title: Magnetic resonance evaluation of the knee in children and adolescents with achondroplasia.
abstract: BACKGROUND
  Achondroplasia is the most common form of skeletal dysplasia. Although the radiographic features are well described, MRI features of the knee in achondroplasia have not been reported.
  
  
  OBJECTIVE
  To describe common MRI characteristics of the knee joint in symptomatic children and adolescents with achondroplasia.
  
  
  METHODS
  We retrospectively evaluated 10 knee MRI examinations in 8 children and young adults (age range 11-20 years, mean 16.3 years) with achondroplasia. We measured modified Insall-Salvati index, knee flexion angle, anterior cruciate ligament (ACL)-Blumensaat line angle, ACL-tibial angle, posterior cruciate ligament (PCL) angle, intercondylar notch width index, and intercondylar notch depth index. We compared our findings with an age- and gender-matched control group of 20 children (age range 15-18 years; mean 16 years) with normal knee MRIs.
  
  
  RESULTS
  All 10 knees in the achondroplasia group had discoid lateral meniscus; 8 meniscal tears were identified. Patella baja was present in half of the study cases. Greater knee flexion and increased ACL-Blumensaat line and PCL angles were seen in all achondroplasia knees. ACL-tibial angle was similar in the study and in the control group. Children with achondroplasia had deeper A-shape femoral notches that extended more anteriorly than those seen in the control group. MRI findings were confirmed in all seven knees with arthroscopic correlation.
  
  
  CONCLUSIONS
  Discoid lateral meniscus, often with tear, is a consistent feature in knee MRIs of symptomatic children and adolescents with achondroplasia. Other findings include patella baja, knee flexion, deep A-shape intercondylar notch, increased ACL-Blumensaat line angle and taut PCL.
authors.affiliation: Department of Medical Imaging, Nemours/Alfred I. duPont Hospital for Children, 1600 Rockland Road, Wilmington, DE, 19803-3607, USA.
authors.forename: Yakup
authors.initials: Y
authors.lastname: Akyol
authors.forename: Lauren W
authors.initials: LW
authors.lastname: Averill
authors.forename: Alfred
authors.initials: A
authors.lastname: Atanda
authors.forename: Heidi H
authors.initials: HH
authors.lastname: Kecskemethy
authors.forename: Michael B
authors.initials: MB
authors.lastname: Bober
authors.forename: William G
authors.initials: WG
authors.lastname: Mackenzie
mesh_terms: D000130:Achondroplasia / Q000473:pathology*; D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012189:Retrospective Studies; D055815:Young Adult