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What can you tell me about a knee problem called spontaneous osteonecrosis? This is something a family member has developed. We're all concerned and wondering how it started, if it's contagious, and what will happen to our family member who's got the condition.

Osteonecrosis of the knee is a condition where a portion of the femur (thigh bone) loses its blood supply, dies, and collapses. Another term used for osteonecrosis is avascular necrosis. The term avascular means that a loss of blood supply to the area is the cause of the problem and necrosis means death. This condition can affect other joints as well (e.g., hip, shoulder). When the knee is involved, the problem usually occurs on the medial femoral condyle -- that's the large round knob of bone (called a condyle) at the bottom of the femur. The medial condyle is affected most often. That's the side closest to the other knee. There are three separate types of knee osteonecrosis. Each one is associated with different causes. In the case of spontaneous osteonecrosis, as the name suggests -- it just happens without warning or known cause. There probably is an underlying cause but we just don't know what it is yet. For example, some experts think that a mini-fracture of the layer of bone just under the knee cartilage (called the subchondral layer) may later become osteonecrotic. Separately, there has been some suspicion that osteopenia (decreased bone density prior to developing osteoporosis) is also part of the initial process in spontaneous osteonecrosis. If it turns out that either of these conditions leads to osteonecrosis then this type of osteonecrosis won't be called spontaneous any longer. There is no evidence that this condition (no matter what causes it) is hereditary or contagious. Spontaneous osteonecrosis is the most likely to respond to conservative (nonoperative) treatment. If the lesion does not improve and get smaller with nonsurgical management in the first three months after diagnosis, then the surgeon may scrape the bone clean of any dead cells and give the joint a chance to heal. Transferring bone cells from a healthy part of the joint to the osteonecrotic section is another treatment option for spontaneous osteonecrosis. This procedure is called mosaicplasty. There are other surgical procedures available for the treatment of severe spontaneous osteonecrosis (e.g., joint replacement). But that's farther down the road for anyone just diagnosed with the problem. With early diagnosis, it's highly likely that your family member will have a good result with conservative treatment.

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