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Recurrence of Achilles tendon injuries in elite male football players is more common after early return to play: an 11-year follow-up of the UEFA Champions League injury study
  1. Mariann Gajhede-Knudsen1,2,
  2. Jan Ekstrand1,2,3,
  3. Henrik Magnusson2,4,
  4. Nicola Maffulli5,6
  1. 1Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden
  2. 2Football Research Group, Linköping University, Linköping, Sweden
  3. 3UEFA Medical Committee, Nyon, Switzerland
  4. 4Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden
  5. 5Department of Musculoskeletal Disorders, University of Salerno, School of Medicine and Surgery, Salerno, Italy
  6. 6Queen Mary University of London, Centre for Sports and Exercise Medicine, London, UK
  1. Correspondence to Professor Jan Ekstrand, Solstigen 3, S-589 43, Linköping, Sweden; jan.ekstrand{at}telia.com

Abstract

Background There is limited information about Achilles tendon disorders in professional football.

Aims To investigate the incidence, injury circumstances, lay-off times and reinjury rates of Achilles tendon disorders in male professional football.

Methods A total of 27 clubs from 10 countries and 1743 players have been followed prospectively during 11 seasons between 2001 and 2012. The team medical staff recorded individual player exposure and time-loss injuries.

Results A total of 203 (2.5% of all injuries) Achilles tendon disorders were registered. A majority (96%) of the disorders were tendinopathies, and nine were partial or total ruptures. A higher injury rate was found during the preseason compared with the competitive season, 0.25 vs 0.18/1000 h (rate ratio (RR) 1.4, 95% CI 1.1 to 2.0; p=0.027). The mean lay-off time for Achilles tendinopathies was 23±37 (median=10, Q1=4 and Q3=24) days, while a rupture of the Achilles tendon, on average, caused 161±65 (median=169, Q1=110 and Q3=189) days of absence. Players with Achilles tendon disorders were significantly older than the rest of the cohort, with a mean age of 27.2±4 years vs 25.6±4.6 years (p<0.001). 27% of all Achilles tendinopathies were reinjuries. A higher reinjury risk was found after short recovery periods (31%) compared with longer recovery periods (13%) (RR 2.4, 95% CI 2.1 to 2.8; p<0.001).

Conclusions Achilles tendon disorders account for 3.8% of the total lay-off time and are more common in older players. Recurrence is common after Achilles tendinopathies and the reinjury risk is higher after short recovery periods.

  • Achilles tendon
  • Elite performance
  • Epidemiology
  • Lower extremity injuries
  • Soccer

https://doi.org/10.1136/bjsports-2013-092271

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    Introduction

    The elastic properties of the Achilles tendon are important for locomotion.1–3 The tendon has a capacity to withstand loads up to 12.5 times the body weight,4 but nevertheless many athletes sustain Achilles tendon disorders.5–7 The cause of Achilles tendon disorder is unclear,8 but it is suggested that the essential lesion of tendinopathy is a failed healing response.9–12 Achilles tendinopathy often manifests with a gradual onset of pain during tendon load (especially 2–6 cm proximal to the tendon insertion),13 morning stiffness and sometimes a localised swelling.6 ,14

    Achilles tendinopathies are often difficult to treat, have a poor prognosis13 ,15 ,16 and a tendency to chronicity and recurrence,17 with long periods of absence from sports.17 ,18

    Achilles tendon disorders are frequently seen in sports including running and jumping.7 ,8 ,15 ,19 ,20 Achilles tendinopathy or an Achilles tendon rupture can be career altering or career ending for professional athletes,6 ,17 ,21 ,22 but only a few studies have focused on Achilles tendon disorders in professional football players.17 ,23 ,24 Woods et al25 did not report Achilles tendon disorders as a separate diagnosis, but when evaluating ankle injuries during two seasons in English professional football, they found that 1% of all injuries were classified as tendonitis or paratendonitis. Nearly one-third of these occurred during the preseason period.24

    The present study investigated the incidence of Achilles tendon disorders and the risk of reinjury in a large population of elite male football players.

