Background: Football (soccer) is one of the most popular sports in Norway as well as in the rest of the world, and the injury risk is considerable and high compared to most other team sports. Studies have shown that the majority of football injuries occur in the lower extremities, especially affecting the ankle, knee, hamstrings and groin. Ankle and knee sprains and hamstring and groin strains may leave athletes out of play for several weeks, and in many cases full recovery takes much longer. These common injuries therefore represent a concern.
Aims: The main aims of this thesis were to identify risk factors for the four most common injury types in football, ankle and knee sprains and hamstring and groin strains, screen for players with the highest injury risk and to examine if exercise programs targeting the players with an increased risk of injury could prevent these injuries.
Material and methods: A total player population of 508 players representing 31 teams from Norwegian 1st, 2nd and 3rd division of football for men was used for all studies (Paper I-V). A randomized controlled trial was carried out to prevent injuries (Paper I), while prospective cohort studies (Papers II-V) were carried out focusing on potential ankle (Paper II), knee (Paper III), hamstring (Paper IV) and groin risk factors (Paper V). During the preseason the players filled out a questionnaire and went through testing for potential risk factors for ankle, knee, hamstring and groin injury. Based on information from the questionnaire, the players were divided into a high risk and low risk group. The high risk players were randomized individually into an intervention group, which received equipment and training programs, and a control group (Paper I). The preseason testing made out the foundation for investigating the potential risk factors for injury (Paper II-V).
Main results: During the football season, 505 injuries were reported, sustained by 56% of the players. The total incidence of injuries during the season was 4.7 injuries per 1000 playing hours (95% CI 4.3 to 5.1), 12.1 (95% CI 10.5 to 13.7) for match injuries and 2.7 (95% CI 2.4 to 3.1) for training injuries. The total exposure to match play and training was 108 111 player hours. There were 56 acute ankle injuries affecting 46 legs (43 players), 61 acute knee injuries affecting 57 legs (53 players), 76 hamstring injuries affecting 65 legs (61 players) and 61 groin injuries affecting 55 legs (51 players) respectively. There was a significantly lower injury risk in the group of players with no previous injuries and normal function scores compared to the other players. However, the introduction of individual specific preventive training programs did not affect the injury risk in this intervention, most likely due to low compliance with the training programs prescribed (Paper I). In the multivariate analyses, number of previous acute ankle injuries (Paper II), previous acute hamstring injury (yes/no) (Paper IV) and previous acute groin injury and weak adductor muscles as determined clinically (Paper V) proved to be significant predictor of new injuries. Regarding risk factors for knee injuries, none of the tested factors were associated with an increased injury risk (Paper III) in the final multivariate analysis.
Conclusions: Risk factors for the most common injuries in football were mapped in the present study. This is an important step towards prevention of injuries, which make out a considerable concern in sports in general and football in particular. High risk players were successfully identified through simple self-report screening. Due to a low compliance with the training programs prescribed, it is impossible to tell if the preventive measures tested in the present study are useful. Preventive interventions must therefore be tested in future randomized controlled trials.
List of papers. Papers I-IV are removed from the thesis due to copyright restrictions.
Paper I Engebretsen AH, Myklebust G, Holme I, Engebretsen L, Bahr R.: Prevention of injuries among male football players – a prospective, randomized intervention study targeting players with previous injuries or reduced function. The American Journal of Sports Medicine 2008; 36(6):1052-9. doi:10.1177/0363546508314432
Paper II Engebretsen AH, Myklebust G, Holme I, Engebretsen L, Bahr R.: Intrinsic risk factors for acute ankle injuries among male football players – a prospective cohort study. Scandinavian Journal of Medicine & Science in Sports 2010; 20(3):403–410. [Epub ahead of print] 2009 Jun 23. doi:10.1111/j.1600-0838.2009.00971.x
Paper III Engebretsen AH, Myklebust G, Holme I, Engebretsen L, Bahr R. Risk factors for acute knee injuries among male football players – a prospective cohort study. Scandinavian Journal of Medicine & Science in Sports [Epub ahead of print] 2010 Mar 11. doi:10.1111/j.1600-0838.2010.01095.x
Paper IV Engebretsen AH, Myklebust G, Holme I, Engebretsen L, Bahr R. Risk factors for hamstring injuries among male football players – a prospective cohort study. The American Journal of Sports Medicine 2010; 3(6):1147-1153 [Epub ahead of print] 2010 Mar 24. doi:10.1177/0363546509358381
Paper V Engebretsen AH, Myklebust G, Holme I, Engebretsen L, Bahr R.: Risk factors for groin injuries among male football players – a prospective cohort study. Submitted version. The American Journal of Sports Medicine 2010; 38(10):2051-2057 [Epub ahead of print] 2010 August 10. doi:10.1177/0363546510375544