Journal of Athletic Training

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Journal of Athletic Training

2001;36(3):307–311

q

by the National Athletic Trainers’ Association, Inc

www.journalofathletictraining.org

Cerebral Concussion: Causes, Effects, and

John W. Powell

Michigan State University, East Lansing, MI

John W. Powell, PhD, ATC, provided conception and design; analysis and interpretation of the data; and drafting, critical

revision, and final approval of the article.

Address correspondence to John W. Powell, PhD, ATC, 40 IM Sports Circle, Michigan State University, East Lansing, MI

48824. Address e-mail to powellj4@msu.edu.

Objective:

To characterize the causes, effects, and risks as-

sociated with concussion in sports.

Background:

Concussion is an injury associated with sports

and is most often identified with boxing, football, ice hockey,

and the martial arts. In addition, recent research has shown that

concussion occurs in many different sports. In the decade of

the 1990s, concussion became a primary issue for discussion

among the media, sports sponsors, sports medicine profession-

als, and athletes.

Description:

Concussion is an injury that results from a wide

variety of mechanisms and has numerous signs and symptoms

that are common to different types of injury. Continued improve-

ment in prevention and management strategies for concussion

requires a strong body of research from a variety of different

disciplines. It is essential that research efforts focus on both

prevention and management and that researchers and clini-

cians work closely toward their common goals.

Conclusions/Recommendations:

Until the research com-

munity is able to provide sound recommendations for the pre-

vention and management of the concussion, the care of the

injured player falls squarely on the clinician. It is important for

sports medicine professionals to continue to stay up to date on

the advances in understanding concussions and how to care

individually for each player who sustains a concussion.

Key Words:

mild traumatic brain injury, head injury, injury

prevention

I

n today’s competitive sports environment, large numbers

of athletes participate in a wide variety of youth, high

school, collegiate, professional, and recreational sports.

Whereas some sports (eg, football) have maintained a consis-

tent number of participants, others have increasing participa-

tion.

1

For the younger participants, the sport experience pro-

vides an environment in which they can grow and develop

physically, mentally, and socially. For college and professional

athletes, sports offer an opportunity for personal success and

future employment. For recreational athletes, sports provide

opportunities for maintaining a healthier lifestyle and an outlet

for relieving the tensions of modern life. As sports programs

continue to flourish, it is the responsibility of the sponsors of

these programs to provide an environment that minimizes the

risk of injury.

Risk of injury is inherent in sports participation. This risk

stems from the nature of the game and the specific activities

of the participants, both during their participation and during

events that surround their participation. For example, collision

sports such as football and ice hockey characteristically have

more acute traumatic injuries than sports such as swimming

and track. Boxing has more head-related trauma because of

the focus of the sport. Within each sport, a general injury

pattern and specific types of injury are unique to the sport.

One type of injury that can occur in any sport or physical

activity is concussion. This injury represents the most common

type of acute brain injury in sports and is most often associated

with boxing, football, ice hockey, and martial arts.

2

As with

other types of injury, the frequency and severity of concussion

that is associated with a sport is a function of the nature of

the game, specifically, the rules and regulations, the specific

physical activities of participants, and the environmental con-

ditions associated with the game.

HISTORICAL PERSPECTIVE

Concussion has been associated with a range of definitions

that generally focus on the nature of the medical signs and

symptoms present at the time of injury. Concussion has been

described as a clinical syndrome characterized by immediate

and transient posttraumatic impairment of neural function,

such as alteration of consciousness or disturbance of vision or

equilibrium, and other signs and symptoms due to brain stem

involvement.

3

This approach includes the classic ‘‘ding’’ as-

sociated with head injury in sports. Some authors have indi-

cated that concussion must be associated with a loss of con-

sciousness, either short term or long term. Concussion has

been defined as a ‘‘trauma-induced alteration in mental status

that may or may not involve a loss of consciousness.’’

4,5

If

surveyed, the public would probably associate concussion with

boxing, football, and ice hockey and would not consider the

injury a real problem for other sports. This perception is most

likely related to the visibility of boxing, football, and ice hock-

ey at the professional level. The current thinking among sports

medicine clinicians is that concussion occurs in all sports but

with varying frequencies. In reality, concussions have always

been a part of competitive athletics.