    Materials and methods

    Participants and study cohort

    The present study was performed within the framework of the prospective injury study UEFA (Union of European Football Associations) initiated among male elite level football teams in 2001, the UCL (UEFA Champions League) study.26 This portion of the study included 27 European professional football teams from 10 countries. The teams were followed over a varying number of seasons (1–11 seasons) between February 2001 and December 2011 and consisted of 1743 players (in an average 15 teams per season). All contracted players in the first team were invited to participate in the study. Players who left the team during the season (eg, because of transfer) were included during their time on the team. Teams were followed during the full season, including the preseason and competitive season.

    Data collection and study definitions

    The study design followed the consensus on definitions and data collection procedures in studies of football injuries outlined in the consensus document27 and by UEFA28 for studies of football. The validation of the injury and exposure reporting system and definitions has been described previously.28 To ensure high reliability of data registration, all teams were provided with a study manual describing the definitions used and procedures to record data, including explanatory examples. To avoid language problems, the manual and the study forms were translated from English into five other languages: French, German, Italian, Russian and Spanish. In addition, the study group checked all reports each month, and feedback was sent to the teams correcting any missing or unclear data. The definitions applied in the study are shown in table 1.

    View this table:
    Table 1

    Operational definitions used in the study

    At the start of each season, player baseline data were collected. Individual player participation in training and matches (minutes of exposure) was recorded by the club contact person on a standard exposure form sent to the study group on a monthly basis. This included exposure with the first and the second teams, as well as any national team exposure, for all players. The training content was not recorded. The team medical staff recorded all time-loss injuries on a standard injury form that was sent to the study group every month. The injury form provided information about the diagnosis, nature and circumstances of injury occurrence. All injuries resulting in the player being unable to fully participate in training or match play (ie, time-loss injuries) were recorded, and the player was considered injured until the team medical staff allowed full participation in training and availability for match selection. Injuries were categorised under 4° of severity based on the number of days of absence from training and/or match. All injuries were followed until the final day of rehabilitation.

    The present study included all recorded Achilles tendon injuries, including Achilles tendinopathies, partial Achilles tendon ruptures and total Achilles tendon ruptures. The diagnosis was based on the clinical examination by the team medical staff, and no specific diagnostic criteria were set out in advance.

    For the 48 severe injuries (>28 days lost) in 43 players, specific data about surgery and location of injuries were collected retrospectively from the team doctors and the club medical records.

    Statistical analyses

    Anthropometric data (age, height, body weight and body mass index (BMI)) are presented with mean±SD and analysed with independent sample t test. Lay-off time is presented with mean±SD and corresponding median and quartiles (Q1 (25th percentile) and Q3 (75th percentile)). Owing to a skewed distribution in the lay-off time, group differences were analysed using the Mann-Whitney U test. Pearson's χ2 test was used to analyse association between categorical variables. Injury rates are reported as the number of injuries per 1000 player-hours and injury burden was calculated as the number of lay-off days per 1000 player-hours. The rate ratio (RR) with 95% CI was used for group comparisons of injury rates and injury burden, and significance was tested using z statistics. Seasonal trend, expressed as the average annual percentage of change, was analysed using linear regression with log-transformed injury rates as the dependent variables. A 2-year moving average (MA) approach, by summarising two consecutive seasons, was also used to smooth out the large seasonal variation. The reinjury risk after the short (0–10 days) and long (>10 days) recovery periods was compared using the risk ratio with 95% CI, and significance was tested using z statistics. Season injury prevalence was calculated as the number of injured players during a season/total number of players in that season ×100. All tests were two-sided and the significance level was set at p<0.05.

    The study design underwent an ethical review at Linköping University, Linköping, Sweden and was approved by the UEFA Football Development Division and the UEFA Medical Committee.

    Results

    Injury rates

    In total, 1 057 201 h of exposure (888 249 h of training and 168 952 h of match play) were recorded. Overall, 8029 injuries were documented during the study period, 203 (2.5%) of which were Achilles tendon disorders. One hundred and ninety-four (96%) disorders were classified as gradual onset tendinopathies, and nine (4%) were acute onset partial or total ruptures. The injury rate was almost 22 times higher in Achilles tendinopathies compared with Achilles tendon ruptures (0.18 vs 0.01 injuries/1000 h, RR 21.6, 95% CI 11.0 to 42.1; p<0.001). As the mean total exposure time for a team of 28 players is about 7000 h per season, a team can roughly expect one Achilles tendinopathy every season, and one Achilles tendon rupture every 17th season.

