The inappropriateness of helmet drop tests in assessing neck protection in head-first impacts.

Protecting the cervical spine in situations of axial compressive loading is indeed complex. Results from a number of crash simulations suggest that the mechanisms of head impact causing brain damage and those causing neck injury are different. The idea that neck injuries can be predicted from results of helmet drop tests or that the helmet is capable of providing protection to the cervical spine is unsupported. In head-first collisions causing axial compressive loading, the cushioning properties of the helmet alone would dictate the maximum force on the neck if both the head and neck were rigid. Since the head and neck are not rigid and appear to be as stiff or less stiff than the helmet, the cushioning influence of the helmet is minimized, so the forces experienced by the neck are dictated largely by its own properties. The helmet does not have a large influence. To be effective, the helmet would have to be much less stiff than it is at present and would have to maintain this low stiffness under very large loads. These conditions would be difficult to achieve without making the helmet disproportionately larger than it is now.