Overview of Osteonecrosis
The bones of the human body are made up of living cells that need a blood supply to stay healthy. In osteonecrosis, blood flow to part of a bone is disrupted. This results in death of bone tissue, and the bone can eventually break down and the joint will collapse. Osteonecrosis is also called:
- Avascular necrosis.
- Aseptic necrosis.
- Ischemic necrosis of bone.
Osteonecrosis can happen to any bone, but most often it develops in the ends of long bones, such as the:
- Thigh bone (femur), especially the upper part—the ball in the hip socket. The lower end, which is part of the knee joint, is also often affected.
- Upper arm bone (humerus), especially the upper part—the ball in the shoulder joint.
When the disease involves part of a bone in a joint, it can lead to the breakdown of the bone and arthritis.
Less often, the bones of the elbows, ankles, feet, wrists and hands are affected.
The primary symptom of osteonecrosis is pain, and doctors usually diagnose the disease using imaging methods such as x-rays or magnetic resonance imaging (MRI). Most people require surgical treatment to prevent further bone damage, to protect the bones and joints, and to improve use of the joints.
Who Gets Osteonecrosis?
People of any age can get osteonecrosis, but it is most common in people in their 30s and 40s. Cases of osteonecrosis that stem from an injury are said to be traumatic, while all other cases are considered nontraumatic or atraumatic.
Doctors have identified a number of risk factors that may make a person more likely to get osteonecrosis. However, some people who get the disease do not have any known risk factors. The risk factors may include:
A broken or dislocated bone or a joint injury may damage the surrounding blood vessels. This can decrease the blood supply to the bone and lead to osteonecrosis.
- Corticosteroids. These medicines, commonly used to treat asthma, arthritis, systemic lupus erythematosus (lupus), and other conditions, act by reducing inflammation. While the reasons are unclear, they increase the risk of osteonecrosis when they are used for long periods at high doses. The risk of osteonecrosis is low when they are used on a short-term basis at lower doses.
Excessive Alcohol and Tobacco Use
Excessive use of alcohol is a risk factor for osteonecrosis, but why it makes people more likely to develop the disease is unclear. Overuse of alcohol can cause fatty substances to build up in the blood vessels and can increase cortisol (hormone that can cause blood vessels to narrow) levels in the blood. Together, these may decrease blood flow to the bone and lead to osteonecrosis. Research has also shown that excessive tobacco use is also a risk factor.
Some medical conditions may increase the risk of osteonecrosis, including:
- Certain blood disorders, such as sickle cell disease.
- Certain types of cancer, such as leukemia.
- Decompression sickness, also known as divers’ disease, the bends, or caisson disease.
- Gaucher disease.
- HIV infection.
- Rheumatoid arthritis.
Some medical interventions may increase the risk of osteonecrosis, including:
- Kidney or other organ transplantation. The use of corticosteroids to avoid organ rejection may be a contributing factor.
- Radiation treatment.
Types of Osteonecrosis
Health care professionals describe two types of osteonecrosis:
- Traumatic, which follows an injury. The most common causes of traumatic osteonecrosis are a bone fracture or dislocation.
- Nontraumatic (or atraumatic), when there is no history of injury.
Symptoms of Osteonecrosis
There may be no symptoms of osteonecrosis at first, but as the disease progresses, you may gradually start to feel pain, especially in weight-bearing bones such as the thigh bone (femur). The disease most commonly affects the hip joint, and the pain is usually felt in the groin or, less commonly, in the buttock area.
Most people first experience pain when they put weight on the affected joint, but eventually the joint may feel painful even when resting. Over time, the joint may stiffen and lose its range of motion, and osteoarthritis may set in. If the end of the bone collapses, the pain may intensify abruptly.
The time period between the start of symptoms and loss of function of the joint varies from person to person and ranges from a few weeks to more than a year.
Cause of Osteonecrosis
Osteonecrosis happens when the blood supply to part of a bone is disrupted, depriving bone tissue of essential nutrients and oxygen. If the affected part of the bone is small and not subject to major weight-bearing forces, it may not cause a problem or the body’s repair processes may be able to rebuild the damaged area. But in most cases, the repair mechanisms do not work and the bone erodes or develops fractures; eventually, it may break down and collapse.
In traumatic osteonecrosis, which develops from an injury, the loss of blood flow is likely due to damage to blood vessels. The reasons for the loss of blood supply are less clear in nontraumatic cases, but may be due to blood clots blocking the circulation or elevated pressure within the bone constricting the vessels and decreasing blood flow.
While the underlying causes of nontraumatic osteonecrosis are not fully understood, scientists believe that genetics, along with other factors—such as alcohol overconsumption, certain medications, or other diseases--may play a role.