title: Radiographic threshold values for hip screening in cerebral palsy.
abstract: OBJECTIVE
  To analyse the consequences of using different radiographic measurements and different threshold values for hip screening in children with cerebral palsy (CP).
  
  
  METHODS
  In a total sample of children with CP a standardised radiological follow-up of the hips was carried out as a part of a hip prevention programme. Acetabular index (AI) and migration percentage (MP) were measured on all radiographs. In this study, 1,067 radiographs of 272 children born 1992-1998 were analysed.
  
  
  RESULTS
  Lateral displacement of the femoral head was common without acetabular dysplasia, and acetabular dysplasia occurred at a later stage than femoral head lateralisation. Hip dysplasia without lateral displacement of the femoral head was rare. In 16 of the 56 hips (29%) with AI >/= 27 degrees and in 23 of the 71 (32%) hips with MP >/= 33% the values decreased below the threshold value without operative treatment. In hips with AI >/= 30 degrees only 2 of 31 hips (6%) and in hips with MP >/= 40% only 5 of 44 hips (11%) decreased below the threshold values without operative treatment.
  
  
  CONCLUSIONS
  Radiographic follow-up with only measurement of the MP seems sufficient in screening for dislocation in children with CP. MP >/= 33% is recommended as threshold for reaction or intensified observation. In children with MP >/= 40%, the lateral displacement increased over time in most hips, thus indicating the need for operative intervention. In children with MP 33-40%, treatment should be based on other clinical signs and the progression of MP over time.
authors.affiliation: Department of Orthopaedics, Lund University Hospital, 221 85, Lund, Sweden, gunnar.hagglund@ort.lu.se.
authors.forename: Gunnar
authors.initials: G
authors.lastname: Hägglund
authors.forename: Henrik
authors.initials: H
authors.lastname: Lauge-Pedersen
authors.forename: Måns
authors.initials: M
authors.lastname: Persson