Avascular necrosis (AVN), also known as osteonecrosis, aseptic necrosis and ischemic necrosis, results from temporary or permanent loss of blood supply to a section of bone that, if undetected and untreated, may lead to fragmentation and complete bony collapse. It’s important to diagnose the condition long before the late stages of disease, when the only option may be prosthetic replacement of the bone involved — if that’s still possible.

There are many potential causes of AVN, the most common being injury, corticosteroid therapy, alcohol intake and diabetes. Other disease entities linked to AVN include systemic malignancy, lupus erythematosus, sickle cell disease, Gaucher’s disease, Caisson’s disease (hyperbaric), gout, osteoarthritis, osteoporosis, radiation therapy, chemotherapy, infection (including tuberculosis), HIV, meningococcemia and organ transplantation. A large proportion of cases, however, have no obvious etiologic factor and are reported as idiopathic.

Unfortunately, plain radiographs (x-rays) are notoriously insensitive for detecting early development of AVN. If signs of AVN are present on x-ray films, it means the condition is well advanced. In such cases, x-ray signs include subchondral radiolucency “crescent sign,” followed by patchy linear sclerosis, remodelling (i.e. flattening of femoral heads), joint space narrowing and eventual progressive joint destruction and osseous collapse. As many cases of AVN develop without any symptoms, x-rays are still often the first modality to discover the disease.

For early detection of suspected AVN, the imaging modality of choice is MRI. If unavailable, nuclear medicine bone scan with SPECT, or CT scan could be considered.

References

1. Agarwal R et al. Journal of Medical Case Reports 2008;2:361-3.
2. Imhof H et al. European Radiology 1997;7:180-6.