title: Knee joint stiffness in individuals with and without knee osteoarthritis: a preliminary study.
abstract: METHODS
  Descriptive, case-matched comparison.
  
  
  OBJECTIVE
  To compare the knee joint stiffness and damping coefficients of individuals with knee osteoarthritis (KOA) to those of age- and gender-matched individuals without KOA. A secondary purpose was to investigate relationships between these coefficients and complaints of stiffness in individuals with KOA.
  
  
  BACKGROUND
  KOA is a leading cause of disability, and stiffness is a common complaint in individuals with KOA. Yet the most common method of assessing knee joint stiffness is through a self-report questionnaire.
  
  
  METHODS
  Stiffness and damping coefficients at the knee were calculated in 10 volunteers (mean age +/- SD, 64.1+/-15.5 years) with KOA and compared to coefficients from age-and gender-matched individuals without KOA, collected in a previous study (mean age +/- SD, 62.1+/-13.9 years). Stiffness and damping coefficients were calculated from the angular motion of the knee during a relaxed oscillation. Spearman correlation coefficients were calculated between stiffness and damping coefficients and WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index) scores for subjects with KOA.
  
  
  RESULTS
  Independent 2-tailed t tests revealed significantly larger damping coefficients (P = .035) among those with KOA (95% CI, 0.10-2.32 Nm s/rad). Spearman rank correlations revealed a significant positive relationship (r = .85, P = .003) between the damping coefficient and the stiffness subscore of the WOMAC.
  
  
  CONCLUSIONS
  This study offers preliminary data demonstrating the feasibility of measuring stiffness and damping coefficients in individuals with KOA. Additionally, the damping coefficient is increased in people with KOA when compared to age- and gender-matched individuals without KOA. The damping coefficient appears to be associated with the complaints of stiffness reported by the WOMAC.
authors.affiliation: Department of Physical Therapy, Arcadia University, 450 S. Easton Road, Glenside, PA 19038, USA. oatis@arcadia.edu
authors.forename: Carol A
authors.initials: CA
authors.lastname: Oatis
authors.forename: Edward F
authors.initials: EF
authors.lastname: Wolff
authors.forename: Sandra K
authors.initials: SK
authors.lastname: Lennon
mesh_terms: D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology*; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires