SOCCER INJURIES 0278-5919/98 $8.00 + .00

YOUTH SOCCER:AN EPIDEMIOLOGIC PERSPECTIVE

Jordan D. Metzl, MD, and Lyle J. Micheli, MD

The purpose of this article is fourfold: (1) to review the trends insoccer participation by children and adolescents in the United States; (2)to explore the patterns of injuries seen in youth soccer; (3) to analyzewhat epidemiologic studies have been done, to date, specific to soccerinjuries in this age group; and (4) to make recommendations for futurestudy, which will monitor trends in injury occurrence and assist indetecting risk factors for injury in this age group.

Soccer (football) is the most popular participant sport in the worldand has been since soon after the codification of its rules in Great Britainin 1863. In the United States, the first intercollegiate football game,played between Princeton and Rutgers in 1869, was actually played byassociation or "soccer" rules.

Although the rest of the world continued to follow the associationcode of play, football in this country evolved into American gridironfootball and traced its style of play, with tackling and passing, moredirectly to rugby football than to soccer.

Organized sports for children and younger adolescents had its be-ginnings in the United States shortly after the close of World War II. Thefirst organized children's sport in this country was baseball. Organizedcompetitions and leagues in children's gridiron football and basketball,the other two "traditional" sports in the United States, followed shortlythereafter.

Soccer at this juncture had a small participant base in some of themore traditional eastern prep schools and among certain recently arrivedimmigrant groups, notably the Italians and Portuguese. Organized soc-

From the Division of Sports Medicine, Children's Hospital, Boston, Massachusetts

CLINICS IN SPORTS MEDICINE

663VOLUME 17. NUMBER 4 .OCTOBER 1998

664 METZL & MICHELI

cer for children in the United States began in the year 1914 in NewEngland. This initial league, called the LASA league (Lusitano AmericanSoccer Association), was composed mainly of Portuguese immigrants inMassachusetts and Rhode Island. The first national level youth cham-pionship, the under 19-year-old boys division, was played in 1935. Fromthese beginnings, soccer grew rather slowly, primarily on the easternand western seaboards.

Since the 1970s, organized soccer for children and early adolescentshas grown rapidly and has been paralleled by a concomitant growth inhigh school and collegiate competition across the entire country. One ofthe unique features of youth soccer in the United States is the highparticipation in the sport by girls and young women, which stands inparticular contrast to soccer play in Latin America and Asia whereparticipation by girls is rare. The usual explanation for this is that thesport is deemed "too dangerous for girls."

The World Cup of Soccer, directed by Federation Internationale deFootball Association (FIFA), the international governing body of soccer,was held in the United States in 1994. This provided a center stage forthe American public for the sport and provided further impetus towardthe growth of soccer participation at all levels, and in particular, at theyouth level.

The growth of soccer participation by children and adolescents inthis country has been due to at least four factors: (1) the relative simplic-ity of the rules; (2) the relative lack of expense of the equipment anduniforms (particularly when compared to gridiron football, baseball, orhockey); (3) the relative ease of accessibility to play for both boys andgirls; and (4) finally the widely held belief that soccer is a "safer" gamefor children and adolescents, particularly when compared with otherorganized "contact sports" including football, ice hockey, and basketball.

EPIDEMIOLOGY

Participation

Soccer is played by at least 40 million people worldwide.9 A gamethat is accessible and relatively safe, soccer is the fastest growing teamsport in the United States. When driving through American cities ofevery size, it is now common to find soccer fields filled with soccer-playing youths. Once confined to the East and West Coasts, the "soccercraze" now extends all across the American continent, from Boston toLos Angeles with all cities in between. Yet despite such widespreadpopularity, remarkably little comprehensive study has been performedregarding specific injury rates within the United States. The two majoryouth soccer organizations in the United States are the US Youth SoccerAssociation (USYSA) and the American Youth Soccer Association(AYSO) with 2,645,062 and 473,666 players under the age of 18 yearsregistered, respectively, in these leagues during 1994.22 The Soccer Indus-

665YOUTH SOCCER: AN EI;'IDEMIOLOGIC PERSPEcnvE

Table 1. THE NATIONAL FEDERATION OF STATE HIGH SCHOOL ASSOCIATIONSSTATISTICS ON HIGH SCHOOL SOCCER

6159702574458182

208,935236,082255,538283,728

3697466554636526

103,173135,302166,173209,287

try Council of America estimates that more than 6 million childrenunder the age of 12 years played on some form of soccer team in 1990.22Clearly, this trend is reflected in the increasing number of soccer-playingpatients who present to emergency rooms, primary care offices, andsports medicine clinics across the country.

