The purpose of this study was to determine the effect of head-neck position on cervical facet stretch during low speed rear end impact. Twelve tests were conducted on four Post Mortem Human Subjects (PMHS) in a generic vehicle bucket seat environment. Three head positions, namely Normal (neutral), Zero Clearance between the head and head restraint, and Body Forward positions were tested. A high-speed x-ray system was used to record the motion of cervical vertebrae during these tests. Three ATDs (Hybrid III, RID2, BioRID) were also tested under the same conditions.

Results demonstrated that:​ a) the maximum mean facet stretch at head restraint contact occurs at MS4 and MS5 for the Body Forward condition, b) the lower neck flexion moment, prior to head contact, shows a non-linear relationship with facet stretch, c) "differential rebound" during rear end impact increases facet stretch, d) the lower torso motion contributed significantly to the facet stretches seen in the PMHS, e) in this test series, there was no significant difference between normal and zero clearance seated conditions for the ATDs, f) in this test series, there were no significant correlation between PMHS facet stretches and ATD forces and moments, and g) since, lower torso motion was the driving factor for facet stretches, Hybrid III and RID2 lower neck moments could provide an indirect means of assessing facet stretches in PMHS.