Head Injuries in Soccer

What's so great about soccer, or as it is known in most parts of the world, football? It's only the greatest sport on earth, played by more people than any other team sport. Millions world-wide have enjoyed soccer for over a thousand years.¹

When most people think of soccer, they correctly think of people trying to advance a ball into a small net using their legs, feet, and head but not their hands and arms, while an opposing team tries to prevent them getting the ball into the net. It's so simple you need nothing more than a ball to get a backyard game going. The players are in constant motion, making it a highly exciting sport to watch, to say nothing of the fitness benefits for players of all ages. It is an activity for everyone.

One of the most exciting and unique features of soccer is the act of "heading" the ball – advancing the ball by striking it with the head. No other sport endorses this act, and there are few events in all of sports more thrilling than seeing a well-passed ball being headed past the goalie into the net for a goal.

But while we're enjoying all of the positive aspects of soccer, we must not forget that, as in any sport, there are some risks. Because of the extremely physical nature of the game, injuries are not infrequent, and some of them can be quite serious. A torn anterior cruciate ligament (ACL) can require surgery and several weeks or months of rehabilitation before the player can return to his game. Ankle injuries occur with some frequency, and there are even broken bones once in a while.

A type of injury that is often overlooked and is probably less frequent, but potentially much more serious than leg injuries, is a concussion. A concussion is a jarring of the brain, usually as a result of a blow to the head. It can result in anything from a fleeting headache to coma; the brain may recover completely within a day or two, or it may never completely recover. Unlike most knee and ankle injuries, concussions may cause mental deficits that will stay with a person his entire life. The purpose of soccerheadinjury.org is to provide information to you, the players and others associated with soccer, about soccer concussions, their causes, their dangers, and their prevention.

While much has been learned about concussions in the past several years, there is still much that is not understood about exactly how concussions occur and what the resulting impact on the brain may be.

According to the First International Conference in Concussion in Sport, a concussion is a complex pathophysiological process affecting the brain, induced by traumatic biomechanical forces², or in less technical terms, a disruption of brain activity. The disruption is believed to be functional rather than structural,³ meaning a concussion usually does not result in any permanent physical damage to the brain; it only has to do with the way the brain operates for some period until it recovers.

Here are a few of the issues that have been clarified about soccer concussions recently:

Concussions do occur with significant frequency in soccer.
It is becoming clear that concussions occur in soccer, as well as in many other sports, much more frequently than was suspected only a few years ago. This may or may not represent a real increase in the number of soccer concussions, but rather a growing awareness of the incidence of concussions. Concussions are difficult to diagnose because of the subtlety and non-specificity of the symptoms. A player with a concussion may not present any physical symptoms, even though his brain may not be working at 100% efficiency. In addition, even if a player is aware that he has some symptoms, he may deliberately mask his deficiencies in an effort to remain in the game. His coach or trainer, in the excitement of the match, may not notice that the player seems a bit confused or "foggy." This is very dangerous, because it is at this time – when the brain has been jolted but has not yet fully recovered – that the player is at the highest risk of more serious injury.

A recent study of university soccer teams at McGill University⁴ found that more than 60% of the players reported concussion symptoms in a single year. Others dispute this high injury frequency, but in general people seem to agree that concussions are not an uncommon injury in soccer. In comparing the concussion rate in soccer to that in American football, Baroff⁵ concluded that the rates – while not identical – are comparable, even though American football is generally thought to carry a much higher head injury risk than soccer.

The National Institutes of Health (NIH) has long recognized that only a small percentage of the concussions that occur in sports are actually recognized. In 1999 NIH published a report⁶ estimating that the number of sports-related concussions is under-reported by 90%, meaning that of ten concussions that really occur, nine are believed to be unrecognized or unreported.

Concussions are seldom caused by heading the ball.
When most people think of head injuries in soccer, they immediately connect those injuries with the act of heading the ball, because heading is the most common head impact situation in soccer. However, several studies have shown⁷ that the force of a soccer ball striking a person's head is almost never sufficient to create a high risk of concussion, particularly if the player is prepared for the impact and has stiffened his neck in anticipation of the blow. One of the few situations in which a ball impact is likely to cause a concussion is when the player is not aware of the impending impact, and does not have a chance to prepare his neck for the collision.

