Spinal canal narrowing during simulated whiplash.

STUDY DESIGN: A biofidelic whole cervical spine model with muscle force replication was used to evaluate spinal canal pinch diameter (CPD) narrowing during simulated whiplash.

OBJECTIVES: To quantify CPD narrowing during simulated whiplash and to determine if whiplash resulted in a narrower post-whiplash CPD.

SUMMARY OF BACKGROUND DATA: Spinal cord injuries are uncommon in whiplash patients, although such injuries have been reported in those with narrow canals. It has been hypothesized that increased cerebral spinal fluid pressure during whiplash could injure neural tissues.

METHODS: The biofidelic model and a bench-top whiplash apparatus were used to simulate whiplash at 3.5, 5, 6.5, and 8 g accelerations of the T1 vertebra. The CPD was measured in the intact specimen in the neutral posture (neutral posture CPD) and under a 1.5 Nm static extension load (pre-whiplash CPD), during simulated whiplash (dynamic whiplash CPD), and again under a 1.5 Nm extension load following each whiplash simulation (post-whiplash CPD).

RESULTS: The average dynamic whiplash CPDs were significantly narrower (P < 0.05) than the corresponding pre-whiplash CPDs at accelerations of 3.5 g and above. The narrowest CPD was observed at C5-C6 during the 6.5 g simulation and was 3.5 mm narrower than the neutral posture CPD. In general, the average post-whiplash CPDs were not significantly narrower than the corresponding pre-whiplash CPDs.

CONCLUSIONS: Spinal cord injury during whiplash is unlikely in patients with average normal canal diameters. Cord compression following whiplash due to physiologic extension loading is not likely. Previous clinical studies have found that whiplash patients with narrow canals may be at risk of injury, and our results do not disprove it.