title: The unstable slipped capital femoral epiphysis: risk factors for osteonecrosis.
abstract: BACKGROUND
  The incidence of avascular necrosis (AVN) after unstable slipped capital femoral epiphysis (SCFE) varies widely in the literature (10% to 60%), and few studies have examined why certain unstable slips develop osteonecrosis whereas others do not. Our purpose was to determine risk factors for developing AVN after unstable SCFE.
  
  
  METHODS
  We reviewed all unstable SCFEs treated primarily at our center. Medical records were reviewed to determine weight-percentile, age, length of prodromal symptoms, and time to treatment. Operative notes were used to classify treatment as either: (group 1) in situ screw fixation, (group 2) purposeful or inadvertent closed reduction and screw fixation, or (group 3) open reduction and internal fixation, and to determine whether or not the joint was decompressed during surgery. Preoperative radiographs were used to measure slip angle and percent translation. For group 2, these were compared with postoperative radiographs to calculate a Deltaslip angle and Deltatranslation. Student t tests and Fisher exact tests were used for statistical analysis.
  
  
  RESULTS
  Of the 70 patients in our series, 14 developed AVN (20%). On the basis of treatment, 3 of 16 patients in group 1 (19%), 10 of 38 patients in group 2 (26%), and only 1 of 16 patients in group 3 (6%) developed AVN. Patients who developed osteonecrosis were significantly younger (11.67 y vs. 12.83 y, P=0.04) and had a significantly shorter duration of prodromal symptoms (17.5 d vs. 65.9 d, P=0.03) compared with those who did not develop AVN. None of the other factors were found to be significant. In a subgroup analysis looking solely at group 2 patients, those who developed AVN had a significantly higher initial slip angle compared with those who did not (62 degrees vs. 51 degrees, P=0.03).
  
  
  CONCLUSIONS
  In this, the largest reported series of unstable slips treated with internal fixation, AVN seemed more likely to develop in younger patients with a shorter duration of prodromal symptoms. Patients undergoing open reduction may have a lower incidence of AVN, but our limited power precludes definitive conclusions.
  
  
  METHODS
  Level IV (case series).
authors: Division of Orthopaedic Surgery, The Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors: Wudbhav N
authors: WN
authors: Sankar
authors: Thomas G
authors: TG
authors: McPartland
authors: Michael B
authors: MB
authors: Millis
authors: Young-Jo
authors: YJ
authors: Kim
mesh_terms: D000293:Adolescent; D000367:Age Factors; D002648:Child; D004839:Epiphyses, Slipped / Q000150:complications* / Q000473:pathology / Q000601:surgery; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging / Q000473:pathology; D005271:Femur Head Necrosis / Q000000981:diagnostic imaging / Q000209:etiology*; D005500:Follow-Up Studies; D005593:Fracture Fixation, Internal / Q000379:methods; D006801:Humans; D008297:Male; D011183:Postoperative Complications / Q000209:etiology*; D011859:Radiography; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors