*Simbex, Lebanon, New Hampshire
†Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire
‡Bioengineering Laboratory, Department of Orthopaedics, Alpert Medical School of Brown University and Rhode Island Hospital, Providence, Rhode Island.
Corresponding Author: Richard M. Greenwald, PhD, Simbex, 10 Water St, Ste 410, Lebanon, NH 03766 (firstname.lastname@example.org).
The authors have a financial interest in the head impact monitoring technology discussed in the article.
Received April 25, 2011
Accepted January 24, 2012
The topic of brain injury and concussion in helmeted sports, including football, has received significant media attention in recent months, particularly with respect to the potential long-term negative consequences of repeated impacts to the head. Initiatives to reduce brain injuries in helmeted sports include: recommendations for reduced contact in practice; concussion awareness education; training programs for athletes, parents, coaches, and sideline medical personnel; and more rigorous and conservative return-to-play guidelines. A key element in efforts to reduce both the potential short-term and long-term consequences of brain injury in sports that has largely been ignored is the identification of events that might predispose to such injuries. It is known that at least 50% of all head injuries in football go unreported.1 Furthermore, many of the well-documented signs and symptoms of brain injury, including dizziness, amnesia, and lethargy, may not be immediately apparent. We typically cannot “see” a brain injury, and even with increased public and medical awareness about the serious nature of any brain injury, a “warrior mentality” inspires many athletes to continue to play. Contemporary, more stringent guidelines proscribing a same-day return to play may actually fuel underreporting of symptoms by some athletes. It is therefore critical that improved techniques for identifying athletes at increased risk of developing brain injury be implemented at all levels of play.
Prevention of brain injury should be a priority. Athletes in contact sports are exposed to head impacts, the incidence of which can be mitigated to some degree by rules, education, and equipment. Head impacts will, however, continue to occur in sport. We propose the widespread monitoring of head impact exposure (eg, number, severity, location, and cumulative effect of impacts) at all levels of football, and other sports where practical, as a method of providing objective feedback to medical personnel regarding the head impact exposure an athlete experiences during practices and games, thus potentially enhancing the identification of brain injury by reducing the underreporting of events and symptoms by athletes who may be disposed to conceal the same from coaches and medical personnel.
Recent research activities, partially funded by the National Institutes of Health, the Centers for Disease Control and Prevention (CDC), and the National Operating Committee on Standards for Athletic Equipment, have enabled the development and introduction of technology for monitoring head impact exposure in athletes wearing athletic headgear.2–4 This technology can be used to alert sideline personnel when an athlete is approaching or has reached a level of head impact exposure (either from a single head impact or multiple head impacts) that places the athlete at risk for brain injury, triggering appropriate evaluation and management of the athlete. Specific threshold values for alerting to head impact exposure that optimize sensitivity and specificity of concussion diagnosis are not empirically known at this time but can be based on variables, including head impact count, impact magnitude, impact location, and as a function of gender, experience level, and sport based on existing published literature. In cases where medical staff trained in concussion management are available, the athlete can be evaluated for evidence of brain injury and appropriate protocols for management initiated. In cases where the appropriate expertise is not available, the athlete can be referred for further medical evaluation. Because there are likely individual differences in threshold to injury (eg, genetics, gender, cognitive reserve, history of brain injury), it should be left to medical staff to make clinical decisions after a direct examination of the athlete.
The concept of limiting exposure to reduce the likelihood of injury is not new. Little League baseball has instituted an age-specific “pitch count” in an attempt to reduce pitching-related arm injuries among its young players. Exposure in baseball is measured in number of pitches; a maximum number of pitches is established and thereafter rest periods are mandated. In a similar fashion, governing bodies and other regulatory agencies for contact sports can impose or recommend similar guidelines for the use of head impact exposure data. The addition of a measure of impact severity to impact count may further increase the utility and potential contributions of such an approach.
