title: Knee joint biomechanics in open-kinetic-chain flexion exercises.
abstract: BACKGROUND
  Different rehabilitation exercises such as open-kinetic-chain flexion and extension exercises are currently employed in non-operative and post-operative managements of joint disorders. The challenge is to strengthen the muscles and to restore the near-normal function of the joint while protecting its components (e.g., the reconstructed ligament) from excessive stresses.
  
  
  METHODS
  Using a validated 3D nonlinear finite element model, the detailed biomechanics of the entire joint in open-kinetic-chain flexion exercises are investigated at 0 degrees, 30 degrees, 60 degrees and 90 degrees joint angles. Two loading cases are simulated; one with only the weight of the leg and the foot while the second considers also a moderate resistant force of 30 N acting at the ankle perpendicular to the tibia.
  
  
  RESULTS
  The addition of 30 N resistant force substantially increased the required hamstrings forces, forces in posterior cruciate and lateral collateral ligaments and joint contact forces/areas/stresses.
  
  
  CONCLUSIONS
  At post-anterior cruciate ligament reconstruction or injury period, the exercise could safely be employed to strengthen the hamstrings muscles without a risk to the anterior cruciate ligament. In contrast, at post-posterior cruciate/lateral collateral ligaments reconstructions or injuries, the open-kinetic-chain flexion exercise should be avoided under moderate to large flexion angles and resistant forces.
authors.affiliation: Laboratory of Biomechanical Orthopedics, Ecole Polytechnique Fédérale de Lausanne, Switzerland.
authors.forename: W
authors.initials: W
authors.lastname: Mesfar
authors.forename: A
authors.initials: A
authors.lastname: Shirazi-Adl
mesh_terms: D000842:Ankle / Q000502:physiology; D016118:Anterior Cruciate Ligament / Q000502:physiology; D003198:Computer Simulation; D015444:Exercise / Q000502:physiology*; D020342:Finite Element Analysis; D006801:Humans; D007719:Knee Joint / Q000502:physiology*; D017844:Lateral Ligament, Ankle / Q000502:physiology; D007866:Leg / Q000502:physiology; D008954:Models, Biological; D009119:Muscle Contraction; D053580:Muscle Strength; D018482:Muscle, Skeletal; D016119:Posterior Cruciate Ligament / Q000502:physiology; D013977:Tibia / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology*