title: Muscle impairments in patients with knee osteoarthritis.
abstract: BACKGROUND
  Muscle impairments associated with knee osteoarthritis (OA) are the primary underlying cause of functional limitations. Understanding the extent of muscle impairments, its relationship with physical function and disease progression, and the evidence behind exercise therapy that targets muscle impairments is crucial.
  
  
  METHODS
  An electronic search for relevant articles using MEDLINE and CINHAL databases up to September 2011 was performed. In addition to the electronic search, retrieved articles were searched manually for relevant studies.
  
  
  RESULTS
  Quadriceps, hamstrings, and hip muscles are significantly impaired in subjects with knee OA compared with age-matched controls. Muscle strength, especially quadriceps, is a major determinant of both performance-based and self-reported physical function. Whether stronger quadriceps is protective against knee OA onset and progression is not clear. Exercise therapy, including global and targeted resistance training, is effective in reducing pain and improving function in subjects with knee OA.
  
  
  CONCLUSIONS
  Subjects with knee OA have significant muscle impairments. These muscle impairments affect physical function and should be targeted in therapy. Further research is needed to explore the relationship between quadriceps strength and knee OA initiation and progression and to determine the optimal exercise prescription that augments outcomes in this patient population.
authors.affiliation: Graduate Program in Biomechanics and Movement Science, University of Delaware, Newark, Delaware, and King Saud University, Riyadh, Saudi Arabia.
authors.forename: Ali H
authors.initials: AH
authors.lastname: Alnahdi
authors.forename: Joseph A
authors.initials: JA
authors.lastname: Zeni
authors.forename: Lynn
authors.initials: L
authors.lastname: Snyder-Mackler