Dynamic Intervertebral Foramen Narrowing During Simulated Rear Impact

In Brief Study Design. A biomechanical study of intervertebral foraminal narrowing during simulated automotive rear impacts. Objectives. To quantify foraminal width, height, and area narrowing during simulated rear impact, and evaluate the potential for nerve root and ganglion impingement in individuals with and without foraminal spondylosis. Summary of Background Data. Muscle weakness and paresthesias, documented in whiplash patients, have been associated with neural compression within the cervical intervertebral foramen. To our knowledge, no studies have comprehensively examined dynamic changes in foramen dimensions. Methods. There were 6 whole cervical spine specimens (average age 70.8 years) with muscle force replication and surrogate head that underwent simulated rear impact at 3.5, 5, 6.5, and 8 g, following noninjurious baseline 2 g acceleration. Peak dynamic narrowing of foraminal width, height, and area were determined during each impact and statistically compared to baseline narrowing. Results. Significant increases (P < 0.05) in average peak foraminal width narrowing above baseline were observed at C5–C6 beginning with 3.5 g impact. No significant increases in average peak foraminal height narrowing were observed, while average peak foraminal areas were significantly narrower than baseline at C4–C5 at 3.5, 5, and 6.5 g. Conclusions. Extrapolation of the present results indicated that the highest potential for ganglia compression injury was at the lower cervical spine, C5–C6 and C6–C7. Acute ganglia compression may produce a sensitized neural response to repeat compression, leading to chronic radiculopathy following rear impact. A whole cervical spine model with muscle force replication and a surrogate head underwent an incremental simulated rear impact, and dynamic foraminal width height and area narrowing were quantified. Dynamic width narrowing occurred at C5–C6 during the 3.5 g impact. Extrapolation of the present results indicated that compression injury of ganglions may occur at C5–C6 and C6–C7, and lead to chronic radiculopathy.