Overview
Avascular necrosis (AVN) is the death of bone tissue caused by a lack of blood supply. It's also called osteonecrosis. The hip is one of the joints it affects most often.
The hip is a ball-and-socket joint. The ball is the rounded top of the thighbone (femur), called the femoral head. The socket is a cup-shaped part of the pelvis. Together, they form the hip joint.
The femoral head gets its blood in an unusual way. Blood vessels form a ring around the base of the femoral neck — the narrow section just below the ball. Small vessels then travel up along the neck to reach the head. Because the head relies on these few vessels, anything that damages or squeezes them can cut off its blood supply.
Without blood, the bone in the femoral head begins to die. Dead bone can't support the smooth cartilage that lines the joint. Over time, the bone weakens and collapses, and the ball loses its round shape. The ball and socket no longer fit together properly, which leads to arthritis.
AVN of the hip can affect one or both hips. Finding it early gives you more treatment options.
Symptoms
Many people have no symptoms in the early stages of avascular necrosis. As the condition gets worse, symptoms may include:
- Pain in the groin, which is the most common location
- Pain in a C-shaped area around the side and front of the hip
- Pain that spreads down to the knee
- Pain when walking or standing that gets better with rest at first
- Stiffness and reduced movement in the hip
- Limping
Pain usually builds slowly. As the condition progresses, pain may be present even at rest or at night.
When to see a doctor
See your doctor if you have ongoing pain in your groin, hip or thigh, especially if you have a risk factor for avascular necrosis.
With AVN, the sooner the diagnosis is made, the better. In most people, the condition gets worse over time. Once the bone collapses and the ball changes shape, the damage can't be reversed, and treatments that save the natural joint may no longer work well.
Causes
Avascular necrosis happens when blood flow to the bone is reduced or blocked. This can happen when:
- An injury damages blood vessels. A hip fracture or dislocation can tear or kink the vessels that supply the femoral head.
- Pressure builds up inside the joint. Injury, swelling or fluid within the joint capsule — the tough sleeve around the joint — can squeeze the blood vessels.
- Fat or other material blocks small blood vessels. Fatty deposits can narrow or clog the tiny vessels inside the bone.
- Certain diseases affect blood flow. In sickle cell disease, abnormally shaped red blood cells can block small vessels.
In some people, no clear cause is found.
Risk factors
Factors that can increase your risk of avascular necrosis of the hip include:
- Steroid medicines. Long-term or high-dose use of corticosteroids, such as prednisone, is one of the most common causes of AVN not related to injury.
- Heavy alcohol use. Drinking a lot of alcohol over many years can cause fatty deposits that block blood vessels.
- Hip injury. Fractures and dislocations of the hip raise the risk.
- High cholesterol and fat levels in the blood. High levels of fats (lipids) may contribute to blockage of small vessels.
- Sickle cell disease and certain other blood disorders.
- Certain other medicines and treatments, including some cancer treatments and radiation therapy.
- Other medical conditions, such as an organ transplant, lupus, HIV and Gaucher disease.
Complications
Without treatment, avascular necrosis of the hip usually gets worse over time. Doctors describe this in stages, from stage 1 (early changes, often seen only on MRI) to stage 4 (collapse of the femoral head and arthritis).
Moving from stage 1 to stage 4 usually takes 1 to 3 years. In a small number of people, the condition stops at one stage and doesn't progress.
As bone collapses and the joint surfaces no longer fit together, AVN can lead to:
- Severe hip arthritis
- Long-lasting pain
- Loss of hip movement and difficulty walking
Diagnosis
Your doctor will ask about your symptoms and medical history and examine your hip. Tests may include:
- X-rays. These show changes in later stages but may look normal early on.
- MRI. This is the most sensitive test and can detect AVN before changes appear on X-rays. It's often used to check the other hip as well.
Treatment
Treatment depends on the stage of the disease, the size of the affected area and whether the bone has collapsed.
- Medicines. In early stages, medicines may help relieve pain and may slow progression. Your doctor may also suggest reducing weight on the hip for a time, often with crutches.
- Core decompression. A surgeon drills one or more small channels into the femoral head. This relieves pressure inside the bone and encourages new blood vessels to grow. It works best before the bone collapses.
- Stem cell therapy. Cells taken from your own bone marrow may be placed into the drilled area during core decompression to support healing. This is an evolving treatment that is most useful in early stages.
- Total hip replacement. Once the disease reaches stage 3 or 4 and the femoral head has collapsed, replacing the damaged ball and socket with artificial parts is the only treatment that reliably relieves pain and restores function.
Frequently asked questions
What is avascular necrosis of the hip? It's a condition in which part of the ball of the hip joint (femoral head) dies because it doesn't get enough blood. Over time, the bone can collapse and lead to arthritis.
Is avascular necrosis the same as osteonecrosis? Yes. Avascular necrosis, osteonecrosis, aseptic necrosis and ischemic bone necrosis all describe the same condition.
What are the early signs of AVN of the hip? Early AVN often causes no symptoms. When symptoms start, the first sign is usually a dull ache or pain in the groin that gets worse with walking or standing.
Can avascular necrosis of the hip heal on its own? Rarely. In a small number of people, the disease stops progressing. But in most people, it gets worse over time without treatment.
How fast does AVN of the hip progress? It usually moves from early to advanced stages over 1 to 3 years. Speed varies from person to person.
Can steroids cause avascular necrosis? Yes. Long-term or high-dose corticosteroid use is one of the leading causes of AVN not related to injury. Don't stop taking a prescribed steroid without talking to your doctor first.
Which test is best to detect AVN early? MRI. It can find avascular necrosis before any changes show up on X-rays.
Can AVN of the hip be treated without surgery? In early stages, medicines and limiting weight on the hip may help ease pain and possibly slow progression. But many people eventually need a procedure such as core decompression.
Is core decompression successful? Core decompression has the best results when it's done early, before the femoral head collapses. It's less effective once the bone has started to collapse.
When is hip replacement needed for AVN? Total hip replacement is usually recommended at stage 3 or 4, when the femoral head has collapsed and arthritis has developed.
Can AVN affect both hips? Yes. AVN often affects both hips, especially when it's caused by steroid use or alcohol. Your doctor may check the other hip with an MRI even if it doesn't hurt.
Can I prevent avascular necrosis? You can lower your risk by limiting alcohol, keeping cholesterol under control and using steroid medicines only at the lowest dose and shortest time your doctor recommends.