Cognitive effects of one season of head impacts in a cohort of collegiate contact sport athletes.

OBJECTIVE: To determine whether exposure to repetitive head impacts over a single season negatively affects cognitive performance in collegiate contact sport athletes. METHODS: This is a prospective cohort study at 3 Division I National Collegiate Athletic Association athletic programs. Participants were 214 Division I college varsity football and ice hockey players who wore instrumented helmets that recorded the acceleration-time history of the head following impact, and 45 noncontact sport athletes. All athletes were assessed prior to and shortly after the season with a cognitive screening battery (ImPACT) and a subgroup of athletes also were assessed with 7 measures from a neuropsychological test battery. RESULTS: Few cognitive differences were found between the athlete groups at the preseason or postseason assessments. However, a higher percentage of the contact sport athletes performed more poorly than predicted postseason on a measure of new learning (California Verbal Learning Test) compared to the noncontact athletes (24% vs 3.6%; p < 0.006). On 2 postseason cognitive measures (ImPACT Reaction Time and Trails 4/B), poorer performance was significantly associated with higher scores on several head impact exposure metrics. CONCLUSION: Repetitive head impacts over the course of a single season may negatively impact learning in some collegiate athletes. Further work is needed to assess whether such effects are short term or persistent.

Reducing chest injuries in automobile collisions: rib fracture timing and implications for thoracic injury criteria.

The purpose of this study was to quantify the biomechanical response of the human thorax during dynamic shoulder belt loading representative of that seen in a severe automotive collision. Two post-mortem human surrogates (PMHSs) (one male and one female) were instrumented with 26 single-axis strain gages on the ribs, sternum, and clavicle. The thorax of each PMHS was placed on a custom spine support bracket designed to support the thorax on either side of the spinous process, thereby allowing free motion at the costovertebral joints. In addition, the support bracket raised the thorax above the flat base plate, which could otherwise constrain the deformation and motion of the posterior region of the rib cage. The thorax of each PMHS was then loaded using a custom table-top belt loading system that generated thoracic displacement rates representative of a severe automotive collision, 1.3 m/s for the male PMHS and 1.0 m/s for the female PMHS. The rib fracture timing data, determined by analyzing the strain gage time histories, showed that severe thoracic injury (AIS = 3) occurred at 16% chest compression for the male and 12% chest compression for the female. However, these values are well below the current thoracic injury criteria of 29% chest compression for the male and 23% chest compression for the female. This data illustrates that serious thoracic injury (AIS = 3) occurs at lower chest compressions than the current ATD thoracic injury criteria. Overall, this study provides critical data that can be used in the design and validation of advanced ATDs and finite element models, as well as the establishment of improved, more stringent thoracic injury criteria.

Rib fracture timing in dynamic belt tests with human cadavers.

The purpose of this article is to present data from dynamic belt loading tests on the thorax of human cadavers where the exact timing of all rib fractures is known. To quantify rib fracture timing, a total of 47 strain gages were placed throughout the thorax of two human cadavers (one male, one female). To simulate thoracic loading observed in a severe car crash, a custom table-top belt loading device was developed. The belt loading pulse was configured to result in approximately 40% chest compression during a 150 ms load and unload cycle. The time histories of each strain gage were analyzed to determine the time of each rib fracture which was then directly compared with the reaction loads and chest displacements at that exact time, thereby creating a noncensored data set. In both cadavers, all rib fractures occurred within the first 35% compression of the thorax. As a general trend, fractures on the left side of the thorax, where the passenger belt passed over the abdomen, occurred first followed by fractures to the upper ribs on the right side of the thorax. By utilizing this technique, the exact timing of each injury level can be characterized relative to the mechanical parameters. For example, using rib fractures as the parameter for Abbreviated Injury Scale (AIS) scores in the female test, it was shown that AIS 1 injury occurred at a chest compression of 21.1%, AIS 2 at 21.6%, AIS 3 at 22.0%, and AIS 4 at 33.3%.

Biomechanical risk estimates for mild traumatic brain injury.

