title: What is the effect of physical activity on the knee joint? A systematic review.
abstract: OBJECTIVE
  Although several studies have examined the relationship between physical activity and knee osteoarthritis, the effect of physical activity on knee joint health is unclear. The aim of this systematic review was to examine the relationships between physical activity and individual joint structures at the knee.
  
  
  METHODS
  Computer-aided searches were conducted up until November 2008, and the reference lists of key articles were examined. The methodological quality of selected studies was assessed based on established criteria, and a best-evidence synthesis was used to summarize the results.
  
  
  RESULTS
  We found that the relationships between physical activity and individual joint structures at the knee differ. There was strong evidence for a positive association between physical activity and tibiofemoral osteophytes. However, we also found strong evidence for the absence of a relationship between physical activity and joint space narrowing, a surrogate method of assessing cartilage. Moreover, there was limited evidence from magnetic resonance imaging studies for a positive relationship between physical activity and cartilage volume and strong evidence for an inverse relationship between physical activity and cartilage defects.
  
  
  CONCLUSIONS
  This systematic review found that knee structures are affected differently by physical activity. Although physical activity is associated with an increase in radiographic osteophytes, there was no related increase in joint space narrowing, rather emerging evidence of an associated increase in cartilage volume and decrease in cartilage defects on magnetic resonance imaging. Given that optimizing cartilage health is important in preventing osteoarthritis, these findings indicate that physical activity is beneficial, rather than detrimental, to joint health.
authors.affiliation: School of Public Health and Preventive Medicine, Department of Epidemiology and Preventive Medicine, Monash University, Alfred Hospital, Melbourne, Victoria, Australia. Donna.Urquhart@med.monash.edu.au
authors.forename: Donna M
authors.initials: DM
authors.lastname: Urquhart
authors.forename: Jephtah F L
authors.initials: JF
authors.lastname: Tobing
authors.forename: Fahad S
authors.initials: FS
authors.lastname: Hanna
authors.forename: Patricia
authors.initials: P
authors.lastname: Berry
authors.forename: Anita E
authors.initials: AE
authors.lastname: Wluka
authors.forename: Changhai
authors.initials: C
authors.lastname: Ding
authors.forename: Flavia M
authors.initials: FM
authors.lastname: Cicuttini
mesh_terms: D002357:Cartilage Diseases / Q000000981:diagnostic imaging / Q000503:physiopathology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000502:physiology*; D008279:Magnetic Resonance Imaging; D008297:Male; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging / Q000503:physiopathology; D054850:Osteophyte / Q000000981:diagnostic imaging / Q000503:physiopathology; D011859:Radiography