Osteonecrosis (Avascular Necrosis)

Osteonecrosis is the medical term used to describe a temporary or permanent bone-blood supply deficit. The disease is sometimes referred to as avascular necrosis, ischaemic necrosis or aseptic necrosis. Around 10,000 to 20,000 Americans develop the condition annually and are typically aged between 20 and 50.

What is Osteonecrosis?

Blood naturally circulates through the body into cells, tissues, muscles, bones and organs for good health. When osteonecrosis occurs the blood supplied to the bones is lost, which causes bone tissue to degenerate and the bones to weaken. As bone tissue dies the bones and joints begin to disintegrate.

The disease may impact any bone within the body, though the tips of the femur or the epiphysis joining the hip and knee joints are commonly affected. Blood supply may be lost to single or multiple bones at any time. Typically the bones of the ankles, knees, upper arms and shoulders are vulnerable.

The disease is frequently identified by orthopaedic specialists who are concerned with the diagnosis, treatment and prevention of musculoskeletal diseases. Around 10 per cent of patients undergoing hip replacement operations are diagnosed with osteonecrosis.

The degree to which an individual's health is impacted by osteonecrosis depends on the bone position and the severity and number of bones affected. Healthy bones go through a process of renewal as part of the new bone growth regulating skeletal function. The same process is commonly known as that which occurs after bone trauma when existing bone degenerates and is then replaced by new bone structure.

However, with osteonecrosis new bone growth and repair cannot keep pace with bone degeneration. Without treatment the disease can continue to develop and break down bone and joints, leading to painful arthritis and disability.

What are the Causes of Osteonecrosis?

The reason for the loss of blood supply to the bones is not always obvious. Furthermore the rate at which the disease progresses is not fully understood. Those with pre-existing medical conditions and bone injuries may be at higher risk of suffering from the disease.

For example, steroid medications high in corticosteroid (such as prednisone) may be a contributor, as can excessive alcohol consumption. Possible causes of osteonecrosis include:

• Corticosteroid Treatments
• Excessive Alcohol Consumption
• Inflammatory Diseases
• Medical Treatments and Transplants
• Bone or Joint Trauma

Corticosteroid Treatments

Research indicates that the prolonged use of corticosteroids, whether through oral or IV intake, contributes to non-traumatic osteonecrosis and may severely affect an individual's hips. These treatments are used for inflammatory diseases including rheumatoid arthritis, vasculitis, inflammatory bowel disease, systemic lupus erythematosus and chronic asthma.

The reason why corticosteroids raise the risk of osteonecrosis is not clear. However, studies reveal that the medications may inhibit the body's capacity to break down lipids, which then expand in the blood vessels and cause obstruction, reducing the supply of blood to the bones.

Excessive Alcohol Consumption

Excessive alcohol consumption may also impede lipid breakdown and cause fatty build-up in the blood vessels, which then restricts blood supply to the bones.

Inflammatory Diseases

Other health conditions and diseases can raise the threat of developing osteonecrosis. These conditions include osteoarthritis, osteoporosis, gout, blood disorders, vasculitis, sickle cell disease, lupus, caisson disease, Gaucher's disease, HIV infection and cancer.

Medical Treatments and Transplants

Medical treatments such as chemotherapy, radiation therapy and kidney or organ transplantation have the potential to increase the risk of contracting the disease.

Bone or Joint Trauma

Where blood vessels are damaged as a result of bone or joint injury, the blood supply to the bones may be halted and result in osteonecrosis. Those who experience hip fractures and dislocations are particularly vulnerable to osteonecrosis. Seniors are at higher risk as are individuals whom suffer from muscular-skeletal disorders.

The condition of the bones, such as pressure and density, may also be a contributing factor. When bone pressure rises the blood vessels may become restricted and this in turn limits blood supply to the bones. The reason for increased bone pressure is not clear and research in this field is still ongoing.

Who is at higher risk of developing Osteonecrosis?

People of any age and gender (including children and seniors) may be at risk of developing osteonecrosis within their lifetime. The age group mostly affected are those aged between 30 and 50.

What are the symptoms of Osteonecrosis?

Some cases may not even display obvious symptoms of the condition. However, initial symptoms of osteonecrosis may manifest as painful joints, which is mainly felt when weight is placed on the joints where osteonecrosis is present. As the disease progresses pain is felt in the impacted bones and joints when the body is relaxed.

An individual affected by the disease may have difficulty moving the limb or joint with limited range of motion. The condition may be accompanied by osteoarthritis, such as in the hip, which can be quite debilitating to the sufferer. Gradually, usually over a 12-month period, the symptoms worsen until the individual loses joint function.

What is involved in the diagnosis of Osteonecrosis?

Diagnosis and early intervention treatments are critical to restore bone health. Initially the doctor will examine a patient physically, discuss medical history and if necessary refer the individual for further diagnostic tests, such as:

• X-Rays or Radiographs
• Computerised Tomography (CT) Scan
• Bone Scan
• Magnetic Resonance Imaging (MRI)
• Bone Functional Evaluation
• Bone Biopsy

X-Rays or Radiographs

If joint pain is present in the early stages of osteonecrosis the doctor will refer the individual for an X-ray to attain images of the bone structure. However, further tests may be required to assess bone changes not accessible by X-rays. If osteonecrosis disease has progressed X-rays will display the bone trauma and can later be used in monitoring development of the disease.

