title: Patellofemoral instability in children: T2 relaxation times of the patellar cartilage in patients with and without patellofemoral instability and correlation with morphological grading of cartilage damage.
abstract: BACKGROUND
  Patellofemoral instability is one of the most common causes of cartilage damage in teenagers.
  
  
  OBJECTIVE
  To quantitatively evaluate the patellar cartilage in patients with patellofemoral instability using T2 relaxation time maps (T2 maps), compare the values to those in patients without patellofemoral instability and correlate them with morphological grades in patients with patellofemoral instability.
  
  
  METHODS
  Fifty-three patients with patellofemoral instability (mean age: 15.9 ± 2.4 years) and 53 age- and gender-matched patients without patellofemoral instability were included. Knee MR with axial T2 map was performed. Mean T2 relaxation times were obtained at the medial, central and lateral zones of the patellar cartilage and compared between the two groups. In the patellofemoral instability group, morphological grading of the patellar cartilage (0-4) was performed and correlated with T2 relaxation times.
  
  
  RESULTS
  Mean T2 relaxation times were significantly longer in the group with patellofemoral instability as compared to those of the control group across the patellar cartilage (Student's t-test, P<0.05) with the longest time at the central area. Positive correlation was seen between mean T2 relaxation time and morphological grading (Pearson correlation coefficiency, P<0.001). T2 increased with severity of morphological grading from 0 to 3 (mixed model, P<0.001), but no statistical difference was seen between grades 3 and 4.
  
  
  CONCLUSIONS
  In patellofemoral instability, patellar cartilage damage occurs across the entire cartilage with the highest T2 values at the apex. T2 relaxation times directly reflect the severity in low-grade cartilage damage, which implies an important role for T2 maps in differentiating between normal and low-grade cartilage damage.
authors.affiliation: Department of Radiology, Korea University Anam Hospital, Korea University College of Medicine, Seoul, South Korea.
authors.forename: Chang Ho
authors.initials: CH
authors.lastname: Kang
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA. Hee.Kim@cchmc.org.
authors.forename: Hee Kyung
authors.initials: HK
authors.lastname: Kim
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA.
authors.forename: Sahar
authors.initials: S
authors.lastname: Shiraj
authors.affiliation: Department of Radiology, Cincinnati Children's Hospital Medical Center, 3333 Burnet Ave., Cincinnati, OH, 45229-3039, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Anton
authors.affiliation: Korea University College of Medicine, Seoul, South Korea.
authors.forename: Dong Hoon
authors.initials: DH
authors.lastname: Kim
authors.affiliation: Divisions of Neurology and Biostatistics & Epidemiology, Cincinnati Children's Hospital Medical Center, Cincinnati, OH, USA.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Horn
mesh_terms: D000293:Adolescent; D000328:Adult; D002358:Cartilage, Articular / Q000000981:diagnostic imaging / Q000293:injuries*; D002648:Child; D002675:Child, Preschool; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging / Q000293:injuries*; D006801:Humans; D007593:Joint Instability / Q000000981:diagnostic imaging*; D007718:Knee Injuries / Q000000981:diagnostic imaging*; D007719:Knee Joint / Q000000981:diagnostic imaging; D008279:Magnetic Resonance Imaging; D008297:Male; D010329:Patella / Q000000981:diagnostic imaging / Q000293:injuries*; D012189:Retrospective Studies; D055815:Young Adult
keywords: Cartilage; Children; Knee; Magnetic resonance imaging; Patellofemoral instability; Patellofemoral joint; T2 mapping