Fat intensity within the hypointense zone on MR imaging of avascular necrosis of the femoral head.

In some patients with avascular necrosis of the femoral head (ANFH), an area of signal intensity similar to that of subcutaneous fat tissue is found within or proximal to the hypointense zone of spin echo MR images. We refer to these MR findings as the "fat intensity" sign. This fat intensity sign was positive in 62 (47%) of 133 MR examinations of femoral heads with radiographically proven ANFH; this sign was negative in all hips with other diseases including degenerative joint disease, transient osteoporosis, rapidly destructive coxoarthrosis, and rheumatoid arthritis.