title: Increased knee muscle strength is associated with decreased activity limitations in established knee osteoarthritis: Two-year follow-up study in the Amsterdam osteoarthritis cohort.
abstract: OBJECTIVE
  To examine the association between changes in knee muscle strength (extensor and flexor muscles separately, and mean values) and changes in activity limitations in patients with established knee osteoarthritis at 2 years.
  
  
  METHODS
  Data from 186 patients with knee osteoarthritis, part of the Amsterdam Osteoarthritis cohort, were gathered at baseline and at 2-year follow-up. Strength of the knee extensor and flexor muscles were assessed using an isokinetic dynamometer. Activity limitations were assessed using the Western Ontario and McMaster University Osteoarthritis Index (WOMAC) - Physical Function subscale, the Get Up and Go test (GUG), and the 12-steps stairs test. Univariate and multivariate linear regression analyses were used to assess the association between changes in muscle strength and changes in activity limitations, adjusting for relevant confounders and baseline activity limitations.
  
  
  RESULTS
  There was an overall 16% increase in mean knee muscle strength (p < 0.001), 19% increase in knee extensor muscle strength (p < 0.001), and 17% increase in knee flexor muscle strength (p < 0.001) at 2 years. Increased mean knee muscle strength and knee flexor muscle strength were associated with better self-reported physical function (WOMAC) (b = -5.7, p = 0.03 and b = -6.2, p = 0.05), decreased time on the GUG (b = -1.2, p = 0.003 and b = -1.4, p = 0.05) and decreased time on the stairs test (b = -4.4, p < 0.001 and b = -6.6, p < 0.001). Increased extensor muscle strength was associated only with decreased time on the stairs test (b = -2.7, p < 0.001).
  
  
  CONCLUSIONS
  Increased knee muscle strength, mainly in the knee flexors, was associated with decreased activity limitations in patients with knee osteoarthritis at 2 years. Thus, differences in muscle strength may partially explain the between-patients variability in activity limitations.
authors.affiliation: University of Alberta, School of Public Health-Injury Prevention Centre, RTF 3-100A, T6G 2E1 Edmonton, Canada. d.c.sanchezramirez@vu.nl, diana.sanchez@ualberta.ca, diana1@ualberta.ca.
authors.forename: Diana C
authors.initials: DC
authors.lastname: Sanchez-Ramirez
authors.forename: Marike
authors.initials: M
authors.lastname: van der Leeden
authors.forename: Martin
authors.initials: M
authors.lastname: van der Esch
authors.forename: Leo D
authors.initials: LD
authors.lastname: Roorda
authors.forename: Sabine
authors.initials: S
authors.lastname: Verschueren
authors.forename: Jaap
authors.initials: J
authors.lastname: van Dieën
authors.forename: Willem F
authors.initials: WF
authors.lastname: Lems
authors.forename: Joost
authors.initials: J
authors.lastname: Dekker
mesh_terms: D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007717:Knee / Q000502:physiology*; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D053580:Muscle Strength / Q000502:physiology*; D009426:Netherlands; D020370:Osteoarthritis, Knee / Q000150:complications*; D013997:Time Factors