title: Primary and coupled motions of the native knee in response to applied varus and valgus load.
abstract: BACKGROUND
  Knowledge of the complex kinematics of the native knee is a prerequisite for a successful reconstructive procedure. The aim of this study is to describe the primary and coupled motions of the native knee throughout the range of knee flexion, in response to applied varus and valgus loads.
  
  
  METHODS
  Twenty fresh-frozen cadaver knees were affixed to a six degree of freedom robotic arm with a universal force-moment sensor, and loaded with a 4Nm moment in varus and valgus at 0, 15, 30, 45, and 90° of knee flexion. The resulting tibiofemoral angulation, displacement, and rotation were recorded.
  
  
  RESULTS
  For each parameter investigated, the knee joint demonstrated more laxity at higher flexion angles. Varus angulation increased progressively from zero (2.0° varus) to 90 (5.2° varus) degrees of knee flexion (p<0.001). Valgus angulation also increased progressively, from zero (1.5° valgus) to 90 (3.9° valgus) degrees of knee flexion (p<0.001). At all flexion angles, the magnitude of tibiofemoral angle deviation was larger with varus than with valgus loading (p<0.05).
  
  
  CONCLUSIONS
  We conclude that the native knee exhibits small increases in coronal plane laxity as the flexion angle increases, and that the knee has generally more laxity under varus load than with valgus load throughout the Range of Motion (ROM). Larger differences in laxity of more than 2 to 3°, or peak laxity specifically during the range of mid-flexion, were not found in our cadaver model and are not likely to represent normal coronal plane kinematics.
  
  
  METHODS
  Level V, biomechanical cadaveric study.
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States. Electronic address: gladnickb@hss.edu.
authors.forename: Brian P
authors.initials: BP
authors.lastname: Gladnick
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: James
authors.initials: J
authors.lastname: Boorman-Padgett
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: Kyle
authors.initials: K
authors.lastname: Stone
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: Robert N
authors.initials: RN
authors.lastname: Kent
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Cross
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: David J
authors.initials: DJ
authors.lastname: Mayman
authors.affiliation: Department of Orthopaedic Surgery, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pearle
authors.affiliation: Department of Biomechanics, Hospital for Special Surgery, 535 E. 70th Street, New York, NY 10021, United States.
authors.forename: Carl W
authors.initials: CW
authors.lastname: Imhauser
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D016474:Weight-Bearing / Q000502:physiology*; D055815:Young Adult
keywords: Coronal plane stability; Knee kinematics; Mid-flexion laxity; Range of motion