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Measuring head impacts in sports can further our understanding of brain injury biomechanics and, hopefully, advance concussion diagnostics and prevention. Although there are many head impact sensors available, skepticism on their utility exists over concerns related to measurement error. Previous studies report mixed reliability in head impact sensor measurements, but there is no uniform approach to assessing accuracy, making comparisons between sensors and studies difficult. The objective of this paper is to introduce a two-phased approach to evaluating head impact sensor accuracy. The first phase consists of in-lab impact testing on a dummy headform at varying impact severities under loading conditions representative of each sensor's intended use. We quantify in-lab accuracy by calculating the concordance correlation coefficient (CCC) between a sensor's kinematic measurements and headform reference measurements. For sensors that performed reasonably well in the lab (CCC ≥ 0.80), we completed a second phase of evaluation on-field. Through video validation of impacts measured by sensors on athletes, we classified each sensor measurement as either true-positive and false-positive impact events and computed positive predictive value (PPV) to summarize real-world accuracy. Eight sensors were tested in phase one, but only four sensors were assessed in phase two. Sensor accuracy varied greatly. CCC from phase one ranged from 0.13 to 0.97, with an average value of 0.72. Overall, the four devices that were implemented on-field had PPV that ranged from 16.3 to 91.2%, with an average value of 60.8%. Performance in-lab was not always indicative of the device's performance on-field. The methods proposed in this paper aim to establish a comprehensive approach to the evaluation of sensors so that users can better interpret data collected from athletes. [ABSTRACT FROM AUTHOR]

Concussion tolerance and head impact exposure are highly variable among football players. Recent findings highlight that head impact data analyses need to be performed at the subject level. In this paper, we describe a method of characterizing concussion risk between individuals using a new survival analysis technique developed with real-world head impact data in mind. Our approach addresses the limitations and challenges seen in previous risk analyses of football head impact data. Specifically, this demonstrative analysis appropriately models risk for a combination of left-censored recurrent events (concussions) and right-censored recurrent non-events (head impacts without concussion). Furthermore, the analysis accounts for uneven impact sampling between players. In brief, we propose using the Consistent Threshold method to develop subject-specific risk curves and then determine average risk point estimates between subjects at injurious magnitude values. We describe an approach for selecting an optimal cumulative distribution function to model risk between subjects by minimizing injury prediction error. We illustrate that small differences in distribution fit can result in large predictive errors. Given the vast amounts of on-field data researchers are collecting across sports, this approach can be applied to develop population-specific risk curves that can ultimately inform interventions that reduce concussion incidence [ABSTRACT FROM AUTHOR]

The high incidence rate of concussions in football provides a unique opportunity to collect biomechanical data to characterize mild traumatic brain injury. The goal of this study was to validate a six degree of freedom (6DOF) measurement device with 12 single-axis accelerometers that uses a novel algorithm to compute linear and angular head accelerations for each axis of the head. The 6DOF device can be integrated into existing football helmets and is capable of wireless data transmission. A football helmet equipped with the 6DOF device was fitted to a Hybrid III head instrumented with a 9 accelerometer array. The helmet was impacted using a pneumatic linear impactor. Hybrid III head accelerations were compared with that of the 6DOF device. For all impacts, peak Hybrid III head accelerations ranged from 24 g to 176 g and 1,506 rad/s2 to 14,431 rad/s2. Average errors for peak linear and angular head acceleration were 1% ± 18% and 3% ± 24%, respectively. The average RMS error of the temporal response for each impact was 12.5 g and 907 rad/s2. [ABSTRACT FROM AUTHOR]

Purpose: The present article reviews data from biomechanical and clinical studies which indicate that rotational instability can cause failure of fixation due to the particular characteristics of the fracture, the mechanical properties of the chosen implant or flaws in surgical technique. Methods: Although radiographs give a similar impression in failure of fractures fixed with cephalomedullary nails, different mechanisms involving rotation of the femoral head may play a key role. Results: The incidence of failure in pertrochanteric fracture fixation is decreasing as implants continue to evolve. It is possible that currently reported low failure rates do not apply equally to all subtypes of this diverse group of fractures. Since the introduction of sliding hip screws, "cut-out" due to varus collapse of the proximal fracture fragment has been the only reported mode of failure. Conclusion: Excessive rotation leading to eventual "cut-out" has not been adequately studied, and thus, available evidence is not sufficient to definitely prove this theoretical approach. As nailing is gradually overtaking extramedullary fixation as the treatment of choice, especially for comminuted pertrochanteric fractures which can be rotationally unstable, further research is warranted to improve our understanding of the pathogenetic mechanisms of failure. [ABSTRACT FROM AUTHOR]

