title: Self-reported knee joint instability is related to passive mechanical stiffness in medial knee osteoarthritis.
abstract: BACKGROUND
  Self-reported knee joint instability compromises function in individuals with medial knee osteoarthritis and may be related to impaired joint mechanics. The purpose of this study was to evaluate the relationship between self-reported instability and the passive varus-valgus mechanical behaviour of the medial osteoarthritis knee.
  
  
  METHODS
  Passive varus-valgus angular laxity and stiffness were assessed using a modified isokinetic dynamometer in 73 participants with medial tibiofemoral osteoarthritis. All participants self-reported the absence or presence of knee instability symptoms and the degree to which instability affected daily activity on a 6-point likert scale.
  
  
  RESULTS
  Forward linear regression modelling identified a significant inverse relationship between passive mid-range knee stiffness and symptoms of knee instability (r = 0.27; P < 0.05): reduced stiffness was indicative of more severe instability symptoms. Angular laxity and end-range stiffness were not related to instability symptoms (P > 0.05).
  
  
  CONCLUSIONS
  Conceivably, a stiffer passive system may contribute toward greater joint stability during functional activities. Importantly however, net joint stiffness is influenced by both active and passive stiffness, and thus the active neuromuscular system may compensate for reduced passive stiffness in order to maintain joint stability. Future work is merited to examine the role of active stiffness in symptomatic joint stability.
authors.affiliation: School of Exercise Science, Australian Catholic University, Brisbane, Queensland 4014, Australia. mark.creaby@acu.edu.au.
authors.forename: Mark W
authors.initials: MW
authors.lastname: Creaby
authors.forename: Tim V
authors.initials: TV
authors.lastname: Wrigley
authors.forename: Boon-Whatt
authors.initials: BW
authors.lastname: Lim
authors.forename: Rana S
authors.initials: RS
authors.lastname: Hinman
authors.forename: Adam L
authors.initials: AL
authors.lastname: Bryant
authors.forename: Kim L
authors.initials: KL
authors.lastname: Bennell
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000503:physiopathology*