The Journal of Bone and Joint Surgery (American). 2006;88:35-40.
doi:10.2106/JBJS.F.00535
© 2006 The Journal of Bone and Joint Surgery, Inc.
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Prediction of Collapse in Femoral Head Osteonecrosis: A Modified Kerboul Method with Use of Magnetic Resonance Images

Yong-Chan Ha, MD, Woon Hwa Jung, MD, Jang-Rak Kim, MD, Nak Hoon Seong, MD, Shin-Yoon Kim, MD and Kyung-Hoi Koo, MD

Corresponding author:
Kyung-Hoi Koo, MD
Department of Orthopaedic Surgery, Seoul National University Bundang Hospital, 300 Gumi-dong, Bundang-gu, Seongnam, Gyeonggi-do 463-707, South Korea.
E-mail address: khkoo{at}snu.ac.kr

The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

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°), grade 2 (200° to 249°), grade 3 (250° to 299°), and grade 4 (≥300°). 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° (the low-risk group) collapsed, all twenty-five hips with a combined necrotic angle of ≥240° (the high-risk group) collapsed, and four (50%) of the eight hips with a combined necrotic angle between 190° and 240° (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.

Level of Evidence: Prognostic Level I. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.


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