title: Patellofemoral Instability in Children: Correlation Between Risk Factors, Injury Patterns, and Severity of Cartilage Damage.
abstract: OBJECTIVE
  The purpose of this study was to compare MRI findings between groups with and without patellofemoral instability and to correlate the MRI findings with the severity of patellar cartilage damage.
  
  
  METHODS
  Fifty-three children with patellofemoral instability and 53 age- and sex-matched children without patellofemoral instability (15.9 ± 2.4 years) were included. Knee MRI with T2-weighted mapping was performed. On MR images, femoral trochlear dysplasia, patellofemoral malalignment, medial retinaculum injury, and bone marrow edema were documented. The degree of patellar cartilage damage was evaluated on MR images by use of a morphologic grading scale (0-4) and on T2 maps with mean T2 values at the medial, central, and lateral facets. MRI findings were compared between the two groups. In cases of patellofemoral instability, MRI findings were correlated with the severity of cartilage damage at each region.
  
  
  RESULTS
  Trochlear structure and alignment were significantly different between the two groups (Wilcoxon p < 0.0001). In patellofemoral instability, a high-riding patella was associated with central patellar cartilage damage with a higher morphologic grade and T2 value (Spearman p < 0.05). The severity of medial retinacular injury and presence of bone marrow edema at either the medial patella or the lateral femoral condyle were associated with a higher grade of medial patellar cartilage damage (Wilcoxon p < 0.05). None of the other findings correlated with the severity of patellar cartilage damage.
  
  
  CONCLUSIONS
  Patients with patellofemoral instability have significantly different trochlear structure and alignment than those who do not, and these differences are known risk factors for patellofemoral instability. However, the only risk factors or injury patterns that directly correlated with the severity of patellar cartilage damage were patella alta, medial stabilizer injury, and bone marrow edema.
authors.affiliation: 1 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45229.
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Kim
authors.affiliation: 1 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45229.
authors.forename: Sahar
authors.initials: S
authors.lastname: Shiraj
authors.affiliation: 2 Departments of Radiology, Korea University Anam Hospital and Korea University College of Medicine, Seoul, Korea.
authors.forename: Chang Ho
authors.initials: CH
authors.lastname: Kang
authors.affiliation: 1 Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave, Cincinnati, OH 45229.
authors.forename: Christopher
authors.initials: C
authors.lastname: Anton
authors.affiliation: 3 Korea University College of Medicine, Seoul, Korea.
authors.forename: Dong Hoon
authors.initials: DH
authors.lastname: Kim
authors.affiliation: 4 Divisions of Neurology and Biostatistics and Epidemiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Horn
mesh_terms: D000293:Adolescent; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000293:injuries*; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging* / Q000209:etiology; D008279:Magnetic Resonance Imaging; D008297:Male; D057071:Patellofemoral Joint; D012189:Retrospective Studies; D012307:Risk Factors; D055815:Young Adult
keywords: T2 relaxation time mapping; cartilage damage; children; patellofemoral instability