At the high school level, interscholastic competition between formalhigh school programs also continues to rise. Because most studies re-garding injury data indicate that serious injury is quite rare in soccerplayers younger than 12 years of age, the increasing number of highschool programs correlates with a suspected increase in the number ofsignificant injuries caused by playing soccer?1 Comparing the data be-tween the years 1987 and 1995, significant increases in the number ofhigh school soccer programs are visible. In 1987, 6,159 schools sponsoredhigh school programs for boys and 3,697 schools sponsored programsfor girls. These numbers translate to 208,935 boys and 103,173 girlsplaying soccer in the year 1987 to 1988. In comparison, during the year1995 to 1996, there were 8,182 boys high school programs and 6,526 girlsprograms. By census, the number of boys grew to 283,728, whereas thenumber of girls more than doubled to 209,287 (Table 1). ,

Table 2 explores the trends between soccer participation and otherpopular high school sports including basketball, baseball, football, andwrestling over the 9-year period between 1987 and 1996. Although thefirst three sports all demonstrate increases in the number of participants,none matches soccer in the percentage increase of 60% during this 9-year period. Extrapolating these data, soccer participation at the highschool level, a reflection of the game's general popularity, should con-

Table 2. THE NATIONAL FEDERATION OF STATE HIGH SCHOOL ASSOCIATIONSNUMBERS OF HIGH SCHOOL PARTICIPANTS BY SPORTS

666 METZL & MICHEU

.Basketball

.Baseball

C Football

.Wrestling

.Soccer

1987 1992 1994 1996

Year

Figure 1. Comparison of trends in high school sport participation between the years 1987and 1996.

tinue to increase in the future. Figure 1 demonstrates this trend clearly.Note the increasing popularity of soccer compared with other sports.

Injury Data

Within the United States, the numbers of injuries resulting fromsoccer has clearly risen during the past 10 years. Though most likelyattributable to the sheer increase in numbers of participants, analysis ofthe available studies regarding soccer injury provides important infor-mation.

To date, most studies regarding youth soccer injury have beenperformed outside the United States. Complicating this issue further, thedefinition of injury is not universal. Certain authors have defined injuryas every recorded injury during a specific time period, whereas othershave used a more functional definition that evaluates time away fromplay. Reviewing the findings of these major studies is helpful in ad-dressing specific questions regarding incidence of injury in youth soccer.

Nilsson and Roaas17 followed 25,000 elite level, adolescent soccerplayers, ages 11 to 18 years, at the Norway cup soccer tournament.Performed in 1975 and 1977, this prospective study was helpful indefining the specific types of injury suffered by adolescent athletes.17The findings of this study indicate that the most common injuries insoccer occur in the lower extremity, are minor in nature, and ofteninvolve minimal loss from playing time. Furthermore, the study sug-gested that the older aged adolescents were more prone to injury thanthe younger aged participants. The authors chose to define injury asany traumatic event that was reported to medical personnel duringcompetition (excluding practice time), a definition that included suchminor injuries as abrasions, blisters, and contusions. Using these criteria,the authors reported 522 injuries. By defining injury in this manner, theauthors reported an injury exposure rate (number of injuries/1000 hours)

WOO-"0c: c:co coCoW

--:.u.-0tJ::co-D..,§.