The objective of this study was to characterize the risk of mild traumatic brain injury (MTBI) in living humans based on a large set of head impact data taken from American football players at the collegiate level. Real-time head accelerations were recorded from helmet-mounted accelerometers designed to stay in contact with the player's head. Over 27,000 head impacts were recorded, including four impacts resulting in MTBI. Parametric risk curves were developed by normalizing MTBI incidence data by head impact exposure data. An important finding of this research is that living humans, at least in the setting of collegiate football, sustain much more significant head impacts without apparent injury than previously thought. The following preliminary nominal injury assessment reference values associated with a 10% risk of MTBI are proposed: a peak linear head acceleration of 165 g, a HIC of 400, and a peak angular head acceleration of 9000 rad/s2.

Retrospective identification of subject anthropometry using computed tomography of the leg.

Lower extremity injuries from car crashes are associated with decreased quality of life. To better evaluate the forces seen by the lower extremity during car crashes accurate models of the lower extremities must be created. This effort is motivated by a need to identify CT scans of a 5th female and a 50th and 95th male leg for use in finite element model development. Our goal is to outline a method for obtaining retrospective data on skeletal anthropometry and relate this data to the population when subject anthropometry is unavailable. Landmark data was collected from axial slices of lower extremity CT scans without skeletal pathology and CT scout films. The two methods used to collect data were compared and published data was used to create normal distribution curves for the leg lengths of males and females across the adult population. Knowledge of how lower extremity geometry quantitatively relates to subject height was also used to find patient scans representing lower extremity lengths of the 5th female, and 50th and 95th percentile male standard models. From the data collected on the two methods we found that CT 3-D reconstructions are superior for assessing length compared to using CT scouts. This methodology is useful for mining the large database of clinical patient scans retrospectively to create models that can predict injury in humans of all shapes and sizes.

Eye injuries from airbags with seamless module covers.

BACKGROUND: A recent trend in automotive interior design has the airbag placed behind a seamless module cover. Airbag deployment through these seamless module covers may release foam particles at high velocities that could result in eye injuries. METHODS: Twenty-one tests (n = 21) were performed in which foam particles, similar to those observed from airbag deployments, were impacted onto porcine eyes. Injury analysis was performed by using fluorescein dye, ophthalmic ultrasound, and necropsy. RESULTS: As seen in case reports of airbag-induced eye injuries, corneal abrasions were the most recorded injuries in the porcine eye impact tests. A logistic regression analysis demonstrated that kinetic energy was the most significant contributor to injury (p = 0.0023), whereas foam type was a poor contributor to the model (p = 0.45). An injury risk curve was generated based on kinetic energy that gave a 50% risk of corneal abrasion at 0.183 J. CONCLUSION: If the production of foam particles during airbag deployment is unavoidable, the injury risk function presented for the kinetic energy of the particles offers a design guide to minimize corneal abrasions.

Driver and right-front passenger restraint system interaction, injury potential, and thoracic injury prediction.

Restrained driver and right-front passenger kinematics and injury outcome in frontal collisions are compared using FARS data and human cadaver sled tests. The FARS data indicate that a frontal airbag may provide greater benefit for a passenger than for a driver. The thoracic injuries sustained by passenger subjects restrained by a force-limited, pretensioned belt and airbag are evaluated, and kinematics are compared to driver-side subjects. The injury-predictive ability of existing thoracic injury criteria is evaluated for passenger-side occupants. Driver and passenger kinematic differences are identified and the implications are discussed. The chest acceleration of the passenger-side subjects exhibited a bimodal profile with an initial (and global) maximum before the subject loaded the airbag. A second acceleration peak occurred as the subject loaded both the belt and the airbag. A similarly restrained driver-side subject loaded the belt and airbag concurrently at the time of peak chest acceleration and therefore did not exhibit this bimodal chest acceleration.

A protocol system for testing biohazardous materials in an impact biomechanics research facility.

