Current decision making in prevention of sport related craniomaxillofacial injury is based on available data derived from surveillance and attitude based studies. The literature on this type of injury prevention lacks the high quality scientific design and evidence on which mandatory interventions can be based. Currently available prevention methodology can provide a better understanding of injury mechanisms and produce valid interventions.
- injury prevention
- craniomaxillofacial injuries
- facial injuries
- face guards
- mouth guards
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A physically active lifestyle is important for all age groups. Reasons to participate in sports and physical activity are many, such as pleasure, relaxation, competition, socialisation, and maintenance and improvement of fitness and health.1 A negative aspect of this active participation in sport and recreational activities is an increasing number of childhood and adult reported sport related injuries world wide. A study by Birjur et al2 found that sport related injuries account for 36% of injuries from all causes (representing 4 279 000 sport injuries annually in the United States, 1 363 000 of them serious). Scandinavian studies also document that sports injuries constitute a large percentage (10–19%) of all acute injuries seen in the emergency room.1
About 12% of craniomaxillofacial injuries seen in large trauma centres are sport related.3 Medical literature on sport related injuries has been concerned primarily with injury identification and treatment, with very little emphasis on a comprehensive epidemiological approach to prevention. Discussion and implementation of preventive measures is controversial because of the quality of scientific evidence on this topic.
This review is divided into three sections. The first critically reviews sport related craniomaxillofacial injury prevention literature. The next two describe the status of current craniomaxillofacial research and existing methodological sport injury research designs that are needed to provide an improved scientific basis for preventive interventions.
A computerised database search restricted to English language and human subjects was performed by accessing Medline (1966–2004), Cinahl (1982–2004), and SportDiscus (1830–2004) (table 1⇓). The search yielded 106 citations, the abstracts of which were scanned. Reference lists of relevant and recent articles were scanned to ensure that all potential references were examined. Fifty eight articles were flagged and fully reviewed. These articles were critiqued with a summary of the results presented (table 2⇓). The quality of the critiqued studies was assessed on the quality of experimental design.
A summary of craniomaxillofacial study evidence (table 3⇓) shows a greater percentage of prospective than retrospective studies (76% v 24%). Surveillance design studies comprised a majority (52%) of the reviewed articles, whereas cohort (11%) and case-control (2%) designs were seldom used. The strength of study design was limited by a small number of studies that included interventions (26%), controls (33%), randomisation (17%), and self report data (48%). Surveillance study design was used by over half of the reviewed studies, whereas cohort (11%) and case-control (2%) designs were seldom used. Sex analysis showed male and female subjects (33%), male subjects only (40%), and female subjects only (5%). Most studies examined collision/contact sports (93%), whereas few studies examined non-contact/other sports (12%). The attitudes of the athlete/coach/medical professional to the use of protective devices were correlated in 52% of the studies. Only two investigations examined the real time game forces experienced by the athlete.
Most studies have a prospective surveillance or attitude related design, with a low percentage of controls, randomisation, and interventions. These studies also lack field design and a more equal sex distribution of the population. These results are comparable to the ideal model of scientific research—that is, randomised, controlled, and double blinded.
Injury prevention research
There is debate in the literature and news media about the prevention of sport related craniomaxillofacial injuries. For protective devices and rule changes to gain wide acceptance, there must be enough valid scientific evidence to overcome existing attiduinal bias. A multidimensional scientific approach is required to accurately predict these injuries and create prevention strategies. Most existing craniomaxillofacial injury prevention literature focuses on individual surveillance and attitude studies that examine the effect of helmets, eye/face guards, mouth guards, and rule changes.
