title: Restriction in hip internal rotation is associated with an increased risk of ACL injury.
abstract: OBJECTIVE
  Evidence suggests that femoroacetabular impingement (FAI) in athletes may increase the risk of anterior cruciate ligament (ACL) injury. This study correlates ACL injury with hip range of motion in a consecutive series of elite, contact athletes and tests the hypothesis that a restriction in the available hip axial rotation in a dynamic in silico model of a simulated pivot landing would increase ACL strain and the risk of ACL rupture.
  
  
  METHODS
  Three hundred and twenty-four football athletes attending the 2012 NFL National Invitational Camp were examined. Hip range of internal rotation was measured and correlated with a history of ACL injury and surgical repair. An in silico biomechanical model was used to study the effect of FAI on the peak relative ACL strain developed during a simulated pivot landing.
  
  
  RESULTS
  The in vivo results demonstrated that a reduction in internal rotation of the left hip was associated with a statistically significant increased odds of ACL injury in the ipsilateral or contralateral knee (OR 0.95, p = 0.0001 and p < 0.0001, respectively). A post-estimation calculation of odds ratio for ACL injury based on deficiency in hip internal rotation demonstrated that a 30-degree reduction in left hip internal rotation was associated with 4.06 and 5.29 times greater odds of ACL injury in the ipsilateral and contralateral limbs, respectively. The in silico model demonstrated that FAI systematically increased the peak ACL strain predicted during the pivot landing.
  
  
  CONCLUSIONS
  FAI may be associated with ACL injury because of the increased resistance to femoral internal axial rotation during a dynamic maneuver such as a pivot landing. This insight may lead to better interventions to prevent ACL injury and improved understanding of ACL reconstruction failure.
  
  
  METHODS
  Cohort study, Level IV.
authors.affiliation: MedSport, Department of Orthopaedic Surgery, University of Michigan, 24 Frank Lloyd Wright Drive, Lobby A, Ann Arbor, MI, 48106, USA. abedi@umich.edu.
authors.forename: Asheesh
authors.initials: A
authors.lastname: Bedi
authors.affiliation: Orthopaedic Surgery, Hospital for Special Surgery, New York, NY, 10021, USA.
authors.forename: Russell F
authors.initials: RF
authors.lastname: Warren
authors.affiliation: MedSport, Department of Orthopaedic Surgery, University of Michigan, 24 Frank Lloyd Wright Drive, Lobby A, Ann Arbor, MI, 48106, USA.
authors.forename: Edward M
authors.initials: EM
authors.lastname: Wojtys
authors.affiliation: Departments of Mechanical and Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: You Keun
authors.initials: YK
authors.lastname: Oh
authors.affiliation: Departments of Mechanical and Biomedical Engineering, University of Michigan, Ann Arbor, MI, 48109, USA.
authors.forename: James A
authors.initials: JA
authors.lastname: Ashton-Miller
authors.affiliation: MedSport, Department of Orthopaedic Surgery, University of Michigan, 24 Frank Lloyd Wright Drive, Lobby A, Ann Arbor, MI, 48106, USA.
authors.forename: Hanna
authors.initials: H
authors.lastname: Oltean
authors.affiliation: Orthopaedic Surgery, Hospital for Special Surgery, New York, NY, 10021, USA.
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Kelly
mesh_terms: D000070598:Anterior Cruciate Ligament Injuries / Q000503:physiopathology*; D001696:Biomechanical Phenomena / Q000502:physiology; D015331:Cohort Studies; D003198:Computer Simulation; D005538:Football / Q000293:injuries; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D008954:Models, Biological; D016059:Range of Motion, Articular / Q000502:physiology*; D012307:Risk Factors; D012399:Rotation
keywords: Anterior cruciate ligament; Femoroacetabular impingement; Football; Hip; In silico model; Knee