Soft tissue injury threshold during simulated whiplash: a biomechanical investigation.

STUDY DESIGN: A newly developed biofidelic whole cervical spine (WCS) model with muscle force replication (MFR) was subjected to whiplash simulations of varying intensity, and the resulting injuries were evaluated through changes in the intervertebral flexibility.

OBJECTIVES: To identify the soft tissue injury threshold based on the peak T1 horizontal acceleration and the association between acceleration magnitude and injury severity resulting from simulated whiplash using the WCS + MFR model.

SUMMARY OF BACKGROUND DATA: Whiplash has been simulated using mathematical models, whole cadavers, volunteers, and WCSs. The measurement of injury (difference between prewhiplash and postwhiplash flexibilities) is possible only using the WCS model.

METHODS: Six WCS + MFR specimens (C0-T1) were incrementally rear-impacted at nominal T1 horizontal maximum accelerations of 3.5, 5, 6.5, and 8 g, and the changes in the intervertebral flexibility parameters of neutral zone and range of motion were determined. The injury threshold acceleration was the lowest T1 horizontal peak acceleration that caused a significant increase in the intervertebral flexibility.

RESULTS: The first significant increase (P <0.01) of 39.8% occurred in the C5-C6 extension neutral zone following the 5 g acceleration. At higher accelerations, the injuries spread among the surrounding levels (C4-C5 to C7-T1).

CONCLUSIONS: A rear-end collision is most likely to injure the lower cervical spine by intervertebral hyperextension at a peak T1 horizontal acceleration of 5 g and above. These results may aid in the design of injury prevention systems and more precise diagnoses of whiplash injuries.