title: Anterior knee pain in younger adults as a precursor to subsequent patellofemoral osteoarthritis: a systematic review.
abstract: BACKGROUND
  Patellofemoral osteoarthritis (PFOA) is a common form of knee OA in middle and older age, but its relation to PF disorders and symptoms earlier in life is unclear. Our aim was to conduct a systematic review to investigate the strength of evidence for an association between anterior knee pain (AKP) in younger adults and subsequent PFOA.
  
  
  METHODS
  The search strategy included electronic databases (Pubmed, EMBASE, AMED, CINAHL, Cochrane, PEDro, SportDiscus: inception to December 2009), reference lists of potentially eligible studies and selected reviews. Full text articles in any language, - identified via English titles and abstracts, were included if they were retrospective or prospective in design and contained quantitative data regarding structural changes indicative of PFOA, incident to original idiopathic AKP. Eligibility criteria were applied to titles, abstracts and full-texts by two independent reviewers. Data extraction included study location, design, date, sampling procedure, sample characteristics, AKP/PFOA definitions, follow-up duration and rate, and main findings. Foreign language articles were translated into English prior to examination.
  
  
  RESULTS
  Seven articles satisfied eligibility (5 English, 2 German). Only one case-control study directly investigated a link between PFOA and prior AKP, providing level 3b evidence in favour of an association (OR 4.4; 95%CI 1.8, 10.6). Rough estimates of the annual risk of PFOA from the remaining six small, uncontrolled, observational studies (mean follow-up range: 5.7 to 23 years) ranged from 0% to 3.4%. This was not the primary aim of these studies, and limitations in design and methodology mean this data should be interpreted with caution.
  
  
  CONCLUSIONS
  There is a paucity of high-quality evidence reporting a link between AKP and PFOA. Further, well-designed cohort studies may be able to fill this evidence gap.
authors.affiliation: Arthritis Research UK Primary Care Centre, Primary Care Sciences, Keele University, Keele, Staffordshire, ST5 5BG, UK. m.thomas@cphc.keele.ac.uk
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: Laurence
authors.initials: L
authors.lastname: Wood
authors.forename: James
authors.initials: J
authors.lastname: Selfe
authors.forename: George
authors.initials: G
authors.lastname: Peat
mesh_terms: D000328:Adult; D015897:Comorbidity; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology*; D020370:Osteoarthritis, Knee / Q000453:epidemiology* / Q000209:etiology / Q000503:physiopathology; D017847:Patellar Ligament / Q000503:physiopathology*; D046788:Patellofemoral Pain Syndrome / Q000150:complications / Q000453:epidemiology* / Q000503:physiopathology; D055815:Young Adult