Osteonecrosis

Osteonecrosis is a disease resulting from the temporary or permanent loss of blood supply to the bones. Without blood, the bone tissue dies, and ultimately the bone may collapse. If the process involves the bones near a joint, it often leads to collapse of the joint surface.

Although it can happen in any bone, osteonecrosis most commonly affects the ends (epiphysis) of the femur, the bone extending from the knee joint to the hip joint. Other common sites include the upper arm bone, knees, shoulders, and ankles. The disease may affect just one bone, more than one bone at the same time, or more than one bone at different times. According to the American Academy of Orthopedic Surgeons, 10,000 to 20,000 people develop osteonecrosis each year, and most of them are between 20 and 50 years of age. Osteonecrosis is the underlying diagnosis in approximately 10% of hip replacements. Orthopedists – doctors who specialize in the diagnosis and treatment of injuries and diseases of the musculoskeletal system – most often diagnose this disease.

The amount of disability that results from osteonecrosis depends on what part of the bone is affected, how large an area is involved, and how effectively the bone rebuilds itself. Normally, bone continuously breaks down and rebuilds – old bone is replaced with new bone. This process, which takes place after an injury as well as during normal growth, keeps the skeleton strong and helps it to maintain a balance of minerals. In the course of osteonecrosis, however, the healing process is usually ineffective and the bone tissues break down faster than the body can repair them. If left untreated, the disease progresses, the bone collapses, and the joint surface breaks down, leading to pain and arthritis.

Other Names

 * Avascular necrosis
 * Aseptic necrosis
 * Ischemic necrosis

Causes
Osteonecrosis is caused by impaired blood supply to the bone, but it is not always clear what causes that impairment. Osteonecrosis often occurs in people with certain risk factors (such as high-dose corticosteroid use and excessive alcohol intake) and medical conditions. However, it also affects people with no health problems and for no known reason. Following are some potential causes of osteonecrosis and other health conditions associated with its development.

Steroid medications
One of the most common causes of osteonecrosis is the use of corticosteroid medications such as prednisone. Corticosteroids are commonly used to treat inflammatory diseases such as systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, severe asthma, and vasculitis. Studies suggest that long-term use of oral or intravenous (IV) corticosteroids is associated with nontraumatic osteonecrosis, which is a type of osteonecrosis not caused by direct injury to the bone.

Doctors are not sure exactly why the use of corticosteroids sometimes leads to osteonecrosis. They speculate that the drugs may interfere with the body's ability to break down fatty substances called lipids. These substances then build up in and clog the blood vessels, causing them to narrow and reduce the amount of blood that gets to the bone. Some studies suggest that corticosteroid-related osteonecrosis is more severe and more likely to affect both hips (when occurring in the hip) than osteonecrosis resulting from other causes.

Bisphosphonates
Bisphosphonates are drugs used to promote bone preservation. They include zoledronate (Zometa) and alendronate]] (Fosamax). They are used in people who are at risk of developing weak bones and osteoporosis. However, after they entered the U.S. market in the 1990s, some bisphosphonates had reportedly caused osteonecrosis of the jaw in a small population of users. Many initial cases included people with cancer who had underwent major dental surgery. However, osteonecrosis of the jaw due to bisphosphonate use has now been identified in people with other diseases, such as osteoporosis, Paget disease, arthritis, diabetes, and maxillary fibrous dysplasia. The majority of cases occur following major dental surgery. The mechanism is thought to be impaired growth of blood vessels into the jaw following the dental surgery.

Alcohol use
Excessive alcohol use is another common cause of osteonecrosis. People who drink alcohol in excess can develop fatty substances that may block blood vessels, causing a decreased blood supply to the bones.

Injury
When a fracture, a dislocation, or some other joint injury occurs, the blood vessels may be damaged. This can interfere with the blood circulation to the bone and lead to trauma-related osteonecrosis. In fact, studies suggest that hip dislocation and hip fractures are major risk factors for osteonecrosis.

Increased pressure within the bone may be another cause of osteonecrosis. When there is too much pressure within the bone, the blood vessels narrow, making it hard for them to deliver enough blood to the bone cells. The cause of increased pressure is not fully understood.

