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Abstract
Objectives To investigate the prevalence and burden of overuse injuries in children’s football as well as player characteristics and their association with overuse injury risk.
Methods This investigation is based on the control arm (10 clubs) of a randomised controlled trial investigating prevention of injuries in youth football. We conducted a prospective 20-week follow-up study on overuse injuries among Finnish football players (n=733, aged 9–14 years). Each week, we sent a text message to players’ parents to ask if the player had sustained any injury during the past week. Players with overuse problem were interviewed over the phone using an overuse injury questionnaire. The main outcome measures were prevalence of all overuse injuries and substantial overuse injuries (those leading to moderate or severe reductions in participation or performance) and injury severity.
Results The average response rate was 95%. In total, 343 players (46.8%) reported an overuse problem while in the study. The average weekly prevalence of all overuse problems and substantial overuse problems was 12.8% and 6.0%, respectively. Injuries affecting the knee had the highest weekly prevalence (5.7% and 2.4% for all and substantial knee problems, respectively). Girls had a higher likelihood of knee problems (OR 2.70; 95% CI 1.69 to 4.17), whereas boys had a higher likelihood of heel problems (OR 2.82; 95% CI 1.07 to 7.44). The likelihood of reporting an overuse problem increased with age (OR 1.21; 95% CI 1.00 to 1.47).
Conclusion Overuse injuries are prevalent in children’s competitive football. Knee overuse injuries represent the greatest burden on participation and performance.
Trial registration number ISRCTN14046021.
- sporting injuries
- adolescent
- soccer
- overuse injury
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Introduction
Football is the world’s most popular sport and a large proportion of registered players are under 18 years of age (The Fédération Internationale de Football Association, FIFA Big Count 2006, available from https://www.fifa.com/mm/document/fifafacts/bcoffsurv/bigcount.statspackage_7024.pdf). Participation in organised football during childhood can induce significant health benefits1 2 and support a physically active lifestyle in later life.3 However, playing football entails a risk of injury.4 Injuries can diminish health benefits, have long-term consequences such as pain, dysfunction and early osteoarthritis,5 6 and discourage children from playing football or other sports.7
While many studies have investigated the epidemiology of football injuries among adolescent and adult players,4 8–11 only a few prospective studies regarding injuries in children’s (under 14 years old) competitive football have been published.7 12 Some studies have suggested that children’s organised football is associated with a low risk of injuries.12–14 However, these studies have mainly used time-loss injury definition,15 which is likely to substantially underestimate the full extent of overuse injuries16—thought to be the main injury type in children’s sports.17 One recent study recorded all physical complaints that resulted in time loss or required medical attention. The authors reported that half of children’s football injuries did not lead to medical consultation.12 In children’s sports, where clubs rarely have access to medical staff, even using a medical attention injury definition can underestimate the prevalence of injuries, in particular for less severe injuries.7 Thus, epidemiological studies using data collection methods specifically designed to record overuse injuries are needed in children’s sports. Recording the injury severity based on players’ self-assessment of their pain and the impact that the injury has had on their participation and performance, rather than focusing solely on time loss from sports, is a more accurate way of describing the full injury burden caused by overuse problems.16
Exercise-based injury prevention programmes have been shown to be effective in various sports18–20 including football.21 22 These studies have focused mainly on acute injuries, whereas studies on prevention of overuse injuries, especially among children, are lacking. Prospective epidemiological data on overuse injury prevalence is needed to inform future injury prevention strategies.23
The main aim of this prospective cohort study was to investigate the prevalence and burden of overuse injuries in children’s football. In addition, we examined player characteristics and their association with overuse injury risk.
Methods
Study design and participants
This study is based on the control arm of a cluster-randomised controlled trial to investigate the effect of a prevention programme for acute and overuse injuries (ISRCTN14046021).
We carried out this study in collaboration with Sami Hyypiä Academy (SHA), the national training and research centre for Finnish football. Every second year, the SHA selects 20 youth clubs to participate in a player development programme in which talented U11–U14 boys and girls participate in a 3-day player monitoring event held twice a year at the Eerikkilä Sports Institute, Tammela, Finland. In August 2014, we invited all SHA clubs (92 junior teams, 1643 players) to participate in the randomised controlled trial. Participating clubs included male and female players aged 9‒14 years. The clubs were located around Finland and were among the best junior football clubs in Finland. Participating children played for their club’s highest-level teams for their age group.