This article presents a protocol system, comprised of a review process and a series of checklists, that was developed for testing cadaveric tissue in an impact biomechanics research facility. The use of cadaveric tissue may expose personnel to bloodborne pathogens including HIV and hepatitis B, which have been shown to remain virulent in a cadaver for several weeks after death. To minimize exposure risks, the protocol system presented emphasizes initial blood screening to keep infectious tissue from entering the laboratory, and adopts universal precautions to prevent exposure by treating all tissue as though it were infected. All lab employees must read, sign, and demonstrate proficiency in the protocol. Well-developed test procedures for the handling of biohazardous materials along with an annual individual protocol review have proven effective for the past 6 years in minimizing exposure risks.

Dynamic injury tolerances for long bones of the female upper extremity.

This paper presents the dynamic injury tolerances for the female humerus and forearm derived from dynamic 3-point bending tests using 22 female cadaver upper extremities. Twelve female humeri were tested at an average strain rate of 3.7+/-1.3%/s. The strain rates were chosen to be representative of those observed during upper extremity interaction with frontal and side airbags. The average moment to failure when mass scaled for the 5th centile female was 128+/-19 Nm. Using data from the in situ strain gauges during the drop tests and geometric properties obtained from pretest CT scans, an average dynamic elastic modulus for the female humerus was found to be 24.4+/-3.9 GPa. The injury tolerance for the forearm was determined from 10 female forearms tested at an average strain rate of 3.94+/-2.0%/s. Using 3 matched forearm pairs, it was determined that the forearm is 21% stronger in the supinated position (92+/-5 Nm) versus the pronated position (75+/-7 Nm). Two distinct fracture patterns were seen for the pronated and supinated groups. In the supinated position the average difference in fracture time between the radius and ulna was a negligible 0.4+/-0.3 ms. However, the pronated tests yielded an average difference in fracture time of 3.6+/-1.2 ms, with the ulna breaking before the radius in every test. This trend implies that in the pronated position, the ulna and radius are loaded independently, while in the supinated position the ulna and radius are loaded together as a combined structure. To produce a conservative injury criterion, a total of 7 female forearms were tested in the pronated position, which resulted in the forearm injury criterion of 58+/-12 Nm when scaled for the 5th centile female. It is anticipated that these data will provide injury reference values for the female forearm during driver air bag loading, and the female humerus during side air bag loading.

Baseball hardness as a risk factor for eye injuries.

BACKGROUND: Baseball is the leading cause of sports-related eye injuries in young persons. It is known that softer baseballs reduce the potential for brain and cardiac injury, but it has been speculated that softer baseballs may increase eye injuries by intruding more into the orbit. It also has been claimed that softer baseballs would change the "feel" of the game. OBJECTIVES: To determine the orbital intrusion and eye injury potential of baseballs of varying hardness, and whether a player can feel the difference between these different baseballs. MAIN OUTCOME MEASURES: Orbital force and penetration of baseballs of various hardness into an artificial orbit. Ability of subjects of varying age and baseball experience to determine the hardness of baseballs. RESULTS: The peak orbital force and force onset rate from softer baseballs, at all impact velocities, were less than the force and force onset rate from baseballs that had hardness equal to, or greater than, major league baseballs. The softest (10% of major league hardness) baseballs intruded into the orbit significantly more than balls that were 15% of major league hardness or harder. Children younger than 14 years could not differentiate balls 15% of major league hardness or harder, and adults could not differentiate 20% of major league hardness or harder from each other or from major league balls. CONCLUSION: The potential for injury to the unprotected eye from soft baseballs is significant, but not greater than that from a major league baseball. Baseballs that are 15% to 20% of major league ball hardness are recommended for youth baseball because these balls feel like major league balls, reduce the potential for brain injury and commotio cordis, cause less pain on impact, and do not increase the potential for eye injury to the unprotected player. Eye injuries in youth baseball could be minimized by the use of protective eyewear that conforms to the standard specifications of the American Society of Testing and Materials (Philadelphia, Pa), standards F910 (for batters and baserunners) and F803 (for fielders).

A technique for using strain gauges to evaluate airbag interaction with cadaveric upper extremities.

