Concussion in Professional Football: Summary of the Research Conducted by the National Football League's Committee on Mild Traumatic Brain Injury

Elliot J. Pellman, MD; David C. Viano, Dr. Med., PhD


Neurosurg Focus. 2006;21(4) 

In This Article

Injury Collection and Data Analysis

I: Prevalence of Mild TBI

Mild TBI is a major public health problem in the US, with an estimated annual incidence of 160 to 375 cases per 100,000 persons per year. Officials at the Centers for Disease Control and Prevention have estimated that the number of mild TBIs has reached 300,000 cases per year in all sports. In an attempt to better understand mild TBI in the NFL, the Committee supervised prospective collection of data on this condition in NFL players from 1996 to 2001.

All data were collected using standardized forms, and the information was assessed in a blinded fashion. In all, 787 game-related cases (1913 games) were reported, and all players were examined by team physicians, with information reported on player position, type of helmet, symptoms, medical actions, and playing days lost.[5] All patients were evaluated by physicians immediately after the injury and underwent follow-up physician evaluations until they returned to play. Forms were completed by the physicians, which increased the medical validity and reliability of the information collected. Because the Committee did not man date case management for mild TBI, the patients' medical course reflects the true natural history of mild TBIs among professional football players during this 6-year period.

Mild TBIs are relatively common injuries sustained by professional football players. The data indicate that quarterbacks, wide receivers, defensive backs, and special-team players on kicking units are more likely to sustain these injuries than are offensive and defensive linemen ( Table 1 ). The clinical information helped validate the biomechanical data on professional football–related mild TBIs derived from the earlier studies.

The most common initial symptoms for players who sustained concussions were headaches, dizziness, memory problems, cognitive problems, and somatic complaints. Headaches were observed in 55% (95% CI 51.5–58.5%) of NFL players who suffered concussions.[5] For the great majority of these players, mild TBIs did not cause prolonged disability or prolonged absence from play. In the NFL, 56.5% of players with concussions returned to play on the day of the injury and 97.1% returned to play by Day 9 after the injury. Only 2.9% of the players missed more than 9 days before returning to play. This indicates that most mild TBIs sustained in the NFL are self-limiting and that players recover fully and spontaneously in a short time. Be cause a significant percentage of players returned to play in the same game and the overwhelming majority of players with concussions were kept out of football-related activities for less than 1 week, it can be concluded that mild TBIs in professional football are not serious injuries.

Only 9.3% (95% CI 7–11.6%) of the NFL players experienced an LOC as a result of severe concussive head impacts (58 of 623 reported cases of mild TBI). It is important for all physicians who care for athletes with head injuries to know that most of the concussions they treat are not associated with LOC, and that when this symptom occurs it is for a relatively short duration.

II: Repeated Mild TBI

Despite the findings and conclusions in the preliminary clinical study, questions remained concerning NFL players who suffered repeated mild TBIs. Physicians have been concerned for many years about the possible deleterious effects of multiple concussions on the brains of athletes.[8] In this study, data on 887 concussions sustained in practices and games involving 650 players from all 30 NFL teams between 1996 and 2001 were prospectively collected and analyzed. A total of 160 players experienced repeated injury, with 51 suffering three or more concussions during the study period. The median time between injuries was 374.5 days, with only six concussions occurring within 2 weeks of the initial injury. Repeated concussions were more prevalent in the secondary, the kick unit on special teams, and in wide receivers.

There have been reports in which researchers have concluded that there may be an increased risk of repeated concussive injuries, and there may be a slower recovery of neurological function after repeated concussions in those who have a history of previous ones. The results of this study in professional football players do not support that conclusion. Although approximately one half of players returned to play during the same game or practice session, and approximately 90% returned within 1 week, recurrent injury caused by an increased vulnerability in the immediate postconcussion period does not seem to be a factor in professional football players.

No cases of "second-impact syndrome" were detected during the 6-year period of this NFL study. There were no deaths, prolonged comas, or evidence of diffuse cerebral edema in any player. Furthermore, there have been no case reports of second-impact syndrome in the history of the NFL. It is possible that this syndrome does not truly exist in this population of athletes. Many of the mild TBI guidelines have established exclusion periods based at least partially on the belief that everyone who experiences a symptomatic mild TBI is at risk for the development of second-impact syndrome. The absence of the syndrome in this patient population supports the suggestion that such arbitrary return-to-play guidelines may be too conservative for professional football.