    Between-season and within-season variation of injury rates

    The injury rate of Achilles tendon disorders has fluctuated, between 0.12 and 0.35 injuries/1000 h, over the 11 seasons. The highest injury rate was found in the February 2001 season and the lowest notations were found in the 2006 and 2007 seasons. The crude injury rates and the ‘smoother’ 2-year MA injury rates are illustrated in figure 1. The MA approach indicated an average annual decrease of 1.8% in the injury rate. The fitted regression model, however, indicated a non-significant seasonal trend in the log-transformed injury rates (R2=0.23, b=−0.056, 95% CI −0.131 to 0.020; p=0.132).

    Figure 1
    Figure 1

    Seasonal variations in injury rates of Achilles tendon disorders in male professional football players.

    The within-season variation, measured as quarterly injury rates, are shown in figure 2 and table 2. A higher injury rate was found during the preseason (July–August) compared with the competitive season (September–May), 0.25 vs 0.18 injuries/1000 h (RR 1.4, 95% CI 1.1 to 2.0; p=0.027).

    View this table:
    Table 2

    Achilles tendon disorders in the UCL cohort, comparison of preseason and competitive season in male professional football

    Figure 2
    Figure 2

    Monthly variations in injury rates of Achilles tendon disorders in male professional football players.

    Injury severity and consequences

    The severity of injuries and consequences in the form of lay-off time and injury burden are shown in table 3. The mean lay-off time for Achilles tendinopathies was 23±37 (median=10, Q1=4 and Q3=24) days, while a rupture of the Achilles tendon, on average, caused an almost seven times longer lay-off time, with 161±65 (median=169, Q1=110 and Q3=189) days of absence. Achilles tendon disorders account for 3.8% of the total lay-off time reported in the study. The injury burden was approximately three times higher in Achilles tendinopathies compared with Achilles tendon ruptures (4.24 vs 1.37 days lost/1000 h, RR 3.1, 95% CI 2.9 to 3.3; p<0.001).

    View this table:
    Table 3

    Achilles tendon disorders in the UCL cohort, comparison of Achilles tendinopathies and Achilles tendon ruptures in male professional football

    Reinjuries

    Twenty-seven per cent of all Achilles tendinopathies were reinjuries (table 3). No early recurrences were seen among the nine Achilles tendon ruptures. The reported recurrence rate of all injuries is 12% in the cohort. A higher reinjury risk was found after short (0–10 days) recovery periods (31%) compared with longer (>10 days) recovery periods (13%), (risk ratio 2.4, 95% CI 2.1 to 2.8; p<0.001).

    Anthropometric data

    Players with Achilles tendon disorders were significantly older than the rest of the cohort, with a mean age of 27.2±4 years vs 25.6±4.6 years (p<0.001). No differences could be found in height (182.1±6.2 cm vs 182.3±6.4 cm, p=0.607), body weight (78.4±7.1 kg vs 78±7.1 kg, p=0.473) or BMI (23.6±1.3 vs 23.4±1.4, p=0.092).

    Location and treatment of severe injuries

    Information about surgery and location was provided for 34 of the 39 severe (>28 days lost) Achilles tendinopathies and information about surgery was received for eight of the nine severe Achilles tendon ruptures.

    Twenty-three per cent of the proximal Achilles tendinopathies were operated on (3/13), two of them with resection of the plantaris tendon. Forty-five per cent (9/20) of the insertional tendinopathies were operated on. One player had surgery after problems both in the main body and at the insertion. The mean lay-off time for tendinopathy of the main body was 66±49 (median=43, Q1=35 and Q3=78) days, and for insertional tendinopathies 79±50 (median=61, Q1=41 and Q3=109) days (p=0.320). Surgery was performed on all seven total ruptures. The partial rupture, from which we received information about treatment, was not operated on.

    Discussion

    A team of 28 players can roughly expect one Achilles tendon disorder every season, and older players are more frequently affected. Most absence periods for Achilles tendinopathies were short (median of 10 days), but the recurrence rate was high (27%). There was a significantly higher risk of sustaining a reinjury if the player rested for less than 10 days. Finally, Achilles tendinopathy was more common during the preseason period.