The study of Gerberich et al

6

published in 1983 was one of

the first widely cited articles to deal with concussions in high

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school football and spanned the years 1978–1982. They found

that 20% of the reported injuries in high school football were

concussions and that 14% of the high school football players

included in their study reported a history of concussion asso-

ciated with a loss of consciousness. From this work, other

authors have projected a frequency of 200 000 concussions per

year in high school football. It is important to consider the era

for the data collection in this article. In the early 1970s, em-

phasis was on the use of the head and the face mask as the

initial points of contact for blocking and tackling. Risks as-

sociated with this technique were documented, and in 1976,

the National Federation of State High School Associations

Football Rules Committee banned the use of the face mask as

the initial point of contact. The players surveyed by Gerberich

et al

6

had participated before the ban. In addition, football

players in the 1970s wore a variety of helmets that are no

longer in use or manufactured. Therefore, these data may not

accurately reflect the magnitude of the problem for today’s

high school football player.

In the early 1980s, the discussion of concussion took a giant

leap forward with the work of Rimel et al

7

and Barth et al.

8

Their research efforts identified neuropsychological effects as-

sociated with the injury. During the decade that followed, a

great deal of discussion flourished among members of the neu-

roscience community regarding the description, classification,

and management of concussions and guidelines for the return

to competition after concussion.

4,5,9–12

As the medical com-

munity learned more about the natural history of concussion,

the importance of the injury, regardless of the sport, was rec-

ognized.

The discussion of concussions related to sports received

very little attention until the early 1990s. The media and fans

fostered a heightened awareness for sport concussion as they

learned of high-profile professional athletes who attributed

their retirements to repetitive concussions. Additionally, post-

concussion syndrome was identified in players who retired for

other reasons in the months and years after their injuries. As

a result, the current research concerned with the identification,

management, and long-term effects of concussion is adding

new and exciting information to the professional body of

knowledge required to reduce the risk of injury.

In 1994, the National Athletic Trainers’ Association

(NATA) Research and Education Foundation conducted the

Mild Brain Injury Summit.

13

The program brought together

professionals from neurosurgery, neuropsychology, neurology,

sports medicine, and athletic training. The objective was to

examine the current knowledge regarding the risk of concus-

sion in sports. Panel members discussed the definition of con-

cussion and the various types of programs designed to provide

medical care and management for concussion, examined the

status of existing research, and made recommendations for fu-

ture research.

13

During the past few years, a plethora of articles, papers, and

symposia have discussed the concussion. Much of the discus-

sion has focused on refinements of the grading and manage-

ment systems identified during the 1980s and early

1990s.

5,10,14

Many in the medical professions and media have

encouraged the use of the consensus practice option identified

by the American Academy of Neurology, but there is still no

consensus on which concussion grading system is the best.

4

Another issue that has received much discussion and been the

focus of numerous papers and several research projects is the

role of neuropsychological screening and follow-up as a tool

for managing concussion. Within the many articles are a num-

ber of common points as well as continuing points of disagree-

ment, especially regarding the grading and management of the

injury. It is important for us to be able to integrate the new

knowledge regarding concussion with the past knowledge to

move forward in the area of prevention.

One of the most challenging issues facing medical and para-

medical professionals is the identification of concussions. The

main problem with identification is the variety of signs and

symptoms that may or may not be present. For example, head-

ache, dizziness, nausea, or memory alterations may be symp-

toms of concussion, or they may be symptoms of other injury.

The injury may result in short-term or long-term unconscious-

ness or no loss of consciousness. The signs and symptoms

present at the time of injury may disappear very quickly, or

they may linger for long periods. In some rare cases, the initial

signs and symptoms may disappear and then reappear with

dramatic consequences. Some of the common symptoms result

from different types of injury; for example, dizziness may re-

sult from brain injury or from vestibular injury (W. Meeu-

wisse, oral communication, 2000).

Once a concussion has been identified in a player, it war-

rants professional evaluation by clinicians who are trained and

up to date on the management of concussion. Team physicians

and athletic trainers must realize that concussions occur in ev-

ery sport and that, although the injury may have occurred in

volleyball, its proper management is just as important as if the

concussion had occurred in football.

After the identification and management of concussion, the

question of return to participation becomes most important.

How long should the athlete wait to return to collision sports?

