A numerical investigation of factors affecting cervical spine injuries during rollover crashes.

STUDY DESIGN: Factors affecting the risk of cervical spine injury in rollover crashes were investigated using a detailed finite element human head-neck model.

OBJECTIVE: Analyze systematically neck responses and associated injury predictors under complex loading conditions similar to real-world rollover scenarios and use the findings to identify potential design improvements.

SUMMARY OF BACKGROUND DATA: Although many previous experimental and numerical studies have focused on cervical spine injury mechanisms and tolerance, none of them have investigated the risk of cervical spine injuries under loading condition similar to that in rollovers.

METHODS: The effects of changing the coefficient of friction (COF), impact velocity, padding material thickness and stiffness, and muscle force on the risk of neck injuries were analyzed in 16 different impact orientations based on a Taguchi array of design of experiments.

RESULTS: Impact velocity is the most important factor in determining the risk of cervical spine fracture (P = 0.000). Decreases in the COF between the head and impact surface can effectively reduce the risk of cervical spine fracture (P = 0.038). If the COF is not 0, an impact with lateral force component could sometimes increase the risk of cervical spine fracture; and the larger the oriented angle of the impact surface, the more important it becomes to reduce the COF to protect the neck. Soft (P = 0.033) and thick (P = 0.137) padding can actually decrease the neck fracture risk, which is in contrast to previous experimental data.

CONCLUSION: A careful selection of proper padding stiffness and thickness, along with a minimized COF between the head and impact surface or between the padding and its supporting structure, may simultaneously decrease the risk of head and neck injuries during rollover crashes. A seatbelt design to effectively reduce/eliminate the head-to-roof impact velocity is also very crucial to enhance the neck protection in rollovers.