title: Relationships between performance and kinematic/kinetic variables of stair descent in patients with medial knee osteoarthritis: An evaluation of dynamic stability using an extrapolated center of mass.
abstract: BACKGROUND
  The ability to descend stairs independently is impaired from a relatively early stage in patients with knee osteoarthritis. The purpose of this study was to evaluate the performance in patients with knee osteoarthritis when stepping down a step by evaluating the dynamic stability using the extrapolated center of mass.
  
  
  METHODS
  Twenty-three individuals with medial knee osteoarthritis were evaluated during step descent without any assistance. Kinematic/kinetic data were collected using a three-dimensional motion analysis system and force platforms. The extrapolated center of mass and its deviation from the anterior boundary on the base of support (margin of stability) were calculated at the initiation of descent. Joint angles and internal joint moments were collected at the stance limb. The relationship between patients' dynamic stability control, which was measured by the timed up and go test, and the length of margin of stability was analyzed. Relationships between the length of the margin of stability and each kinematic/kinetic variable were also evaluated.
  
  
  RESULTS
  The margin of stability positively correlated with the time taken for a timed up and go test. A positive correlation was additionally observed between the ankle dorsiflexion angle and the margin of stability. It was also found that a higher ratio of ankle plantar flexion moment by support moment was associated with a larger margin of stability.
  
  
  CONCLUSIONS
  Patients with knee osteoarthritis who had high ability in dynamic stability control were observed to move their center of mass anteriorly at the initiation of stepping down. It was also suggested that these patients could dorsiflex their ankle joint and generate sufficient ankle plantar flexor torque.
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan. Electronic address: koyama.yumiko.52c@st.kyoto-u.ac.jp.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Koyama
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Hiroshige
authors.initials: H
authors.lastname: Tateuchi
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Riho
authors.initials: R
authors.lastname: Nishimura
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Xiang
authors.initials: X
authors.lastname: Ji
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Umegaki
authors.affiliation: Kobayashi Orthopedic Clinic, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Kobayashi
authors.affiliation: Human Health Sciences, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Noriaki
authors.initials: N
authors.lastname: Ichihashi
mesh_terms: D000368:Aged; D000843:Ankle Joint / Q000502:physiology; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000502:physiology; D005684:Gait / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D004856:Postural Balance / Q000502:physiology*; D016138:Walking / Q000502:physiology*
keywords: Dynamic stability; Knee osteoarthritis; Stair descent