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Abstract
Background Medial collateral ligament (MCL) injury is the most common knee ligament injury in professional football.
Aim To investigate the rate and circumstances of MCL injuries and development over the past decade.
Methods Prospective cohort study, in which 27 professional European teams were followed over 11 seasons (2001/2002 to 2011/2012). Team medical staffs recorded player exposure and time loss injuries. MCL injuries were classified into four severity categories. Injury rate was defined as the number of injuries per 1000 player-hours.
Results 346 MCL injuries occurred during 1 057 201 h (rate 0.33/1000 h). The match injury rate was nine times higher than the training injury rate (1.31 vs 0.14/1000 h, rate ratio 9.3, 95% CI 7.5 to 11.6, p<0.001). There was a significant average annual decrease of approximately 7% (p=0.023). The average lay-off was 23 days, and there was no difference in median lay-off between index injuries and reinjuries (18 vs 13, p=0.20). Almost 70% of all MCL injuries were contact-related, and there was no difference in median lay-off between contact and non-contact injuries (16 vs 16, p=0.74).
Conclusions This largest series of MCL injuries in professional football suggests that the time loss from football for MCL injury is 23 days. Also, the MCL injury rate decreased significantly during the 11-year study period.
- Knee
- Epidemiology
- Injury Prevention
- Knee injuries
- Soccer
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Introduction
The overall injury rate of professional footballers is approximately 1000 times higher than that of typical industrial occupations, generally regarded as high risk.1 Several studies have investigated the injury epidemiology in high-level football,2–8 but few have reported the data on medial collateral ligament (MCL) injuries. After hamstring injury, MCL injury is the most common severe injury subtype.2
The objective of this study was to investigate the rate and circumstances of MCL injuries and their development over the past decade. The hypotheses of this study were that the MCL injury rate decreased during the study period and that MCL injuries are more frequently caused by contact mechanisms.
Material and methods
A prospective cohort study of professional men's football in Europe has been carried out since 2001 in collaboration with the Union of European Football Associations (UEFA): the UEFA Champions League study.2 For the purpose of this study, 27 European teams (1743 players) were followed for 11 seasons from 2001 to 2012.3 All contracted players in the first teams were invited to participate in the study. The mean squad size was 25 players.3
Study design and definitions
The full methodology and the development of the study design have been reported elsewhere.9 The study design followed the consensus on definitions and data collection procedures in studies of football injuries.10 Specifically for this study, MCL injury was defined as ‘a traumatic distraction injury to the superficial MCL (sMCL), deep MCL (dMCL) and the posterior oblique ligament (POL) leading to a player being unable to participate fully in training or match play’. General definitions are given in table 1.
Operational definitions used in the study
Data collection
Player baseline data were collected once a year at player inclusion. Individual player exposure in training and matches was registered by the clubs on a standard exposure form sent to the study group on a monthly basis. The teams’ medical staff recorded injuries on a standard injury form that was also sent to the study group each month. The injury form provided the information about the diagnosis, nature and circumstances of injury occurrence, for example. All injuries resulting in a player being unable to participate fully in training or match play (ie, time loss injuries) were recorded. The player was regarded as injured until the team medical staff allowed full participation in training and availability for match selection. All injuries were followed until the final day of rehabilitation. Contact/non-contact was recorded on the injury form from 2004 to 2005, match minute of injury from 2005 to 2006 and injury mechanisms from 2008 to 2009.
Statistical analyses
Lay-off time is presented as the mean±SD and the corresponding median and quartiles (Q1=25th percentile and Q3=75th percentile). Owing to skewed distribution in lay-off time, group differences were analysed using the Mann-Whitney U test. Pearson's χ2 test was used to analyse the association between categorical variables. Injury rate was 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 a 95% CI was used for group comparisons of injury rates and injury burden, while significance was tested using z-statistics.11 Seasonal trend, expressed as the average annual percentage of change, was analysed using linear regression with log-transformed injury rates as the dependent variable. A 2-year moving average approach, by summarising two consecutive seasons, was also used to smooth out large seasonal variation. A one-sample proportional z-test was used to analyse the differences between 15 min periods in matches. All tests were two-sided and the significance level was set at p<0.05.
