title: The presence of an ossific nucleus does not protect against osteonecrosis after treatment of developmental dysplasia of the hip.
abstract: BACKGROUND
  Osteonecrosis (ON) is a major complication after treatment of developmental dysplasia of the hip (DDH). Several studies have explored the absence of the femoral head ossific nucleus at the time of hip reduction as a risk factor for the development of ON, but findings have been inconsistent.
  
  
  OBJECTIVE
  We therefore determined the incidence of ON in children who underwent reduction of a dislocated hip in the presence or absence of the ossific nucleus.
  
  
  METHODS
  We retrospectively reviewed the radiographs of 105 hips in 89 patients treated for DDH at the age of 18 months or younger. Radiographs were graded for the presence of the ossific nucleus at the time of hip reduction and for the presence of ON, as graded by the Bucholz and Ogden classification, for patients at a mean age of 10 years. We used log-binomial regression to estimate if the presence of the ossific nucleus was associated with a lower incidence of ON.
  
  
  RESULTS
  We identified ON in 37 of the 105 hips (35%). The incidence of ON at 10 years was 40% in the absence of the ossific nucleus and 32% in the presence of the ossific nucleus (adjusted relative risk, 0.86; 95% confidence interval, 0.36-1.81). When only radiographic changes of Grade II and greater were considered ON, the risk was still not increased (relative risk, 1.26; 95% confidence interval, 0.62-2.56).
  
  
  CONCLUSIONS
  Patients with an ossific nucleus at the time of hip reduction showed a slight tendency toward better outcomes. The ossific nucleus did not protect for ON.
  
  
  METHODS
  Level III, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Great Ormond Street Hospital for Children, Great Ormond Street, London WC1N 3JH, UK. a.roposch@ich.ucl.ac.uk
authors.forename: Andreas
authors.initials: A
authors.lastname: Roposch
authors.forename: Odeh
authors.initials: O
authors.lastname: Odeh
authors.forename: Andrea S
authors.initials: AS
authors.lastname: Doria
authors.forename: John H
authors.initials: JH
authors.lastname: Wedge
mesh_terms: D000293:Adolescent; D016009:Chi-Square Distribution; D002648:Child; D002675:Child, Preschool; D005260:Female; D005271:Femur Head Necrosis / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control* / Q000601:surgery; D006618:Hip Dislocation, Congenital / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D015994:Incidence; D007223:Infant; D008131:London; D008297:Male; D009864:Ontario; D019637:Orthopedic Procedures / Q000009:adverse effects*; D011859:Radiography; D012044:Regression Analysis; D012086:Reoperation; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012720:Severity of Illness Index; D013997:Time Factors