Abstract
This study offers the first comprehensive investigation of human head-neck response to low-speed lateral impact. Fourteen volunteers (9 males, 5 females; mean 32.7 years) were instrumented with a sensor package (gyroscopes and accelerometers) to measure three-dimensional linear accelerations and angular velocities of the head during lateral impacts inside an amusement park bumper car. Coronal plane vehicle and occupant kinematics were captured with a high-speed digital camera, speed trap, and vehicle-mounted accelerometers. EMG electrodes captured muscular activity bilaterally of the upper trapezius, sternocleidomastoid (SCM) and upper cervical neck muscles at the C2-C3 level. Each volunteer experienced four right-sided lateral impacts. Two of the four impacts were conducted with the volunteer wearing visual and auditory baffles. During the simulated lateral impact collisions, the closing speed of the bullet vehicle ranged from 7.7 to 17.2 km/h (13.1 ± 1.8 km/h), the target vehicle delta-V ranged from 8.9 to 14.7 km/h (11.3 ± 1.1 km/h), and the target vehicle peak acceleration ranged from 3.3 to 6.4 Gs (4.5 ± 0.6 Gs). The peak resultant linear head accelerations of the fourteen volunteers ranged from 2.3 to 14.7 Gs (5.5 ± 2.3 Gs), with the largest component typically (75% occurrence) in the left lateral direction. The peak resultant angular accelerations ranged from 89.9 to 984 rad/s2 (317.2 ± 155.2 rad/s2). The peak resultant neck moments ranged from 5.9 to 47.7 Nm (15.6 ± 7.5 Nm). The peak resultant force ranged from 96.3 to 720.4 N (222.7 ± 106.9 N), with the largest component typically (75% occurrence) the left lateral force. EMG studies found the left C2-C3 neck muscles and the left SCM muscles had the most significant activity relative to the other muscle groupings, consistent with eccentric contraction of the left-sided neck muscles and observed right lateral bending during impact. There were no complaints of pain or injury by any of the volunteers immediately following testing or at one-week followup. Clinical assessments for cervical spine range-of-motion and strength were performed by a licensed physical therapist. Head accelerations were compared with a database of previously published volunteer head acceleration data associated with vigorous, non-injurious activities of daily living. Peak head accelerations and neck loads were found to be significantly less than the Injury Assessment Reference Values (IARVs) for side impacts.
Keywords:Coronal, Biomechanics, Side Impact, High-speed video, EMG