    Achilles tendinopathies are common overuse injuries—Achilles tendon ruptures are rare

    The season prevalence of Achilles tendinopathies in this study was 2.1–5.1%. Woods et al25 did not report Achilles tendon disorders as a separate diagnosis, but when evaluating ankle injuries during two seasons in English professional football, they found that 1% of all injuries were classified as tendonitis or paratendonitis. Fredberg et al17 reported that 15% of the players reported time loss attributable to Achilles tendinopathy in Danish professional football players. The difference in injury prevalence may reflect a true difference in injury prevalence or differences in study methodology, reporting thresholds or varying treatment regiments (ie, to let players with symptoms carry on playing or take them out of training). Achilles tendon ruptures were rare at 0.01 injuries/1000 h of exposure.

    Higher risk of Achilles tendinopathy during preseason

    The incidence of Achilles tendon disorders was significantly higher during the preseason. All the teams in this cohort followed an autumn–spring season with preseason training in July–August, and a competitive season between September and May. One team had a longer break between December and February and contributed half the injuries in January, but the injury incidence was still significantly higher in the preseason.

    More overuse, especially tendon injuries, occurs during the preseason period.24 ,29–31 Woods et al24 reported that 32% of all Achilles tendon disorders occurred during the preseason, but this study did not account for exposure, so the high number of injuries could just reflect more training sessions. The intense preseason follows a period of rest. These sudden changes in intensity, training load and training type are suggested to be risk factors for overuse injuries such as Achilles tendinopathies,6 ,7 ,14 ,20 ,24 ,32 because the Achilles tendon may not be able to adapt fast enough to changes in loading pattern.14

    Varying absence periods for Achilles tendinopathy

    The absence period for Achilles tendinopathy in this study varied, with a median of 10 days and an average of 23 days. Both Sankey et al18 in rugby (mean=30 days) and Oztekin et al23 in Turkish professional football (median=30 days) reported longer absences. This may reflect differences in methodology and in the demands of the sport.

    The variations in lay-off time can be explained by the nature of the injury. Achilles tendinopathy often manifests with a gradual onset of pain,6 ,13 ,14 and it can be difficult to decide if and when a player should rest. Many players continue to participate in training even with symptoms of Achilles tendinopathy,33 ,34 especially if they want to play an important match.35 This affects the rehabilitation time needed. The player's importance to the team can also explain why some players rest less than others.

    Achilles tendon ruptures cause long absences from football

    The median absence period for the Achilles tendon rupture in this study was 169 days (mean=161). Both professional rugby players (mean=185.5 days)18 and professional Turkish football players (median and mean=180 days)23 reported longer absences. This may result from differences in methodology and study size, or in rugby, differences between sports. Also, with only nine ruptures in 11 years, the average is vulnerable to outliers.

    Six of the nine players sustaining ruptures of the tendon had been followed in our study before the season when the rupture occurred, and none of these players had any Achilles disorders resulting in time loss before their rupture. Symptoms before ruptures are reported to vary between 10% and 25%.19 ,36–38 Since degenerative changes are found in almost all ruptured tendons,38 it seems plausible that tendons undergo changes during an asymptomatic period of several months, where the tendon might be injured but the player does not experience symptoms, before the pathology results in pain and the changes become symptomatic.17 ,38 Therefore, some tendons might rupture before signs of Achilles tendinopathy occur.38

    Short absence time increases the risk of reinjury

    The high recurrence rate for Achilles tendinopathy found in this study (27%) reflects the chronic and recurrent character of this condition. The frequent relapse of symptoms when players return to football after a short rehabilitation period could be explained if pain is only the tip of the iceberg. Even if pain recedes to below the threshold, the pathological changes in the tendon could still exist and could therefore become symptomatic when the player resumes his activity level.14 Players who abstained from training and matches for less than 10 days at their index injury experienced a significantly higher risk of reinjury than players who rested for more than 10 days (p<0.001). Inadequate rehabilitation, with a premature return to activity, is a risk factor for reinjury.30 ,39 ,40 Therefore, it could be suggested that a longer rehabilitation period at the first signs of Achilles tendinopathy could be beneficial to avoid recurrences. A functional test before returning to play might also reduce recurrences.41

    There is little evidence on how to prevent these recurrences. Fredberg et al17 showed that prophylactic eccentric and stretching exercises did not reduce the frequency of ultrasonographic abnormalities in Achilles tendons in professional football players. On the other hand, the lack of effect might be because the training was not intense enough (2.25 times/week).17