How long should he or she wait to return to noncollision

sports? What is the potential for the player to sustain a second

concussion? And, does this second injury create more signif-

icant damage than the first one? How can the player be sure

that the brain has truly ‘‘returned to normal’’? Current research

is focusing directly on the answers to these questions. Until

that research is complete, the clinician should treat the players

who sustain concussions on an individual basis. Decisions re-

garding return to play should be based on the signs and symp-

toms associated with the player’s injury and not simply

grouped into one of the many current classification and injury

management systems. Among the new tools being placed in

the hands of clinicians is the ability to compare baseline brain

function parameters with the same parameters after a concus-

sion. The research in this area is most promising and will be

an asset to the management of concussions.

15–18

The sponsors of sports programs have challenges of their

own to face. They must design and maintain injury prevention

programs that minimize the risk of injury, including concus-

sion. They must take into consideration the nature of the sport

and the activities of the players as they make decisions that

affect the injury risk pattern. Specific areas that require atten-

tion are facilities and equipment, player protective equipment,

and competition rules and regulations. Combining and using

information from medicine, program sponsors, athletic train-

ers, coaches, and players is essential to improving player safe-

ty.

RESEARCH ISSUES

As concussion became the sports injury ‘‘issue’’ of the

1990s, numerous researchers began projects regarding concus-

sions. It became apparent from the findings of the earlier pro-

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Journal of Athletic Training

309

jects that a variety of different methods of identifying a con-

cussion exist. Some clinicians described a concussion as a loss

of consciousness. Others identified a concussion only if mem-

ory problems were associated with the injury. Still other cli-

nicians considered a very minor impact to the head, often

called a ‘‘ding,’’ to be a concussion. The confusion over the

definition created problems for multicenter research programs.

To be comfortable with the consistency of data coming from

different locations, researchers’ projects began to identify mild

traumatic brain injury (MTBI) as a synonym for concussion.

19

MTBI represents an injury that meets specific criteria regard-

ing the presence of signs and symptoms, and when these min-

imum conditions exist, the injury is considered reportable for

the research project.

19

In general, the MTBI approach to injury

identification encompasses all of the qualities that have been

associated with concussion. The use of an operational defini-

tion of a reportable MTBI allows researchers and clinicians to

begin their analysis from a common reference point for injury.

EPIDEMIOLOGY OF CONCUSSION

Among a wide variety of sports, the potential for concussion

is related to the number of opportunities within the sport for

activities that produce collisions. For example, in football, the

number of collisions involving the head is very high. Some

players on the field experience a head impact on every play.

In other sports such as ice hockey, impacts with the head are

expected but not inherent in the design of the sport. Sports

such as tennis and swimming have little potential for collision,

although falls on the court or collisions with walls may occur.

The frequency of collisions associated with a specific sport is

a function of the opportunity for collision to occur within the

context of the sport. The number of collisions in a practice or

game is directly related to the potential for concussion.

To evaluate the potential for injury, we must have a general

understanding of the likelihood that injury will occur. In the

case of concussion, the likelihood of injury is a function of

the number of times a player’s head sustains an impact within

the context of participation. These impacts may be incidental

(unintentional) and occur as a result of the nature of the game,

or they may be impacts that result from intentional acts (eg,

fighting). There may be head impacts from objects associated

with the game, such as sticks, surfaces, boundary obstructions,

or game operations equipment. These impacts may be frequent

and considered a part of the game, as in football, or very

unusual, as in tennis. The important consideration is that the

concussion can occur in any activity, regardless of the nature

of the activity, and that when the injury occurs, it has the

potential for a lasting effect on the player. Since high school

football has the largest number of participants and is most

often associated with concussion, an estimate of the number

of head impacts would provide perspective on the risk of in-

jury.

CONCUSSION IN HIGH SCHOOL SPORTS

The NATA conducted a study of the frequency, type, and

severity of injury in high school football for the 1995 through

1997 seasons. The purpose of the study was to examine the

frequency patterns associated with participation in 10 high

school sports: football, boys’ and girls’ basketball, boys’ and

girls’ soccer, wrestling, field hockey, baseball, softball, and

girls’ volleyball.