The diagnosis of a brain injury can represent a significant clinical challenge, and often the severity and significance of an injury cannot be determined definitively until after symptoms and deficits resolve. Sideline injury screening techniques, which include symptom checklists, cognitive tests, and evaluation of balance, are reasonably sensitive and specific for the initial diagnosis of a concussion. Two critical factors surround sideline screening: first, the athlete must be identified as having a problem requiring a screening examination; second, there must be someone to perform and interpret the screen and to recommend a subsequent course of action. Neither of these is routine or easily accomplished in many sport environments. Such experience is regularly available on the sidelines in elite sport settings. In these environments, the biggest hurdle to appropriate clinical management of a possible brain injury is often the identification of an athlete who is in distress.
More common, however, is the situation at many of the 10 000 or so high schools and countless youth-sport practices and games where there is likely no one with the requisite experience to either identify an injured athlete or to assess them when an injury is suspected. Furthermore, there seems to be wide disparity in the training and knowledge of contemporary concussion management among many health care professionals.5,6 There remain an alarming number of incidents in which a significant blow or blows to the head are not identified by either the athlete or the sideline staff and which, in retrospect through self-reporting or other means, subsequently led to symptoms or cognitive changes in the athlete.1,7,8 The identification of a potentially injurious impact, or series of impacts, via real-time monitoring of head impact exposure in athletes may facilitate the early recognition and management of brain injury in helmeted sports.
The scientific evidence regarding the level of head impact exposure associated with brain injury is unclear. Recent attention to long-term cognitive declines and early dementia in professional football players has renewed older debates and findings regarding brain injury in boxing and has raised many new questions about what triggers both short-term and long-term brain injuries.9 Football players at the collegiate level are exposed to between several hundred to more than 2000 head impacts per season in both practices and games.4,10,11 Linemen are routinely exposed to 30 to 50 relatively low-magnitude head impacts each game, often amounting to a measurable impact each play. Individual impacts produce linear and rotational head accelerations consistent with automotive crashes in excess of 30 mph. Similar levels of exposure to head impact have been shown at the high school level.12 There are no published data available for youth sports at this time.
The effects of cumulative head impacts on brain function are not clearly understood and are the focus of current research efforts. The time window, after an initial injury, of increased vulnerability to structural and/or functional damage is not precisely known in humans; there is widespread evidence in animal models, and anecdotal evidence in humans, to suggest that recent head impacts increase the likelihood and severity of impaired function.13–15 The long-term effects of repeated head trauma are linked to dementia, depression, and chronic traumatic encephalopathy, among other clinical conditions.9,16–18
Additional scientific evidence will allow more sensitive and specific definition of injury tolerance to head impact. A challenge in head injury research of all kinds is simply to collect data from, and regarding, injured athletes. This is a practical issue. It has been established that more than 50% of athletes do not report signs or symptoms associated with concussion injury to coaches or to medical staff.1 Additionally, approximately 40% of helmeted athletes tested in-season exhibited 1 or more measures of cognitive decline while remaining asymptomatic,15,19 indicating that self-report of symptoms are not correlated with clinical measures of cognition. Research intended to quantify head impact exposure with specific clinical sequelae of brain injury is dependent on the identification of an injured athlete, which does not occur in many cases. Currently, a database of more than 100 medically diagnosed concussions in which both head impact exposure data and clinical data, including symptoms and balance and cognitive testing, collected at the time of diagnosed injury and during the recovery period is being evaluated and compared with results derived from a cohort of athletes not diagnosed with a concussion.
As the science evolves, a conservative approach to the management of head injuries is recommended, consistent with many of the current proposals for reducing head impacts in practice and more stringent return-to-play guidelines after the identification of an injury. Use of head impact exposure monitoring may improve the identification of athletes at increased risk of brain injury and permit early intervention, potentially in advance of an injury, rather than simply as a management tool postinjury. It should be clear that such monitoring will not eliminate the incidence of brain injuries in sports, but the benefits of early identification and the prevention of further injury may emerge. Sideline medical personnel could benefit from objective data that might inform their medical decisions. Athletes and their parents will benefit from reduced reliance on self-reporting. Teams benefit by having healthy, unimpaired athletes on the field more often. The student–athlete or the professional athlete benefit the most from reduced exposure to potentially injurious blows and from the conundrum of having to self-report an injury that they may not recognize as being potentially injurious or dangerous in the moment of competition. As often is the case, an ounce of prevention is worth a pound of cure (Ben Franklin).
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