evaluation of the intervertebral neck injury criterion using simulated rear impacts the intervertebral neck injury criterion ivnic is based on the hypothesis that intervertebral motion beyond the physiological limit may injure spinal soft tissues during whiplash while the neck injury criterion nic hypothesizes that sudden changes in spinal fluid pressure may cause neural injury goals of the present study using a biofidelic whole cervical spine model with muscle force replication were to correlate ivnic with softtissue injury determine the ivnic injury threshold and compare ivnic and nic using a benchtop apparatus rearimpacts were simulated at 35 5 65 and 8 g horizontal accelerations of the t1 vertebra pre and postwhiplash flexibility tests measured the soft tissue injury threshold ie significant increases in the intervertebral neutral zone nz or range of motion rom above corresponding baseline values extension ivnic peaks correlated well with nz and rom increases at c0c1 and at c3c4 through c7t1 r064 and 062 respectively p0001 average ivnic injury thresholds 95 confidence limits varied among the intervertebral levels and ranged between 15 11 19 at c5c6 and 34 24 44 at c7t1 the nic injury threshold was 87 77 97 m2s2 substantially less than the proposed threshold of 15 m2s2 results support the use of ivnic for determining the cervical spine injury threshold and injury severity advantages of ivnic include the ability to predict the intervertebral level mode severity and time of the cervical spine softtissue injury