Relationship between Localized Spine Deformation and Cervical Vertebral Motions for Low Speed Rear Impacts Using Human Volunteers

It is important to more clearly identify the relationship among the ramping-up motion, straightening of the whole spine, and cervical vertebrae motion in order to clarify minor neck injury mechanism. The aim of the current study is to verify the influence of the change of the spine configuration on human cervical vertebral motion and on head/neck/torso kinematics under low speed rear-end impacts. Seven healthy human volunteers participated in the experiment under the supervision of an ethics committee. Each subject sat on a seat mounted on a sled that glided backward on rails and simulated actual car impact acceleration. Impact speeds (4, 6, and 8 km/h), and seat stiffness (rigid and soft) without headrest were selected. During the experiment, the change of the spine configuration (measured by a newly developed spine deformation sensor with 33 paired set strain gauges and placed on the skin) and the interface load-pressure distribution was recorded. This was measured by means of a Tekscan system at a rate of 100 f/s, placed between the seat and subject. The cervical vertebrae motion was also recorded by 90 f/s cineradiography. Furthermore, analysis was made to quantify the relationship between the cervical vertebrae motion and the change of the spine configuration.

The localized straightening of the lumbar spine starts at around 30 ms with the rigid seat. The localized straightening of the thoracic spine reaches the maximum at around 80 ms when the load-pressure distribution is at its peak value due to the interaction between the shoulder and the seatback. On the other hand, for the softer seat, the pelvis starts to sink into the seat back and cushion at around 70 ms. As for such seat the load-pressure is distributed over a large area, the localized straigthening of the middle thoracic spine occurred together with deflection of seatback itself at around 120 ms. The results of this study can help clarify the relationship between the localized straightening of the spine and cervical vertebrae motion with respect to the difference in seat characteristics.