Ten clubs (48 teams, 740 players) from the control arm (not receiving any injury prevention intervention) were included in the current investigation (figure 1). Players who were official members of the participating teams were eligible. Players who joined the teams after January 2015 were not included. All players and their parents/guardians were informed about the study procedure and provided their written informed consent before entering the study.
Flow of participants.
Procedures
We delivered the study materials (including information about the study, consent forms and a baseline questionnaire) to the clubs by mail before each player monitoring event in the fall 2014. The coaches distributed study materials to each of their team members. Players, together with their parents/guardians, signed the informed consents and completed the baseline questionnaire including demographic information, information on their playing experience, previous orthopaedic procedures, injuries during the past 12 months and chronic illnesses (such as diabetes and asthma). We collected the consents and baseline questionnaires during the event. During their team’s event (end of September to January 2015), height and weight were measured. All official team members were eligible to participate in the study regardless of their participation in the player monitoring event.
Participating players were followed prospectively from January to June 2015 (20 weeks). We used an automated text message system (Hopealuoti, Tampere, Finland) to identify players who had experienced an overuse problem each week. Every Sunday, parents/guardians received a text message regarding new injuries: “Has your child had any musculoskeletal complaint or injuries during the previous 7 days (yes/no)?” A reminder was sent to non-responders 3 days later. After 7 days of non-response, the player (or the parent) was contacted by phone.
All players (or their parents) who responded ‘yes’ to the text message were contacted by a research physiotherapist within 1 week for a telephone interview to determine the type and nature of each problem reported. Based on the interview, all cases were classified as either acute or overuse injuries. Acute injuries were defined as injuries with a specific, identifiable injury event.15 All other cases were regarded as overuse injuries. In case of an overuse injury, the Oslo Sports Trauma Research Centre Overuse Injury Questionnaire (OSTRC-O)16 was completed over the phone by a study physiotherapist. Only overuse injuries were included in the current investigation.
Overuse injury registration
The OSTRC-O consists of four key questions on the consequences of overuse problems on sports participation, training volume, performance and perceived pain. Each item is scored with a 4-point or 5-point scale, ranging from 0 (no problem, no reduction, no effect and no pain, respectively) to 25 (cannot participate at all or severe pain). If the player had experienced more than one overuse injury during the past week, OSTRC-O was filled for each anatomical area separately.
Each week, the severity score for each overuse problem was calculated as the sum of the item scores (ranging from 0 to 100), as proposed by Clarsen et al.16 A cumulative severity score was calculated for each anatomical area for boys and girls separately by summing the severity scores for all players over the 20 weeks and dividing by the mean number of weekly respondents in each group. This score formed the basis for comparisons of the relative injury burden between anatomical areas.24
Prevalence measures
The prevalence of injuries was calculated for each anatomical area each study week. This was done by dividing the number of players that reported any overuse problem (a severity score higher than 0) by the number of respondents that week. At the end of the study, the average weekly prevalence was calculated for each anatomical area. The average weekly prevalence of substantial overuse problems was calculated in the same way as described above. Substantial overuse problems included only problems leading to moderate or severe reductions in training volume or performance, or an inability to participate (responses 3, 4 or 5 in either question 2 or 3).
The incidence of overuse injuries was expressed as a number of injuries per 100 person-years.
Statistical analyses
Baseline characteristics were described as means with SD. Cut-off points for body mass index were applied according to Cole et al 25 26 to define normal weight, underweight and overweight. Group differences were analysed by independent-samples t-test and χ2 test. Missing data (1.3%) were not imputed in any way.
The relationship between demographic characteristics (sex, age, height and body mass) and the risk of overuse problems over time were analysed by generalised linear mixed model. Multiple models with different additional variables (such as body mass index, years of participation, previous orthopaedic surgical procedures as well as other competitive sports) were compared by using the Bayesian Information Criteria (BIC) value. Variables that did not improve the model in the sense of BIC and showed no association with the various injury outcomes (p>0.2) were excluded from the final models. Sporting club was used as a random effect for each model. All analyses were conducted using SPSS V.24 (IBM).
