Avascular Necrosis of the Knee

What is avascular necrosis?

Avascular necrosis, also known as osteonecrosis, is a condition that results when blood flow to the bone is reduced or stopped, resulting in the death of cells in the bone tissue. This can ultimately cause weakening and collapse of the bone. As a result of the collapse, the normal contour of the knee joint may become irregular, leading to further destruction of the joint. The pain and loss of motion from avascular necrosis can be corrected by total knee replacement or partial knee replacement, depending on the extent of bony collapse. In the knee, there are two types of osteonecrosis: spontaneous osteonecrosis of the knee (SPONK) and secondary osteonecrosis.

Spontaneous Osteonecrosis of the Knee (SPONK)

SPONK is poorly understood but seems to be the result of some type of trauma to the knee. This trauma may be minor or severe. It usually affects only one knee and most often a single area within the knee. The area of bone in the knee loses its normal blood supply and may eventually weaken and collapse. This typically leads to pain and functional limitations. The pain is often sudden onset and increases with weight bearing, stair climbing, and at night. SPONK is most often seen in elderly women with osteoporosis. When collapse has occurred, surgical intervention is often necessary. Total or partial knee replacement can provide dramatic improvement in pain, function, and quality of life.

Secondary Osteonecrosis of the Knee

The cause of secondary osteonecrosis is unknown. However, several risk factors are associated with the disease. Corticosteroid use (such as oral Prednisone) is the most significant risk factor. Other risk factors include alcohol abuse, sickle cell disease, systemic lupus erythematosus (SLE), caisson disease (barotrauma), and Gaucher disease. Multiple areas of the knee are often affected, and 80% of people have both knees affected. Other areas of the body (such as the hip) also may be affected. The pain is usually longstanding and insidious in nature. When joint collapse has occurred, surgical intervention is often necessary. Total knee replacement can provide dramatic improvement in pain, function, and quality of life.

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