IS Case 260: Avascular necrosis (AVN)
Imaging Sciences uRMC 2009
Publication Date: 2009-06-26
Avascular necrosis (AVN)
Avascular necrosis is the cellular death of bone tissue. It occurs when the bone is deprived of sufficient oxygen by interruption of the arterial blood supply. This can occur by numerous mechanisms including fracture, dislocation, mechanical stress, pregnancy, pancreatitis and radiation exposure to name a few. In the US, the two most common causes of AVN are steroid use and Sickle cell disease.
Initial radiographs may be completely normal; the earliest radiographic sign on plain film is a radiolucent crescent in the region of necrosis (crescent sign), which can be seen approximately 4-6 weeks after injury. In later stages, radiographs will demonstrate both lucencies, signifying the structural collapse of subchondral matrix, and sclerosis, which is due to a combination of new bone deposition and bone compression. Eventually, radiographs will demonstrate flattening of the articular head. MRI and nuclear medicine studies can also be done to diagnose this entity.
- Greenspan A. Orthopedic Imaging: A Practical Approach, 4th ed. Philadelphia: Lippincott Williams. & Wilkins, 2004: 75-78.