Results
Characteristics of participants and response rate
A total of 740 players entered the study. Of these, seven players (1%) did not participate in the injury data collection and were excluded from the analyses. Seven hundred and thirty-three players (570 boys, 163 girls) participated in the 20-week data collection. Altogether, 18 players (2.5%) dropped out during the study (figure 1). Data from these players were included from the time they participated. Anthropometric data (height, weight) were available from 569 players who participated in the physical tests at baseline (table 1).
Characteristics of participants
Prevalence of overuse injuries
The average response rate for the 20 text messages was 95% (girls 96%, boys 95%). Seventy-one per cent of players answered every week and 94% responded 15 times or more.
During the follow-up, 343 players (46.8%) reported at least one episode of an overuse problem. In addition, 228 players (31.1%) reported at least one episode of a substantial overuse problem. Players suffered from an overuse problem for a mean of 3.9 weeks (median 2; range 1–20). The incidence of overuse problems was 171.8 injuries per 100 person-years (95% CI 156.6 to 188.0).
The average prevalence of all overuse problems and substantial overuse problems over the 20 weeks was 12.8% and 6.0%, respectively (in boys: 11.5% and 5.6%; in girls: 17.4% and 7.4%) (figure 2). Of the anatomical areas, the knee displayed the highest prevalence throughout the study (5.7% and 2.4% average prevalence for all overuse problems and substantial overuse problems, respectively) (figure 3). Other prevalent areas were the heel (2.6% and 1.1%), hip/groin (1.1% and 0.5%) and the lower back (0.8% and 0.5%).
Prevalence of all overuse problems (light area) and substantial overuse problems (dark area) in all players, boys and girls over the 20-week follow-up.
Prevalence of all overuse problems (light area) and substantial overuse problems (dark area) located at the knee, heel, hip/groin and lower back in boys and girls aged 9–11 years and 12–14 years over the 20-week follow-up period.
The prevalence of all overuse problems (rate ratio 1.3; 95% CI 1.2 to 1.5) as well as substantial overuse problems (rate ratio 1.6; 95% CI 1.4 to 1.9) was greater in older boys (aged 12–14 years) compared with younger boys (aged 9–11 years). Older boys displayed more knee problems (rate ratio 1.6; 95% CI 1.3 to 1.9 and 1.7; 95% CI 1.2 to 2.3 for all problems and substantial problems, respectively), hip/groin problems (rate ratio 1.8; 95% CI 1.2 to 2.8 and 3.1; 95% CI 1.7 to 6.0) and lower back problems (rate ratio 3.9; 95% CI 2.2 to 7.1 and 3.8; 95% CI 2.1 to 7.7) compared with younger boys. Younger boys displayed more heel problems compared with older boys (rate ratio 0.7; 95% CI 0.5 to 0.8).
In girls, no differences in the prevalence of all overuse problems (rate ratio 0.9; 95% CI 0.8 to 1.1) or substantial overuse problems (rate ratio 1.1; 95% CI 0.9 to 1.5) between the two age groups were observed. In older girls, the prevalence of hip/groin (rate ratio 2.4; 95% CI 1.1 to 5.9) as well as lower back problems (rate ratio 5.1; 95% CI 1.4 to 32.7) was greater compared with younger girls.
Relative burden of overuse problems by anatomic site
Knee problems had the greatest relative burden as assessed by the adjusted cumulative severity score (figure 4) both in boys and girls.
Relative burden of overuse problems, shown as the adjusted cumulative severity score for boys and girls.
Association between player demographics and the risk of overuse injury
Multivariate analyses showed that girls were more likely to report knee overuse problems and substantial knee overuse problems, whereas boys were more likely to report heel overuse problems (table 2). In addition, older players were more likely to report any overuse problems, knee overuse problems and substantial knee overuse problems.
Multivariate analyses of the effect of player characteristics on overuse and substantial overuse problems
Discussion
This study was carried out to describe the prevalence and burden of overuse injuries in children participating in competitive football. To our knowledge, this is the first study investigating overuse injuries in children’s organised football using the OSTRC-O questionnaire. Using an injury definition based on all complaints and describing the overuse problem by prevalence and severity measures, we found a high weekly prevalence (12.8%) of overuse problems.