    Older players sustain Achilles tendinopathy

    The players who sustained an Achilles tendon disorder were significantly older than the rest of the cohort (27.2 vs 25.6 years), as reported in other studies.6 ,22 The incidences of muscle calf injuries increase with age42 and, if the calf muscle is more exposed to injury, this could affect the risk of injury in the Achilles tendon as well. Further, it is well established that prolonged, strenuous endurance exercise induces muscle damage and impairs muscle function.43 Normally, the muscle tendon unit is able to repair and adapt, but there might be a limit to the regenerative capacity and adaptability, resulting in pathology.44

    If the calf muscles of older players theoretically have impaired function, there is a risk that the muscles become more easily fatigued. Fatigued muscles lose their ability to absorb shock,6 which theoretically can put a greater stress on the Achilles tendon.

    Treatment of the severe injuries

    In accordance with other studies, all the total Achilles tendon ruptures in this study were managed surgically.18 ,23 Many Achilles tendinopathies can be treated conservatively, but around 25% require surgery.20 ,45 Of the severe (>28 days lost) tendinopathies in the present study, 38% were operated on.

    Most severe tendinopathies in this study were located at the insertion (20 of the 34 we had information about). The insertional lesions also required surgery more often (45% vs 23%) and caused longer absences from football than the proximal lesions (mean=79 vs 66 days).

    Methodological considerations

    The prospective design and the 11-season study period are the strengths of the present study, together with the large and homogeneous sample of professional footballers.

    However, this study also has some limitations. First, no treatment details were requested on the general injury card. Additionally, no substudy specific injury card was sent to the clubs as was done for some of our previous substudies. Distinction between insertional and proximal Achilles tendon disorders was therefore not possible, which was a limitation in the study. We did, however, retrospectively collect data about the location and surgery for injuries causing an absence of greater than 28 days and since most clubs preserve files with objective data such as images and surgery protocols of previous injuries, we did receive data for most of these injuries.

    Second, our study manual did not provide the participating clubs with specific diagnostic or return-to-play criteria: it is therefore possible that the reported subclassifications, lay-off times and reinjury rates varied between clubs due to different diagnostics and treatment algorithms. Third, no reliable history of injury was collected at player inclusion; it was therefore not possible to compare the rates of Achilles disorders between uninjured players and players with prior Achilles disorders.

    Fourth, with the current time-loss definition, the number of overuse injuries, such as Achilles tendinopathy, captured in this surveillance study might only be the tip of the iceberg.45 Overuse injuries might be underestimated, because many players with Achilles tendinopathy keep participating in training and matches despite having problems, and are therefore not captured in our time-loss definition.35 ,45 However, this definition was chosen for the general injury surveillance study to capture the injuries, which had a substantial effect on the players and the teams' ability to perform.35

    What are the new findings?

    • Achilles tendon disorders account for 2.5% of all injuries and 3.8% of lay-off times in male professional football.

    • Achilles problems are more common in older players.

    • A majority (96%) of the disorders are gradual onset tendinopathies, and 4% are acute onset partial or total ruptures.

    • The incidence of Achilles disorders is higher during the preseason compared with the competitive season.

    • The median lay-off time for Achilles tendinopathies is 10 days and for ruptures it is 169 days.

    • Twenty-seven per cent of Achilles tendinopathies are reinjuries and these are more common after short (>10 days) recovery periods.

    How might it impact on clinical practice in the near future?

    • Players with Achilles tendinopathies might need longer recovery periods since the reinjury risk is significantly higher after recovery periods of less than 10 days.

    • The team medical and coaching staffs should be aware of the increased risk of Achilles problems during the preseason training period and observant of overuse to Achilles tendons.

    • The team medical and coaching staffs should be observant of the higher risk of older players who suffer from muscle-tendon problems after repetitive hard training sessions.

    Acknowledgments

    The authors would like to thank the participating clubs, medical staffs and players.

