Avascular (aseptic) necrosis

also known as osteonecrosis,

Causes: e.g. Steroid therapy , Sickle cell & Fractures

The plain radiographic features:

• Increased density of the subchondral bone
• Irregularity of the articular contour or even fragmentation of the bone.
• A characteristic crescentic lucent line may be seen just beneath the articular cortex.
• MRI has now become the imaging modality of choice for demonstrating avascular necrosis A- Avascular necrosis. There is fragmentation with some sclerosis of both femoral heads

B- Coronal MRI scan showing avascular necrosis of both femoral heads. The changes on the left are very severe and advanced. The changes in the right hip are relatively early and show a rim of low signal demarcating the ischemic area (arrows)