title: Magnetic Resonance Imaging Findings After Acute Patellar Dislocation in Children.
abstract: BACKGROUND
  Acute patellar dislocation (APD) is a common knee injury in children. The pattern and frequency of injury to the medial patellofemoral ligament (MPFL) is different in pediatric compared with adult populations.
  
  
  OBJECTIVE
  To report on injury patterns sustained to the MPFL after APD in children and to determine whether predisposing factors for APD cited in adults hold true in the pediatric population.
  
  
  METHODS
  Case series; Level of evidence, 4.
  
  
  METHODS
  Magnetic resonance imaging (MRI) studies were reviewed for 36 children sustaining APD. Evidence of injury to the MPFL was documented, and when the MPFL was torn, the location of tear was determined. Presence of trochlear dysplasia, patella alta, tibial tubercle-trochlear groove (TTTG) distance, and thickness of the lateral patellofemoral retinaculum (LPR) were recorded and correlated with MPFL tear.
  
  
  RESULTS
  Of the 36 patients sustaining APD, only 16 tore the MPFL. The location of MPFL tear was equally divided between the origin, the insertion, or both, with no case of midsubstance tear. There was a significant correlation identified between MPFL rupture and both LPR thickness greater than 3 mm and TTTG distance greater than 19 mm.
  
  
  CONCLUSIONS
  The MPFL does not always tear in children who sustain APD, and the tear location is variable. A thickened LPR and increased TTTG distance predispose to MPFL tear.
authors.affiliation: Bone & Joint Sports Medicine Institute, Naval Medical Center, Portsmouth, Virginia, USA.
authors.forename: Addison
authors.initials: A
authors.lastname: Wilson
authors.affiliation: Department of Radiology, Naval Medical Center, Portsmouth, Virginia, USA.
authors.forename: Afshin
authors.initials: A
authors.lastname: Afarin
authors.affiliation: Department of Radiology, Naval Medical Center, Portsmouth, Virginia, USA.
authors.forename: Corey
authors.initials: C
authors.lastname: Shaw
authors.affiliation: Nemours Children's Hospital, Jacksonville, Florida, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Shirley
authors.affiliation: University of Virginia, Charlottesville, Virginia, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Pierce
authors.affiliation: Bone & Joint Sports Medicine Institute, Naval Medical Center, Portsmouth, Virginia, USA.
authors.forename: Joseph B
authors.initials: JB
authors.lastname: Slakey
keywords: dislocation; lateral patellofemoral retinaculum; medial patellofemoral ligament; patella