title: Quadriceps strength and osteoarthritis progression in malaligned and lax knees.
abstract: BACKGROUND
  Quadriceps muscle strengthening is a common goal in the management of knee osteoarthritis. In healthy knees, strength protects against new osteoarthritis. In arthritic knees, greater strength may protect joints and thereby delay osteoarthritis progression. Alternatively, in certain joint environments, such as malalignment or laxity, greater strength may translate into damaging joint reaction forces. The relationship between quadriceps strength and progression of knee osteoarthritis may differ according to these factors.
  
  
  OBJECTIVE
  To determine whether greater quadriceps strength is associated with greater probability of tibiofemoral osteoarthritis progression in malaligned knees and in high-laxity knees.
  
  
  METHODS
  Prospective, longitudinal cohort study.
  
  
  METHODS
  Academic medical center.
  
  
  METHODS
  237 persons with primary knee osteoarthritis, definite tibiofemoral osteophytes, and at least some difficulty with knee-requiring activity. Two hundred thirty completed the 18-month evaluation. The current study primarily involved those without advanced osteoarthritis in either knee (n = 171).
  
  
  METHODS
  Quadriceps strength, knee laxity and alignment, and osteoarthritis progression.
  
  
  RESULTS
  The predicted probability of tibiofemoral progression was 0.153 (95% CI, 0.100 to 0.228) in high-strength knees and 0.098 (CI, 0.061 to 0.155) in low-strength knees. In malaligned knees, high strength was associated with a significant increase (P = 0.03) in the likelihood of progression (predicted probability, 0.406 [CI, 0.226 to 0.615] vs. 0.187 [CI, 0.081 to 0.375] in high-strength vs. low-strength knees). Strength was also associated with increased likelihood of progression in high-laxity knees (P = 0.003 when high laxity was defined as > or =6.75 degrees). The probability of patellofemoral progression did not differ between high- and low-strength knees in the full sample or within subsets.
  
  
  CONCLUSIONS
  Greater quadriceps strength at baseline was associated with increased likelihood of tibiofemoral osteoarthritis progression in malaligned knees and lax knees. Subset-specific approaches beyond strengthening exercises should be developed to enhance joint-protective muscle activity.
authors.affiliation: Department of Medicine, Feinberg School of Medicine, Northwestern University Medical School, 300 East Superior Avenue, Tarry Building 3-715, Chicago, Illinois 60611, USA.
authors.forename: Leena
authors.initials: L
authors.lastname: Sharma
authors.forename: Dorothy D
authors.initials: DD
authors.lastname: Dunlop
authors.forename: September
authors.initials: S
authors.lastname: Cahue
authors.forename: Jing
authors.initials: J
authors.lastname: Song
authors.forename: Karen W
authors.initials: KW
authors.lastname: Hayes
mesh_terms: D015992:Body Mass Index; D018450:Disease Progression; D015444:Exercise / Q000502:physiology; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000502:physiology*; D020370:Osteoarthritis, Knee / Q000503:physiopathology*; D011446:Prospective Studies; D012044:Regression Analysis; D013848:Thigh