Martin Hägglund

Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries

Variations in definitions and methodologies have created differences in the results and conclusions obtained from studies of football (soccer) injuries, making interstudy comparisons difficult. Therefore an Injury Consensus Group was established under the auspices of Fédération Internationale de Football Association Medical Assessment and Research Centre. A nominal group consensus model approach was used. A working document on definitions, methodology, and implementation was discussed by the group. Iterative draft statements were prepared and circulated to members of the group for comment before the final consensus statement was produced. Definitions of injury, recurrent injury, severity, and training and match exposures in football together with criteria for classifying injuries in terms of location, type, diagnosis, and causation are proposed. Proforma for recording players’ baseline information, injuries, and training and match exposures are presented. Recommendations are made on how the incidence of match and training injuries should be reported and a checklist of issues and information that should be included in published reports of studies of football injuries is presented.

Injury incidence and injury patterns in professional football: the UEFA injury study

Objective To study the injury characteristics in professional football and to follow the variation of injury incidence during a match, during a season and over consecutive seasons. Design Prospective cohort study where teams were followed for seven consecutive seasons. Team medical staff recorded individual player exposure and time-loss injuries from 2001 to 2008. Setting European professional mens football. Participants The first team squads of 23 teams selected by the Union of European Football Associations as belonging to the 50 best European teams. Main outcome measurement Injury incidence. Results 4483 injuries occurred during 566 000 h of exposure, giving an injury incidence of 8.0 injuries/1000 h. The injury incidence during matches was higher than in training (27.5 vs 4.1, p<0.0001). A player sustained on average 2.0 injuries per season, and a team with typically 25 players can thus expect about 50 injuries each season. The single most common injury subtype was thigh strain, representing 17% of all injuries. Re-injuries constituted 12% of all injuries, and they caused longer absences than non re-injuries (24 vs 18 days, p<0.0001). The incidence of match injuries showed an increasing injury tendency over time in both the first and second halves (p<0.0001). Traumatic injuries and hamstring strains were more frequent during the competitive season, while overuse injuries were common during the preseason. Training and match injury incidences were stable over the period with no significant differences between seasons. Conclusions The training and match injury incidences were stable over seven seasons. The risk of injury increased with time in each half of matches.

Epidemiology of Muscle Injuries in Professional Football (Soccer)

Background: Muscle injuries constitute a large percentage of all injuries in football. Purpose: To investigate the incidence and nature of muscle injuries in male professional footballers. Study Design: Cohort study; Level of evidence, 2. Methods: Fifty-one football teams, comprising 2299 players, were followed prospectively during the years 2001 to 2009. Team medical staff recorded individual player exposure and time-loss injuries. The first-team squads of 24 clubs selected by the Union of European Football Associations as belonging to the best European teams, 15 teams of the Swedish First League, and another 15 European teams playing their home matches on artificial turf pitches were included. A muscle injury was defined as “a traumatic distraction or overuse injury to the muscle leading to a player being unable to fully participate in training or match play.” Results: In total, 2908 muscle injuries were registered. On average, a player sustained 0.6 muscle injuries per season. A squad of 25 players can thus expect about 15 muscle injuries per season. Muscle injuries constituted 31% of all injuries and caused 27% of the total injury absence. Ninety-two percent of all muscle injuries affected the 4 major muscle groups of the lower limbs: hamstrings (37%), adductors (23%), quadriceps (19%), and calf muscles (13%). Sixteen percent of the muscle injuries were reinjuries. These reinjuries caused significantly longer absences than did index injuries. The incidence of muscle injury increased with age. When separated into different muscle groups, however, an increased incidence with age was found only for calf muscle injuries and not for hamstring, quadriceps, or hip/groin strains. Conclusion: Muscle injuries are a substantial problem for players and their clubs. They constitute almost one third of all time-loss injuries in men’s professional football, and 92% of all injuries affect the 4 big muscle groups in the lower limbs.

