© 2000 ExRA Inc.

EXERCISE RESEARCH ASSOCIATES OF OREGON

Athletic Injury Monitoring System

FOOTBALL INJURY RESEARCH PROJECT

REPORT FOR 1998 FOOTBALL SEASON

 

  1. General Results Regarding Head Injuries
  2. Football injury data were collected from a national sample of 36 high schools and 46 colleges during the 1998 football season. The high school sample was distributed by four geographic regions, and the college data was distributed by four geographic regions and by size of program (NCAA and NAIA divisions). Statistical analyses of the distributions in these samples indicated that the college sample was representative of the entire country by region and size of program, and therefore the results presented here for the collegiate level can be reasonably projected to the country as a whole. The nature of the high school sample precludes a rigorously representative sampling. The data collection procedures require a medically trained person on site (i.e., the certified athletic trainer), and only a relatively small proportion of the more than 1700 high schools that sponsor football teams in the country have athletic trainers on staff (compared with essentially all colleges). Very few of the athletic trainers who are working at the high school level are in smaller schools. In this case the most reasonable approach is to sample a large number of high schools (albeit a small proportion of the total) and at least keep the sample representative by geographic region. The 36 high schools in this sample were statistically representative by geographic region, and with nearly 3000 players it is considered adequate for the purposes of this project.

    Data on exposure to the possibility of injury in practices and games, and data on any injury that kept a player out for one day or more (including any head injury whether on not time loss was involved), were returned on a weekly basis throughout the season by certified athletic trainers at each participating school. As data arrived, it was logged in and screened for completeness and consistency before being entered into computer storage files. One problem with surveillance systems of this sort is incomplete data submission from the field creating "gaps" in the data. To prevent this problem in this project, the AIMS staff maintains frequent mail and telephone contact with the athletic trainers, obtaining corrections of any inconsistencies in the reported data and reminding them to submit missing data. Through this process of "preventive maintenance" the response rate for data submission has been extremely high for this project. For the college sample 98.7% of the weekly reports were submitted, and for the high school sample the response rate was 96.9%. There were a total of 308 concussions observed in this seasonís sample.

    The cerebral concussion rates at the high school and college levels were quite similar, with a rate of 0.60 concussions per 1000 Athlete-Exposures (A-E) for high school players and 0.62 per 1000 A-E for college players. (An Athlete-Exposure is one player participating in one game or one practice where he is exposed to the possibility of being injured.) The combined rate is 0.62 concussions per 1000 A-E. Looked at another way, this is equivalent to one concussion in every 1613 times a player participates in a game or practice. For a team of 100 players (generating 100 A-E in every daily practice and every game, assuming they all played in the game), this would be one concussion in every 16 days of activity. A less accurate and less useful "rate" that is still commonly seen in sports medicine literature is the number of injuries per 100 players. For concussions in this sample, there were 3.72 concussions per 100 high school players and 4.54 concussions per 100 college players. While this appears to indicate that the rate for college players is about 20 percent higher, because college players typically have more exposures (practices and games) during a season, the actual rates for high school and college players are really quite similar. This illustrates one of the major weaknesses of using injuries per 100 players

    Because this project collects data on all types of injuries, it is possible to look at the occurrence of cerebral concussions in relation to other types of injuries. The national data summaries for high school and college teams show that the head is the third most frequently injured body part at the high school level, exceeded only by the ankle and the knee. At the college level, the head is the fourth most frequently injured body part, following the knee, ankle and shoulder in that order. With regard to type of injury, cerebral concussions are the fourth most frequent injury at both levels, after ligament sprains, muscle strains and contusions. What cannot be seen in these raw data summaries is how cerebral concussions rank in relation to other specific body part/injury type combinations (i.e., not all knee injuries are ligament strains; they include such injuries as contusions and meniscus injuries as well). When broken down further, cerebral concussions turn out to be the second most frequent injury at the high school level (ankle sprains being the most common), and the third most frequent injury at the college level, following ankle sprains and knee ligament sprains and tears.

    The rate of concussions in practice for high school players was 0.26 per 1000 A-E, while in games it was 3.01 per 1000 A-E. For college players the concussion rate in practices was 0.32 per 1000 A-E, and in games it was 4.20 per 1000 A-E. High school players were 11.6 times as likely to sustain a cerebral concussion in a game as they were in practice, while college players were 13.1 times as likely. It is not surprising that the concussion rate is higher in games, since the rate for all injuries in games has previously been found to be eight or nine times higher than in practices. This is most likely due to a much higher intensity level sustained throughout a game as compared to most practices. However, it is of concern that the increased concussion rate in games considerably exceeds the increased rate for all injuries in games. This could be an indication that the head tends to be an initial contact point more often in games than it is in practice, or that the head is more "sensitive" than the rest of the body to the increased intensity of hitting during games.

