title: The incidence of occult dysplasia of the contralateral hip in children with unilateral hip dysplasia.
abstract: BACKGROUND
  The purpose of this study is to determine the incidence of contralateral hip dysplasia in children with unilateral hip dysplasia.
  
  
  METHODS
  We reviewed all patients with developmental dysplasia of the hip (DDH) who were evaluated at our institution until skeletal maturity (at least age 13 years). In the contralateral ("normal") hip, radiographic measurements of the acetabular angle >46 degrees, center edge angle <20 degrees, and migration index >20% were considered abnormal.
  
  
  RESULTS
  Of the 43 patients in the study, 18 (42%) were diagnosed with bilateral hip dysplasia as an infant or toddler; 8 on the initial visit, and 10 after repeated evaluations. Twenty-five patients had no evidence of contralateral hip dysplasia, even on repeated examinations. Of this group, 10 of 25 (40%) had mild acetabular dysplasia at maturity (mean center edge angle, 31 degrees; acetabular angle, 43 degrees; and migration index, 14%). No child in this group was diagnosed with significant hip dysplasia at skeletal maturity that required treatment to date.
  
  
  CONCLUSIONS
  The results of this study indicated that mild acetabular dysplasia occurs at maturity in the contralateral hip in up to 40% of patients diagnosed with unilateral DDH, even when the contralateral hip was carefully evaluated as a child. The significance of mild acetabular dysplasia is not well defined, but intermittent evaluation of the contralateral hip in children with DDH would seem prudent.
  
  
  METHODS
  IV.
authors.affiliation: Shriners Hospitals for Children, Philadelphia, PA, USA.
authors.forename: Frederick S
authors.initials: FS
authors.lastname: Song
authors.forename: James J
authors.initials: JJ
authors.lastname: McCarthy
authors.forename: G Dean
authors.initials: GD
authors.lastname: MacEwen
authors.forename: Katherine E
authors.initials: KE
authors.lastname: Fuchs
authors.forename: Susan E
authors.initials: SE
authors.lastname: Dulka
mesh_terms: D000077:Acetabulum / Q000002:abnormalities; D000293:Adolescent; D000328:Adult; D000365:Age Determination by Skeleton; D005500:Follow-Up Studies; D006617:Hip Dislocation / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology; D006618:Hip Dislocation, Congenital / Q000503:physiopathology*; D006801:Humans; D015994:Incidence