What Is Osteonecrosis (ON)?
Osteonecrosis (ON) affects approximately 20,000newpatients per year in the United States. Although new any age group may develop ON, most patients are between 20 and 50 years old, with the average age in the late 30’s. The diagnosis of ON does not affect life expectancy, and for this reason several hundred thousand patients are living with this disease in the U.S. alone.
What is osteonecrosis?
First, you should understand that bone is a living tissue with living cells and a blood supply. Osteonecrosis means death of bone which can occur from the loss of the blood supply or by some other mean. It has been known by a number of other names including ischemic necrosis of bone, aseptic necrosis or avascular necrosis (AVN). AVN has been quite popular in its use because it is shorter to say and write. More recently the term ON (osteonecrosis)has been adopted. In the following sections, a review of the factors that play a role in your individual treatment and results of those treatments are discussed. It is important to understand that each patient is unique. Differences in the amount of bone involvement, other diseases that you may have, your level of activity, and other factors are extremely important in determining the appropriate treatment for each individual patient. None of the information presented here is intended to take the place of the individual patient-physician encounter. Rather, this brochure is designed to help you understand more about the disease and will assist you in discussing specific treatment options with your physician.
Who’s at Risk?
If a person is completely healthy, the risk of getting osteonecrosis is quite small, probably less than one in 100,000. Another way to understand this is that most of the people who get ON probably have an underlying health problem. Most patients are between 20 and 50 years old with an average age of 38. Patients over the age of 50 are likely to have developed ON either by a fracture of the hip or more rarely in association with disease of the major blood vessels to the lower leg.
What Causes Osteonecrosis?
There are two major forms of ON, post-traumatic and non traumatic. Examples of post-traumatic ON, a common cause of ON, include displaced fractures or dislocations. Minor trauma is not believed to cause ON. Even major injury does not often result in ON. Certain kinds of fracture, where the blood vessels to part of the bone have been physically damaged, may result in ON. Non-traumatic ON occurs when their is no history of trauma. Scientists have identified a number of risk factors that may be associated with non-traumatic ON. We do not know how these risk factors may lead to the development of the disease. There are many different ideas (also called hypotheses). But these ideas have not been proven. There are some cases of osteonecrosis that occur in patients that are otherwise completely healthy with no detectable risk factors. This catagory is called “idiopathic”, a word meaning “of unknown cause”.
What are the Risk Factors?
One of the most common causes of osteonecrosis of the hip and of other joints is a displaced fracture or a dislocation. However, this brochure focuses on non traumatic osteonecrosis. The risk factors for osteonecrosis can be separated into two catagories: definite and probable. The most common risk factor is a history of high dose steroid treatment for some medical condition (e.g., Lupus). Low dose steroids (cortisone, prednisone, etc.)commonly used for bee stings, poison ivy and acute allergies are not thought to cause osteonecrosis. The next most common associated condition is a history of high alcohol use. The greater the alcohol consumption, the higher the risk of osteonecrosis.
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