AVASCULAR NECROSIS

OVERVIEW

Avascular necrosis, also known as Osteonecrosis, is caused due to interruption of blood supply to the bone tissue causing its death, which leads to its breaking and eventually collapses.

It most commonly affects people between the ages of 30 and 50 but can occur at any age. Men develop osteonecrosis of the hip more often than women.

It commonly occurs secondary to bone breakage/fracture or joint dislocation, long-term use of high-dose steroid medications and excessive alcohol intake.

Pathophysiology

Although the pathophysiology of AVN is not fully understood, the final common pathway is interruption of blood flow to the bone.

AVN often affects bones with a single terminal blood supply, such as the Femoral Head, Carpals, Talus, and Humerus.

The earliest pathologic characteristics of osteonecrosis are necrosis of hematopoietic cells and adipocytes followed by interstitial marrow edema.

Osteocyte necrosis occurs after approximately 3 hours of anoxia, but histological signs of osteocyte death do not appear until approximately 24 to 72 hours after oxygen deprivation.

STAGES OF OSTEONECROSIS

CAUSES & RISK FACTORS

Avascular necrosis is caused due to loss/reduction of blood supply to the bone tissue.

Reduced blood supply can be caused by:

Joint or bone trauma
An injury, such as fracture/ dislocation, may damage nearby blood vessels and impairing circulation thus reducing blood flow to bones.

Alcohol abuse
Overconsumption of alcohol over time can cause fatty deposits to form in the blood vessels and can elevate cortisone levels, resulting in a decreased blood supply to the bone.

Medical conditions
Osteonecrosis is associated with other diseases, including

1. Caisson disease (diver’s disease or “the bends”)
2. Sickle Cell Disease
3. Pancreatitis
4. Diabetes
5. Myeloproliferative Disorders
6. Gaucher’s Disease
7. Systemic Lupus Erythematosus(SLE)
8. Crohn’s disease
9. Arterial embolism
10. Thrombosis
11. Vasculitis

Medications

• Steroids
  Use of high-dose corticosteroids, for treating diseases like asthma, rheumatoid arthritis, and systemic lupus erythematosus is a common cause of avascular necrosis.
• Bisphosphonates
  Although rare but long-term high dose use, to increase bone density for cancers, such as multiple myeloma and metastatic breast cancer, has been linked to osteonecrosis of the jaw.
• Idiopathic
  For about 25 percent of people with avascular necrosis, the cause of interrupted blood flow is unknown.

DIAGNOSIS

Radiological

X-rays They can reveal bone changes that occur in the later stages of avascular necrosis.
In the condition’s early stages, X-rays usually appear normal.

MRI It can also be used as a screening tool for the opposite hip (to show early AVN that has yet to cause symptoms).
Osteonecrosis in a patient’s right hip, denoted by ‘white arrow’ & the ‘red arrows’ denotes the border between the dead bone & the living bone.

CT Scan It gives detailed images of the degree of bone destruction and arthritic changes.

Bone Scan Radioactive material is injected into the vein. This tracer travels with blood to bones depending on its vascularity and shows up as bright spots on the imaging plate.

TREATMENT

Prevention of further bone loss is the goal of management. As most people are asymptomatic until avascular necrosis is fairly advanced, surgery might be recommended early. Conservative treatment can help relieve pain and slow the progression of the disease, but the most successful treatment options are surgical. Hip-preserving procedures are recommended for patients with AVN in the very early stages (before the femoral head collapses).

Medications and therapy

These are effective in the early stages of avascular necrosis.

• Nonsteroidal anti-inflammatory drugs. Selective or non-selective COX2 inhibitors are effective analgesics.
• Osteoporosis drugs. Bisphosphonates slow the progression of avascular necrosis
• Cholesterol-lowering drugs. Drugs lowering the amount of cholesterol and fat in blood help prevent vessel blockages preventing avascular necrosis.
• Anticoagulants. Blood thinners might be recommended in patients with clotting disorder to prevent clots from the vessels feeding your bones.
• Lifestyle modification. Weight reduction and reducing stress on affected bone by using crutches to keep weight off your joint can slow the damage.
• Physiotherapy. Exercises to help maintain or improve the range of motion in the joint. Electrical stimulation wherein electrical currents is used to encourage to growth of new bone to replace the damaged bone.

Surgical Management

There are several surgical procedures used to treat AVN of the hip. The options include:

• Core decompression – Ideally indicated when osteonecrosis of the hip is diagnosed early because it is sometimes successful in preventing the collapse of the femoral head and the development of arthritis. It involves drilling holes into the femoral head reducing intraosseous pressure and creating channels for new blood vessels to nourish the affected areas of the hip, thus reducing pain and stimulating the production of healthy bone tissue and new blood vessels.
• Osteochondral Grafting – Core decompression is often combined grafting to help regenerate healthy bone and support cartilage. The tissue may be taken from another bone in the body (autograft) or a donor (allograft). It may be Vascularised or non-vascularised or synthetic bone graft.
• Stem cell therapy – Appropriate for early stage avascular necrosis of the hip. Stem cells are harvested from bone marrow. It combined with core decompression to, potentially allow for the growth of new bone. More study is needed.
• Osteotomy – A wedge of bone is removed, to help change the weight-bearing axis and shift weight off the damaged bone.
• Joint replacement – In a total hip replacement, both the head of the femur and the socket are replaced with an artificial device. Indicated if osteonecrosis has advanced to the stage of arthritis. Total hip replacement is successful in relieving pain and restoring function in the majority of patients with osteonecrosis

PREVENTION

To reduce your risk of avascular necrosis and improve your general health:

• Limit alcohol: Heavy drinking is one of the top risk factors for developing avascular necrosis.
• Keep cholesterol levels low: Tiny bits of fat are the most common substance blocking the blood supply to bones.
• Monitor steroid use: Make sure your doctor knows about your past or present use of high-dose steroids. Steroid-related bone damage appears to worsen with repeated courses of high-dose steroids.
• Don’t smoke: Smoking increases the risk.