentally produced injuries will be necessary to develop comprehensive neck injury model s and criteria.