Several studies have confirmed that soccer headgear that is currently (early 2006) available commercially does not significantly reduce the forces reaching the head in a ball-to-head impact⁸, but this may not be a crucial question since few concussions are caused by heading or ball impacts anyway.

Most soccer concussions are caused by impacts between a player's head and some hard object.
If concussions are relatively common in soccer, but almost none of them are caused by heading the ball, how do they occur? Most are caused by impacts between the player's head and some hard object. Collisions between players are common in soccer, and in many of these collisions the head of at least one player is impacted. Head-to-head impacts are believed to be the most frequent cause of concussions⁹; in many of these cases two players compete for the same ball in the air, and strike each other instead of or in addition to the ball. So although an attempt to head the ball may be the ultimate culprit in many concussions, it is not the actual act of heading the ball that causes the injury. In addition to head-to-head impacts, concussions may also be caused by elbow-to-head, knee-to-head, head-to-ground, head-to-goal post, and other head-to-hard object events.

Even some recognized concussions are not reported.
Most people who join soccer teams do so because they really want to play, not to sit on the sidelines and watch others. A player may realize that he is a bit woozy after a head impact, but may, for a variety of reasons, not tell anyone. In fact, despite his symptoms he may not recognize their significance. In the McGill University study¹⁰ only one-fifth of the concussed soccer players were aware of their injury. A survey of high school football players¹¹ concluded that less than half of the players who were concussed bothered to report the injury to their trainer, coach or parent. The most common reasons given for not reporting the injuries were (1) the player did not think his injury was serious enough to warrant medical attention, (2) the player did not want to be withheld from competition, and (3) the player was not aware that his symptoms were due to a concussion. Concussion diagnosis is difficult even when players are forthcoming about their symptoms; without their full cooperation it will be nearly impossible to understand the entire concussion problem in soccer.

What happens after the concussion occurs?
Sometimes when a person has a broken bone, he works so hard at rehabilitation that the bone may be stronger after he recovers than it was prior to the injury. Unfortunately this is not the case with the brain. Each concussion seems to reduce the person's resistance to additional concussions, even if he recovers his full pre-concussion cognitive abilities. In a landmark study¹² it was shown that after a player has suffered one concussion, he is about four times as likely to have a second one, compared to a player who has never been concussed. After a second concussion, the player is also more likely to have a third, and the cycle seems to continue with greater numbers of concussions.

And that's not all. If a player receives an impact that causes a concussion of some particular severity, a following impact of similar magnitude is likely to result in a more severe second concussion¹³, with a longer period required for recovery.

To make matters worse, if a player who has been concussed returns to physical activity before his brain has fully recovered, he is at increased risk for Second Impact Syndrome¹⁴, in which a seemingly minor head impact may cause severe brain swelling and potentially dire outcome.

These facts make it clear that having a concussion greatly increases a person's risk of more and more serious subsequent head injuries. The best way to avoid these increased risks is to prevent the first concussion from happening.

Some of the symptoms of concussion include¹⁵:

Depression Dizziness Drowsiness Excess sleep Fatigue Feel "in a fog" Feel "slowed down" Headache Irritability Memory problems Nausea

Nervousness Numbness/tingling Poor balance Poor concentration Ringing in ears Sadness Sensitive to light Sensitive to noise Trouble falling asleep Vomiting

If you have one of these symptoms, does that automatically mean you have a concussion? Absolutely not. Some of these symptoms, such as headache and nausea, can be very common, even if there has been no blow to the head. Individually, the symptoms can be caused by any number of physical or mental events in a person's life. But if you have recently been struck in the head, and now feel one of these symptoms (especially if you have several of them), it would be best for you to be evaluated by competent medical personnel.

It is important to note here, which may surprise some people, that loss of consciousness, which is not even listed among the concussion symptoms, is not required for a concussion to occur; in fact, loss of consciousness is quite rare in common concussion situations, and may not be a good indicator of the severity of a concussion. On the contrary, it is now believed that the presence of amnesia, either retrograde or anterograde, is a better predictor of concussion severity¹⁶ than the presence or absence of loss of consciousness.