    At the high school level, 46.4% of the concussions occurred in offensive players and 39.1% in defensive players, with the remaining 14.5% in kickers and special team players. At the college level the situation was very similar, with 50.0% of the concussions occurring in offensive players and 34.3% in defensive players. The remaining 15.7% occurred in kickers and special team players. At the high school level, being tackled accounted for 29.1% of the concussions and blocking accounted for 20.9%, while tackling was the mechanism for 22.7% and being blocked was the cause of 16.4% of the concussions. Tackling was the causative mechanism for 22.7% of the college concussions and being blocked for 11.6%. On the offensive side of the ball, being tackled caused 22.2% and blocking caused 32.3% of the college concussions. At both the high school and college levels, impact with the playing surface caused about 4-5% of the concussions.

    The athletic trainers noted whether or not an injury was directly caused by impact from another playerís helmet. For all injuries at the high school level, impact from a helmet was the cause of 22.4% to 29.8% of the recorded time-loss injuries. (This is estimated by using the percentage of injuries definitely attributed to helmet impact as the minimum value and adding the percentage of injuries where the athletic trainer indicated that whether or not a helmet was involved was unknown, to give a maximum estimate.) At the collegiate level the estimates are 13.9% to 25.0%. Combining the high school and college data, direct impact from another playerís helmet appears to be the causative mechanism of a minimum of 17.2% of all football injuries, and possibly as much as 26.9% of all football injuries. When only cerebral concussions are considered, impact from another helmet was the direct cause of 61.8% to 79.1% of all concussions at the high school level, and 55.6% to 76.3% of concussions at the college level. Overall, helmet to helmet impact was the direct cause of a minimum of 58.1% of all cerebral concussions in football, and possibly as much as 77.3% of all concussions in this sport.

    This project uses a grading system for severity of cerebral concussion developed by the American Academy of Neurology (Neurology 48:581-585 (1997)). Grade 1 on this scale indicates transient confusion that resolves in less than 15 minutes (the "bell ringer"); Grade 2 indicates symptoms that last longer than 15 minutes, but there is still no loss of consciousness; and Grade 3 is used for any concussion involving loss of consciousness. For the purposes of this project, in order to provide greater sensitivity at the "low" end of the scale, we use an additional grade, Grade 0, to pick up situations where there is no immediate indication of concussive injury but the player later complains of headache and difficulty concentrating. From the data collected during this season, the average time loss for a Grade 1 concussion was 2.8 days, the average time loss for a Grade 2 concussion was 12.0 days and for Grade 3 it was 22.0 days. The average time loss for those injuries classified as Grade 0 was 2.7 days. Because the average number of days lost can be skewed to the high side by a few instances where players were held out for the rest of the season, a more informative statistic in this case would be the median. (The median is the midpoint in a listing of the number of days lost per injury in ascending order; i.e., half the injuries were for that number of days or less and half were for that number of days or more.) The median number of days lost for Grade 0 concussions was 1.5 days, for Grade 1 concussions it was 2 days, for Grade 2 it was 8 days, and for Grade 3 it was 7.5 days.

    A new item added to the data collection forms for the 1998 season looked at the impact of the new heavily padded chinstraps being used by many players. Presumably, one of the effects of using these padded chin straps is to reduce the shock of blows to the chin, which should help prevent or at least reduce the severity of concussions from such blows, in a manner similar to the protection found to be provided by using mouthguards. At the beginning of the season athletic trainers were asked how many players on their team were wearing the heavily padded chinstraps, to get baseline data on the use of this piece of equipment. Then every concussion that was reported also included information on whether or not the player was wearing a padded chinstrap. For the high school sample, 27.85% of the players were wearing the padded chinstrap, while in the college sample 29.53% wore the padded chinstrap. At the end of the season 5.51% of the high school players wearing a padded chinstrap had suffered a concussion, while 2.84% of the players wearing regular chinstraps had suffered a concussion. These data indicate that high school players wearing the padded chinstrap were 1.9 times as likely to suffer a concussion during the season. For the college sample, the risk also was slightly higher for those wearing the padded chinstrap. During the season, 4.82% of the college population wearing the padded chinstrap suffered a concussion, while 4.01% of the those wearing regular chinstraps were concussed, indicating the players wearing the padded chinstrap were 1.2 times as likely to incur a concussion.

