Avascular Necrosis

Picture by Frank Gillard from Radiopaedia

Seeing this x-ray reminds me of what I was suspected of having when I started having persistent knee pain back in early 2002, which then led me to having 3 knee surgeries. A doctor I consulted suspected I had early avascular necrosis in my lateral femoral condyle. 

Avascular necrosis (also know as osteonecrosis) is the dying of bone tissue due to lack of blood supply. Depending on where it is, it can lead to tiny breaks in the bone and cause the bone to collapse. This process can take years to occur.

A dislocated joint or a fracture in parts of the bone can also hinder or stop blood flow to a section of the remaining bone. This commonly occurs at the epiphysis (end part) of long bones at weight bearing joints. Some common sites include the femoral head, talus, humeral head, knee and the scaphoid bone (in the wrist).

Avascular necrosis is associated with long term use of steroid medications and injections and too much alcohol. Anyone can be affected. It tends to be most common in people between the ages of 30 and 50.

Repetitive trauma can also cause avascular necrosis. This is not as commonly discussed in the medical journals. This form of avascular necrosis is most common in athletes. Rafael Nadal has a chronic left foot ailment, Mueller-Weiss syndrome where there is avasular necrosis in his navicular bone. Young gymnasts that I have previously treated are also prone to this in the wrist, knee and hips.

The doctor I consulted for my persistent knee pain back then felt that my super high mileage  (I was training for the 100 km Trailwalker event in Hong kong and the full Ironman) caused my knee pain.

The cause of avascular necrosis brought on by trauma (or repetitive stress like running and jumping) is not fully understood. Genetics combined with certain medication (like corticisteroids), excessive alcohol intake and other diseases like sickle cell anemia and Gaucher's disease can play a role as well.

Fatty deposits (or lipids) in blood vessels can block blood vessels and reduce blood flow to bone as well. There are suggestions that long term and high doses of corticisteroids (like prednisone) can increase lipid levels in blood, reducing blood flow to the bones.

Some people have no pain or symptoms at all in the early stages of avascular necrosis. As it worsens, the affected joints may hurt when weight bearing. Eventually there may be pain even at rest. Pain can be mild or severe and develops gradually. 

Having too many alcoholic drinks over several years can also cause fatty deposits to form in blood vessels.

Certain medical treatments like radiation therapy for cancer can also weaken bone. Kidney transplant patients have also been known to be associated with avascular necrosis.

To reduce the risk of avascular necrosis, please limit your alcohol intake since heavy drinking is one of the top risk factors for developing avascular necrosis. 

Keep your cholesterol levels low as tiny bits of fats (lipids) are the most common substance blocking blood supply to bones. Stop smoking as smoking narrows blood vessels which will reduce blood flow.

For those doing repetitive sports, I always suggest running on softer surfaces like grass or sand. Do not be in a hurry to increase your mileage, your bones and joints need time to get used to the load.

Lessen the junk miles or better still ride the stationary bike or use the elliptical trainer to target different areas. Strength training is very important for your bone health.

Reference

Shah KN, Racine J, Jones LC et al (2015). Pathophysiology And Risk Factors For Osteonecrosis. Curr Rev Muscu Med. 8(3): 201-209. DOI: 10.1007/s12178-015-9277-8