Radius and ulna fractures from airbag deployment onto the forearm have been reported in the literature. Based on laboratory experiments with eight cadaveric upper extremities, this paper presents a method for using strain gages to evaluate upper extremity loading during airbag deployment. The technique provides strain rates, bending moments, and time of fracture for the radius and ulna. Planar rosettes (350 omega, 5% strain) were selected as the best choice given the application to bone with a rosette being placed mid-shaft on both the anterior and posterior surfaces of the radius and ulna. Forearm incisions were intended to be minimally invasive and to limit damage to the interosseous membrane. The bone surface was prepared with Ether, and the gauges were bonded to the surface with methyl-2-cyanoacrylate. A thin latex cover was installed over the surface of the rosettes to isolate the gauges from the surrounding tissue. Strain relief of the gauges was provided by securing the wire leads to the bone with tie-wraps, as well as suturing the wires to the skin. With this technique all gauges reported accurate data throughout the duration of the impact.

An experimental study of airbag impact to the orbit using an instrumented Hybrid III headform.

This paper provides the results from an experimental study intended to assess airbag impact to the orbit. Twenty-seven airbags were deployed onto an instrumented Hybrid III headform. Seven different types of airbags were used that included tethered and nontethered, light to heavy nylon weaves, and different coating types. The airbags were deployed via a pneumatic deployment system. Seven individual force transducers, each having a 2.25 cm2 contact area, were placed on the right orbital region to evaluate the force patterns. The midpoint of the two ocular regions of the headform was positioned 12.5 cm above and 15.0 cm away from the center of the airbag, a position determined from previous airbag deployments to yield the highest leading edge velocity. The average maximum force per sensor ranged from 15.4 N to 63.6 N, and peak pressure ranged from 68 kPa to 282 kPa. The upper center of the orbit presented the highest values while the center of the orbit recorded the lowest values, a comparison that was proven to be statistically significant. For this configuration, the maximum force on the ocular region was found to be independent of the presence of a tether or the maximum internal airbag pressure.

Airbag-induced eye injuries: experiments with in situ cadaver eyes.

In an attempt to investigate eye injuries from airbags, a set of experiments was performed that involved the deployment of several types of airbags onto thirteen unembalmed, previously frozen cadaver heads. The airbags differed in the material, coating, presence of a tether, and folding pattern, and were deployed via a pneumatic deployment system. The eyes were impacted in situ after being repressureized with saline injected through a 30-gauge needle. Injury determination was achieved by ophthalmic ultrasound imaging, staining with fluorescein dye, and dissection. All twenty-six eyes revealed detached retinas, as shown by the ultrasound, before impact as a result of decaying tissue and the freezing process. High speed video and film were used to capture the events. The impact velocities of the airbags were recorded from the digitized film at the first contact location with the eye and ranged from 30 m/s to 66 m/s. Eyeglasses were placed on four of the specimens, and the presence of eyeglasses seemed to provide protection to the eye because of the lack of contact between the airbag and ocular region. Minimal ocular damage was recorded for all experiments.

Airbag-induced eye injuries: a report of 25 cases.

OBJECTIVE: To acquire a better understanding of airbag-induced eye injuries, 25 cases are reviewed and an attempt is made to identify the causal mechanisms associated with each injury. DESIGN AND METHODS: The National Highway Traffic Safety Administration's National Accident Sampling System for the years 1984-1994 was accessed to identify automobile accidents that included airbag deployment and injury to the ocular region. The search provided 25 such cases with detailed studies of the accident scene and medical records of the injuries. The cases were comprehensively reviewed to determine the casual mechanisms associated with each group of injuries. RESULTS: The study determined that the injuries range from mild corneal abrasions to retinal detachment. Causation for each injury was determined and is detailed. The injuries were grouped according to location within the ocular region, and the distribution is shown. CONCLUSIONS: Most of the injuries were induced by impact with the fully deployed airbag, but the more severe ocular trauma resulted from the actively deploying airbag striking the occupant. Thus, ocular trauma from airbags can occur in very minor impacts. Additionally, the left eye seemed more vulnerable to injury than the right. Nontethered airbags have greater inflation distances that tend to increase the probability of injury. External parameters that may also increase the severity of eye injury include an unfastened seat belt, sitting too close to the steering wheel, or wearing glasses.