    If the padded chinstraps are not reducing the numbers of concussions in players wearing them, they might still have a positive effect by reducing the severity of the concussions that do occur while wearing them. The data on the distribution of grade of concussion in players wearing padded chinstraps were analyzed, with expected frequencies of each grade in the players wearing padded chinstraps based on the distribution of concussions in each grade among players wearing regular chinstraps. The results showed no statistically significant difference in the distribution of grades of concussion between players wearing padded chinstraps and players wearing regular chinstraps. Although not statistically significant, there was a consistent trend toward greater numbers of concussions in the higher grades for players wearing padded chinstraps, and fewer than expected for the less severe grades. This is the opposite of what might be expected if the padded chinstraps were reducing the severity of concussions.

    Obviously these results do not indicate that heavily padded chinstraps are having the effect hoped for in reducing the number or severity of concussions, although they may be having other positive effects (e.g., reducing contusions and lacerations to the chin and jaw). A few explanations come to mind for these results, including: 1) this year's results are a statistical anomaly that do not indicate the true picture; 2) related to the previous explanation, the sample size from one season is too small to produce accurate results; 3) the padded chinstraps may tend to be used by players with a higher intrinsic risk for concussion; and 4) for whatever physical or biomechanical reasons, heavily padding the chin to help reduce the risk or severity of concussions just does not work. The only way to resolve this question is to collect more data and see what results a larger database produce.

    On the forms the athletic trainers used to submit data on the helmets being used by their teams, they also indicated who was primarily responsible for fitting the football helmets and whether or not these individuals had received specific training on helmet fitting. At the college level just over 55% of the responsible individuals were equipment managers, of whom all but 6% had specific training in fitting helmets. About a quarter of the individuals were athletic trainers, all but 14% of whom had training. About 20% of the responsible individuals were coaches, and 18% of them did not have any training. All of the individuals at the college level who did not have training were in the smaller (Division II and Division III) schools. There were a total of 11% of the individuals responsible for fitting helmets at the college level who did not have any specific training. At the high school level the situation was different, because high schools usually do not have professional equipment managers and the coach is most often the one responsible for fitting helmets. Coaches comprised just over 50% of the responsible individuals, and 20% of the coaches did not have any training in fitting helmets. Most of the rest of the responsible individuals were the athletic trainers, and all of them had training. Overall, in this sample about 15% of the individuals responsible for fitting helmets at the high school level had no training. Compared with the previous year, the situation has improved at the college level with a great improvement in the proportion of coaches who now have training in fitting helmets, and an overall drop by nearly one-half in the percent with no training. At the high school level the situation was nearly the same as last year, except for a slight drop in the percentage of coaches responsible for fitting. Given that most high schools do not have either equipment managers or athletic trainers, it still can be estimated that at about one in five high schools the person responsible for fitting football helmets has no training to do so.

     

  3. Relative Risk: History vs No History of Concussion
  4. An unknown factor for many years has been the relative risk for sustaining a cerebral concussion among football players who have previously received such an injury compared with players with no history of concussion. As part of the data collected from the athletic trainers regarding helmets used by their teams, they also indicated how many of their players had any history of concussion during the previous five years and what model of helmet these individuals were wearing. From this information, plus data from the individual injury forms indicating whether or not a concussion being reported occurred in a player with a previous concussion, it is possible to calculate a relative risk for those players with a previous history of cerebral concussion.

    At the high school level the sample for the calculation of relative risk consisted of 2879 players. Of those, 110 players (3.8%) had a history of concussion sometime during the previous five years. There were a total of 110 concussions recorded in this sample, 31 among those players with a previous history, and 79 in players with no previous history. Using this information, the relative risk is calculated as follows:

    Relative Risk =

    (31/110) =

    0.2818

    = 9.9

    (High School)

    (79/2769)

    0.0285

     

    Among those high school players with a previous history of cerebral concussion, 28% sustained a new concussion during the season, while among the players with no previous history of concussion only 3% sustained a concussion. At the high school level the relative risk of sustaining a cerebral concussion during the season among those players with a previous history of concussion is nearly ten times greater than for those with no previous history of concussion.