Another often-expressed concern underlying the development of mild TBI guidelines is the occurrence of chronic brain damage as a result of multiple head injuries. A recent letter to the editor in Neurosurgery addressed the case of an NFL player who was alleged to have died of complications of chronic traumatic encephalopathy, underscoring this concern.[1] Chronic traumatic encephalopathy in boxers is a well-accepted and documented clinical and pathological syndrome. The clinical features include a combination of cerebellar, extrapyramidal, and pyramidal dysfunction, along with cognitive and personality changes. In the NFL study, none of these features was identified in any player, including those with repeated injury. There were no signs of chronic traumatic encephalopathy in this group of active, contemporary football players.

In players with four or more concussions there was a greater chance of personality change and fatigue, but the number did not reach statistical significance. The incidence of LOC at the time of mild TBI was no different with successive concussions. Overall, however, the signs and symptoms reported in the NFL study were very similar in players with single and multiple mild TBIs. There was no evidence of increased severity of injury in multiple compared with single mild TBI cases.

III: Postconcussion Syndrome

In the data analysis there were a small number of athletes in whom persistent postconcussion symptoms developed, and these individuals were unable to return to play for an extended period. Often the postconcussion symptoms were seen 1 or more weeks after the injury. The postconcussion syndrome follows head injury that is usually mild, and consists of any combination of the symptoms and signs that occur after mild TBI. The Committee decided to analyze the data obtained in players in whom postconcussion syndrome was diagnosed.[7]

When does cerebral concussion end and postconcussion syndrome begin? Very few data are available on the evolution of head injury to postconcussion syndrome in athletes. The purpose of this part of the study was to compare the small group of NFL players who did not return for more than 7 days after a mild TBI with the majority of NFL players who do return within 7 days. The 7-day dividing line between the groups does not reflect an arbitrary distinction. Because NFL teams play games once a week, the players in this study cohort all missed at least one game. The NFL teams play only 16 games per season. Therefore, missing one game involves a significant loss of playing time. The study cohort all had significant functional impairment caused by mild TBI.

There were 72 cases with more than 7 days away from play among the 887 cases of mild TBI analyzed between 1996 and 2001. Of these injuries, 38 were single concussions experienced in the study period, eight were the first of repeated concussions, 16 were the second, seven were the third concussion, and so on in the study period. The median duration between the first injury and 7 or more days away from play was 364 days, and the median duration between the last injury and 7 or more days away was 329 days, which is statistically similar.

For the whole sample, there were 650 players who experienced 887 concussions during the study period, and the position they were playing was recorded in this analysis. Individually, the position groups most often associated with loss of 7 or more days are the defensive secondary (23.6%), kick unit (19.4 %), quarterbacks (12.5%), and wide receivers (12.5%). The fraction of players in a position with 7 or more days away from play compared with all in that group was highest for the quarterback (14.8%), the return unit on special teams (11.8%), and the secondary (10.8%), followed by the kick unit (10.4%) on special teams. Quarterbacks had the highest odds ratio of 7 or more days away from play with concussion, whereas running backs had the lowest relative risk.

The majority of players with concussions (88.9%) are rested, with 7 or more days out, compared with 90.7% with fewer than 7 days out. Overall, the data show a conservative treatment of concussion. There was no statistical difference in players' treatment in comparisons between the two groups.

Between the initial examination and the first follow-up review, most of the signs and symptoms started to decrease, except for increases in the general category of memory problems, fatigue, irritability, and sleep problems. By the fourth follow-up examination (median 4.7 days), all memory and cognitive problems had cleared. Nevertheless, some players still reported headaches, dizziness, and photophobia. Somatic complaints continued in some players, including personality change and fatigue. By the seventh examination (median 13 days) only headaches remained to clear.

The data analysis allowed the development of profiles for two groups of NFL players with concussions. The first group is the small minority of players who ultimately do not return to play for 7 or more days postinjury. They are more likely to experience LOC as a result of the head injury, and they are more likely to be hospitalized on the day of the injury. At the time of the initial evaluation, these players have a significantly increased number of the signs and symptoms of mild TBI. On initial examination, they are very likely to have retrograde amnesia, difficulties with immediate recall, and overall difficulties with cognition and general memory.

