title: MRI findings in adolescent patients with acute traumatic knee hemarthrosis.
abstract: BACKGROUND
  Physical examination may be inconclusive in adolescents presenting with an acute traumatic knee effusion because of pain and guarding. The purpose of this study was to describe the magnetic resonance imaging (MRI) findings in adolescents with traumatic knee effusions and to compare injuries based on age, sex, and physeal maturity.
  
  
  METHODS
  All MRIs using a knee trauma protocol performed at our institution over a 2-year period were evaluated. One hundred thirty-one patients between the ages of 10 to 18 years of age with a clinical history of acute knee trauma and an effusion confirmed on MRI met our study inclusion criteria. They were divided into 2 age groups: 10 to 14 and 15 to 18 years old. Pathology was confirmed using clinical history, MRI, and any available surgical reports.
  
  
  RESULTS
  Of the 131 patients with an acute knee effusion, there were 59 patients in the younger group (10 to 14 y old) and 72 patients in the older group (15 to 18 y old). In the younger group, patellar dislocations (36%), anterior cruciate ligament (ACL) tears (22%), and isolated meniscus tears (15%) were the most common injuries. In the older group, ACL tears (40%), patellar dislocations (28%), and isolated meniscus tears (13%) were the most common injuries. ACL injuries represented 28% of injuries in males and 38% of injuries in females, whereas patellar dislocations represented 28% of injuries in males and 37% of injuries in females. There was a trend toward adolescents with active growth plates sustaining more patellar dislocations and adolescents with closed growth plates sustaining more ACL injuries. Forty-one percent of patients in this study underwent surgery.
  
  
  CONCLUSIONS
  Patellar dislocation is a common injury in children who present with a traumatic knee effusion, especially in young adolescents and females. Adolescents presenting with a traumatic knee effusion should undergo MRI because of the high rate of positive findings missed by physical examination and plain radiographs that may warrant surgical repair or reconstruction.
  
  
  METHODS
  Level III.
authors.affiliation: Department of Orthopaedic Surgery, University of Cincinnati, Cincinnati, OH, USA.
authors.forename: David
authors.initials: D
authors.lastname: Abbasi
authors.forename: Megan M
authors.initials: MM
authors.lastname: May
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Wall
authors.forename: Gilbert
authors.initials: G
authors.lastname: Chan
authors.forename: Shital N
authors.initials: SN
authors.lastname: Parikh
mesh_terms: D000208:Acute Disease; D000293:Adolescent; D000367:Age Factors; D016118:Anterior Cruciate Ligament / Q000473:pathology; D000070598:Anterior Cruciate Ligament Injuries; D002648:Child; D005260:Female; D006132:Growth Plate / Q000378:metabolism; D006395:Hemarthrosis / Q000175:diagnosis* / Q000473:pathology; D006801:Humans; D007718:Knee Injuries / Q000175:diagnosis* / Q000473:pathology; D007719:Knee Joint / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008592:Menisci, Tibial / Q000473:pathology; D031222:Patellar Dislocation / Q000175:diagnosis* / Q000473:pathology; D012189:Retrospective Studies; D012737:Sex Factors; D000070600:Tibial Meniscus Injuries