    At the college level the sample for this calculation consisted of 4308 players. A total of 307 players from this sample (7.1%) had sustained a concussion within the previous five years. Out of the total of 187 concussions recorded during the season, 63 occurred in players with a previous history and 124 occurred in players with no previous history. The relative risk is therefore calculated as follows:

    Relative Risk =

    (63/307) =

    0.2052

    = 6.5

    (College)

    (126/4001)

    0.0315

    Just over 20% of college players with a previous history of cerebral concussion sustained a new concussion during the season, while just over 3% of those players with no previous history sustained concussions. At the college level the relative risk of sustaining a cerebral concussion during the season among those players with a history of concussion during the previous five years is more than six times greater than for those with no previous history of concussion.

    Combining the high school and college data results in the following calculation of risk:

    Relative Risk =

    (94/417) =

    0.2254

    = 7.4

     

    (205/6770)

    0.0303

     

     

    Adding the previous year's data to these data results in the following calculations of risk for the 1997 and 1998 seasons combined:

    Relative Risk =

    (61/297) =

    0.2054

    = 6.8

    (HS)

    (203/6770)

    0.0300

     

    Relative Risk =

    (109/654) =

    0.1667

    = 5.4

    (College)

    (232/7350)

    0.0316

     

    Relative Risk =

    (170/951) =

    0.1788

    = 5.8

     

    (441/14243)

    0.0310

     

    Therefore, in this large two-year national sample of high school and college football players, the risk of sustaining a cerebral concussion during the season was nearly six times greater for those players with a history of concussion during the previous five years than for those players with no previous history of concussion.

     

  5. Conclusions

The second year of this football injury data collection project again proved very successful, with data collected on nearly 7000 players and over 500,000 Athlete-Exposures for the season. There were data on over 300 cerebral concussions from this sample. The cumulative data for the 1997-1998 seasons covers over 16,000 player-seasons, over 1,126,000 athlete-exposures, and over 5,700 injuries including 671 concussions. This project provides what is undoubtedly one of the largest current database on football injuries available, providing a rich data source for analyzing football injuries. The cooperation from the certified athletic trainers at the schools involved in the project has been excellent, and has resulted in an extremely high response rate for the weekly submission of data forms, as noted in the first section of this report.

As was noted in the report for the 1997 season, several of the results presented in the first section of this report, when taken together, still appear to imply the need for a more vigorous and sustained education program for athletes, coaches and parents regarding the head and the helmet in this sport. The fact that cerebral concussion is the second or third most frequent injury by itself should raise some warning flags, especially when considering research showing that measurable cognitive deficits in memory and information processing for up to thirty days occur following a closed head injury, even when there is no loss of consciousness (e.g., Lancet 2:605-609 (1974); Lancet 2:995-997 (1975). In addition, anywhere from one-half to three-quarters of all football concussions involve direct impact from another playerís helmet, which implies that the head is still being used as an initial contact point far too often. Given the nature of this sport, there undoubtedly are many instances where such contact is accidental or unavoidable. But when the helmet is the causative agent in three to four times the percentage of concussions as it is for injuries in general, this is a strong indication that players still tend to use the head as a battering ram and are not keeping the head up, particularly in head on collisions. This also has implications for the risk of neck injuries. This is supported by the observation that tackling and being tackled are generally the most frequent mechanisms for concussion. Finally, the observation that at about one in five high schools the person responsible for fitting helmets has no training to do so has implications for ensuring the optimal protective capabilities of the helmet as well. To a certain degree all of these problems may be inter-related, and can be addressed by a comprehensive education program aimed at players (and their parents at the high school level) and coaches. It needs to be more coordinated and more comprehensive than the sporadic attempts of the past. Football helmet companies could be the driving force of such an education program, and in turn would reap obvious benefits from such an effort to reduce the incidence of cerebral concussion in football. It also would be appropriate for football helmet companies to encourage governing bodies (state and national high school associations, NCAA, NAIA, etc.) to put much more emphasis on enforcement by game officials of the existing rules regarding use of the head as an initial contact point. This is not the appropriate forum for going into detail on the design of such an educational program, but it can be explored in the future if desired.

It has been known for many years that players with a previous concussion appear to be more likely to incur a new concussion than players with no history of previous concussions, but prior to the initiation of this project there has been little data on exactly how much more likely. The data presented here indicates that players with a history of concussion within the previous five years are nearly six times as likely to suffer a new concussion during the season than those with no history of concussion. Among other areas, this information will have implications for questions regarding when it is appropriate to allow a concussed player to return to activity, and for research on the "second impact" syndrome.

 

Eric D. Zemper, Ph.D.

Principal Investigator