    References

    1. ↵
      1. Muramatsu T,
      2. Muraoka T,
      3. Takeshita D,
      4. et al
      . Mechanical properties of tendon and aponeurosis of human gastrocnemius muscle in vivo. J Appl Physiol 2001;90:1671–8.
      OpenUrlAbstract/FREE Full Text
    2. ↵
      1. Muraoka T,
      2. Muramatsu T,
      3. Fukunaga T,
      4. et al
      . Elastic properties of human Achilles tendon are correlated to muscle strength. J Appl Physiol 2005;99:665–9.
      OpenUrlAbstract/FREE Full Text
    3. ↵
      1. Collins M,
      2. Posthumus M
      . Type V collagen genotype and exercise-related phenotype relationships: a novel hypothesis. Exerc Sport Sci Rev 2011;39:191–8.
      OpenUrlPubMed
    4. ↵
      1. Komi PV,
      2. Fukashiro S,
      3. Järvinen M
      . Biomechanical loading of Achilles tendon during normal locomotion. Clin Sports Med 1992;11:521–31.
      OpenUrlPubMedWeb of Science
    5. ↵
      1. Kujala UM,
      2. Sarna S,
      3. Kaprio J
      . Cumulative incidence of Achilles tendon rupture and tendinopathy in male former elite athletes. Clin J Sport Med 2005;15:133–5.
      OpenUrlCrossRefPubMedWeb of Science
    6. ↵
      1. Kvist M
      . Achilles tendon injuries in athletes. Sports Med 1994;18:173–201.
      OpenUrlCrossRefPubMedWeb of Science
    7. ↵
      1. Maffulli N,
      2. Wong J,
      3. Almekinders LC
      . Types and epidemiology of tendinopathy. Clin Sports Med 2003;22:675–92.
      OpenUrlCrossRefPubMedWeb of Science
    8. ↵
      1. Maffulli N,
      2. Sharma P,
      3. Luscombe KL
      . Achilles tendinopathy: aetiology and management. J R Soc Med 2004;97:472–6.
      OpenUrlFREE Full Text
    9. ↵
      1. Cook JL,
      2. Khan KM,
      3. Purdam C
      . Achilles tendinopathy. Man Ther 2002;7:121–30.
      OpenUrlCrossRefPubMedWeb of Science
    10. ↵
      1. Järvinen M,
      2. Józsa L,
      3. Kannus P,
      4. et al
      . Histopathological findings in chronic tendon disorders. Scand J Med Sci Sports 1997;7:86–95.
      OpenUrlPubMedWeb of Science
    11. ↵
      1. Maganaris CN,
      2. Narici MV,
      3. Almekinders LC,
      4. et al
      . Biomechanics and pathophysiology of overuse tendon injuries: ideas on insertional tendinopathy. Sports Med 2004;34:1005–17.
      OpenUrlCrossRefPubMedWeb of Science
    12. ↵
      1. Rees JD,
      2. Maffulli N,
      3. Cook J
      . Management of tendinopathy. Am J Sports Med 2009;37:1855–67.
      OpenUrlAbstract/FREE Full Text
    13. ↵
      1. Maffulli N,
      2. Kader D
      . Tendinopathy of tendo achillis. J Bone Joint Surg Br 2002;84:1–8.
      OpenUrlCrossRef
    14. ↵
      1. Fredberg U,
      2. Stengaard-Pedersen K
      . Chronic tendinopathy tissue pathology, pain mechanisms, and etiology with a special focus on inflammation. Scand J Med Sci Sports 2008;18:3–15.
      OpenUrlCrossRefPubMedWeb of Science
    15. ↵
      1. Alfredson H,
      2. Lorentzon R
      . Chronic Achilles tendinosis: recommendations for treatment and prevention. Sports Med 2000;29:135–46.
      OpenUrlCrossRefPubMedWeb of Science
    16. ↵
      1. Maffulli N,
      2. Walley G,
      3. Sayana MK,
      4. et al
      . Eccentric calf muscle training in athletic patients with Achilles tendinopathy. Disabil Rehabil 2008;30:1677–84.
      OpenUrlCrossRefPubMedWeb of Science
    17. ↵
      1. Fredberg U,
      2. Bolvig L,
      3. Andersen NT
      . Prophylactic training in asymptomatic soccer players with ultrasonographic abnormalities in Achilles and patellar tendons: the Danish super league study. Am J Sports Med 2008;36:451–60.
      OpenUrlAbstract/FREE Full Text
    18. ↵
      1. Sankey RA,
      2. Brooks JH,
      3. Kemp SP,
      4. et al
      . The epidemiology of ankle injuries in professional rugby union players. Am J Sports Med 2008;36:2415–24.
      OpenUrlAbstract/FREE Full Text
    19. ↵
      1. Józsa L,
      2. Kvist M,
      3. Balint BJ,
      4. et al
      . The role of recreational sport activity in Achilles tendon rupture. A clinical, pathoanatomical, and sociological study of 292 cases. Am J Sports Med 1989;17:338–43.
      OpenUrlAbstract/FREE Full Text
    20. ↵
      1. Kvist M
      . Achilles tendon injuries in athletes. Ann Chir Gynaecol 1991;80:188–201.
      OpenUrlPubMedWeb of Science
    21. ↵
      1. Langberg H,
      2. Ellingsgaard H,
      3. Madsen T,
      4. et al
      . Eccentric rehabilitation exercise increases peritendinous type I collagen synthesis in humans with Achilles tendinosis. Scand J Med Sci Sports 2007;17:61–6.
      OpenUrlPubMedWeb of Science
    22. ↵
      1. Parekh SG,
      2. Wray WH,
      3. Brimmo O,
      4. et al
      . Epidemiology and outcomes of Achilles tendon ruptures in the National Football League. Foot Ankle Spec 2009;2:283–6.
      OpenUrlAbstract/FREE Full Text
    23. ↵
      1. Oztekin H,
      2. Boya H,
      3. Ozcan O,
      4. et al
      . Foot and ankle injuries and time lost from play in professional soccer players. Foot (Edinb) 2009;19:22–8.
      OpenUrlCrossRefPubMed
    24. ↵
      1. Woods C,
      2. Hawkins R,
      3. Hulse M,
      4. et al
