title: Injury recurrence is lower at the highest professional football level than at national and amateur levels: does sports medicine and sports physiotherapy deliver?
abstract: BACKGROUND
  Previous injury is a well-documented risk factor for football injury. The time trends and patterns of recurrent injuries at different playing levels are not clear.
  
  
  OBJECTIVE
  To compare recurrent injury proportions, incidences and patterns between different football playing levels, and to study time trends in recurrent injury incidence.
  
  
  METHODS
  Time-loss injuries were collected from injury surveillance of 43 top-level European professional teams (240 team-seasons), 19 Swedish premier division teams (82 team-seasons) and 10 Swedish amateur teams (10 team-seasons). Recurrent injury was defined as an injury of the same type and at the same site as an index injury within the preceding year, with injury <2 months defined as an early recurrence, and >2 months as a delayed recurrence. Seasonal trend for recurrent injury incidence, expressed as the average annual percentage of change, was analysed using linear regression.
  
  
  RESULTS
  13 050 injuries were included, 2449 (18.8%) being recurrent injuries, with 1944 early (14.9%) and 505 delayed recurrences (3.9%). Recurrence proportions were highest in the second half of the competitive season for all cohorts. Recurrence proportions differed between playing levels, with 35.1% in the amateur cohort, 25.0% in the Swedish elite cohort and 16.6% in the European cohort (χ(2) overall effect, p<0.001). A decreasing trend was observed in recurrent injury incidence in the European cohort, a -2.9% average annual change over the 14-year study period (95% CI -5.4% to -0.4%, p=0.026). Similarly, a decreasing tendency was also seen in the Swedish premier division.
  
  
  CONCLUSIONS
  Recurrence proportions showed an inverse relationship with playing level, and recurrent injury incidence has decreased over the past decade.
authors.affiliation: Division of Physiotherapy, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden Football Research Group, Linköping, Sweden.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-6883-1471
authors.initials: M
authors.lastname: Hägglund
authors.affiliation: Football Research Group, Linköping, Sweden Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Markus
authors.initials: M
authors.lastname: Waldén
authors.affiliation: Football Research Group, Linköping, Sweden Division of Community Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
authors.forename: Jan
authors.initials: J
authors.lastname: Ekstrand
mesh_terms: D001265:Athletic Injuries / Q000453:epidemiology / Q000534:rehabilitation; D005060:Europe / Q000453:epidemiology; D000070633:Hamstring Muscles / Q000293:injuries; D006801:Humans; D015994:Incidence; D007718:Knee Injuries / Q000453:epidemiology; D008297:Male; D026741:Physical Therapy Modalities / Q000706:statistics & numerical data; D012008:Recurrence; D012916:Soccer / Q000293:injuries*; D013178:Sports Medicine; D013180:Sprains and Strains / Q000453:epidemiology; D013708:Tendon Injuries / Q000453:epidemiology; D013997:Time Factors
keywords: Cohort study; Football; Injury; Recurrent; Soccer