YOUTH SOCCER: AN EPillEMIOLOGIC PERSPECTIVE 667

of 14.0 for boys and 32.0 for girls. This statistic is much higher thanexposure rates reported from any other study, a difference that seemsindicative of the definition of the term injury and subsequent datacollection methods. The Norwegian Cup study was repeated in 1984,using the same parameters for injury definition. In this case, the authorsfound an 8.9 and 17.6 injury exposure rate for boys and girls, respec-tively.lS

In America, Sullivan and associates24 studied the injury rate foradolescent soccer players over the course of a season in Oklahoma.Using questionnaires to gather data, the study sought to define injuryrate for American soccer-playing youths, aged 7 to 18 years. In thisprospective study, injury was defined as any medical condition thatprevented participation. Using these criteria, the authors found a totalof 34 injuries from a sample of 1272. This translated to an injury exposurerate of 0.5 for boys and 1.1 for girls per 1000 hours played. Unlike theNorwegian Cup studies, no on-site data collection was performed.

More recently, Schmidt-Olsen and co-workers21 performed a compa-rable study in Denmark. Using 496 male soccer players, aged 12 to18 years, a 1-year prospective study was performed using a similarquestionnaire format to the Oklahoma study. Injury definition was basedon the terms formally adopted in 1986 by the European council inPapendal, Holland. This defines injury as "acquired during a game orpractice, causing one or more of the following: reduction of activity, theneed for treatment or medical advice, and/or negative social and eco-nomic consequences."21 The Danish study found a 3.7 injury exposurerate per 1000 hours played. Like other studies, the study indicated thatthe rate of injury was higher for older aged adolescents.

Comparing these data with adult soccer injuries is helpful. Ekstrandand Gillquist6 studied 180 Swedish, male, amateur players with anaverage age of 25. This prospective study sought to define injury rate inthe adult soccer player. Like the Danish study, the Swedish study definedinjury in functional terms. The results of this study found an injury rateof 7.6 per 1000 hours of practice time and 16.9 per 1000 hours ofgame time.

Table 3 summarizes the data from the studies mentioned previously.There are significant differences between these studies including defini-~

Table 3. MAJOR STUDIES REGARDING INJURY RATES IN SOCCER

668 METZL & MICHEli

tion of injury, method of reporting injury, and skill level of playersinvolved. Though different in method, the similarities between thesestudies suggest the following trends: (1) the risk of injury from soccer issmall.. compared with other sports, (2) the risk seems higher for girlsthan boys, and (3) the risk of injury is higher in older-aged adolescentsand adults than for children.

Comparative Studies of Injury Between Sports

Largely because studies comparing injury rate between differentsports are difficult to perform, few studies exist that evaluate injury ratebetweeff. sports. In children under 12 years of age, soccer and gridironfootball seem to have similar rates of injury.B Goldberg and associatesBcompared the injury rate in different divisions of Pop Warner footballleagues in New England and found that the injury rate increased inolder age divisions. The overall incidence of major injury in the under10-year-old division was only 5% compared with 38% in the under 14-year,.old division. Overall, the incidence of injury in the younger ageswas comparable with soccer. Once the football players entered the under14-year-old division, however, the rate of major injury rose substantially.B

At the high school, college, and professional level, the rate of majorinjury in gridiron football greatly exceeds that of soccer}' 5, 7, B, 13 Althoughmajor injury accounts for only 5% of all injuries in Pop Warner Football,the percentage of injury is 16% at the high school level, 27% at thecollege level, and 46% at the professional level.B Garrick and Requa7compared injury rates of different sports in adolescent athletes. In thisstudy, football players had an 85% risk of injury during the season,whereas soccer players had a 30% risk of injury.7 As is the case with thesoccer studies, terminology regarding injury definition varies widelybetween studies and makes such comparison difficult.

Clearly, more comparison-type studies are needed to help betterevaluate injury rate between sports. Unfortunately, because of an embar-rassing lack of injury data for soccer in this country, we do not havebaseline injury rates for soccer and therefore cannot effectively analyzerisk factors or the efficacy of interventions needed to reduce injury.