      . The football association medical research programme: an audit of injuries in professional football-analysis of preseason injuries. Br J Sports Med 2002;36:436–41.
      OpenUrlAbstract/FREE Full Text
    25. ↵
      1. Woods C,
      2. Hawkins R,
      3. Hulse M,
      4. et al
      . The football association medical research programme: an audit of injuries in professional football: an analysis of ankle sprains. Br J Sports Med 2003;37:233–8.
      OpenUrlAbstract/FREE Full Text
    26. ↵
      1. Ekstrand J,
      2. Hägglund M,
      3. Waldén M
      . Injury incidence and injury patterns in professional football: the UEFA injury study. Br J Sports Med 2011;45:553–8.
      OpenUrlAbstract/FREE Full Text
    27. ↵
      1. Fuller CW,
      2. Ekstrand J,
      3. Junge A,
      4. et al
      . Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries. Br J Sports Med 2006;40:193–201.
      OpenUrlAbstract/FREE Full Text
    28. ↵
      1. Hägglund M,
      2. Waldén M,
      3. Bahr R,
      4. et al
      . Methods for epidemiological study of injuries to professional football players: developing the UEFA model. Br J Sports Med 2005;39:340–6.
      OpenUrlAbstract/FREE Full Text
    29. ↵
      1. Hawkins RD,
      2. Fuller CW
      . A prospective epidemiological study of injuries in four English professional football clubs. Br J Sports Med 1999;33:196–203.
      OpenUrlAbstract
    30. ↵
      1. Hawkins RD,
      2. Hulse MA,
      3. Wilkinson C,
      4. et al
      . The association football medical research programme: an audit of injuries in professional football. Br J Sports Med 2001;35:43–7.
      OpenUrlAbstract/FREE Full Text
    31. ↵
      1. Waldén M,
      2. Hägglund M,
      3. Ekstrand J
      . Injuries in Swedish elite football—a prospective study on injury definitions, risk for injury and injury pattern during 2001. Scand J Med Sci Sports 2005;15:118–25.
      OpenUrlCrossRefPubMedWeb of Science
    32. ↵
      1. Nichols AW
      . Achilles tendinitis in running athletes. J Am Board Fam Pract 1989;2:196–203.
      OpenUrlAbstract/FREE Full Text
    33. ↵
      1. Ekstrand J,
      2. Torstveit MK
      . Stress fractures in elite male football players. Scand J Med Sci Sports 2012;22:341–6.
      OpenUrlCrossRefPubMed
    34. ↵
      1. Fahlström M,
      2. Lorentzon R,
      3. Alfredson H
      . Painful conditions in the Achilles tendon region in elite badminton players. Am J Sports Med 2002;30:51–4.
      OpenUrlAbstract/FREE Full Text
    35. ↵
      1. Hägglund M,
      2. Zwerver J,
      3. Ekstrand J
      . Epidemiology of patellar tendinopathy in elite male soccer players. Am J Sports Med 2011;39:1906–11.
      OpenUrlAbstract/FREE Full Text
    36. ↵
      1. Årøen A,
      2. Helgø D,
      3. Granlund OG,
      4. et al
      . Contralateral tendon rupture risk is increased in individuals with a previous Achilles tendon rupture. Scand J Med Sci Sports 2004;14:30–3.
      OpenUrlCrossRefPubMedWeb of Science
    37. ↵
      1. Fahlström M,
      2. Björnstig U,
      3. Lorentzon R
      . Acute Achilles tendon rupture in badminton players. Am J Sports Med 1998;26:467–70.
      OpenUrlAbstract/FREE Full Text
    38. ↵
      1. Kannus P,
      2. Józsa L
      . Histopathological changes preceding spontaneous rupture of a tendon. A controlled study of 891 patients. J Bone Joint Surg Am 1991;73:1507–25.
      OpenUrlWeb of Science
    39. ↵
      1. Chomiak J,
      2. Junge A,
      3. Peterson L,
      4. et al
      . Severe injuries in football players. Influencing factors. Am J Sports Med 2000;28:S58–68.
      OpenUrlPubMedWeb of Science
    40. ↵
      1. Hägglund M,
      2. Waldén M,
      3. Ekstrand J
      . Injury incidence and distribution in elite football—a prospective study of the Danish and the Swedish top divisions. Scand J Med Sci Sports 2005;15:21–8.
      OpenUrlCrossRefPubMedWeb of Science
    41. ↵
      1. Fuller CW,
      2. Walker J
      . Quantifying the functional rehabilitation of injured football players. Br J Sports Med 2006;40:151–7.
      OpenUrlAbstract/FREE Full Text
    42. ↵
      1. Ekstrand J,
      2. Hägglund M,
      3. Waldén M
      . Epidemiology of muscle injuries in professional football (soccer). Am J Sports Med 2011;39:1226–32.
      OpenUrlAbstract/FREE Full Text
    43. ↵
      1. Grobler LA,
      2. Collins M,
      3. Lambert MI,
      4. et al
      . Skeletal muscle pathology in endurance athletes with acquired training intolerance. Br J Sports Med 2004;38:697–703.
      OpenUrlAbstract/FREE Full Text
    44. ↵
      1. Alfredson H,
      2. Öhberg L,
      3. Forsgren S
      . Is vasculo-neural ingrowth the cause of pain in chronic Achilles tendinosis? An investigation using ultrasonography and colour Doppler, immunohistochemistry, and diagnostic injections. Knee Surg Sports Traumatol Arthrosc 2003;11:334–8.
      OpenUrlCrossRefPubMedWeb of Science
    45. ↵
      1. Bahr R
      . No injuries, but plenty of pain? On the methodology for recording overuse symptoms in sports. Br J Sports Med 2009;43:966–72.
      OpenUrlAbstract/FREE Full Text