Symptoms
In the early stages of osteonecrosis, people may not have any symptoms. As the disease progresses, however, most experience joint pain. At first, the pain occurs only when putting weight on the affected joint. Later, it occurs even when resting. Pain usually develops gradually, and may be mild or severe. If osteonecrosis progresses and the bone and surrounding joint surface collapse, pain may develop or increase dramatically. Pain may be severe enough to limit range of motion in the affected joint. In some cases, particularly those involving the hip, disabling osteoarthritis may develop. The period of time between the first symptoms and loss of joint function is different for each person, but it typically ranges from several months to more than a year.

Diagnosis
After performing a complete physical examination and asking about the patient's medical history, the doctor may use one or more bone imaging techniques to diagnose osteonecrosis. As with many other diseases, early diagnosis increases the chances of treatment success. The tests described below may be used to determine the amount of bone affected and how far the disease has progressed.

X-Ray
A radiograph, or x-ray, is usually the first imaging test used to examine the bone. An x-ray is often useful in diagnosing the cause of joint pain. For osteonecrosis, however, x-rays are not sensitive enough to detect bone changes in the early stages of the disease. So if the x-ray is normal, a doctor may order more tests. In later stages of osteonecrosis, x-rays may show bone damage, and once the diagnosis is made, they are often used to monitor disease progression.

Magnetic resonance imaging (MRI)
Research studies have shown that magnetic resonance imaging, or MRI, is the most sensitive method for diagnosing osteonecrosis in the early stages. Unlike x-rays, bone scans, and CT (computed/computerized tomography) scans, MRI detects chemical changes in the bone marrow. MRI provides the doctor with a picture of the affected area and the bone-rebuilding process. In addition, MRI may show diseased areas that are not yet causing any symptoms. Some doctors caution against aggressive treatment of osteonecrosis that has been detected by MRI but is not causing symptoms. One study has shown evidence that for a select group of patients in the early stages of osteonecrosis, the disease may improve spontaneously.

Computed/Computerized tomography (CT scan)
A CT scan is an imaging technique that provides a three-dimensional picture of the bone. It also shows "slices" of the bone, making the picture much clearer than x-rays and bone scans. Some doctors disagree about the usefulness of this test to diagnose osteonecrosis. Although a diagnosis usually can be made without a CT scan, the technique may be useful in determining the extent of bone damage. CT scans are less sensitive than MRIs.

Bone scan
A type of test called technetium-99m bone scanning is used most commonly in patients who have normal x-rays and no risk factors for osteonecrosis. In this test, a harmless radioactive material is injected through an intravenous line, and a picture of the bone is taken with a special camera. The picture shows how the injected material travels through blood vessels in bone. A single bone scan finds all areas in the body that are affected, thus reducing the need to expose the patient to more radiation.

Biopsy
A biopsy is a surgical procedure in which a tissue sample from the affected bone is removed and studied. Although a biopsy is a conclusive way to diagnose osteonecrosis, it is rarely used because it requires surgery.

Functional evaluation of bone
Tests to measure the pressure inside a bone may be used when a doctor strongly suspects that a patient has osteonecrosis, despite normal results of x-rays, bone scans, and MRIs. These tests are very sensitive for detecting increased pressure within the bone, but they require surgery.

Treatment
Appropriate treatment for osteonecrosis is necessary to keep joints from breaking down. Without treatment, most people with the disease experience severe pain and limitation in movement within two years. To determine the most appropriate treatment, a doctor considers the following:


 * age of the patient
 * stage of the disease (early or late)
 * location and whether bone is affected over a small or large area
 * underlying cause; with an ongoing cause such as corticosteroid or alcohol use, treatment may not work unless use of the substance is stopped.

The goal in treating osteonecrosis is to improve use of the affected joint, stop further damage to the bone, and ensure bone and joint survival. Several approaches are used to achieve these goals.

Nonsurgical treatments
Usually, doctors begin with nonsurgical treatments, alone or in combination. Unfortunately, although these treatments may relieve pain or help in the short term, for most people they don't bring lasting improvement.


