title: Prediction of collapse in femoral head osteonecrosis: a modified Kerboul method with use of magnetic resonance images.
abstract: BACKGROUND
  The hypothesis that the combined necrotic angle measurement from magnetic resonance imaging scans predicts the subsequent risk of collapse in hips with femoral head necrosis was tested.
  
  
  METHODS
  Thirty-seven hips with early stage osteonecrosis in thirty-three consecutive patients were investigated. With use of the modified method of Kerboul et al., we measured the arc of the femoral surface involved by necrosis on a midcoronal as well as a midsagittal magnetic resonance image (rather than an anteroposterior and a lateral radiograph) and then calculated the sum of the angles. On the basis of the magnitude of the resulting combined angle, hips were classified into four categories: grade 1 (<200 degrees), grade 2 (200 degrees to 249 degrees), grade 3 (250 degrees to 299 degrees), and grade 4 (>/=300 degrees). After the initial evaluations, the hips were randomly assigned to a core decompression group or a nonoperative group. Patients underwent regular follow-up until femoral head collapse or for a minimum of five years.
  
  
  RESULTS
  Seven grade-4 hips and sixteen grade-3 hips had development of femoral head collapse by thirty-six months. Six of the nine grade-2 hips and none of the five grade-1 hips collapsed (log-rank test, p < 0.01). None of the four hips with a combined necrotic angle of </=190 degrees (the low-risk group) collapsed, all twenty-five hips with a combined necrotic angle of >/=240 degrees (the high-risk group) collapsed, and four (50%) of the eight hips with a combined necrotic angle between 190 degrees and 240 degrees (the moderate-risk group) collapsed during the study period.
  
  
  CONCLUSIONS
  The Kerboul combined necrotic angle, as ascertained with use of magnetic resonance imaging scans instead of radiographs, is a good method to assess future collapse in hips with femoral head osteonecrosis.
  
  
  METHODS
  Prognostic Level I. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.
authors.forename: Yong-Chan
authors.initials: YC
authors.lastname: Ha
authors.forename: Woon Hwa
authors.initials: WH
authors.lastname: Jung
authors.forename: Jang-Rak
authors.initials: JR
authors.lastname: Kim
authors.forename: Nak Hoon
authors.initials: NH
authors.lastname: Seong
authors.forename: Shin-Yoon
authors.initials: SY
authors.lastname: Kim
authors.forename: Kyung-Hoi
authors.initials: KH
authors.lastname: Koo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001837:Body Weights and Measures / Q000379:methods*; D005260:Female; D005271:Femur Head Necrosis / Q000473:pathology* / Q000601:surgery*; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D016896:Treatment Outcome