title: Jump-landing biomechanics and knee-laxity change across the menstrual cycle in women with anterior cruciate ligament reconstruction.
abstract: BACKGROUND
  Of the individuals able to return to sport participation after an anterior cruciate ligament(ACL) injury, up to 25% will experience a second ACL injury. This population may be more sensitive to hormonal fluctuations, which may explain this high rate of second injury.
  
  
  OBJECTIVE
  To examine changes in 3-dimensional hip and knee kinematics and kinetics during a jump landing and to examine knee laxity across the menstrual cycle in women with histories of unilateral noncontact ACL injury.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Laboratory.
  
  
  METHODS
  A total of 20 women (age = 19.6 ± 1.3 years, height = 168.6 ± 5.3 cm, mass = 66.2 ± 9.1 kg) with unilateral, noncontact ACL injuries.
  
  
  METHODS
  Participants completed a jump-landing task and knee-laxity assessment 3 to 5 days after the onset of menses and within 3 days of a positive ovulation test.
  
  
  METHODS
  Kinematics in the uninjured limb at initial contact with the ground during a jump landing, peak kinematics and kinetics during the loading phase of landing, anterior knee laxity via the KT-1000, peak vertical ground reaction force, and blood hormone concentrations (estradiol-β-17, progesterone, free testosterone).
  
  
  RESULTS
  At ovulation, estradiol-β-17 (t = -2.9, P = .009), progesterone (t = -3.4, P = .003), and anterior knee laxity (t = -2.3, P = .03) increased, and participants presented with greater knee-valgus moment (Z = -2.6, P = .01) and femoral internal rotation (t = -2.1, P = .047). However, during the menses test session, participants landed harder (greater peak vertical ground reaction force; t = 2.2, P = .04), with the tibia internally rotated at initial contact (t = 2.8, P = .01) and greater hip internal-rotation moment (Z = -2.4, P = .02). No other changes were observed across the menstrual cycle.
  
  
  CONCLUSIONS
  Knee and hip mechanics in both phases of the menstrual cycle represented a greater potential risk of ACL loading. Observed changes in landing mechanics may explain why the risk of second ACL injury is elevated in this population.
authors.affiliation: Department of Kinesiology, Department of Orthopedics and Rehabilitation, University of Wisconsin-Madison.
authors.forename: David R
authors.initials: DR
authors.lastname: Bell
authors.forename: J Troy
authors.initials: JT
authors.lastname: Blackburn
authors.forename: Anthony C
authors.initials: AC
authors.lastname: Hackney
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Marshall
authors.forename: Anthony I
authors.initials: AI
authors.lastname: Beutler
authors.forename: Darin A
authors.initials: DA
authors.lastname: Padua
mesh_terms: D000328:Adult; D016118:Anterior Cruciate Ligament / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D059549:Anterior Cruciate Ligament Reconstruction; D001696:Biomechanical Phenomena; D005260:Female; D006615:Hip / Q000502:physiology; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007718:Knee Injuries / Q000503:physiopathology* / Q000601:surgery*; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008597:Menstrual Cycle / Q000502:physiology*; D059385:Plyometric Exercise; D012399:Rotation; D012737:Sex Factors