Following a concussion, many people will feel better after a short time, and will conclude that they are completely recovered and can resume their normal activities. This is not usually the case. Even if you feel completely normal within minutes, hours or days after your concussion, there is a reasonable chance that your brain is still operating at less than normal functionality because it has not fully recovered. Neuropsychological testing, often computerized, can determine with excellent sensitivity whether your brain is back to normal (more on this below). Many people do completely recover from many mild concussions within a week or so after a concussion, but this is usually a few days later than they believe they have recovered – deficits that are observable with neuropsychological testing may remain measurable for several days after you think you feel fine.

Problems within the brain that are caused by a concussion are usually invisible by most brain-scanning methods, since they do not involve structural brain alterations, so no confidence should be placed in the fact that these tests give normal results. Once your visible and "feeling" symptoms are gone, you should not go back to physical activity until a physician with understanding of neurological deficits has given you clearance to return to action.

If you do still feel lingering symptoms of your concussion (post-concussion syndrome), you can assume that neuropsychological testing will confirm that you have not fully recovered, and you should not return to play. If you have physical symptoms, that means you have not recovered; if you don't have physical symptoms, you still may not have recovered. The importance of full medical clearance by a knowledgeable physician cannot be over-emphasized.

How do you evaluate the severity and track recovery from a concussion?

As we described earlier, diagnosis of a concussion is very difficult because the symptoms are often fleeting and not recognized. But once a diagnosis of concussion has been made, there are things that can be done to assess the severity of the concussion, as well as to determine how well and how quickly you are recovering.

1. Neuropsychological (NP) testing was mentioned above as being useful in determining when the concussed person might be able to return to action. The ideal method for using NP testing is to have each athlete take a series of tests before the season begins, to establish a "baseline" for his performance. The tests include measures of learning, memory, motor and processing functions, and each person has a unique overall "normal" score for the full complement of tests. The baseline tests have to be taken when the person has all of his regular capacities; otherwise the results may be skewed and unreliable. Then, after a person is concussed, he is asked to complete a similar series of tests after his physical symptoms have disappeared. The difference between the baseline scores and the post-injury scores provides a measure of the extent of the cognitive deficits resulting from the concussion.

   The NP tests can then be repeated periodically to ensure that recovery is progressing. Assuming recovery is eventually completed, the person's test scores should be very similar to his baseline scores, indicating that all mental deficits have been overcome. There are at least three commercially available computerized NP testing batteries.

2. In addition to NP testing, there is a Standardized Assessment of Concussion (SAC) protocol that is better suited to sideline evaluation of a player's condition, but is not as sensitive or as thorough as NP testing. It is intended to be a quick evaluation that can be conducted by non-medical personnel, and should be followed up with additional diagnostics, such as NP testing. With SAC, a trainer or coach can give the player a series of simple tests on the sideline immediately after his injury has occurred. The neurocognitive assessment includes measures of orientation, immediate memory, concentration, and delayed recall, along with unquantified neurological screening of amnesia, strength, sensation and coordination. The four quantified tests are graded in accordance with a numerical scale, so an overall total score indicates the severity of any deficits that are present. In this way, one can get a good quick idea of the condition of his player, although without the quantitative knowledge that is available with NP testing.

3. Yet another tool that can be useful in evaluating a concussion is the Balance Error Scoring System, or BESS. It has been shown¹⁷ that when a person is concussed his ability to balance is compromised. By having the injured person stand in various ways on a piece of foam and counting the "errors" he makes related to his balance, a coach or trainer can quickly estimate the severity of any deficits caused by the injury. Again, this tool is not as quantitative as NP testing, but is quite easy to conduct on the sideline during a game, and allows a reasonable evaluation while awaiting later NP testing.

