MR imaging of avascular necrosis of the femoral head: value of small-field-of-view sagittal surface-coil images.

We compared coronal, large-field-of-view, body-coil MR images with sagittal, small-field-of-view, surface-coil images of 30 hips for their sensitivities in establishing the diagnosis of avascular necrosis; spatially localizing the avascular necrosis; and detecting joint-space narrowing, femoral head collapse, articular cartilage fracture, and joint fluid. We also compared the two separate plane/coil combinations for detection of the "double-line" sign (high signal inside a band of low signal, believed to be characteristic for avascular necrosis) and intertrochanteric conversion of hematopoietic marrow to fatty marrow. Coronal, large-field-of-view, body-coil images provided an adequate screening examination for the presence of avascular necrosis (sensitivity of 94%) and were preferred in all cases for mediolateral localization of focal abnormality. They were also better for assessing joint fluid and detecting fatty conversion of marrow. Sagittal, small-field-of-view, surface-coil images were preferred for anteroposterior localization in all cases and for superoinferior localization of focal abnormality in 15 of 18 cases. They detected additional cases of joint-space narrowing, articular cartilage fracture, and the double-line sign missed by coronal, body-coil images. Sagittal, small-field-of-view, surface-coil images are a valuable adjunct to MR evaluation of femoral avascular necrosis because they provide additional information that may be useful for planning surgical therapy.