In this study, overuse injuries were more common in girls compared with boys. The average weekly prevalence of all overuse problems in girls was 17.4% (11.5% in boys), whereas the average prevalence of substantial overuse problems was 7.4% (5.6% in boys). Girls in our study were 11.8 years in average, and mainly (83%) pre-menarche. In comparison, Richardson et al,27 using comparable data collection, reported a weekly prevalence of 10.1% for all overuse problems and 4.9% for substantial overuse problems in adolescent female football players (mean age 17.2 years). Maturation status has been suggested to have an influence on injury characteristics.7 28 In our study, we were not able to determine individual maturation status for most of the players. However, our findings on higher overuse injury rate in younger players are consistent with Le Gall et al,28 who demonstrated that French football players under 14 years old were at high risk of sustaining overuse injuries no matter what their individual maturation status was. Thus, effective strategies to prevent overuse injuries should be implemented early.
The most prevalent location for overuse problem was the knee. Knee complaints also had clearly the greatest burden on self-reported perceived performance and participation, and were especially common among the girls. These findings are in line with previous studies on female youth football players27 29 and children (aged 8 to 15 years) from various sports including football.30 O’Kane et al 29 investigated risk factors for overuse knee injuries and found that increased knee valgus, decreased lower extremity strength and playing on more than one team were associated with increased injury risk in female football players aged 12 to 15 years. Similar risk factors have been associated with acute knee injuries as well.31 32 Enhancing knee alignment and lower extremity/core strength might be of value in children participating in football in order to reduce the risk of both acute and overuse knee injuries21 as well as to improve motor performance.33
The location and type of overuse injuries among young footballers varies between different age34 and maturity groups.28 Volpi et al 34 followed young Italian footballers and found that players under 14 years old had a high prevalence of traction apophysitis, whereas older players sustained more tendinopathies. Similarly, Le Gall et al 28 reported that late and normal maturers among French footballers under 14 years old had a high incidence of apophysitis, Osgood-Schlatter disease in particular, while the main overuse injury type in normal and early maturers was tendinopathy. Although we were not able to confirm the exact diagnoses for most of the players, the high prevalence of knee and heel overuse problems we observed was presumably due to apophysites. Traction apophysites (such as Osgood-Schlatter and Sinding-Larsen-Johansson diseases involving the knee and Sever’s disease involving the heel), which are one type of osteochondroses in growing bone, are common disorders in growing athletes.35 36 Osgood-Schlatter disease has its peak prevalence in footballers under 13 to 14 years.37 38 Sinding-Larsen-Johansson disease is also another common cause of anterior knee pain in athletes aged 10 to 13 years.39 Sever’s disease has been reported to be most common in football players under 11 years.38 Similarly, in our study, older boys suffered more knee injuries, while younger boys displayed a higher prevalence of heel problems. Although traction apophysites often resolve without treatment,40 41 these conditions often cause significant discomfort and require a long resting period.17 36
In accordance with previous work by Rössler et al,12 we found that the likelihood of sustaining an overuse problem increased with age. Overuse injuries are suggested to be more common during the adolescent growth spurt, as the growing musculoskeletal system is vulnerable to tensile, shear and compressive forces.17 Furthermore, the growth spurt causes rapid changes in limb length, body mass and moments of inertia affecting coordination, flexibility and movement patterns, which may play a role in the increased injury risk.42 Identifying the onset of growth spurt28 and careful monitoring of training load during the rapid growth phase are recommended to decrease the excessive loading of the growing skeleton.17 36 Properly planned and supervised strength and conditioning training is safe for children and can improve bone health, body composition and possibly prevent injuries.17 Informing coaches about injuries that are common in young athletes is of great importance. Early detection of these injuries is essential in order to start effective treatment and management,38 and to avoid more serious consequences.