Results
In all, 10 57 201 h of exposure (8 88 249 h of training and 1 68 952 h of match play) were registered. In overall terms, 8029 injuries were documented, 346 (4.3%) of which were MCL injuries. The total MCL injury rate was 0.33/1000 h (table 2); a team of 25 players can therefore expect roughly two MCL injuries every season. The match injury rate was nine times higher than the training injury rate (1.31 vs 0.14/1000 h, RR 9.3, 95% CI 7.5 to 11.6, p<0.001).
Medial collateral ligament injuries of the knee in professional football
Between-season and within-season variation
The MCL injury rate fluctuated between 0.19 and 0.57/1000 h over the 11 seasons; the lowest was in 2008/2009 and the highest in 2004/2005. The crude injury rate and the 2-year moving average injury rate are illustrated in figure 1. The moving average approach indicated an average annual decrease of 3%, while the log-transformed regression model indicated a significant annual average decrease of approximately 7% (R2=0.46, b=−0.069, 95% CI −0.125 to −0.012, p=0.023). No significant differences could be found within the seasons.
Seasonal variation in injury rates for medial collateral ligament injuries in professional football.
Lay-off time
The mean lay-off time in MCL injuries was 23±23 (median=16, Q1=8, Q3=31) days. The mean lay-off time in other knee ligament injuries such as anterior cruciate ligament (ACL), posterior cruciate ligament (PCL) and lateral collateral ligament (LCL) was 194±75 (median=194, Q1=166, Q3=228) days, 52±57 (median=31, Q1=12, Q3=85) days and 23±26 (median=12, Q1=6, Q3=27) days, respectively. Sixty per cent of the MCL injuries affected the dominant leg. There was no difference in lay-off time between MCL injuries to the dominant leg compared with the non-dominant leg (median=19, Q1=7, Q3=33 vs median=15, Q1=8, Q3=28, p=0.39).
Circumstances and mechanism
Almost 70% (182/264) of all MCL injuries were due to contact with another player or an object, which could be compared with 37% (21/57) among ACL injuries, 70% (7/10) among PCL injuries and 57% (24/42) among LCL injuries. There was a significant association between the distribution of contact/non-contact injuries and the type of knee ligament injury (p<0.001). The most common mechanisms of contact injuries were collision (26%), being tackled (25%) and being blocked (15%). Thirty-eight per cent of the non-contact injuries, representing a small fraction of the data, were the consequence of twisting/turning. No difference in lay-off times between contact (median=16, Q1=8, Q3=29) and non-contact (median=16, Q1=7, Q3=30) injuries was detected (p=0.74).
Foul play
A higher percentage of foul play injuries were found in MCL contact injuries compared with other contact injuries during match play (24% vs 18%, p=0.015).
Variation of injury risk during matches
Approximately 43% (53/123) of the MCL match injuries occurred during the last 15 min of the first or second half of the game (see figure 2). This finding is significantly higher than would be expected (1/3) of the injuries in each quarter of an hour (p=0.022). No difference was found in the quarterly distribution between the first and second halves (p=0.76).
Distribution of medial collateral ligament injuries during 15 min periods of match play in professional football.
Reinjuries
Eleven per cent of all MCL injuries were classified as reinjuries, which is approximately the same as the reported recurrence rate for other injuries in the study cohort (12%). There were no differences in lay-off time between index injuries (median=18, Q1=8, Q3=32) and reinjuries (median=13, Q1=7, Q3=25; p=0.20).
Playing position
A significantly higher injury rate was found among outfielders compared with goalkeepers (0.33 vs 0.17/1 000 h, RR 2.1, 95% CI 1.3 to 3.2, p=0.001).
Discussion
The principal finding in this study was that MCL injury causes an average lay-off from professional football for slightly more than 3 weeks. Another important finding was that MCL injuries were more frequently caused by contact than non-contact situations, but, interestingly, lay-off times do not differ significantly between these two mechanisms. Also, the MCL injury rate decreased significantly over the 11-year study period.
Injury epidemiology
A professional football team with a typical 25-player squad can expect around two MCL injuries every season. In spite of a somewhat fluctuating rate over the seasons, the MCL injury rate has decreased slightly over time. It is possible to speculate about whether this is a consequence of (1) less contact between players during matches and training nowadays, (2) because of the development of football into a more technically skilled game or (3) the referees being stricter and more observant of dangerous contact situations. Another plausible explanation is that radiological imaging is used more frequently nowadays compared with the beginning of the study period; there may have been clinical ‘overdiagnosis’ historically. There is, however, no study showing that the use of radiological imaging reduces injury rates, shortens lay-off times or reduces injury recurrence.
