Whiplash injury prevention with active head restraint.

BACKGROUND Previous epidemiological studies have observed that an initial head restraint backset greater than 10 cm is associated with a higher risk of neck injury and persistent symptoms. The objective of this study was to investigate the relation between the active head restraint position and peak neck motion using a new human model of the neck. METHODS The model consisted of an osteoligamentous neck specimen mounted to the torso of a rear impact dummy and carrying an anthropometric head stabilized with muscle force replication. Rear impacts (7.1 and 11.1g) were simulated with and without the active head restraint. Physiologic rotation was determined from intact flexibility tests. Significant reductions (P<0.05) in the spinal motion peaks with the active head restraint, as compared to without, were identified. Linear regression analyses identified correlation between head restraint backset and peak spinal rotations (R(2)>0.3 and P<0.001). FINDINGS The active head restraint significantly reduced the average peak spinal rotations, however, these peaks exceeded the physiologic range in flexion at head/C1 and in extension at C4/5 through C7/T1. Correlation was observed between the head restraint backset and the extension peaks at C4/5 and C5/6. INTERPRETATION Correlation between head restraint backset and spinal rotation peaks indicated that a head restraint backset in excess of 8.0 cm may cause hyperextension injuries at the middle and lower cervical spine. The active head restraint may not be fully activated at the time of peak spinal motions, thus reducing its potential protective effects.