MRI-negative, bone scintigram-positive in early osteonecrosis of the knees.

Nontraumatic avascular necrosis (AVN) of bone is a well-reported complication of glucocorticoid therapy for immunologic and malignant disease. We present the case of a 13-year-old girl with no history of trauma who presented with a 5-day history of increasing pain in both knees after cord blood transplantation for acute lymphoblastic leukemia. Plain film and magnetic resonance imaging (MRI) were reported as normal. Bone scintigraphy revealed evidence of bilateral avascular necrosis in the distal femora. MRI subsequently became abnormal several weeks later. The case illustrates the natural history of AVN, in which changes that are detected by MRI can take several weeks to develop. The scintigraphic findings influenced early management of the condition.