MR imaging of osteonecrosis of the knee in children with acute lymphocytic leukemia.

This essay illustrates various patterns of progression of osteonecrosis of the knee and the relationship between early MR imaging findings and radiologic outcome in children with acute lymphocytic leukemia. It also includes a review of nonosteonecrosis signal abnormalities, which are common in the knee region and are often transient. Such abnormalities must be distinguished from osteonecrosis, which can lead to joint collapse and predispose to secondary arthritis.