Background: Direct impacts with the head (linear acceleration or pressure) and inertial loading of the head (rotational acceleration or strain) have been postulated as the 2 major mechanisms of head-related injuries such as concussion. Although data are accumulating for soccer and American football, there are no published data for nonhelmeted collision sports such as rugby union. Purpose: To quantify head impacts via instrumented mouthguard acceleration analyses for rugby union players over a season of matches. Study Design: Descriptive epidemiology study. Methods: Data on impact magnitude and frequency were collected with molded instrumented mouthguards worn by 38 premier amateur senior rugby players participating in the 2013 domestic season of matches. Results: A total of 20,687 impacts >10g (range, 10.0-164.9g) were recorded over the duration of the study. The mean ± SD number of impacts per player over the duration of the season of matches was 564 ± 618, resulting in a mean ± SD of 95 ± 133 impacts to the head per player, per match over the duration of the season of matches. The impact magnitudes for linear accelerations were skewed to the lower values (Sp = 3.7 ± 0.02; P<.001), with a mean linear acceleration of 22.2 ± 16.2g. Rotational accelerations were also skewed to the lower values (Sp = 2.0 ± 0.02; P < .001), with a mean rotational acceleration of 3902.9 ± 3948.8 rad/s2. Conclusion: The acceleration magnitudes and number of head impacts in amateur rugby union players over a season of matches, measured via instrumented mouthguard accelerations, were higher than for most sports previously reported. Mean linear acceleration measured over a season of matches was similar to the mean linear accelerations previously reported for youth, high school, and collegiate American football players but lower than that for female youth soccer players. Mean rotational acceleration measured over a season of matches was similar to mean rotational accelerations for youth, high school, and collegiate American football players but less than those for female youth soccer players, concussed American collegiate players, collegiate American football players, and professional American football players. [ABSTRACT FROM AUTHOR]

The head impact exposure experienced by football players at the college and high school levels has been well documented; however, there are limited data regarding youth football despite its dramatically larger population. The objective of this study was to investigate head impact exposure in middle school football. Impacts were monitored using a commercially available accelerometer array installed inside the helmets of 17 players aged 12-14 years. A total of 4678 impacts were measured, with an average (±standard deviation) of 275 ± 190 impacts per player. The average o f impact distributions for each player had a median impact of 22 ± 2 g and 954 ± 122 rad/s², and a 95th percentile impact of 54 ± 9 g and 2525 ± 450 rad/s². Similar to the head impact exposure experienced by high school and collegiate players, these data show that middle school football players experience a greater number of head impacts during games than practices. There were no significant differences between median and 95th percentile head acceleration magnitudes experienced during games and practices; however, a larger number of impacts greater than 80 g occurred during games than during practices. Impacts to the front and back of the helmet were most common. Overall, these data are similar to high school and college data that have been collected using similar methods. These data have applications toward youth football helmet design, the development of strategies designed to limit head impact exposure, and child specific brain injury criteria. [ABSTRACT FROM AUTHOR]