19

The subjects in the NATA study were athletes on the varsity

sports rosters at the study schools. Athletic trainers certified

by the NATA Board of Certification recorded data from 236

high schools over the 3-year study period. Before the project

began, the operational definitions and reporting requirements

were included in a user’s manual and distributed to all data

recorders. The definition of

reportable injury

included injuries

necessitating removal of athletes from participation for the re-

mainder of the current practice or game or longer. Addition-

ally, all fractures, dental injuries, and MTBIs were reportable,

regardless of time lost. Because of the variations in the defi-

nition, classification, and management of concussion that exist

among the different classification systems, it was important

that the study employ a definition for concussion that could

be used by all study participants. Rather than ask the athletic

trainers to report a ‘‘concussion,’’ the study identified a defi-

nition for a reportable MTBI. An MTBI represented an event

identified by the athletic trainer as an incident that required

the cessation of a player’s participation for initial observation

and evaluation of the injury signs and symptoms before re-

turning to play, either in the current session or subsequent

sessions.

19

In the NATA study, data were collected for 23 566 report-

able injuries in 3 years, of which 1291 (5.5%) were MTBIs.

19

The injury rates per 100 player-seasons for each sport were

3.66 for football, 1.58 for wrestling, 1.14 for girls’ soccer, 0.92

for boys’ soccer, 1.04 for girls’ basketball, 0.75 for boys’ bas-

ketball, 0.46 for softball, 0.23 for baseball, 0.46 for field hock-

ey, and 0.14 for volleyball. Among the players with MTBI,

76.1% missed fewer than 8 days, with a median time lost for

all MTBIs of 3 days. Rates of MTBI were higher in a game

than in a practice for all sports except volleyball.

Based on this study, the rates of MTBI varied among sports,

and no sport was without the occurrence of an MTBI. The

prevention of MTBI, given its close association with a variety

of different types of collisions, may be most successful using

interventions aimed at controlling the participation environ-

ment. Decision makers in sports safety should focus their pre-

vention efforts on programs that minimize the potential for

head impacts from collisions, both intentional and uninten-

tional. The continued cooperation of sports sponsors, research-

ers, medical professionals, and sports participants is essential

to help minimize the risk of concussion.

CONCUSSION PREVENTION

The foundation for developing a sports injury prevention

program is that regardless of the preventive steps taken to avert

sports injuries, including concussion, some players will con-

tinue to be injured. It becomes the task of the injury prevention

team to work toward limiting the numbers of injuries by using

regulatory controls, educating participants, designing special-

ized protective products, and monitoring the injury frequency

patterns through ongoing surveillance programs.

20

First, the

program must emphasize prevention by focusing on decisions

relevant to the rules and regulations of the games. Continual

review of this area allows the governing agency to require that

the sport meet the current standards of injury prevention. Sec-

ond, the coaches must continue to review the up-to-date tech-

niques for teaching appropriate skills that facilitate player per-

formance and, at the same time, provide consistent protection

from injury. In addition, coaches need to be sensitive to both

general and sport-specific conditioning to properly prepare the

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Countermeasures: Concussion in Sports

21

Factors

Phase

Pre-event

Event

Postevent

Host (player)

Preparticipation evaluation of

concussion history

Properly designed and maintained

player head protection, when

appropriate

Recognition and management of

players evaluated for concussion

Agent (sport)

Rules and regulations relating to

minimizing the risk of injury

Maintenance of standards related to

the safety issues for the sport

(eg, rule enforcement)

Evaluation of injury incidents to es-

tablish procedures for preventing

future injury

Environment

(ambient

conditions)

Playing facilities free of inherent

hazards (eg, padded sideline

equipment for collision games)

Resources (personnel) immediately

available to evaluate and manage

the injured

Availability of emergency medical

services and medical support for

injury management

athletes for the rigors of competition. Continuing investigation

of the products that are used to protect players from the in-

herent hazards associated with the sport should occur. The con-

tinued monitoring of the injury patterns associated with sports

will go a long way in providing the safety decision makers

with up-to-date information regarding the status of injury pre-

vention programs.

The early recognition of concussion provides for the imple-

mentation of proper management for even the least severe in-

jury. This early identification and management minimizes the

risk of a negative outcome and maximizes the probability of

the player’s returning to competition without an increased risk

of reinjury. The process of monitoring concussion in players

should include player-reported symptoms, apparent signs of

incomplete recovery, and the development of protocols for as-

sessing brain function (ie, neuropsychological assessment).