Sport related helmet studies reviewed primarily involve American football, soccer, rugby, lacrosse, and ice hockey. The documented incidence of intracranial haemorrhage associated with severe head injuries or traumatic brain injury in American football has decreased with an improved helmet design involving a hard outer shell, which attenuates direct impact. Helmet testing, design improvement, and standardisation by national or international organisations—for example, The American Society for Testing and Materials (ASTM), The Canadian Standards Association (CSA), and the International Organisation for Standardisation (IOS)—have focused on increasing helmet energy attenuation of direct impact forces and providing an improved external deflective surface. Concussions or minor traumatic brain injury (mTBI) continue despite improved helmet design in this and other sports.4 Musculoskeletal training techniques—for example, static and dynamic cervical/upper thoracic exercises—and a “ProCap” (Protective Sports Equipment, Erie, Pennsylvania USA) polyurethane helmet cover have been developed to reduce American football neurological trauma, particularly non-catastrophic cervical spine injuries. Neither of these interventions has proven to be effective in mTBI prevention.5,6
Soft rugby headgear was originally developed to protect the player from superficial abrasions and lacerations.7 This type of headgear has recently been investigated for mTBI protective qualities. Laboratory and field observational studies have shown that, although currently available models of rugby headgear will not reduce the likelihood of mTBI,8,9 this can be significantly improved with small design changes.10
A similar laboratory study performed on newly introduced soccer headgear found that this equipment had very little effect on attenuating direct impact forces of simulated heading. The authors stated that this headgear may play a role in decreasing more forceful blows, and further investigation is needed in related impact rotational accelerations.11,12
Studies investigating helmet performance primarily measure direct impact forces, typically involving a direct drop or impact test. mTBI is thought to result from a combination of direct impact forces and the resulting impulse forces. Impulse loading occurs when the head is put into motion and is accelerated or decelerated as a result of an impact to another part of the body or a secondary response to direct impact. Acceleration forces associated with impulse loading tend to cause sheer, tensile, and compression strains within the brain substance, with sheer being the most injurious. Resulting injuries are diffuse and can include contusions at a distance from the site of impact, mTBI, and subdural haematoma.5
Three studies have attempted to measure and correlate the game specific forces experienced by a person who sustains a sport related mTBI.13,14,14a Two of these studies measured the real-time direct helmet impact forces experienced by athletes in game situations.13,14a Duma et al14a recently used the Head Impact Telemetry (HIT) System (Symbex, Lebanon, New Hampshire, USA) to record and correlate the real-time game forces experienced by an athlete that had suffered a clinically diagnosed MTBI. Lewis et al4 suggest the need for continued research to define and record the direct and rotational forces involved in the mTBI. These authors also suggest the need for investigation into a possible linkage between this injury and specific neuropsychological deficits that may occur.
Sport safety rule reform has resulted from the institution and retrospective analysis of sport specific injury and attitude surveillance databases. Studies of rugby and Australian rules football players concerning their attitudes toward headgear suggest that use was affected primarily by proven protective ability and previous head injury.15,16 Examples of this reform include the outlawing of “spear” tackling in football,6 significant penalties imposed on hockey players who check from behind or “head check” an opponent,17,18 and the approved use of head and face protection in female lacrosse players.19
Approximately 40 000–100 000 sport or recreationally related eye injuries occur annually in the United States.20,21 The most common age related causes of North American sport related eye injuries are baseball (leading cause in 5–14 year olds), basketball (leading cause of injury in 15–24 year olds), and racquet sports (a leading cause in 25–65 year olds).21 Prospective surveillance studies of ice hockey related eye and facial injuries performed in the early 1970s resulted in the mandated use of helmets with full face protectors in amateur ice hockey by 1977.22 A 1974 study completed before the mandatory head and face protection regulations reported 245 eye injuries, including 43 that qualified the athlete as functionally one eyed.18 People with acuity measurements of 6/60 (20/200) or less corrected are considered to be functionally one eyed, as the loss of the good eye would result in legal or total blindness. The benefit of wearing certified full face protectors was shown by the fact that no catastrophic eye injuries involving loss of legal vision were reported from 1978 to 2000. Nine severe eye injuries to players wearing visors were reported during this period; all injuries resulted from loose neck straps.23 An improved hockey chinstrap stabilisation system, such as the American football helmet, and rule enforcement may decrease injuries resulting from incorrect visor position.
The effect of protective eyewear and face guards has been investigated in many sports.24–,32 Capao Filipe et al24 conducted an eight year prospective observational study of players who had suffered soccer related eye injuries. These researchers found that the data supported the need for protective eyewear designed specifically for soccer. Matz and Nibelink25 conducted a similar prospective survey of eye injuries in American female collegiate lacrosse players. Data from this study supported the wearing of protective eyewear. Baseball is the leading cause of sports related eye injuries in 5–14 year old children in the United States, accounting for 55% of baseball related injuries treated in emergency rooms.26 Marshall et al27 conducted a two year ecological study of the safety equipment used in youth baseball. The results showed that reduced impact balls and face guards were associated with a reduced risk of injury.