When can one return to play after a concussion?
Over the years there have been several guidelines that were supposed to allow a coach or trainer to determine when it was safe for a concussed player to return to play. Most of these were created prior to development of NP testing, but they are still used by many people. Generally these return-to-play guidelines categorize concussions into about three levels based on physical symptoms. For example, with a mild concussion from which the player appears to recover within 15 minutes, some of the guidelines allow him to return to action during the same game, while others recommend that he forego physical activity for a week or so. These guidelines¹⁸ were based strictly on personal observations of concussed players, and were not governed by any particular medical knowledge. Return-to-play guidelines have been very useful for many years, but now there is an indication that they may be in the process of being replaced in favor of a step-wise set of conditions, all of which the athlete must successfully complete before he can return to action¹⁹. These steps include a period of complete rest, light aerobic exercise, and other steps prior to game play.

Things we suspect, but haven't yet proven

1. In some ways, repeated heading of a soccer ball can be compared to boxing several rounds with a decent slugger. The typical impact forces are similar, but the impact locations are not usually the same and a boxing glove doesn't respond the same way as a soccer ball. However, the similarities are sufficient to suggest that some of the later-life problems that affect boxers might also affect soccer players who do a lot of heading or suffer multiple head impacts. Some studies report that depression, general dementias, Alzheimer's Disease, and Parkinson's Disease may be linked to repeated head impacts that occurred many years previously, although other studies have not identified this link.²⁰ At present we don't have a good understanding of how head impacts lead to these problems – how many impacts are required, how severe must they be, over what time period must they occur, etc – so we don't know how to prevent them, assuming the observed links are real.

2. A large study in Italy²¹ indicated that older soccer players were more likely to suffer from amyotrophic lateral sclerosis (ALS, or Lou Gehrig's disease). Not only was the rate of the disease higher among retired professional soccer players, it also occurred earlier in life than among non-soccer players. Until we have more complete knowledge of this connection, we don't know what we can do to reduce this apparent increased risk of ALS.

3. Taking somewhat different approaches to the concussion issue, some researchers have discovered possible links between acute head injuries and blood serum protein S100b²² in soccer players who regularly head the ball. There are indications that S100b concentration rises immediately after a head impact, and drops back to normal quickly if there is no brain damage, but a continuing elevated level may indicate a brain injury.²³ If this connection really occurs, it may be possible to diagnose the occurrence and estimate the severity of a head injury by analyzing a sample of the player's blood shortly after an impact.

4. One of the alleles of apolipoprotein (APOEe4) in the blood seems to be linked to head injury severity. Of the four alleles that may occur naturally in the blood, only the e4 allele seems to be associated with head injury severity. Some studies have found that the presence of the e4 allele delays recovery from head injury in older people,²⁴ while others²⁵ have concluded that possession of APOEe4 reduces the prospect of a favorable outcome in children and young adults. If this link can be clarified, verified and quantified, it may be possible for us to predict whether those with particular APOEe4 alleles are at higher risk for concussions.

5. Upon head injury, there is often an associated increase in intracranial pressure which, if not detected and treated early, may cause brain herniation or more serious problems. A study at Ohio State University²⁶ discovered that there is a strong link between intracranial pressure and intraocular pressure. Intracranial pressure is difficult to measure noninvasively, but intraocular pressure can be determined quickly with a hand-held tonometer. It may be possible to estimate brain injury severity by using a tonometer on the sidelines.

6. A study of concussed high school and college soccer players by Field and his colleagues at the University of Pittsburgh²⁷ found that, after undergoing similar concussions, younger players seemed to require more time to recover from the concussion than the older players. This concept was recently confirmed in a comparison of high school and professional football players.²⁸ The conclusion to be drawn from these results is that younger athletes may be more susceptible to concussion damage and may be more in need of head protection than older athletes.

7. A finding that has been reported in several studies, but is still somewhat surprising to many people, is that women are nearly 2½ times as likely to sustain a concussion as men²⁹. The exact reasons for this are not completely understood, but may be related in some way to the geometrical structure of the lower extremities, differences in muscular conditioning, or some more subtle gender differences.

Mechanism of injury
We understand that a concussion is caused by a jarring of the brain, but how much of a bump is required to cause a concussion as opposed to just a sore spot on your scalp? What does this particular level of impact cause within the brain that disrupts brain functioning? Can several small impacts generate the same results as one big one? Does the shape of the object you impact have anything to do with concussion risk or severity? Does it matter whether your head, or the impacted object, or both are in motion at the time of impact? What clinical differences occur if the blow is pointed directly at the middle of the head, compared to a tangential or twisting blow?

