title: Elucidation of a potentially destabilizing control strategy in ACL deficient non-copers.
abstract: OBJECTIVE
  The purpose was to differentiate the dynamic knee stabilization strategies of potential copers (individuals who have the potential to compensate for the absence of an ACL without episodes of giving way after return to pre-injury activities) and non-copers (those who have knee instability following ACL rupture with return to pre-injury activities).
  
  
  METHODS
  Twenty subjects with ACL rupture were assigned to potential coper (n=10) and non-coper (n=10) groups via a screening examination. Ten active people without lower extremity injury were also tested. Knee angle, tibial position and muscle activity data were collected while subjects stood in unilateral stance on a platform that moved horizontally in an anterior direction. Analysis included the preparation for platform movement; and monosynaptic, intermediate reflex and voluntary response intervals after platform movement.
  
  
  RESULTS
  Non-copers showed greater knee flexion than uninjured subjects, and had a posterior tibial position and altered hamstring recruitment compared to the other groups. Potential copers demonstrated greater medial quadriceps activity while maintaining knee kinematics similar to uninjured subjects. Both potential copers and non-copers had greater co-contraction between medial hamstrings and quadriceps than uninjured subjects. All excitatory muscle activation occurred in the intermediate reflex interval.
  
  
  CONCLUSIONS
  Non-copers displayed aberrant muscle recruitment that may contribute to knee instability. Potential copers maintained normal tibial position using a strategy that permits quadriceps activation without excessive anterior tibial translation. Muscle recruitment in the intermediate reflex interval suggests neuromuscular training may influence the strategies.
authors.affiliation: Department of Physical Therapy, Graduate Program in Biomechanics and Movement Sciences, and Center for Biomedical Engineering Research, University of Delaware, Newark, DE 19716, USA.
authors.forename: T L
authors.initials: TL
authors.lastname: Chmielewski
authors.forename: W J
authors.initials: WJ
authors.lastname: Hurd
authors.forename: L
authors.initials: L
authors.lastname: Snyder-Mackler
mesh_terms: D000222:Adaptation, Physiological; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000503:physiopathology*; D000070598:Anterior Cruciate Ligament Injuries; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D011434:Proprioception / Q000502:physiology*; D011999:Recruitment, Neurophysiological; D012018:Reflex / Q000502:physiology; D012421:Rupture