title: Determinants of co-contraction during walking before and after arthroplasty for knee osteoarthritis.
abstract: BACKGROUND
  Knee osteoarthritis patients co-contract in knee-related muscle pairs during walking. The determinants of this co-contraction remain insufficiently clear.
  
  
  METHODS
  A heterogeneous group of 14 patients was measured before and one year after knee arthroplasty, and compared to 12 healthy peers and 15 young subjects, measured once. Participants walked on a treadmill at several imposed speeds. Bilateral activity of six muscles was registered electromyographically, and co-contraction time was calculated as percentage of stride cycle time. Local dynamic stability and variability of sagittal plane knee movements were determined. The surgeon's assessment of alignment was used. Pre-operatively, multivariate regressions on co-contraction time were used to identify determinants of co-contraction. Post-operatively it was assessed if predictor variables had changed in the same direction as co-contraction time.
  
  
  RESULTS
  Patients co-contracted longer than controls, but post-operatively, differences with the healthy peers were no longer significant. Varus alignment predicted co-contraction time. No patient had post-operative varus alignment. The patients' unaffected legs were more unstable, and instability predicted co-contraction time in both legs. Post-operatively, stability normalised. Longer unaffected side co-contraction time was associated with reduced affected side kinematic variability. Post-operatively, kinematic variability had further decreased.
  
  
  CONCLUSIONS
  Varus alignment and instability are determinants of co-contraction. The benefits of co-contraction in varus alignment require further study. Co-contraction probably increases local dynamic stability, which does not necessarily decrease the risk of falling. Unaffected side co-contraction contributed to decreasing affected side variability, but other mechanisms than co-contraction may also have played a role in decreasing variability.
authors.affiliation: Research Institute MOVE, Faculty of Human Movement Sciences, VU University, Amsterdam, The Netherlands.
authors.forename: Hamid R
authors.initials: HR
authors.lastname: Fallah-Yakhdani
authors.forename: Hamid
authors.initials: H
authors.lastname: Abbasi-Bafghi
authors.forename: Onno G
authors.initials: OG
authors.lastname: Meijer
authors.forename: Sjoerd M
authors.initials: SM
authors.lastname: Bruijn
authors.forename: Nicolette
authors.initials: N
authors.lastname: van den Dikkenberg
authors.forename: Maria-Grazia
authors.initials: MG
authors.lastname: Benedetti
authors.forename: Jaap H
authors.initials: JH
authors.lastname: van Dieën
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D005684:Gait; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology* / Q000601:surgery*; D004856:Postural Balance; D016138:Walking