INJURY PATTERNS

Minor Injuries

As previously stated, most soccer injuries are minor in nature.Studies focusing on the location and type of injury indicate that bothdegree and location of minor injury are determined by age and skilllevel; Most st\;1dies indicate that injuries occur most frequently at thehi~er levels of competition and during games more frequently than

YOUTH SOCCER: AN EPIDEMIOLOGIC PERSPEcnvE 669

.Lower

.Upper

DGroin

DOther

Figure 2. Most common sites of injury in adult soccer athletes.

during practice}1, 16 In the adult soccer athlete, injury distribution hasbeen documented by various studies. Though exact statistics vary be-tween study, roughly 60% to 70% of injuries are classified as "minor"and cause little or no loss of activity.6 The lower extremity is the mostcommon site of minor injury, accounting for greater than 85% of theseinjuries. The injury distribution of minor injuries in adults is dia-grammed above in Figure 2.

In comparison, minor injuries account for greater than 85% of injur-ies in youth soccer, suggesting that soccer is a relatively safer game foryouths than for adults. Interestingly, the sites of injury for the youthsoccer athlete are a bit different than for older players. These findingsare illustrated below in Figure 3. Note the increased incidence of injuryin the upper extremity (15%), the head and face region (10%), and thelessened frequency of trunk and groin injuries than in the adult studies.1s

Major Injuries

Knee Injuries

Though they represent a very small percentage of all injuries, majorinjuries occur in soccer. As has been previously discussed, the teiminol-ogy regarding injury definition is varied. For the purposes of this discus-sion, major injuries are defined as those injuries that require ongoingmedical care and sideline players for periods of time greater than

.Head/face

.Trunk

C Upper extremity

.Lower extremity

Figure 3. Most common sites of injury in youth soccer athletes.

extremity

extremity

670 METZL & MICHELI

1 month. Most studies indicate that the rate of major injury is between8% and 10% of all injuries.9, 11 As is the case with minor injuries, majorinjuries most commonly occur in the lower extremity. Included in thiscategory are fractures, subluxation episodes, and ligament injuries. Ofall causes of major injury that occur during soccer, ligament injury ofthe knee, including sprain and rupture, represents the most commoncause of major injury. Combined, knee ligament injuries constitute nearly50% of all major injuries obtained from playing soccer.6

Though less common in the preadolescent and adolescent athleticpopulation, the specific incidence of knee ligament injuries has not beendirectly evaluated in the young athlete. Of all knee ligament injuries,damage to the Anterior Cruciate Ligament (ACL) is the most commoncause of major injury. On the college level, data regarding ACL injuryand possible gender differences regarding injury rate has been carefullyreviewed by Arendt and Dick.l The findings of this study, a 5-yearretrospective analysis of the incidence of ACL in collegiate sports, con-firms several theories that had been previously suspected but not conclu-sively proven. Specifically, the incidence of ACL injuries in female col-lege athletes is 0.31 per 1000 hours of combined practice and game time,or 1 ACL injury per 161 sessions of sporting activity. In comparison, theincidence of ACL injuries in male college athletes is 0.13 per 1000 hoursof combined practice and game time, or 1 ACL injury per 385 sessionsof sporting activity. Furthermore, college athletes as a whole are ninetimes more likely to injure the ACL during game than practice time}Arendt and Dickl cite a 60% increase in the incidence of ACL injuries inwomen's college soccer over the past 5 years.

Though exact statistics have not yet been definitively reported,adolescent females clearly constitute an increasing number of patientswho suffer knee ligament injuries. The clinical impression that we havefrom our sports medicine clinics indicate that severe knee injuries, in-cluding ACL tears, are increasing in soccer. Moreover, these trendsare particularly evident in adolescent females. Numerous studies havesuggested that the injury rate for females playing soccer is higher thanfor males, findings that have been duplicated in both youth and adultstudies.1,2, 12, 24 With both the overall incidence of ACL injuries increasingand the number of adolescent females playing soccer increasing, contin-ued research regarding the cause and possible prevention of ligamentinjuries, especially in female athletes, is imperative.

