title: Modelling knee flexion effects on joint power absorption and adduction moment.
abstract: BACKGROUND
  Knee osteoarthritis is commonly associated with ageing and long-term walking. In this study the effects of flexing motions on knee kinetics during stance were simulated. Extended knees do not facilitate efficient loading. It was therefore, hypothesised that knee flexion would promote power absorption and negative work, while possibly reducing knee adduction moment.
  
  
  METHODS
  Three-dimensional (3D) position and ground reaction forces were collected from the right lower limb stance phase of one healthy young male subject. 3D position was sampled at 100 Hz using three Optotrak Certus (Northern Digital Inc.) motion analysis camera units, set up around an eight metre walkway. Force plates (AMTI) recorded ground reaction forces for inverse dynamics calculations. The Visual 3D (C-motion) 'Landmark' function was used to change knee joint positions to simulate three knee flexion angles during static standing. Effects of the flexion angles on joint kinetics during the stance phase were then modelled.
  
  
  RESULTS
  The static modelling showed that each 2.7° increment in knee flexion angle produced 2.74°-2.76° increments in knee flexion during stance. Increased peak extension moment was 6.61 Nm per 2.7° of increased knee flexion. Knee flexion enhanced peak power absorption and negative work, while decreasing adduction moment.
  
  
  CONCLUSIONS
  Excessive knee extension impairs quadriceps' power absorption and reduces eccentric muscle activity, potentially leading to knee osteoarthritis. A more flexed knee is accompanied by reduced adduction moment. Research is required to determine the optimum knee flexion to prevent further damage to knee-joint structures affected by osteoarthritis.
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL) Victoria University, Ballarat Road, Footscray, Victoria, Australia. Electronic address: hanatsu.nagano@vu.edu.au.
authors.forename: Hanatsu
authors.initials: H
authors.lastname: Nagano
authors.affiliation: Knee Joint Replacement Centre, Shounan Kamakura General Hospital, 1370-1, Okamoto, Kamakura City, Kanagawa, Japan.
authors.forename: Ichiroh
authors.initials: I
authors.lastname: Tatsumi
authors.affiliation: Tsukuba University, 3-89-1, Otsuka, Bunkyo, Tokyo, Japan.
authors.forename: Eri
authors.initials: E
authors.lastname: Sarashina
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL) Victoria University, Ballarat Road, Footscray, Victoria, Australia.
authors.forename: W A
authors.initials: WA
authors.lastname: Sparrow
authors.affiliation: Institute of Sport, Exercise and Active Living (ISEAL) Victoria University, Ballarat Road, Footscray, Victoria, Australia.
authors.forename: Rezaul K
authors.initials: RK
authors.lastname: Begg
mesh_terms: D005684:Gait / Q000502:physiology*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D011187:Posture; D016059:Range of Motion, Articular / Q000502:physiology*; D016138:Walking / Q000502:physiology*; D055815:Young Adult
keywords: Adduction moment; Eccentric work; Osteoarthritis; Power absorption