MRI in the diagnosis of Osteonecrosis
How good is MRI in the diagnosis of ON? What about other imaging studies?
Compared with other diagnostic studies, MRI has been found to have the highest sensitivity and best diagnostic accuracy, thus obviating invasive diagnostic procedures such as biopsy and bone marrow pressure determinations. Sensitivity and diagnostic accuracy appear to be 95% to 99%. The characteristic MRI finding is an area or line of decreased signal on both T1 and T2 images ( Fig. 54.2 ). This area appears to correspond with the demarcation between live regenerating bone and necrotic tissue. In patients who cannot undergo an MRI, radionuclide bone scanning can show a subchondral “cold spot” (avascular necrosis) surrounded by a “hot” area (donut sign) where there is increased osteoblastic activity at the interface with the necrotic bone. A computed tomography CT scan will show necrotic and reactive bone.