Head Injuries

Though much less common than knee injuries, head injuries alsooccur during soccer and represent a significant cause of morbidity. Incollege athletes, the NCAA collection data regarding head injury reportsthat females and males athletes have a comparable (0.15/1000) risk insuffering a concussion during a soccer game or practice. Included in thehead injury category are dental injury, ophthalmologic injury, and closedhead injury. Together, these types of injuries represent an estimated 3%

YOUTH SOCCER: AN EPIDEMIOLOGIC PERSPECfIVE 671

to 5% of all soccer injuries suffered by adolescent aged soccer players.20Dental trauma, a significant cause of injury in the older adolescent agegroup, may include tooth avulsion and fracture. Sane and Ylipaaval-nierni20 demonstrated that tooth injury is less common in youth soccerthan in advanced teenaged and adult leagues, likely owing to the in-creased aggressiveness in the older ages. Recently, Rodd and Chesham18studied the mouthguard use among school-aged children and foundonly 14% use among pupils. Ocular trauma, resulting from both player-contact injuries and ball-player injuries, has been reported in the medicalliterature.3

The possibility that repetitive heading of the soccer ball mightpredispose a young soccer player to long-term neurologic sequelae is anissue that has received significant attention in the media. A study pub-lished in 1989 by Tysvaer and Odd-Verjorn25 suggested that EEGchanges, both acute and chronic, were higher in soccer players than in amatched control group of track athletes. In America, this study raisedsignificant concern owing to the increasing numbers of youths participat-ing in soccer. An important follow-up study was performed using mem-bers of the United States National Soccer Team.1o Jordan and co-workers1oused 25 subjects with an average age 24.9 years (and an average of 17.7years of soccer playing) and through both MR imaging and question-naire analysis, compared the soccer group with 20 track athletes ofsimilar age. The study demonstrated an increased incidence of neuro-logic symptoms in the soccer-playing group, likely related to the contactnature of the sport. There was no evidence, however, that repetitiveheading caused chronic neurologic damage. This concept was evaluatedboth by the prevalence of neurologic symptoms in the patient's historyand the anatomic evaluation of brain structure by MRl.IO

By combining the information from these two studies, the readercan develop the several conclusions regarding head injury and soccer.First, the risk of closed-head injury is present in soccer, is more commonin older aged groups, and is most likely the result of acute traumaticepisodes and not from repetitive heading of the soccer ball. Second,EEG, a sensitive diagnostic tool for evaluation of acute head injury,shows voltage changes that reflect closed-head injury. The long-termconsequences of these EEG changes is not known, though clinical studydoes not suggest that long-term neurologic condition is adversely af-fected from normal soccer playing activity. And third, though soccerplayers display a higher incidence of acute head injury when comparedwith matched controls, repetitive heading alone does not seem to predis-pose a player to long-term neurologic damage}O, 25

INJURY PREVENTION

With the numbers of American adolescent and preadolescent soccerplayers growing, greater attention towards the prevention of injury is atopic of increasing importance. From a musculoskeletal perspective,

672 METZL&MICHEU

proper warm-up and stretching technique has been shown to decreasethe risk of injury.19 Because strains and sprains are among the mostcommon of soccer injuries, ensuring that coaches on all levels encouragetheir players to warm-up properly is an effective method of injuryprevention. The advent of mandatory shin protection with shin-guardregulations in junior level soccer is aimed at decreasing the risk of directtrauma to the tibia, as are regulations requiring the use of smaller-sizedsoccer balls in junior league competition. Mouthgards, though optional,are an important and simple measure that can aid in the prevention ofdental trauma. Finally, several studies have indicated that 15% to 25%of injuries occur as a result of a foul being committed (i.e., tackling aplayer from behind).6, 16 With a greater understanding of the completerules and nuances of soccer, and as the level of national soccer sophistica-tion continues to develop, American soccer players should be able toreduce the number of injuries resulting from illegal play.

DISCUSSION

In 1997, the International Federation of Sports Medicine released aposition paper on organized sports for children. One of the specificrecommendations of this position paper was that sports governing bod-ies, as a part of their general responsibility for the training and safety ofyoung athletes, should mention statistics of illness and injury in theirrespective sport. This recommendation should find tremendous supportin youth soccer, which has been noted for its interest in promoting thesafety of the game at the youth level.4

On all levels, soccer is the fastest growing sport in America. Withthe American team having qualified for the World Cup Tournament inFrance this summer, Major League Soccer (MLS) entering its third sea-son, and the numbers of youth players burgeoning, the national popular-ity of soccer will continue to grow. In view of the increasing prevalenceof soccer as an American sport, further studies detailing the specifics ofinjury rate, injury prevention, and injury risk are essential. With thisinformation, the medical community will be better able to counsel theirpatients in more effective methods of injury prevention, thus furtheringtheir enjoyment of the world's most popular sport.

