title: Epidemiology and natural history of acute patellar dislocation.
abstract: BACKGROUND
  The goals of this study were to (1) define the epidemiology of acute patellar dislocation, (2) determine the risk of subsequent patellar instability episodes (subluxation and/or redislocation) during the study period, and (3) identify risk factors for subsequent instability episodes.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  The authors prospectively followed 189 patients for a period of 2 to 5 years. Historical data, injury mechanisms, and physical and radiographic measurements were recorded to identify potential risk factors for poor outcomes.
  
  
  RESULTS
  Risk was highest among females 10 to 17 years old. Patients presenting with a prior history of instability were more likely to be female (P < .05) and were older than first-time dislocation patients (P < .05). Fewer first-time dislocators (17%) had episodes of instability during follow-up than patients with a previous history of instability (49%) (P < .01). After adjusting for demographics, patients with a prior history had 7 times higher odds of subsequent instability episodes during follow-up than first time dislocators (adjusted odds ratio = 6.6, P < .001).
  
  
  CONCLUSIONS
  Patellar dislocators who present with a history of patellofemoral instability are more likely to be female, are older, and have greater risk of subsequent patellar instability episodes than first-time patellar dislocators. Risk of recurrent patellar instability episodes in either knee is much higher in this group than in first-time dislocators.
authors.affiliation: Southern California Permanente Medical Group, San Diego, USA. donald.c.fithian@kp.org
authors.forename: Donald C
authors.initials: DC
authors.lastname: Fithian
authors.forename: Elizabeth W
authors.initials: EW
authors.lastname: Paxton
authors.forename: Mary Lou
authors.initials: ML
authors.lastname: Stone
authors.forename: Patricia
authors.initials: P
authors.lastname: Silva
authors.forename: Daniel K
authors.initials: DK
authors.lastname: Davis
authors.forename: David A
authors.initials: DA
authors.lastname: Elias
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: White
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D001265:Athletic Injuries / Q000150:complications; D002648:Child; D005260:Female; D005500:Follow-Up Studies; D006618:Hip Dislocation, Congenital / Q000150:complications; D006801:Humans; D007593:Joint Instability / Q000150:complications / Q000503:physiopathology; D007719:Knee Joint / Q000473:pathology / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D031222:Patellar Dislocation / Q000453:epidemiology* / Q000209:etiology* / Q000503:physiopathology; D011446:Prospective Studies; D012008:Recurrence; D012307:Risk Factors; D017678:Sex Distribution; D012737:Sex Factors; D014481:United States / Q000453:epidemiology