In several sports including hockey, squash, baseball, basketball, football, and lacrosse, athletes refuse to wear eye protection because they feel that it obstructs their vision.28 Ing et al29 objectively investigated the degree that hockey visors or protective goggles impaired visual function. They found that there was no significant loss of acuity, colour perception, or gross field of vision. A significant decrease (4 db) in the peripheral vision was detected in both devices, and a scotoma of the monocular outer nasal peripheral field of the goggles. Further investigation and improvement in product design and function could lead to increased acceptance.29
A recent joint policy statement issued by the American Academy of Pediatrics and the American Academy of Ophthalmology states that properly fitted appropriate eye protectors reduce the risk of eye injury by 90%. This policy statement recommends the prescription of specific protective eyewear for youths involved in organised sports, based on a risk specific classification system. This classification system differs from the traditional one used by the American Medical Association (collision, contact, and non-contact) model, as it is based on the risk of an unprotected player receiving an eye injury. A person involved in a “non-contact” sport that involves a high speed projectile, such as squash, would be placed in the high risk category, whereas a participant in American football would be placed in a moderate risk category. Mandatory protective eyewear is recommended for all functionally one eyed athletes, athletes who have had eye surgery or trauma, and those who have been advised to wear eye protection.21 This policy statement was based on surveillance and laboratory testing data, as well as expert opinion.28,34,35
Sport related dental injuries are common, disfiguring, disproportionately expensive, and often require long term care. The total cost of tooth avulsions that are not properly preserved or replanted has been estimated to be $10 000–$15 000 per tooth over a lifetime.3 Surveillance based research has shown that mouth guards have a protective effect on dental injuries.3,36–,38 Mouth guards have also been suggested to be effective in mTBI prevention. This claim is controversial and not based on appropriate evidence based studies.39–,41
Amateur sports (boxing, ice hockey, football, lacrosse, and women’s field hockey) in many jurisdictions require mouth guard use.40 Greenberg and Springer42 note that dental and oral injuries have been reduced by half since 1974, when it became mandatory for all college and high school football players in the United States. Rules that officials are empowered to enforce do not always guarantee behavioural compliance. The evidence and positive attitudes about the protective properties of mouth or face guards, in several sports such as soccer, basketball, and ice hockey does not always lead to the universal use of mouth guards.36,43 A survey of high school basketball players revealed that only 4% were wearing a mouth guard, despite the fact that 31% of the players sustained oral-facial injuries in one season alone.44 Rules that officials are empowered to enforce do not guarantee behavioural compliance. The risk of penalties appears to have less influence on the players’ behaviour than other factors involving various existing beliefs or prejudices.3
Eime et al58 suggested that the institution of mandatory protective measures before obtaining a voluntary change in behaviour might not be successful. Reasons suggested for this discordance include the effect of peer pressure or the normative code of social group conduct, lack of knowledge, cost, poor fit/discomfort, and adult/professional modelling.3,37,40–,44 The only professional sport that requires mouth guards is boxing. The National Football League (NFL) and the National Hockey League (NHL) are two of the most visible professional contact sports, and neither league mandates that their players wear mouth guards.
The overall protective effect of the mouth guard is disputed by McCrory,39 however, most of the literature agrees that custom fitted mouth guards are more protective than the stock “over the counter” or boil and bite models.3,30,44,45 Newsome et al3 also describe a lack of epidemiological investigation of mouth guard use and injury prevalence among the adolescent athletic orthodontic population.
