title: Anterior positioning of tibia during motion after anterior cruciate ligament injury.
abstract: OBJECTIVE
  The purpose of this study was to describe the sagittal tibial translation and EMG activity of muscles v. medialis and lateralis, gastrocnemius, and hamstrings, during common locomotion, in patients with an anterior cruciate ligament deficiency (ACL-def) and uninjured controls.
  
  
  METHODS
  In 12 ACL-def patients and 17 controls, sagittal tibial translation was registered with the CA-4000 electrogoniometer during level walking, cutting, and stair walking. Tibial position at each flexion angle was expressed relative to the femuro-tibial position at passive knee extension. EMG activity, measured with ME-4000, was normalized to the individual maximum isometric voluntary contraction for each muscle.
  
  
  RESULTS
  During the weight-bearing phase of motion, the tibia was anteriorly positioned in all legs. In the injured leg, the tibia translated more rapidly to an anterior position that was maintained for a longer time during the gait cycle. In the noninjured knees, motions with increased load lead to an increased anterior tibial translation in contrast to the injured knees, where the maximum displacement was already reached during level walking. The quadriceps and gastrocnemius muscles were simultaneously active during stance phase. Hamstrings were mainly active when the knee was close to extension and translation increased in spite of this activity.
  
  
  CONCLUSIONS
  The mechanism of the anterior positioning of tibia is qualitatively similar in the normal and the injured knee, but that position is obtained much further forward in the ACL deficient knee. Quadriceps and gastrocnemius muscles seem to work synergistically to stabilize the knee by maintaining the anterior position of tibia during weight-bearing motion. The role of hamstrings to restrict anterior translation is questioned.
authors.affiliation: Division of Sports Medicine and Physical Therapy, Department of Neuroscience and Locomotion, Faculty of Health Sciences, Linköping University, SE-581 85 Linköping, Sweden. Joanna.Kvist@hul.liu.se
authors.forename: J
authors.initials: J
authors.lastname: Kvist
authors.forename: J
authors.initials: J
authors.lastname: Gillquist
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology; D013977:Tibia / Q000503:physiopathology*