A Methodology to Evaluate Unrestrained Torso Neck Braces for Near Vertex Impacts

The advent of neck braces for the helmeted motorcycle rider has introduced a pertinent research question: To what extent do they reduce measures related to the major mechanism of neck injury in unrestrained torso accidents, i.e., compression flexion (CF)? This question requires a suitable method of testing and evaluating the measures for a load case resulting in the required mechanism. This study proposes a weighted swinging anvil striking the helmeted head of a supine HIII ATD by means of a near vertex impact with a low degree of anterior head impact eccentricity to induce CF of the neck. The applied impact was chosen for the baseline (no neck brace) so that the upper and lower neck axial forces approached injury assessment reference values (IARV). The head impact point evaluated represents those typically associated with high-energy burst fractures occurring within the first 20 ms, with possible secondary disruption of posterior ligaments. The proposed test can be used to evaluate the initial and secondary period of neck loading resultant from a near vertex impact and the effect of a neck brace thereon. The presented case study shows that unless almost touching the helmet, neck braces are likely to have a negligible effect on the axial load response of the neck within the first 20 ms after impact and are, therefore, unlikely to affect injury risk related to initial compressive loading of the neck. Conversely, a neck brace can affect neck response in bending during a near vertex CF loading event. Hence, assessing these devices is important to determine their potential in stabilizing the spine. The proposed test shows that the neck loading mechanism does not necessarily correspond with the observed head motion, especially in the early stages of neck response. These head/neck kinetics are important to consider when designing an evaluation load case.