The results of this study and the previous ones prompted the Committee to perform a critical analysis of the widely promoted guidelines for the evaluation and management of concussion in sport. This 6-year study indicates that no NFL player experienced second-impact syndrome, chronic cumulative injury, or chronic traumatic encephalopathy from repeated injuries. These are a few of the expressed rationales for developing management guidelines. The proponents of these guidelines recommend grading the severity of concussion by a limited number of criteria, such as presence or absence of LOC, posttraumatic amnesia at time of injury, confusion, and mental status changes soon after injury. The guidelines then make clinical management recommendations on the basis of the grade of concussion diagnosed using these criteria.

Analysis of the NFL data reveals that there are other prognostic factors of equal importance that are not included in the grading systems. These include photophobia, fatigue, and increased absolute numbers of signs and symptoms. Furthermore, the grading systems do not take into account factors such as the position played by the injured athlete and the type of play during which the injury occurred. In the NFL study we found that the presence of signs and symptoms such as fatigue, sleep disturbance, irritability, and/or cognitive or memory impairments on examination the day after the injury also has significant prognostic usefulness. None of the grading systems incorporate results from examinations performed other than on the day of the injury. Although the grading systems use some important prognostic findings, they are limited in their scope and fail to incorporate a number of other factors that have been demonstrated to be predictors of delayed recovery.

The NFL studies also support the contention that grading concussions immediately after injury is prone to error. A number of players with signs and symptoms suggesting a poor prognosis in fact recovered very quickly and returned to play on the day or within a few days of injury. Conversely, there were two players with minimal signs or symptoms, suggesting a good prognosis, who were ultimately kept out of play for 7 or more days after mild TBI. None of the prognostic factors or combinations of factors was 100% accurate in predicting recovery.

It followed from this analysis that the current attempts to link prospective grading of concussion symptoms to arbitrary, rigid management decisions are not consistent with scientific data. We believe that if one insists on grading concussion severity, the best way is retrospectively, on the basis of how long it actually takes the player to become asymptomatic, with normal results on neurological examination. It is the recommendation of the NFL's Committee on Mild Traumatic Brain Injury that team physicians treat their players on a case-by-case basis, using their best clinical judgment and basing their decisions on the most relevant, objective medical data obtained.

IV: Neuropsychological Testing in Evaluating Mild TBI

The development and use of neuropsychological testing in the NFL has been rapid, and it has contributed to the implementation of this testing in other professional sports organizations, including ice hockey, automobile racing, and Australian Rules football. When used in concert with other medical information, neuropsychological test data contribute quantitative information regarding neurocognitive processes, such as attentional, memory, and cognitive processing speed. Neuropsychological testing can provide objective information regarding the recovery process and allows comparisons of the athlete's performance against normative data and the individual's preinjury level of performance.

The NFL's neuropsychological testing program was established as a clinical research program with the goal of investigating the use of such testing to assist team physicians in the return-to-play decision. Athletes in the NFL who underwent neuropsychological testing between 1996 and 2001 and who participated in the study were included.[4] Preseason normative data were collected in 655 NFL athletes. The overall sample of injured players who underwent testing consisted of 143 athletes. This sample represented 22% of the 650 NFL athletes who experienced 887 concussions during the study period. Because participation in the study was voluntary, not all athletes with mild TBI completed neuropsychological testing.

This study supports previous research that has shown that on-field signs of cognitive impairment, such as amnesia, are useful in determining the severity of brain injury.[4] Players identified as having cognitive and memory disturbances are likely to show neuropsychological impairments on follow-up testing. Athletes with no clinically recognized cognitive and memory impairments on physician examination did not, as a group, have more subtle changes in cognitive processes that were missed during the sideline clinical examination. This suggests that the on-field evaluation by team physicians is effective with regard to the identification of cognitive and memory impairments immediately after an injury.

On review of the data, the fact that there were no overall significant differences in test results between a group of injured NFL athletes who had previously undergone baseline neuropsychological testing suggests that NFL athletes with mild TBIs recover quickly after injury (Fig. 6). In contrast to previous studies in which cognitive difficulties lasting 1 week or more were suggested, NFL athletes demonstrated generally intact performance within several days relative to baseline performance levels.

Figure 6.

Bar graph showing the mean and standard deviation in Brief Visuospatial Memory Test-Revised (BVMT-R) (Total) neuropsychological test scores for NFL baselines, players with memory problems, more than three concussions, and out 7 or more days from play. Also shown are data (first two bars) from a sample of high school and college players at Penn State University. (Reprinted with permission from Pellman EJ, Lovell MR, Viano DC, Casson IR, Tucker AM: Concussion in professional football: neuropsychological testing-part 6. Neurosurgery 55: 1290-1305, 2004.)

