title: The acetabulum in Perthes' disease: a prospective study of 123 children.
abstract: OBJECTIVE
  We assessed the radiographic changes of the acetabulum during the course of Perthes' disease and investigated whether they were associated with femoral head sphericity 5 years after diagnosis.
  
  
  METHODS
  We studied 123 children with unilateral Perthes' disease, femoral head necrosis more than 50 % and age at diagnosis 6 years or older. Pelvic radiographs were taken at onset, 1 year and 5 years after diagnosis. Sharp's angle, acetabular depth-to-width ratio (ADR) and lateral acetabular inclination were measured.
  
  
  RESULTS
  Compared to the unaffected hips, the Perthes' hips developed significantly higher Sharp's angles (p < 0.001) and a higher proportion with an upward-sloping lateral acetabular margin (Perthes' hips: 49 %, unaffected hips 1 %). The mean ADR values were significantly lower on the affected side at all stages (p < 0.001). ADR values at diagnosis were associated with a more spherical femoral head at the 5-year follow-up [odds ratio (OR) 1.012, 95 % confidence interval (CI) 1.002-1.022, p = 0.016]. None of the other acetabular parameters were significantly associated with the femoral head shape 5 years after diagnosis.
  
  
  CONCLUSIONS
  The acetabulum developed an increasingly dysplastic shape in the course of Perthes' disease. Early dysplastic changes of the acetabulum were not associated with a poor radiological outcome 5 years after diagnosis. Routine measurement and monitoring of acetabular changes in plain radiographs were of little prognostic value and can, therefore, hardly be recommended in clinical practice.
authors.affiliation: Department of Pediatric Orthopaedic Surgery, Oslo University Hospital, Rikshospitalet, 0027, Oslo, Norway, uxhuhs@ous-hf.no.
authors.forename: S
authors.initials: S
authors.lastname: Huhnstock
authors.forename: S
authors.initials: S
authors.lastname: Svenningsen
authors.forename: A H
authors.initials: AH
authors.lastname: Pripp
authors.forename: T
authors.initials: T
authors.lastname: Terjesen
authors.forename: O
authors.initials: O
authors.lastname: Wiig