Groin pain is a common problem among adult male football players.43 The weekly prevalence of hip/groin overuse problems in our young cohort was low. However, the prevalence of hip/groin problems was two to three times higher in older players (both boys and girls) compared with younger players. Furthermore, the older players sustained four to five times as many lower back problems. Low back pain has been reported to be common in other youth team sports as well,44 and in a growing athlete it is related to a high prevalence of structural pathology, such as spondylolysis.45
Specialisation in a single sport during childhood or adolescence is increasingly common in many sports,46 especially football.47 In our study, only 17% of boys and 6% of girls reported participating in one or more sports other than football, and participation in other sports was more common in younger children compared with older children. The protective effect of multiple sports and recreational activities has been demonstrated previously29 47 and hence should be recommended in children participating in football. Although more studies focusing on overuse injury prevention in youth is needed, neuromuscular warm-up programme including strength, balance, coordination and movement skills has been shown to reduce the risk of overuse injuries in adolescent female footballers,48 and may be effective in children’s football as well.21
Methodological considerations
To our knowledge, this study is the first to prospectively record overuse injuries in children’s sports using methods specifically designed for this purpose. We had a large sample size, we asked about injuries on a weekly basis using a text message system and we had a very high response rate. Besides these strengths, some limitations exist. First, we had no data on training and match exposure, which reduces the comparability with other studies reporting athlete exposures and might influence the group comparisons. Nevertheless, it seems unlikely that girls, who had more overuse problems, trained more or harder than boys. Second, the study was conducted only over a 20-week period. A longer follow-up might have uncovered more overuse complaints and potential variations in injury prevalence better.
Third, we collected injuries by telephone interview and hence were not able to confirm the exact injury diagnoses. Recording exact diagnoses for all reported overuse problems would have required close follow-up from medical staff and was outside the scope of the current study. Instead, we recorded diagnoses when available (injured player had visited a medical doctor), but a minority of players with overuse problems received medical attention. Notwithstanding the lack of diagnoses, we believe that with this approach we were able to record the affected body part reliably. Registration of all complaints regardless of medical attention allowed us to estimate the true burden of overuse complaints.
Another limitation is that the anthropometric data were not available from players who did not participate in the testing event at baseline. Hence, anthropometric data should be interpreted with caution. Nevertheless, this limitation does not affect the main outcomes of our study.
Finally, due to the young age of our participants, we sent the weekly text message to the parents/guardians. It is possible that parents may not have been aware of all overuse symptoms their child had experienced or that they may have considered some normal symptoms (such as fatigue or delayed-onset muscle soreness) as signs of an injury.
Implications
Enhancing the safety of children’s sports is essential in order to promote physical activity both during childhood and later in life. Overuse injuries are common in growing athletes and although often self-limiting, these injuries cause significant discomfort and often interrupt training for a long time. Exercise-based injury prevention programmes have shown to be effective to prevent acute injuries and furthermore shown promising results on reducing overuse injuries also. In the future, more studies focusing on developing and implementing effective methods to prevent overuse injuries, especially in children’s and adolescents sports, are needed.
Conclusion
Children playing competitive football suffer rather often from overuse problems, most commonly from those affecting the lower extremity and knee. Knee overuse complaints represent the greatest burden on self-reported perceived sports participation and performance, and thus, particular focus should be targeted to prevent these complaints.
What are the new findings?
Overuse injuries are prevalent in children’s competitive football.
Knee and heel complaints are the most common overuse problems in children’s football.
Knee overuse problems represent the greatest burden on participation and performance.
How might it impact on clinical practice in the future?
Prevention of overuse injuries, especially those affecting the knee, should be enhanced among children playing football.
Strategies to prevent overuse injuries should be implemented early.
Acknowledgments
The authors acknowledge Sami Hyypiä Academy’s support of this project. We thank all teams, coaches, contact persons, players and their parents for their contribution to the data collection. We also thank study physiotherapists Irja Lahtinen, Elina Myllymäki, Nea Nieminen and Emilia Sivonen for their effort in data collection, statistician Kari Tokola for statistical advice, and all members of research group.
References
Footnotes
Contributors All authors contributed to project planning and manuscript preparations. ML and KP were responsible for the data collection. ML was responsible for the data analysis and drafting of the manuscript. All authors critically revised the manuscript and approved the final version of the manuscript. ML is the guarantor.
Funding This study was financially supported by the Finnish Ministry of Education and Culture, by the Competitive State Research Financing of the Expert Responsibility area of Tampere University Hospital (grant 9S049) and by the Palloilu Säätiö, Tammela.
Competing interests None declared.
Patient consent Not required.
Ethics approval Ethics Committee of Pirkanmaa Hospital District (ETL-code R13110).
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Unpublished data are available upon request.