title: Normal values of bony, cartilaginous, and labral coverage of the infant hip in MR imaging.
abstract: BACKGROUND
  Magnetic resonance imaging (MRI) is becoming more popular in the evaluation of residual hip dysplasia. Normal values of the bony, cartilaginous, and labral coverage in MRI are not published. The aim of our study was to establish reference values for normal hips at different ages and to assess the interobserver variability of such measurements.
  
  
  METHODS
  MRIs of 115 normal hips in 73 children were analyzed. The bony, cartilaginous, and labral acetabular index (AI bone/cartilage/labrum) was measured in the coronal plane just posterior to the inferior branch of the triradiate cartilage. To determine interobserver variability, measurements were made by 3 different observers. Percentile graphs were established from the Student t distribution of the measurements grouped by 2 years of age.
  
  
  RESULTS
  Global interobserver variability for the measurement of the AI bone was excellent [intraclass correlation coefficient (ICC)=0.88]. For the AI cartilage and labrum the ICC was somewhat lower (ICC 0.78) but still rated as good. Age-dependent percentile graphs of the AI bone, cartilage, and labrum are presented. Although the AI bone decreased during childhood, the AI cartilage as well as the AI labrum stays relatively constant with the 50 percentile around 5 degrees for the AI cartilage and -5 degrees for the AI labrum. The 90 percentile is around 10 degrees for the AI cartilage and 0 degrees for the AI labrum.
  
  
  CONCLUSIONS
  We present percentile graphs of age-related normal values. Although bony coverage increases during childhood, cartilaginous and labral coverage stay constant. We think that measuring an AI cartilage above 10 degrees or an AI cartilage above 0 degrees might be a good additional parameter to classify hips into the group of residual dysplasia.
  
  
  CONCLUSIONS
  The knowledge of normal values for cartilaginous and labral coverage is a valuable adjunct in decision-making for secondary surgery in residual dysplasia. This was a retrospective cross-sectional study.
authors.affiliation: *Department of Pediatric Orthopaedic Surgery, CHU Brabois Hôpital d'Enfants, Rue du Morvan, France †Department of Surgery, University Children's Hospital of Zürich, Zürich ‡Division of Paediatrics Orthopaedic, University of Geneva, Geneva, Switzerland.
authors.forename: Hanspeter
authors.initials: H
authors.lastname: Huber
authors.forename: Laurence
authors.initials: L
authors.lastname: Mainard-Simard
authors.forename: Pierre
authors.initials: P
authors.lastname: Lascombes
authors.forename: Fay
authors.initials: F
authors.lastname: Renaud
authors.forename: Meyer
authors.initials: M
authors.lastname: Jean-Baptiste
authors.forename: Pierre
authors.initials: P
authors.lastname: Journeau
mesh_terms: D000077:Acetabulum / Q000033:anatomy & histology*; D000293:Adolescent; D002358:Cartilage, Articular / Q000033:anatomy & histology*; D002648:Child; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006621:Hip Joint / Q000033:anatomy & histology*; D006801:Humans; D007223:Infant; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D012372:ROC Curve; D012016:Reference Values; D012189:Retrospective Studies