Previous injury as a risk factor for injury in elite football - a prospective study over two consecutive seasons

Background: Previous injury is often proposed to be a risk factor for football injury, but most studies rely on players reporting their own medical history and are thus potentially subject to recall bias. Little is known about the natural variation in injury pattern between seasons. Objectives: To study whether prospectively recorded injuries during one season are associated with injuries sustained during the following season, and to compare injury risk and injury pattern between consecutive seasons. Methods: The medical staffs of 12 elite Swedish male football teams prospectively recorded individual exposure and time loss injuries over two full consecutive seasons (2001 and 2002). A multivariate model was used to determine the relation between previous injury, anthropometric data, and the risk of injury. Results: The training and match injury incidences were similar between seasons (5.1 v 5.3 injuries/1000 training hours and 25.9 v 22.7/1000 match hours), but analysis of injury severity and injury patterns showed variations between seasons. Players who were injured in the 2001 season were at greater risk of any injury in the following season compared with non-injured players (hazard ratio 2.7; 95% confidence interval 1.7 to 4.3, p<0.0001). Players with a previous hamstring injury, groin injury, and knee joint trauma were two to three times more likely to suffer an identical injury in the following season, whereas no such relation was found for ankle sprain. Age was not associated with an increased injury risk. Conclusions: This study confirmed previous results showing that previous injury is an important risk factor for football injury. Overall injury incidences were similar between consecutive seasons, indicating that an injury surveillance study covering one full season can provide a reasonable overview of the injury problem among elite football players in a specific environment. However, a prolonged study period is recommended for analyses of specific injury patterns.

Methods for epidemiological study of injuries to professional football players: developing the UEFA model

A problem with epidemiological studies of football injuries is the inconsistent manner in which injury is defined and data are collected. Projects have been initiated to study the incidence and causes of injury in football, but there is no uniformly accepted reporting system. In this report, some common pitfalls encountered in the recording of injury are addressed, and practical guidelines for epidemiological studies are provided. An injury reporting system developed for the UEFA Football Safety Project for studies on professional footballers is used as a starting point for a general discussion on injury registration and compared with other existing reporting systems. The recording definition of injury may vary between studies depending on its purpose. A time loss injury definition is practical for all playing levels, and, as a minimum, results on time loss injuries should therefore always be reported separately to allow direct comparisons between studies. There is a need to agree on a uniform sports injury classification system with corresponding diagnostic criteria, as well as standardised return to play criteria after injury.

UEFA Champions League study: a prospective study of injuries in professional football during the 2001–2002 season

Background: No previous study on adult football involving several different countries has investigated the incidence and pattern of injuries at the highest club competitive level. Objective: To investigate the risk exposure, risk of injury, and injury pattern of footballers involved in UEFA Champions League and international matches during a full football season. Method: Eleven top clubs (266 players) in five European countries were followed prospectively throughout the season of 2001–2002. Time-lost injuries and individual exposure times were recorded during all club and national team training sessions and matches. Results: A total of 658 injuries were recorded. The mean (SD) injury incidence was 9.4 (3.2) injuries per 1000 hours (30.5 (11.0) injuries per 1000 match hours and 5.8 (2.1) injuries per 1000 training hours). The risk of match injury was significantly higher in the English and Dutch teams than in the teams from France, Italy, and Spain (41.8 (3.3) v 24.0 (7.9) injuries per 1000 hours; p  =  0.008). Major injuries (absence >4 weeks) constituted 15% of all injuries, and the risk of major injury was also significantly higher among the English and Dutch teams (p  =  0.04). National team players had a higher match exposure, with a tendency towards a lower training injury incidence than the rest of the players (p  =  0.051). Thigh strain was the most common injury (16%), with posterior strains being significantly more common than anterior ones (67 v 36; p<0.0001). Conclusions: The risk of injury in European professional football is high. The most common injury is the thigh strain typically involving the hamstrings. The results suggest that regional differences may influence injury epidemiology and traumatology, but the factors involved are unclear. National team players have a higher match exposure, but no higher risk of injury than other top level players.