References

1. Arendt E, Dick R: Knee injury patterns among men and women in collegiate basketballand soccer. Am J Sports Med 23:694-701, 1995

2. Bordal JM, Amly F, Hannestad B, et al: Epidemiology of anterior cruciate ligamentinjuries in soccer. Am J Sports Med 25:341-345, 1997

3. Burke MJ, et al: Socerball-induced eye injuries. JAMA 249:2682-2685, 19834. Chan KM, Micheli LJ: In Sports and Children. Baltimore, Williams & Wilkins, 19985. Delee JC, Farney WC: Incidence of injury in Texas high school football. Am J Sports

Med 20:575-580, 1992

673yourn SOCCER: AN EPIDEMIOLOGIC PERSPEC11VE

6. Ekstrand J, Gillquist J: Soccer Injuries and their mechanisms: A prospective shtdy. MedSciSports Exerc 15:267-270, 1983

7. Garrick JG, Requa RK: Injuries in high school sports. Pediatrics 61:465--469, 19788. Goldberg B, Rosenthal PP, Robertson LS, et al: Injuries in youth football. Pediatrics

81:255-261, 19889. Hoy K, Lindblad BE, Terkelsen CJ, et al: European soccer injuries: A prospective

epidemiological and socioeconomic shtdy. Am J Sports Med 20:318-322, 199210. Jordan SE, Green GA, Galanty HL, et al: Acute and chronic brain injury in United

States National Team soccer players. Am J Sports Med 24:205-210, 199611. Keller CS, Noyes FR, Buncher CR, et al: The medical aspects of soccer injury epidemiol-

ogy. Am J Sports Med 15:S105-S112, 198712. Kibler WB: Injuries in adolescent and preadolescent soccer players. Med Sci Sports

Exerc 25:1330-1332, 199313. Lindenfeld TN, Schmitt DJ, Hendy MP, et al: Incidence of injury in indoor soccer. Am

J Sports Med 22:364-371, 199414. Lobnes ]H, Garret WE: Soccer. In Sports Medicine-The School Aged Athlete, ed 2.

Philadelphia, WB Saunders, 1996, pp 715-72715. Maehlum 5: Frequency of injuries in a youth soccer tournament. Physician Sportsmed

12:114-117, 198416. Nielsen AB, Yde J: Epidemiology and traumatology of injuries in soccer. Am J Sports

Med 17:803-807, 198917. Nilsson 5, Roaas A: Soccer injuries in adolescents. Am J Sports Med 6:358-361, 197818. Rodd HD, Chesham: Sports-related oral injury and mouthguard use among Sheffield

school children. Community Dent Health 14:25-30, 199719. Safran MR, Garrett WE Jr, Seaber AV, et al: The role of warm-up in muscular injury

prevention. Am J Sports Med 16:123-128, 198820. Sane J, Ylipaavalniemi P: Maxillofacial and dental soccer injuries in Finland. Br J Oral

Maxillofac Surg 25:383-390, 198721. Schmidt-0lsen 5, Jorgensen U, Kaalund 5, et al: Injuries among young soccer players.

Am J Sports Med 19:273-275, 199122. Soccer Industry Council of America: National Soccer Participation Survey. North Palm

Beach, FL, America Sports Data, Inc, 199523. Statistics on the national associations of FlFA. FlFA News. 235:528, 199224. Sullivan JA, Gross RH, Grana WA, et al: Evaluation of injuries in youth soccer. Am J

Sports Med 8:325-327, 198025. Tysvaer AT, Odd-Verjorn: Soccer Injuries to the brain: A neurologic and electroencepha-

lograph shtdy of active football players. Am J Sports Med 17:573-578, 1989

Address reprint requests to

Lyle J. Micheli, MDChildren's Hospital

300 Longwood AvenueBoston, MA 02115