Progress has been made toward prediction and prevention of sport related craniomaxillofacial injuries. However, recent US government reports failed to make recommendations about the mandatory use of protective headgear in contact sports because of the lack of quality research on their effectiveness.46,47 The literature supports the fact that influential individuals and organisations (parents, coaches, athletic organisations, health professionals, and governments) must not abdicate their responsibility toward the health of the athlete because of a lack of comprehensive evidence.3,27,48,49
Standardisation of specific sport related injury data collection has been improved by using large databases—for example, the International Sports Injury System (ISIS). Surveillance studies are useful in the development of causal factor hypotheses and retrospectively determining whether a hypothesised factor is related to an injury. There are few sport related cohort, or case-control studies, that evaluate both the causal factors and the proposed interventions. Examining only one aspect of an injury can result in naive, ineffective, or even harmful conclusions.50
Future research directions
The quality of evidence concerning the prevention of sport related craniomaxillofacial injuries reviewed in the literature is limited. Individual surveillance and attitude studies provide data essential to the understanding and prevention of sports related injuries. These studies lack a systematic analytical approach that would provide a reliable basis for the development of preventive strategies. A systematic review of prevention strategies addressing sport and recreational injuries among children and youth was preformed by MacKay et al.50 This review found few well designed and controlled studies investigating strategies to prevent injuries and even fewer that evaluated strategies to reduce injury in children and youth.51 A review of a field level New Zealand five year sports injury prevention programme documented the importance of basing prevention strategies on scientific evidence rather than popular belief.44
Research into public health injury prevention has been at the forefront of epidemiologically based interventions. This research has shown that accidental injury and death are not random, unpredictable events, but are scientifically predictable and preventable and must be looked on as a disease in most instances.
Two of the most important models used in injury control are the public health approach (fig 1A⇓) and Haddon’s matrix (fig 1B⇓). The public health approach model is an epidemiological model that defines the problem, identifies the risk factors, devises an intervention, and then evaluates the effectiveness of the intervention before implementation. Haddon’s matrix integrates the basics of disease development (host, vector, and environment) with the circumstances before, during, and after the injury. The importance of including time in the matrix is that it allows the injury to be conceptualised as a predictable and preventable event. Table 4⇓ shows the use of the Haddon’s matrix model in the study of sport related craniomaxillofacial injury.50
Lett et al51 addressed the weaknesses of the public health approach and Haddon’s matrix models, and proposed a comprehensive unified approach (fig 1C⇑, fig 2⇓). The unified model exposed the lack of systematic point of application in the PHA, and a lack of systematic plan of action for the HM. By combining these concepts, a comprehensive three dimensional framework is defined. This model, which includes (a) a scientific basis for injury prevention programme implementation, (b) the different epidemiological components, and (c) all the time factors, will prevent the simplistic arguments about causation and prevention that continue to undermine injury control. The unified approach would delineate each individual study, and define the next logical step in the investigation. It can be used as an inventory and for a complete understanding of a particular injury.50
Meeuweisse52 developed a linear multifactorial model according to the intrinsic and extrinsic risk factors for injury distant from the injury, and the injury itself (fig 3⇓). This model acknowledges that the sport related injuries are a multirisk phenomenon, with a variety of risk factors interacting at any one time. Gissane et al53 proposed a cyclical modification of the Meeuwisse sport injury model (fig 4⇓). These authors thought that the linear Meeuwisse model of sport injury was too simplistic as it did not account for intrinsic factors that varied over time. This model is similar to the unified model. It is a fluid representation of the multifactorial nature of each injury. It accounts for what happens after the injury, how the athlete may return to sport, and how the susceptibility to injury changes, and attempts to bridge the gap between descriptive and analytical sports injury epidemiology.53
Attitude and surveillance based studies have contributed to the development of large injury databases, a better understanding of sport related craniomaxillofacial injury mechanisms, and the development of prevention interventions. Lack of scientific multidimensional injury prevention research can be improved by the application and modification of existing methodological models. This type of evidence based multifactorial research will raise the profile and acceptance of sports medicine. The use of prospective, randomised controlled studies of game situations, within a coherent methodological framework will produce data that will form the basis for sport injury prevention reforms. Further study of injury prevention should also be directed toward female contact sports that have previously required minimum mandatory protective equipment, and non-contact sports—for example, using projectiles or implements—involving both sexes. It will become more difficult for individuals, sport administrators, and governmental agencies to refute injury evidence based on these broad based studies.
We acknowledge Madeleine Echlin, Don Hartshorn BScPhm, Shari Gruman, Alexia D Estabrook MSLS, AHIP, Carole M Gilbert MSLS, AHIP, and Don DeCenzo LTA for their help in the preparation of this review.
REGU is supported by a New Investigator Award from the Canadian Institute of Health Research and a Research Scholar Award from the Department of Family Medicine and Community Medicine, University of Toronto.
Competing interests: none declared