Importance of sagittal MR imaging in nontraumatic femoral head osteonecrosis in children

Background  In nontraumatic femoral head osteonecrosis, characterization of femoral head collapse is important in staging disease progression and planning treatment. Few prior studies have quantitatively compared the ability of sagittal and coronal MR images to detect femoral head collapse. Objective  We hypothesized that sagittal MR images show a greater degree and angular span of femoral head collapse than coronal images. Materials and methods  We reviewed 38 hip MRI scans of nontraumatic femoral head osteonecrosis from 34 pediatric patients. In both sagittal and coronal images, the maximal extent and angular location along with the angular span of the femoral head collapse were measured. Differences were evaluated using a paired t-test. The extent of bone and cartilage loss from the femoral head was evaluated. Results  Sagittal MR images showed 29% maximal femoral head radius collapse, whereas coronal images showed 16% collapse (P<0.001). Sagittal images showed a larger angular span of collapse (115°) than coronal images (55°, P<0.001). Sagittal images showed greater epiphyseal bone loss in the anterior than in the posterior portion (P<0.001), whereas coronal images did not show a significant difference in bone loss between the medial and lateral portion (P=0.32). Conclusion  Sagittal images show greater femoral head collapse than coronal images in nontraumatic femoral head osteonecrosis.