 * Medications – Nonsteroidal anti-inflammatory drugs (NSAIDs) are often prescribed to reduce pain. People with clotting disorders may be given blood thinners to reduce clots that block the blood supply to the bone. Cholesterol-lowering medications may be used to reduce fatty substances (lipids) that increase with corticosteroid treatment (a major risk factor for osteonecrosis). In one study, people who took cholesterol-lowering medications called statins [e.g., atorvastatin (Lipitor)] along with corticosteroids significantly reduced the risk of developing osteonecrosis in the first place.
 * Reduced weight bearing – If osteonecrosis is diagnosed early, a doctor may begin treatment by having the patient remove weight from the affected joint. A doctor may recommend limiting activities or using crutches. In some cases, reduced weight bearing can slow the damage caused by osteonecrosis and permit natural healing. When combined with pain medication, reduced weight bearing can be an effective way to avoid or delay surgery for some patients.
 * Range-of-motion exercises – An exercise program involving the affected joints may help keep them mobile and increase their range of motion.
 * Electrical stimulation – This treatment has been used in several centers to induce bone growth, and in some studies has been helpful when used prior to femoral head collapse.

Surgery
A number of different surgical procedures are used to treat osteonecrosis. Most people with osteonecrosis eventually need surgery.


 * Core decompression – This surgical procedure removes the inner cylinder of bone, which reduces pressure within the bone, increases blood flow to the bone, and allows more blood vessels to form. Core decompression works best in people who are in the earliest stages of osteonecrosis, often before the collapse of the joint. This procedure sometimes reduces pain and slows the progression of bone and joint destruction.
 * Osteotomy – This treatment involves reshaping the bone to reduce stress on the affected area. Recovery can be a lengthy process, requiring 3 to 12 months of very limited activities. This procedure is most effective for patients with early-stage osteonecrosis and those with a small area of affected bone.
 * Bone graft – This is the transplantation of healthy bone from another part of the body. It is often used to support a joint after core decompression. In many cases, the surgeon uses what is called a vascular graft – which includes an artery and vein – to increase the blood supply to the affected area. Recovery from a bone graft can take from 6 to 12 months. The procedure is complex and its effectiveness is unproven. Clinical studies are underway to determine its effectiveness.
 * Arthroplasty/total joint replacement – Total joint replacement is the treatment of choice in late-stage osteonecrosis and when the joint is destroyed. In this surgery, the diseased joint is replaced with artificial parts. Total joint replacement, or sometimes femoral head resurfacing, is often recommended for people for whom other efforts to preserve the joint have failed.

For most people with osteonecrosis, treatment is an ongoing process. Depending upon the stage of the disease, doctors may first recommend the least complex or nonoperative treatment plans, such as medication or reduced weight bearing. If these modalities are unsuccessful, surgical treatments may be needed.

Chances of Developing Osteonecrosis
The chance of developing osteonecrosis is dependent on many factors; some joints and bones are more susceptible than others.

Risk factors
Osteonecrosis affects both men and women. It can occur in people of any age, from children to the elderly. However, it is most common in people in their thirties, forties, and fifties.

Other risk factors for osteonecrosis include radiation therapy, chemotherapy, and organ transplantation (particularly kidney transplantation). Osteonecrosis is also associated with a number of medical conditions, including cancer, lupus, blood disorders such as sickle cell disease, HIV infection, Gaucher disease, Caisson disease, gout, vasculitis, osteoarthritis, and osteoporosis.

Research
With proper treatment, most people with osteonecrosis can lead productive lives. But there is still a lot to learn about prevention, diagnosis, and treatment. Currently, research is proceeding on many fronts:


 * better understanding of the prevalence of osteonecrosis by screening at-risk populations with MRI
 * identifying risk factors such as genetic clotting disorders
 * identifying and/or develop new ways to diagnose osteonecrosis in its earliest stages, when nonsurgical treatment is most likely to help
 * determine whether biological therapies, such as recombinant human bone morphogenic protein, are effective treatments
 * development of new treatments and improve available treatments
 * study of key mechanical factors – such as the alignment of the hips, knees, and ankles – that influence treatment outcomes
 * development of an animal model of osteonecrosis to study the disease
 * improvements in hip replacement techniques and materials so that younger patients will not need more than one hip replacement in their lifetime
 * better understand the body's reaction to steroids and why taking steroids increases a person's risk