title: Effects of applied quadriceps and hamstrings muscle loads on forces in the anterior and posterior cruciate ligaments.
abstract: BACKGROUND
  Muscle contraction can subject healing knee ligament grafts to high loads.
  
  
  OBJECTIVE
  To directly measure the effects of quadriceps and hamstrings muscle loads on forces in the anterior cruciate ligaments and posterior cruciate ligaments.
  
  
  METHODS
  Controlled laboratory study.
  
  
  METHODS
  Thirteen cadaveric knee specimens had load cells installed to record resultant forces in both anterior and posterior cruciate ligaments under 5 loading conditions. Cruciate force measurements were repeated with a 100-N load applied to the quadriceps tendon and again with a combined 50-N biceps load and 50-N semimembranosus-semitendinosus load.
  
  
  RESULTS
  Applied quadriceps loads resulted in mean changes in anterior cruciate ligament and posterior cruciate ligament forces that were less than 20 N for all loading conditions. Hamstrings load significantly increased mean posterior cruciate ligament force between 30 degrees and 105 degrees of flexion with 100 N of applied posterior tibial force.
  
  
  CONCLUSIONS
  At the muscle force levels used in this study, the hamstrings were more effective than the quadriceps in altering cruciate force levels, especially near 90 degrees of flexion, where they have an excellent mechanical advantage for controlling anterior-posterior tibial translation.
  
  
  CONCLUSIONS
  Isolated hamstrings activity generally had little or no effect on anterior cruciate ligament forces but significantly increased forces in the posterior cruciate ligament beyond approximately 30 degrees of flexion.
authors.affiliation: Department of Orthopaedic Surgery, David Geffen School of Medicine at UCLA, University of California Los Angeles, CHS, Box 956902, Los Angeles, CA 90095-6902.
authors.forename: Keith L
authors.initials: KL
authors.lastname: Markolf
authors.forename: Geoffery
authors.initials: G
authors.lastname: O'Neill
authors.forename: Steven R
authors.initials: SR
authors.lastname: Jackson
authors.forename: David R
authors.initials: DR
authors.lastname: McAllister
mesh_terms: D000328:Adult; D000368:Aged; D016118:Anterior Cruciate Ligament / Q000502:physiology*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D016119:Posterior Cruciate Ligament / Q000502:physiology*; D016059:Range of Motion, Articular / Q000502:physiology; D013710:Tendons / Q000502:physiology*; D019415:Torque; D016474:Weight-Bearing / Q000502:physiology*