    Footnotes

    • Contributors JE was responsible for the conception and design of the study. HM has been the statistical advisor and revised the paper. MGK wrote the first draft of the manuscript, which was critically revised by NM, HM and JE. All authors contributed to the interpretation of the findings and approved the final draft of the manuscript. JE is the study guarantor.

    • Funding This study was supported by grants from the Union of European Football Associations (UEFA), the Swedish National Centre for Research in Sports and Praktikertjänst AB.

    • Competing interests None.

    • Patient consent Obtained.

    • Ethics approval The study design underwent an ethical review at Linköping University, Linköping, Sweden and was approved by the UEFA Football Development Division and the UEFA Medical Committee.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    Linked Articles

    • Warm up
      Keeping your top players on the pitch: the key to football medicine at a professional level
      Jan Ekstrand
      British Journal of Sports Medicine 2013; 47 723-724 Published Online First: 11 Jul 2013. doi: 10.1136/bjsports-2013-092771
    • Correction
      Correction
      BMJ Publishing Group Ltd and British Association of Sport and Exercise Medicine
      British Journal of Sports Medicine 2013; 47 856-856 Published Online First: 09 Aug 2013. doi: 10.1136/bjsports-2011-090725corr1
    • Correction
      Correction
      BMJ Publishing Group Ltd and British Association of Sport and Exercise Medicine
      British Journal of Sports Medicine 2013; 47 856-856 Published Online First: 09 Aug 2013. doi: 10.1136/bjsports-2013-092271corr1