Injury circumstances
Almost 70% of all MCL injuries were due to contact with another player or object. Interestingly, the proportion of contact-related MCL injuries is thus of approximately the same percentage as that of non-contact ACL injuries reported in this study (63%) and in another similar study of elite football.12 It therefore appears that the typical injury mechanisms differ between MCL and ACL injuries, and it is reasonable to believe that many MCL injuries are the result of a collision or tackle with physical impact on the outside of the lower part of the thigh or the upper part of the lower leg. We speculate that, if the referees are even stricter while judging these situations, the injury rate may decrease further.
Increased injury rate towards the last 15 minutes
A significant number of MCL match injuries occurred during the last 15 minutes of the first or second half of the game. It is possible to speculate that the players are more fatigued towards the last 15 minutes and therefore fail to react and tackle with the same precision and speed in their technique as in the first 30 min of the halves. Another possible explanation is that the players are aware that the halves of the match are about to end and they perform with greater intensity and more contact in order to change the outcome of the game in their favour.
MCL injury severity related to lay-off
The ability to predict lay-off is very important for the injured player, as well as the coaching staff. It appears logical that the severity of the injury is correlated to the subgrouping of MCL injuries, if the aim is to predict injury lay-off. In the present study, 16 days was the median value for the lay-off from football after an MCL injury. Compared with other ligament injuries in the knee, MCL injury has a rather short lay-off, and can therefore, together with LCL injury, be regarded as a fairly mild knee ligament injury. The median lay-off was 194 days for ACL injuries, 31 days for PCL injuries and 12 days for LCL injuries.
Eleven per cent of all MCL injuries were reinjuries, which is in line with other injuries in the cohort (12%). There was no significant difference in the lay-off time specifically for MCL index injury and reinjuries. In previous studies, in professional football, reinjuries have caused longer lay-off than index injuries,2 ,6 but these studies refer to overall injuries.
Methodological considerations
There are some important methodological issues and limitations to consider with this study. First, 75% of the MCL injuries were moderate or severe (ie, >7 lay-off days), and these two groups could thus be argued to be more relevant to football than slight/minimal injuries due to their longer lay-off time and greater recurrence rate. The number of slight/minimal injuries might be underestimated because, even if the player is seeking medical attention and has some time loss, it is most probably difficult for the medical team in many occasions to differentiate between, for example, a contusion on the medial aspect of the distal femur and an actual slight MCL sprain if the player completes a match and is able to train fully within a few days after the event. Second, the injury form did not include mandatory information about the clinical or radiological grading of MCL injury or whether the injury was partial or complete. Additionally, no information was available on the injury form about which part of the MCL was damaged (sMCL, dMCL and POL) or any associated injuries (eg, an MCL injury with a long lay-off could be associated with occult meniscus or cartilage lesions). Third, only the main diagnosis is reported on the injury form, which means that some associated MCL injuries are missed (eg, in an ACL injury with concomitant MCL injury only the ACL injury is typically recorded on the general injury card). Fourth, no systematic information about the treatment was collected.
What are the new findings?
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Medial collateral ligament (MCL) injury rates appear to have decreased during the last decade.
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MCL injury is more commonly caused by contact than non-contact situations and more frequently caused by foul play than non-foul play.
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There were no differences in return to play between index MCL injury and reinjury.
How might it impact on clinical practice?
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The finding that medial collateral ligament injuries were more frequently caused by contact and foul play warrants discussion in the referee sections of the international governing bodies.
Acknowledgments
The authors would like to thank the participating clubs, medical staff and players. Martin Hägglund is acknowledged for help with data collection and Christoffer Thomeé for technical assistance.
References
Footnotes
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Contributors ML, MW, JK and JE were responsible for the study concept and design. JE was responsible for data collection monitoring and co-ordinated the study. HM was responsible for database management and, together with ML, conducted all the analyses that were planned and checked with MW, JK and JE. ML wrote the first draft of the manuscript. All the authors had full access to all data and contributed to the interpretation of the findings and critical revision of the manuscript. JE is the study guarantor.
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Funding This study was supported by grants from UEFA, the Swedish Centre for Research in Sports and Praktikertjänst AB.
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Competing interests JE is the first vice chairman of the UEFA Medical Committee.
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Patient consent Obtained.
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Ethics approval The study design was approved by the UEFA Medical Committee and the UEFA Football Development Division.
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Provenance and peer review Not commissioned; externally reviewed.