Head impact exposure in youth football has not been well-documented, despite children under the age of 14 accounting for 70% of all football players in the United States. The objective of this study was to quantify the head impact exposure of youth football players, age 9–12, for all practices and games over the course of single season. A total of 50 players (age = 11.0 ± 1.1 years) on three teams were equipped with helmet mounted accelerometer arrays, which monitored each impact players sustained during practices and games. During the season, 11,978 impacts were recorded for this age group. Players averaged 240 ± 147 impacts for the season with linear and rotational 95th percentile magnitudes of 43 ± 7 g and 2034 ± 361 rad/s 2. Overall, practice and game sessions involved similar impact frequencies and magnitudes. One of the three teams however, had substantially fewer impacts per practice and lower 95th percentile magnitudes in practices due to a concerted effort to limit contact in practices. The same team also participated in fewer practices, further reducing the number of impacts each player experienced in practice. Head impact exposures in games showed no statistical difference. While the acceleration magnitudes among 9–12 year old players tended to be lower than those reported for older players, some recorded high magnitude impacts were similar to those seen at the high school and college level. Head impact exposure in youth football may be appreciably reduced by limiting contact in practices. Further research is required to assess whether such a reduction in head impact exposure will result in a reduction in concussion incidence. [ABSTRACT FROM AUTHOR]

The head impact exposure for athletes involved in football at the college and high school levels has been well documented; however, the head impact exposure of the youth population involved with football has yet to be investigated, despite its dramatically larger population. The objective of this study was to investigate the head impact exposure in youth football. Impacts were monitored using a custom 12 accelerometer array equipped inside the helmets of seven players aged 7-8 years old during each game and practice for an entire season. A total of 748 impacts were collected from the 7 participating players during the season, with an average of 107 impacts per player. Linear accelerations ranged from 10 to 100 g, and the rotational accelerations ranged from 52 to 7694 rad/s. The majority of the high level impacts occurred during practices, with 29 of the 38 impacts above 40 g occurring in practices. Although less frequent, youth football can produce high head accelerations in the range of concussion causing impacts measured in adults. In order to minimize these most severe head impacts, youth football practices should be modified to eliminate high impact drills that do not replicate the game situations. [ABSTRACT FROM AUTHOR]

Some reports have shown that head injuries in baseball may comprise up to 18.5% of all competitive sports-related head injuries. The objective of this study was to evaluate the response of catcher and umpire masks to impacts at these different regions to discover the impact conditions that represent the greatest risk of injury. A series of 10 events in which a catcher or umpire in Major League Baseball, who experienced a foul ball to the mask that resulted in a concussion, were analyzed through video and data on pitch characteristics. It was found that the impacts were distributed across the face, and the median plate speed was approximately 38 m/s (84 mph). To determine the relative severity of each identified impact location, an instrumented Hybrid III head outfitted with a catcher or umpire mask was impacted with baseballs. Testing at 27 and 38 m/s (60 and 84 mph) suggested that impacts to the center-eyebrow and chin locations were the most severe. Peak linear and rotational accelerations were found to be lower than the suggested injury thresholds. While impacts to a mask result in head accelerations which are near or below levels commonly associated with the lower limits for head injury, the exact injury mechanism is unclear, as concussions are still experienced by the mask wearers. [ABSTRACT FROM AUTHOR]

Abstract: Traumatic infant shaking has been associated with the shaken baby syndrome (SBS) diagnosis without verification of the operative mechanisms of injury. Intensities for SBS have been expressed only in qualitative, unsubstantiated terms usually referring to acceleration/deceleration rotational injury and relating to falls from great heights onto hard surfaces or from severe motor vehicle crashes. We conducted an injury biomechanics analysis of the reported SBS levels of rotational velocity and acceleration of the head for their injury effects on the infant head-neck. Resulting forces were compared with experimental data on the structural failure limits of the cervical spine in several animal models as well as human neonate cadaver models. We have determined that an infant head subjected to the levels of rotational velocity and acceleration called for in the SBS literature, would experience forces on the infant neck far exceeding the limits for structural failure of the cervical spine. Furthermore, shaking cervical spine injury can occur at much lower levels of head velocity and acceleration than those reported for the SBS. These findings are consistent with the physical laws of injury biomechanics as well as our collective understanding of the fragile infant cervical spine from (1) clinical obstetric experience, (2) automotive medicine and crash safety experience, and (3) common parental experience. The findings are not, however, consistent with the current clinical SBS experience and are in stark contradiction with the reported rarity of cervical spine injury in children diagnosed with SBS. In light of the implications of these findings on child protection and their social and medico-legal significance, a re-evaluation of the current diagnostic criteria for the SBS and its application is suggested. [Copyright &y& Elsevier]