Computerised Tomography (CT scan)

A CT scan is needed to see 3D and slice or sectional bone dimensions for determining the severity of bone trauma. X-rays and bone scans do not provide the level of clarity achieved through a CT scan, though CT scans are not as sensitive as Magnetic Resonance Imaging (MRI) scans.

Bone Scan

Individuals who are experiencing joint pain but not displaying signs of osteonecrosis in X-rays may be referred for technetium-99m bone scans to identify its presence. The test involves an intravenous injection of low-risk radioactive substance to allow for the monitoring on a camera of the flow of the substance in the blood stream to the bones. Bone scans enable the doctor to determine exactly where osteonecrosis is occurring within the body.

Magnetic Resonance Imaging (MRI)

MRI is the most sensitive osteonecrosis diagnostic test and is often used to identify early stages of the disease. MRI's are used to track chemical changes in the bone marrow and to monitor how the bone regenerates. This is so osteonecrosis may be identified even where no symptoms are experienced. In those suffering the early onset of osteonecrosis the body may heal itself, but not all patients will experience this improvement without treatment.

Bone Biopsy

A biopsy of the affected bone area is taken during surgery to diagnose the condition. As the procedure is invasive doctors tend to prefer other diagnostic tests. However, if necessary, bone samples may prove useful in confirming the presence of the disease.

Functional Evaluation of Bone

Where symptoms are noted but X-rays, MRIs and bone scans are normal, a bone functional evaluation may be performed during surgery to assess bone pressure. The monitoring of bone pressure is to see if increases are the cause of osteonecrosis.

What are the treatments for Osteonecrosis?

After diagnosis and severity of osteonecrosis is confirmed the location and progress of the disease is assessed. The doctor is likely to advocate a range of treatments to prevent further bone degeneration and potential disability. If the disease progresses without treatment individuals may experience loss of bone function and severe pain within a period of two years.

Factors considered when determining appropriate treatment include:

• Patient age
• Potential cause or contributor to osteonecrosis
• Osteonecrosis disease stage
• Location of osteonecrosis in the body
• Whether single or multiple bones are affected

Early intervention and treatment is essential to protect the patient from further bone loss and impeded bone and joint function and pain. One or more treatments may be used to preserve bone health, with solutions including those that are non-surgical and surgical.

Non-surgical Osteonecrosis Treatments

Doctors usually aim to treat patients with the most non-invasive treatment possible. Although non-surgical treatments provide relief from osteonecrosis symptoms, they may not prevent the disease from progressing or causing debilitation.

Non-surgical osteonecrosis treatments include:

• Exercise or Physiotherapy Programmes
• Weight-to-joint Reduction
• Electrical Stimulation
• Medications

Exercise or Physiotherapy Programmes

The goal of using exercise or physiotherapy is to aid joint movement and increase motion-range, thereby working to relieve any symptoms of discomfort.

Weight-to-joint Reduction

By altering weight bearing on the joints and affected bones through the use of walking aids (such as crutches) bone trauma is sometimes reduced. The reduction of bone trauma allows the bones to recover from osteonecrosis through the body's self-healing efforts. The treatment can also be combined with medication to relieve pain.

Electrical Stimulation

Electrical stimulation is used to induce bone growth, rejuvenate bone cells and prevent bone loss and collapse. Examples of vulnerable bones which may be affected include the tip of the femur.

Medications

The doctor may prescribe non-steroidal anti-inflammatory medications such as Ibuprofen to provide pain relief from the symptoms. Where blood clots are present and restricting blood supply to the bones, blood-thinning medications may be prescribed. If fatty lipids are causing obstruction to blood flow, medication for the reduction of cholesterol or statins may be recommended. When combined together these medications are likely to reduce the risk of further development.

Surgical Osteonecrosis Treatments

If osteonecrosis progresses surgery may be required to restore bone health and prevent debilitation. Surgeries for osteonecrosis include:

• Bone Grafting
• Joint Replacement or Arthroplasty
• Bone Core Decompression
• Osteotomy

Bone Grafting

During bone grafting or vascular grafting a part of healthy bone in the patient's body is retrieved and transplanted to the area affected by osteonecrosis. By including an artery or vein in the graft and transplant, blood supply to the impacted bone is restored. Research is ongoing into how successful treatment is. Recovery ranges from between 6 to 12 months.

Joint Replacement or Arthroplasty

As osteonecrosis progresses the joint gradually disintegrates and may need replacing to restore joint and limb function. Artificial joints are used to replace joints destroyed by osteonecrosis disease. Varying procedures are used for joint replacement or arthroplasty, such as resurfacing of the femoral head. The physician will discuss the choices available for joint replacement.

Bone Core Decompression

Often used as an early intervention treatment the surgeon will remove the inner bone cylinder where osteonecrosis is present to reduce bone pressure. This should increase blood supply levels to the bone and rejuvenate blood vessel growth. Bone core decompression prevents entire bone and joint collapse, slows down the disease and reduces painful symptoms.

Osteotomy

Patients diagnosed with early osteonecrosis that is only affecting a small bone area may benefit from osteotomy. This is a surgical operation that involves the reshaping of bones to lessen stress on the impacted bone and joint. Recovery may be cumbersome and restrict activities a 3 to 12 month period.

Osteonecrosis treatments, both non-surgical and surgical, aim to provide patients with the disease a chance of recovery and relief from symptoms. For some disease management is continual and a fundamental part of their lives. Surgery is used as a last resort while doctors strive to preserve bone quality and function through non-invasive means.