A DECISION MODEL FOR PREVENTION

Injuries in sports occur in a specific moment when a wide

variety of internal (player-related) and external (sport-related)

risk factors converge. To begin the process of developing an

injury prevention or injury control program, including pro-

grams specifically aimed at concussion, the decision maker

must bring order to the variables that exist at the time of in-

jury. William Haddon Jr

21

developed a model for categorizing

some of the complexity and diversity of the variables that exist

at the time of an injury. His model addresses the conditions

that are present before the injury occurs (pre-event), at the

time that the injury occurs (event), and after the injury occurs

(postevent).

21

In Haddon’s model, the 3 time phases are coupled with the

variables associated with the host (player), agent (sport), and

environment (ambient conditions) to produce a matrix for

planning intervention strategies.

21

For example, a model for

developing intervention programs for preventing sports con-

cussion might resemble the model shown in the Table. The

items in this table represent a general approach to concussion.

Because of the varying nature of each sport, a specific ap-

proach that considers the qualities and conditions for the sport

must be developed.

RECOMMENDATIONS FOR CONCUSSION

MANAGEMENT

The management and prevention of concussion have be-

come paramount issues among sports medicine professionals.

Until we have a better understanding of exactly what consti-

tutes a concussion, especially regarding the amount of force

associated with specific levels of injury, it is difficult to focus

on the most important strategies for preventing the initial in-

jury. We must focus our attention on preventing reinjury by

enhancing our management of injured players. Clinicians as-

sociated with sports may have a variety of ideas regarding the

prevention and management of concussion; the management

recommendations identified by the NATA summit

13

seem to

capture the essence of most of the more common ideas:

1. The injured player should be managed as an individual

case.

2. Clinicians should familiarize themselves with current stan-

dards for the evaluation of concussion on the sideline as

well as in the office.

3. Consistent and routine follow-up procedures should be

implemented to monitor the individual’s progress.

4. Clinicians should provide accurate and consistent infor-

mation to the patient’s ‘‘supporters’’ regarding danger sig-

nals associated with concussion.

5. Accurate documentation of the injury event, findings on

evaluation, and decisions to return to participation should

be encouraged.

Another important area examined by the NATA summit

panel members

13

was the question of the current state of

knowledge regarding the research that must be done to better

understand the risks of concussion both in the short term and

in the long term. The following recommendations provide di-

rection for the research programs associated with concussion:

1. Research requires a multidisciplinary team of profession-

als. The team represents the neuroscience community, the

rehabilitation professions, and sports medicine team phy-

sicians and athletic trainers.

2. Important areas for consideration are the effects of mul-

tiple injuries and the relative risks associated with contin-

ued participation.

3. Emphasis should be placed on developing procedures for

acquiring neuropsychological baselines to evaluate the ef-

fect of concussion over time.

4. Research efforts that focus on pharmacologic intervention

for prevention and management are encouraged.

5. Specific programs must address the recovery time for con-

cussion and its relationship to reinjury and the long-term

effects.

SUMMARY

The problem of concussion in sports is one that has moved

to the forefront in the past few years. The retirement of high-

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Journal of Athletic Training

311

profile professional athletes as a result of repetitive concussion

and postconcussion syndrome has heightened the awareness of

the sports community to the importance of these injuries. The

potential for serious effects of brain injury on the individual

player’s physical and mental status is generally accepted. The

ability to provide objective information regarding the exact

nature of the effects of concussion, both in the short term and

over time, has been lacking. The unpredictability of concus-

sion and the inability to identify cases in the general popula-

tion have made large-scale research projects impossible. Thus,

the focus of research and education regarding brain injury has

been centered on the more serious cases. Recently, the research

community has begun to implement programs for the in-depth

study of concussion in the sports arena. Under these condi-

tions, head injury risks can be identified and patients with

concussion can be followed to assess long-term effects. To-

day’s computer technology has made the uniform documen-

tation of injuries among multiple institutions a reality. The

ability to coordinate information from multiple sites, multiple

professions, and a wide variety of athletes will provide the

foundation for developing intervention programs for prevent-

ing and managing cases of concussion, both for the athlete and

the nonathlete. The potential is bright for the future success

of programs that will minimize the risk of concussion and

techniques to manage the concussions that continue to occur.

The intensity of the light cast depends directly on the contin-

ued cooperation of the sponsors of sports programs, the sports

medicine community, the coaching community, and the con-

sumers of the sport, the players.

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