The issue of the potential cumulative effects of sports-related mild TBI has been a particularly controversial one, and many studies have offered different views on the significance of multiple injuries. In this study we did not find a pattern of worse neuropsychological test scores in a group of professional athletes who received close follow- up care for 6 years. We also did not find worse neuropsychological performance in NFL athletes who were held back from play for 7 or more days compared with a group who returned within 1 week. It is noteworthy that in this group that was kept from play for 7 or more days, the results of neuropsychological tests and medical evaluation of cognitive and memory function were normal within several days of the injury. The results of this study indicate no evidence of worsening injury or chronic cumulative effects of multiple mild TBIs in NFL players.

On the basis of this study, the NFL's Committee on Mild Traumatic Brain Injury makes the following recommendations regarding the proper role of neuropsychological testing in the NFL. Neuropsychological testing is a tool that can assist the physician in evaluating and managing mild TBI. It definitely should not be used in isolation and cannot replace and should not be used to replace the clinical judgment of the treating physician in the diagnosis and management of mild TBI. The main value of neuropsychological testing in this setting is its ability to confirm and corroborate the results of clinical and mental status evaluation.

V: The ImPACT Program

Despite the initial findings, based on neuropsychological testing, that NFL players had a rapid return to baseline after a mild TBI, the Committee was aware that this was in contrast to several studies that found more long-lasting neuropsychological decrements in high school athletes. Members of the committee decided to perform an additional study, in which professional and younger athletes were compared using the same protocol and identical neurocognitive test battery.[3]

The ImPACT program is a computerized neuropsychological testing instrument used by some within the NFL neuropsychology program. The ImPACT program (version 2.0) consists of six neuropsychological tests designed to target different aspects of cognitive functioning, including attention, memory, processing speed, and reaction time. The results of ImPACT testing on NFL and high school players were compared.

In this study,[3] we found no significant neurocognitive deficits in the NFL sample within the 1st week postinjury, suggesting that NFL athletes with mild TBIs recover relatively quickly after injury. In contrast, we found residual difficulties in reaction time and memory in the high school sample but not in professional players. This raises the question of differential response to mild TBI in professional and high school athletes.

VI: Return to Play

There were concerns based on the results of the earlier studies of mild TBI that perhaps some players were being returned to play too soon after injury, thus resulting in more prolonged postconcussion syndrome and perhaps creating the risk of more severe brain injury. The committee therefore decided to do a data analysis on NFL players who returned to play on the same day as their mild TBI.[6]

In the NFL players studied between 1996 and 2001, there were 135 (15.2%) who returned to play immediately after mild TBI and 304 (34.3%) who rested and returned to the same game after concussion. There were few differences in the player position or team activity related to the injury or action taken. However, players who suffered concussions and returned to the same game had fewer initial signs and symptoms than those who were removed from play.

Widely used concussion management guidelines state that athletes can return to play on the day of the injury if they become asymptomatic and if results of examinations performed within 15 minutes of their injury are normal. In the NFL database, 41% of players returned to the same game either immediately or after resting more than 15 minutes. Of those who returned immediately, 17.9% were out more than 15 minutes, and 51.7% of those who rested and returned were out for more than 15 minutes. The data showed no increased risk of repeated mild TBI, prolonged postconcussion syndrome, delayed return to play (≥7 days out), second-impact syndrome, or catastrophic intracranial event. The NFL experience thus supports the suggestion that players who become asymptomatic and have normal results on examinations performed at any time after injury, while the game is still in progress, have been and can continue to be safely returned to play on that day. The data also support the proposition that players who experienced LOC had no increased risk of repeated mild TBI or prolonged postconcussion syndrome compared with other players.

The results of this study indicate that many NFL players can be safely allowed to return to play on the day of the injury after sustaining a mild TBI. These players had to be asymptomatic, with normal results on clinical and neurological examinations, and be cleared by a knowledgeable team physician. There were no adverse effects, and the results once again are in sharp contrast to the recommendations in published guidelines and the standard of practice of most college and high school football team physicians. This data analysis was performed on information obtained in adult professional football players, and these findings are not meant to be carried over to any other patient population, including high school and college football players.


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