title: Knee kinematics following acl reconstruction in females; the effect of vision on performance during a cutting task.
abstract: OBJECTIVE
  Specific movement patterns have been identified as influential in ACL injury; however several key kinematic variables that might be predictive of future performance have not been fully investigated. The purpose of this research was to: 1) determine if subjects with ACL reconstruction display different displacement, velocity, and time to peak ground reaction force (GRF) during cutting activities than healthy subjects, 2) observe if subjects with visual disruption display differences in these variables, and 3) determine if visual disruption alters these variables in subjects with ACL reconstruction relative to healthy subjects.
  
  
  METHODS
  Seventeen healthy female subjects and 17 female subjects with unilateral ACL reconstruction (ACLR) performed 40 trials of a cutting movement during which knee position was measured via a 3D electromagnetic system. Visual conditions were randomized to disrupt vision for 1 second as the subject began the cutting movement, or allow full vision for movement duration. Independent variables were lead/push off leg (ACLR limb or healthy non-dominant limb) and vision (disrupted or full). 2-way ANOVAs were utilized to determine differences between knee kinematics using dependent variables of displacement (m), absolute velocity (m/sec), and time to reach peak GRF (% of cut).
  
  
  RESULTS
  Knee displacement was significantly less for ACLR (.76±.11; .75±.16) than non-dominant (.85±.08; .87±.12). Knee velocity was significantly slower for ACLR (.81±.14; .84±.16) than non-dominant (.92±.11; .97±.14). A significant interaction was noted for displacement and average velocity (p<.05). Time to reach peak GRF was significantly longer for ACLR (79.41±2.28) than non-dominant (76.65±4.41).
  
  
  CONCLUSIONS
  Subjects with ACLR displayed less knee displacement, slower velocity, and an increased time to reach peak GRF relative to healthy subjects' non-dominant knee. Visual disruption appeared to have some effect on movement, as noted by interaction effects. These movement adjustments may be indicative of an altered motor program that allows for successful and safe task completion while reducing the forces and load on the knee.
  
  
  METHODS
  Level 2.
authors.forename: Jaynie
authors.initials: J
authors.lastname: Bjornaraa
authors.forename: Richard P
authors.initials: RP
authors.lastname: Di Fabio