Traumatic brain injury (TBI) is a major worldwide healthcare problem. Despite promising outcomes from many preclinical studies, the failure of several clinical studies to identify effective therapeutic and pharmacological approaches for TBI suggests that methods to improve the translational potential of preclinical studies are highly desirable. Rodent models of TBI are increasingly in demand for preclinical research, particularly for closed head injury (CHI), which mimics the most common type of TBI observed clinically. Although seemingly simple to establish, CHI models are particularly prone to experimental variability. Promisingly, bioengineering-oriented research has advanced our understanding of the nature of the mechanical forces and resulting head and brain motion during TBI. However, many neuroscience-oriented laboratories lack guidance with respect to fundamental biomechanical principles of TBI. Here, we review key historical and current literature that is relevant to the investigation of TBI from clinical, physiological and biomechanical perspectives, and comment on how the current challenges associated with rodent TBI models, particularly those involving CHI, could be improved.

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According to a 1999 report by the U.S. Consumer Product Safety Commission, head injuries represent approximately 14 % of all skiing and snowboarding injuries. In a recent retrospective study of patients treated for snowboarding-related head injuries, Nakaguchi and Tsutsumi (2002) found that major head injuries were most often associated with backward falls (68 %) resulting in occipital impacts (66 % of falls) occurring on a gentle or moderate slope. They concluded that the majority of severe snowboarding head injuries were caused by the “opposite-edge phenomenon” where the snowboarder falls backward and contacts the occiput. In order to determine if the use of skiing helmets would reduce the likelihood of head injury associated with catching an edge snowboarding, we conducted a two-part study. In the first part, we measured the speeds of over 180 snowboarders on beginner and intermediate slopes at Mammoth, CA. Across all locations at the resort, the average speeds of beginner and intermediate snowboarders were 17.7 kph (11.0 mph) and 31.9 kph (19.8 mph), respectively. In the second part of the study, we used an instrumented 50th percentile male Hybrid III anthropomorphic test device (ATD) to determine the head accelerations and neck loads associated with a backward fall onto the occiput, both with and without wearing a helmet. For these tests, the ATD was fitted with snowboarding equipment and accelerated to the speeds associated with an intermediate snowboarder (as measured in the first part of the study). Once the ATD was at speed, the snowboard was snubbed on the back edge, simulating the “opposite-edge phenomena” and the posterior aspect of the ATD head was propelled toward the snow surface or a simulated tree. Film analysis of the ATD fall kinematics demonstrated a rapid transition to whole-body angular motion at opposite edge catch. The use of a helmet reduced substantially the linear accelerations and head injury criterion associated with head-to-ground contact on hard, icy snow and during the simulated tree contact. Also, the neck loads were reduced modestly with helmet use. These findings indicate that helmets can mitigate head-to-ground contact severity associated with a common snowboarding fall scenario, the “opposite-edge-phenomenon.”

A study by Nakaguchi and Tsutsumi [“Mechanisms of Snowboarding-Related Severe Head Injury: Shear Strain Induced by the Opposite-Edge Phenomenon,” J. Neurosurg, Vol. 97, 2002, pp. 542–548] showed that 68 % of all snowboarders’ head injuries were associated with backward falls, with beginner and intermediate snowboarders constituting the majority of the injured. We previously fabricated a test apparatus that replicated the fall kinematics of a snowboarder during a back-edge trip. A Hybrid-III anthropomorphic test device (ATD) outfitted with a snowboard and snowboarding gear was accelerated to a typical intermediate snowboarder’s speed (30.5 ± 1.5 kph) and tripped resulting in a backward fall that terminated in a head-to-slope impact. This test protocol produced repeatable fall kinematics under realistic on-slope conditions. In this study, we characterized the fall kinematics and quantified head velocity in order to evaluate the helmet energy management requirements associated with a back-edge trip. Digital high-speed video recorded at 500 frames per second was used to quantify the snowboarder’s head kinematics: (i) prior to the trip; (ii) during trip phase; (iii) during free fall; and (iv) at ground impact. Translational energy of the ATD was rapidly converted to a combination of linear and angular energy during the trip phase. Although the speed of the ATD’s center of gravity decreased during the trip phase, the test data showed the absolute speed of the head increased rapidly during the fall as a result of the body’s induced angular rotation. The mean head velocity normal to the slope increased from approximately zero at fall initiation to as much as 37.1 kph during the fall (122 % of the initial velocity), and was 29.1 kph at snow contact (95 % of the initial velocity). Resultant head velocity peaked at 54.3 kph (178 % of the initial velocity), and was 38.2 kph at snow contact (125 % of the initial velocity). The data presented here may be useful for assessing drop height requirements for snow helmet evaluations.

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