title: Comparative study of the femoroacetabular impingement (FAI) prevalence in male semiprofessional and amateur soccer players.
abstract: BACKGROUND
  Femoroacetabular impingement (FAI) represents a novel approach to the mechanical etiology of hip osteoarthritis. The cam-type femoroacetabular impingement deformity occurs frequently in young male athletes. The aim of our study was to evaluate the prevalence of FAI in male semiprofessional soccer players using clinical examination and magnetic resonance imaging (MRI), compared to amateur soccer players. In MRI, the α angle of Nötzli is determined for quantifying FAI.
  
  
  METHODS
  According to power analysis, a total of 22 asymptomatic semiprofessional soccer players with a median of 23.3 years of age (range 18-30 years) and 22 male amateur soccer players with a median of 22.5 years of age (control group, range 18-29 years) underwent an MRI to measure the hip α angle of Nötzli. The α angle of the kicking legs of the semiprofessional group and the amateur group were analyzed. The study group was moreover evaluated by the Hip Outcome Score (HOS) and a clinical hip examination including range of motion (ROM) and impingement tests.
  
  
  RESULTS
  In the semiprofessional group, 19 soccer players had a right kicking leg and 1 soccer player had a left kicking leg. 2 soccer players kicked with two feet. In the semi-professional group, the mean value of the α angle of the kicking leg (57.3 ± 8.2°) was significantly higher than in the amateur group (51.7 ± 4.8°, P = 0.008). In the semi-professional group, 15 (62.5 %) of 24 kicking legs had an increased α angle >55°, while 5 (27.3 %) kicking legs of the amateur group had an α angle >55°. Five semi professional soccer players had findings in clinical examination, whereof 4 had an increased α angle >55°. No participant of the amateur group showed pathological results in the clinical examination (P = 0.0484). Overall, semiprofessional soccer players had a higher proportion of an increased α angle than the amateur group.
  
  
  CONCLUSIONS
  Semiprofessional players have a higher prevalence of an increased α angle in the kicking leg than the amateur group at the same age. The kicking leg is predisposed for FAI.
authors.affiliation: Department of Orthopaedic Sports Surgery, St. Josef-Hospital, Ruhr-University Bochum, Gudrunstr. 56, 44791, Bochum, Germany, m.lahner@klinikum-bochum.de.
authors.forename: Matthias
authors.initials: M
authors.lastname: Lahner
authors.forename: Philipp Alexander
authors.initials: PA
authors.lastname: Walter
authors.forename: Christoph
authors.initials: C
authors.lastname: von Schulze Pellengahr
authors.forename: Marco
authors.initials: M
authors.lastname: Hagen
authors.forename: Lars Victor
authors.initials: LV
authors.lastname: von Engelhardt
authors.forename: Carsten
authors.initials: C
authors.lastname: Lukas
mesh_terms: D000293:Adolescent; D000328:Adult; D056352:Athletes; D057925:Femoracetabular Impingement / Q000150:complications / Q000453:epidemiology* / Q000503:physiopathology; D006621:Hip Joint / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015207:Osteoarthritis, Hip / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D015995:Prevalence; D016059:Range of Motion, Articular; D012916:Soccer / Q000502:physiology; D055815:Young Adult