title: High knee abduction moments are common risk factors for patellofemoral pain (PFP) and anterior cruciate ligament (ACL) injury in girls: is PFP itself a predictor for subsequent ACL injury?
abstract: BACKGROUND
  Identifying risk factors for knee pain and anterior cruciate ligament (ACL) injury can be an important step in the injury prevention cycle.
  
  
  OBJECTIVE
  We evaluated two unique prospective cohorts with similar populations and methodologies to compare the incidence rates and risk factors associated with patellofemoral pain (PFP) and ACL injury.
  
  
  METHODS
  The 'PFP cohort' consisted of 240 middle and high school female athletes. They were evaluated by a physician and underwent anthropometric assessment, strength testing and three-dimensional landing biomechanical analyses prior to their basketball season. 145 of these athletes met inclusion for surveillance of incident (new) PFP by certified athletic trainers during their competitive season. The 'ACL cohort' included 205 high school female volleyball, soccer and basketball athletes who underwent the same anthropometric, strength and biomechanical assessment prior to their competitive season and were subsequently followed up for incidence of ACL injury. A one-way analysis of variance was used to evaluate potential group (incident PFP vs ACL injured) differences in anthropometrics, strength and landing biomechanics. Knee abduction moment (KAM) cut-scores that provided the maximal sensitivity and specificity for prediction of PFP or ACL injury risk were also compared between the cohorts.
  
  
  RESULTS
  KAM during landing above 15.4 Nm was associated with a 6.8% risk to develop PFP compared to a 2.9% risk if below the PFP risk threshold in our sample. Likewise, a KAM above 25.3 Nm was associated with a 6.8% risk for subsequent ACL injury compared to a 0.4% risk if below the established ACL risk threshold. The ACL-injured athletes initiated landing with a greater knee abduction angle and a reduced hamstrings-to-quadriceps strength ratio relative to the incident PFP group. Also, when comparing across cohorts, the athletes who suffered ACL injury also had lower hamstring/quadriceps ratio than the players in the PFP sample (p<0.05).
  
  
  CONCLUSIONS
  In adolescent girls aged 13.3 years, >15 Nm of knee abduction load during landing is associated with greater likelihood of developing PFP. Also, in girls aged 16.1 years who land with >25 Nm of knee abduction load during landing are at increased risk for both PFP and ACL injury.
authors.affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Departments of Pediatrics and Orthopaedic Surgery, University of Cincinnati, Cincinnati, Ohio, USA The Sports Health and Performance Institute, OSU Sports Medicine, Ohio State University Medical Center, Columbus, Ohio, USA The Micheli Center for Sports Injury Prevention, Waltham, Massachusetts, USA.
authors.forename: Gregory D
authors.initials: GD
authors.lastname: Myer
authors.affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Departments of Pediatrics and Orthopaedic Surgery, University of Cincinnati, Cincinnati, Ohio, USA Department of Physical Therapy, School of Health Sciences, High Point University, High Point, North Carolina, USA.
authors.forename: Kevin R
authors.initials: KR
authors.lastname: Ford
authors.affiliation: The Sports Health and Performance Institute, OSU Sports Medicine, Ohio State University Medical Center, Columbus, Ohio, USA.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Di Stasi
authors.affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA.
authors.forename: Kim D Barber
authors.initials: KD
authors.lastname: Foss
authors.affiliation: The Micheli Center for Sports Injury Prevention, Waltham, Massachusetts, USA Division of Sports Medicine, Department of Orthopaedics, Boston Children's Hospital, Boston, Massachusetts, USA Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Lyle J
authors.initials: LJ
authors.lastname: Micheli
authors.affiliation: Division of Sports Medicine, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA Departments of Pediatrics and Orthopaedic Surgery, University of Cincinnati, Cincinnati, Ohio, USA The Sports Health and Performance Institute, OSU Sports Medicine, Ohio State University Medical Center, Columbus, Ohio, USA The Micheli Center for Sports Injury Prevention, Waltham, Massachusetts, USA Departments of Physiology and Cell Biology, Family Medicine and of Orthopaedic Surgery and Biomedical Engineering, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Hewett
mesh_terms: D000293:Adolescent; D000070598:Anterior Cruciate Ligament Injuries; D001265:Athletic Injuries / Q000209:etiology / Q000503:physiopathology; D001490:Basketball / Q000293:injuries*; D001696:Biomechanical Phenomena / Q000502:physiology; D005260:Female; D006801:Humans; D007718:Knee Injuries / Q000209:etiology* / Q000503:physiopathology; D007719:Knee Joint / Q000502:physiology*; D009068:Movement / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology; D046788:Patellofemoral Pain Syndrome / Q000209:etiology*; D011446:Prospective Studies; D012307:Risk Factors
keywords: ACL; Biomechanics; Children's injuries; Epidemiology; Knee injuries