title: Occult Intra-articular Knee Injuries in Children With Hemarthrosis.
abstract: BACKGROUND
  Hemarthrosis after acute knee trauma is a sign of a potentially serious knee injury. Few studies have described the epidemiology and detailed injury spectrum of acute knee injuries in a general pediatric population.
  
  
  OBJECTIVE
  To document the current injury spectrum of acute knee injuries with hemarthrosis in children aged 9 to 14 years and to describe the distribution of sex, age at injury, type of activity, and activity frequency in this population.
  
  
  METHODS
  Descriptive epidemiology study.
  
  
  METHODS
  All patients in the Stockholm County area aged 9 to 14 years who suffered acute knee trauma with hemarthrosis were referred to Astrid Lindgren Children's Hospital, Karolinska University Hospital, from September 2011 to April 2012. The patients underwent clinical examination, radiography, and magnetic resonance imaging (MRI). The type of activity when injured, regular sports activity/frequency, and patient sex and age were registered. The diagnoses were classified into minor and serious injuries.
  
  
  RESULTS
  The study included 117 patients (47 girls and 70 boys; mean age, 13.2 years). Seventy percent had a serious knee injury. Lateral patellar dislocations, anterior cruciate ligament ruptures, and anterior tibial spine fractures were the most common injuries, with an incidence of 0.6, 0.2, and 0.1 per 1000 children, respectively. The sex distribution was equal up to age 13 years; twice as many boys were seen at the age of 14 years. The majority of injuries occurred during sports. Forty-six patients (39%) had radiographs without a bony injury but with a serious injury confirmed on MRI.
  
  
  CONCLUSIONS
  Seventy percent of the patients aged 9 to 14 years with traumatic knee hemarthrosis had a serious intra-articular injury that needed specific medical attention. Fifty-six percent of these patients had no visible injury on plain radiographs. Physicians who treat this group of patients should consider MRI to establish the diagnosis when there is no or minimal radiographic findings. The most common serious knee injury was a lateral patellar dislocation. This should be taken into consideration to improve prevention strategies and treatment algorithms in pediatric knee injuries.
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Solna, Sweden Section of Pediatric Orthopaedic Surgery, Karolinska University Hospital, Solna, Sweden marie.askenberger@karolinska.se.
authors.forename: Marie
authors.initials: M
authors.lastname: Askenberger
authors.affiliation: Section of Orthopaedics and Sports Medicine, Department of Molecular Medicine and Surgery, Karolinska University Hospital, Karolinska Institutet, Solna, Sweden.
authors.forename: Wilhelmina
authors.initials: W
authors.lastname: Ekström
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Solna, Sweden Section of Pediatric Radiology, Karolinska University Hospital, Solna, Sweden.
authors.forename: Thröstur
authors.initials: T
authors.lastname: Finnbogason
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Solna, Sweden Capio Artro Clinic, Stockholm, Sweden.
authors.forename: Per-Mats
authors.initials: PM
authors.lastname: Janarv
mesh_terms: D000293:Adolescent; D000465:Algorithms; D002648:Child; D005260:Female; D006395:Hemarthrosis / Q000209:etiology*; D006801:Humans; D015994:Incidence; D007718:Knee Injuries / Q000150:complications / Q000175:diagnosis*; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D031222:Patellar Dislocation / Q000000981:diagnostic imaging / Q000473:pathology*; D010808:Physical Examination; D011446:Prospective Studies; D011859:Radiography
keywords: child; epidemiology; hemarthrosis; knee injury; sports