Delving further into the brain, it is believed that most of the concussive damage is related to variations in the motion of the brain tissue from point to point within the brain. What is the real mechanism of injury? Is it stretching of the neurons? Bending? Twisting? Compressing? Dr. Bayly and colleagues³⁰ at Washington University have developed a way to insert a virtual mesh into a person's brain, and measure the deformation of the mesh under different impact conditions. This promises to lead to vital information relating types of impacts to types of injuries.

Level of risk and severity
Following up on the Bayly study, and extrapolating the results to possible but uncertain lengths, will we ever know enough about the brain and its reaction to predict that a particular impact to a specific location on a particular individual's head will lead to a concussion that will be of a certain severity and will require the person to be out of action for some defined time? Probably not. Much more research will be required just to determine whether there is a generic concussion threshold that applies to all people, or does each person have a unique threshold that is unrelated to anyone else's threshold? What happens to the brain upon impact may be influenced by skull thickness, skull hardness, curvature of the skull at the point of impact, thickness of the scalp, thickness of the cerebro-spinal fluid layer between the skull and the brain, shape/size/density of the struck object, relative motion of the head and the struck object, and countless other factors. The probability that any two people will react identically, or even similarly, is so remote that the idea of a general concussion threshold may not make any sense.

With that said, however, work that has been done to date seems to point to a linear acceleration intensity of about 80-100 g (gravitational units) that is near the midpoint of the impact severities that have led to observed concussions. Early work by Newman³¹ has been verified in the Pellman³² series of reports from a comprehensive study of concussed and impacted but not concussed players in the National Football League. Both found that some concussions occur at lower impact levels, and that some higher impact levels do not result in concussions, but the center of the estimated dividing band between concussion and non-concussion seems to be somewhere near 80-100 g.

But that is only a measure of the linear acceleration of impact. What is the role of rotational acceleration? Nearly every head impact has some component of rotational acceleration, simply because the head is connected to the body by the neck. No matter what direction the head tries to move, it will soon be forced by the neck to turn, generating twisting motions inside the head. How do these rotational movements relate to linear movements? Can an almost purely linear impact cause a concussion just as easily as an impact that turns the head with little lateral motion? Will it be possible to determine a threshold of injury that takes into consideration both linear and rotational acceleration? Newman³³ has suggested possible combinational factors, even including impact duration, that may prove to be useful, but there is insufficient evidence to reach any conclusions about these measures.

We all know that tapping our head with a pencil has very low risk of hurting us. We also know that pounding our head with a large sledge hammer has a much higher risk of hurting us. The total energy input from the hammer blow may be thousands of times as great as the energy of the pencil tap, so it is likely that energy input is related to injury thresholds and severities. But how? If I tap my head a thousand times with a pencil, is the injury risk the same as for a single gentler sledge hammer blow? What if I tap my head once with a thousand pencils all at the same time? If I head a soccer ball ten times in one game, am I taking the same risk as if I headed the ball once in each of ten games? Is there a total energy input level that constitutes a line in the sand between concussion and no concussion? Does it matter whether that energy reaches my head all at once or spread over some time period? Do a number of minor impacts sum to one large impact?

These are just a few of the multitude of questions that need to be answered before we can say we really understand concussions, their causations, and their recovery. We may never know all of the answers, but research that is taking place now or is planned for the future will help us to determine more about what we need to know to predictably reduce the number of concussions in soccer.

The Dangers of Concussion

"Experimental studies have identified metabolic dysfunction as the key postconcussion physiologic event that produces and maintains this state of vulnerability. This period of enhanced vulnerability is characterized by both an increase in the demand for glucose (fuel) and an inexplicable reduction in cerebral blood flow (fuel delivery).58 The result is an inability of the neurovascular system to respond to increasing demands for energy to reestablish its normal chemical and ionic environments. This is dangerous because these altered environments can kill brain cells."
-- The American Orthopaedic Society for Sports Medicine