Prevention of acute knee injuries in adolescent female football players: cluster randomised controlled trial

Objective To evaluate the effectiveness of neuromuscular training in reducing the rate of acute knee injury in adolescent female football players. Design Stratified cluster randomised controlled trial with clubs as the unit of randomisation. Setting 230 Swedish football clubs (121 in the intervention group, 109 in the control group) were followed for one season (2009, seven months). Participants 4564 players aged 12-17 years (2479 in the intervention group, 2085 in the control group) completed the study. Intervention 15 minute neuromuscular warm-up programme (targeting core stability, balance, and proper knee alignment) to be carried out twice a week throughout the season. Main outcome measures The primary outcome was rate of anterior cruciate ligament injury; secondary outcomes were rates of severe knee injury (>4 weeks’ absence) and any acute knee injury. Results Seven players (0.28%) in the intervention group, and 14 (0.67%) in the control group had an anterior cruciate ligament injury. By Cox regression analysis according to intention to treat, a 64% reduction in the rate of anterior cruciate ligament injury was seen in the intervention group (rate ratio 0.36, 95% confidence interval 0.15 to 0.85). The absolute rate difference was −0.07 (95% confidence interval −0.13 to 0.001) per 1000 playing hours in favour of the intervention group. No significant rate reductions were seen for secondary outcomes. Conclusions A neuromuscular warm-up programme significantly reduced the rate of anterior cruciate ligament injury in adolescent female football players. However, the absolute rate difference did not reach statistical significance, possibly owing to the small number of events. Trial registration Clinical trials NCT00894595.

Risk of injury in elite football played on artificial turf versus natural grass: a prospective two-cohort study

Objective: To compare injury risk in elite football played on artificial turf compared with natural grass. Design: Prospective two-cohort study. Setting: Male European elite football leagues. Participants: 290 players from 10 elite European clubs that had installed third-generation artificial turf surfaces in 2003–4, and 202 players from the Swedish Premier League acting as a control group. Main outcome measure: Injury incidence. Results: The incidence of injury during training and match play did not differ between surfaces for the teams in the artificial turf cohort: 2.42 v 2.94 injuries/1000 training hours and 19.60 v 21.48 injuries/1000 match hours for artificial turf and grass respectively. The risk of ankle sprain was increased in matches on artificial turf compared with grass (4.83 v 2.66 injuries/1000 match hours; rate ratio 1.81, 95% confidence interval 1.00 to 3.28). No difference in injury severity was seen between surfaces. Compared with the control cohort who played home games on natural grass, teams in the artificial turf cohort had a lower injury incidence during match play (15.26 v 23.08 injuries/1000 match hours; rate ratio 0.66, 95% confidence interval 0.48 to 0.91). Conclusions: No evidence of a greater risk of injury was found when football was played on artificial turf compared with natural grass. The higher incidence of ankle sprain on artificial turf warrants further attention, although this result should be interpreted with caution as the number of ankle sprains was low.

Hamstring muscle injuries in professional football: the correlation of MRI findings with return to play

Background Hamstring injury is the single most common injury in professional football. MRI is commonly used to confirm the diagnosis and provide a prognosis of lay-off time. Objective To evaluate the use of MRI as a prognostic tool for lay-off after hamstring injuries in professional football players and to study the association between MRI findings and injury circumstances. Methods Prospective cohort study where 23 European professional teams, were followed between 2007 and 2011. Team medical staffs recorded individual player exposure and time-loss injuries. Radiological grading was performed using a modified Peetrons classification into four grades where grades 2 and 3 represent fibre disruption. Results In total, 516 hamstring injuries occurred and 58% of these were examined by MRI. Thirteen per cent were grade 0 injuries, 57% grade 1, 27% of grade 2 and 3% of grade 3. Grade 0 and 1 injuries accounted for 56% (2141/3830 days) of the total lay-off. The lay-off time differed between all four radiological grades of injury (8±3, 17±10, 22±11 and 73±60 days, p<0.0001). Eighty-three per cent of injuries affected the biceps femoris while 11% and 5% occurred to the semimembranosus and semitendinosus, respectively. Re-injuries (N=34/207) constituted 16% of injuries. All re-injuries occurred to the biceps femoris. Conclusion MRI can be helpful in verifying the diagnosis of a hamstring injury and to prognosticate lay-off time. Radiological grading is associated with lay-off times after injury. Seventy per cent of hamstring injuries seen in professional football are of radiological grade 0 or 1, meaning no signs of fibre disruption on MRI, but still cause the majority of absence days.

Consensus statement on injury definitions and data collection procedures in studies of football (soccer) injuries.

Variations in definitions and methodologies have created differences in the results and conclusions obtained from studies of football injuries; this has made inter‐study comparisons difficult.