Avascular Necrosis (Osteonecrosis)

How avascular necrosis happens

Bone is living tissue that depends on a steady blood supply. Some areas, such as the femoral head, have limited blood vessels with few backup routes. When flow is blocked by injury, fat particles, clotting, sickled cells or raised pressure inside the bone, bone cells die. The body tries to repair the area, but the dead bone weakens and can fracture beneath the cartilage. The joint surface then collapses, leading to painful arthritis. This process usually unfolds over months to a few years.

Causes and risk factors

Traumatic

• Hip fractures (especially fractures of the femoral neck) and hip dislocations can tear the blood vessels to the femoral head. See hip fracture.
• Scaphoid fractures in the wrist can cut off blood to part of the bone. See scaphoid fracture.

Non-traumatic

• Corticosteroids: high doses or long courses of prednisone and similar medicines are the most common non-traumatic cause. Risk relates to total dose; even short high-dose courses occasionally cause it.
• Heavy alcohol use over years.
• Sickle cell disease: sickled cells block small vessels; hip AVN is common in adults with sickle cell disease.
• Lupus and other autoimmune diseases, often combined with steroid treatment.
• Radiation therapy and chemotherapy.
• Organ transplantation.
• Decompression sickness in divers.
• Gaucher disease, pancreatitis, HIV and clotting disorders.
• Medication-related osteonecrosis of the jaw: linked to bisphosphonates and denosumab, usually after dental extractions, mainly at high cancer-treatment doses.

In about a quarter of cases no cause is found.

In children

Perthes disease is avascular necrosis of the femoral head in children, usually boys aged 4 to 8, causing a limp. It often heals as the child grows.

Symptoms

Early AVN may cause no symptoms. As it progresses:

• deep aching or throbbing pain in the groin, buttock or thigh for hip AVN, or in the knee, shoulder or ankle
• pain at first only with weight-bearing, later at rest and at night
• limping and stiffness
• reduced range of movement, especially rotating the hip inward
• sudden worsening of pain when the bone collapses

AVN of the hip often affects both sides, sometimes without symptoms on the second side at first.

Stages

Doctors stage AVN on imaging. A simplified version of common systems:

Outcomes are much better when treatment starts before collapse.

Diagnosis

1. History and examination: steroid use, alcohol, injuries, sickle cell disease and other risks; hip movement and walking.
2. X-rays: normal early on, but show later changes and collapse.
3. MRI: the most sensitive test, detecting AVN in its earliest stage and measuring how much of the bone is affected. Both hips are usually imaged.
4. CT scan: shows subtle collapse and helps plan surgery.
5. Bone scan: occasionally used when MRI is not possible.

Treatment

Non-surgical

• Reducing load: crutches or a cane to protect the joint in early stages.
• Pain relief: acetaminophen (paracetamol) or anti-inflammatory medicines at the label dose, if safe for you.
• Treating the cause: reducing steroid doses where possible, stopping alcohol.
• Physical therapy to maintain movement and strength.

Medicines such as bisphosphonates have been studied but their benefit is uncertain.

Joint-preserving surgery (early stages)

• Core decompression: drilling one or more channels into the dead area to reduce pressure and stimulate new blood vessels, sometimes with bone marrow cells or graft.
• Bone grafting, including vascularized fibular grafts with their own blood supply.
• Osteotomy: reshaping the bone to shift weight away from the damaged area, mainly in younger patients.

Joint replacement (late stages)

When the femoral head has collapsed, total hip replacement reliably relieves pain and restores function. Shoulder, knee and ankle replacements are used in those joints.

Outlook

Small lesions found early, especially those that do not bear weight, may stabilize. Larger lesions in the hip often progress to collapse within a few years without treatment. Modern hip replacement gives excellent pain relief and long-lasting results for most people, including younger patients.

Prevention

• Use the lowest effective dose and shortest course of steroids, and discuss bone risks with your doctor.
• Limit alcohol.
• Follow safe ascent rules when diving.
• Get urgent treatment for hip fractures and dislocations.
• Have dental work done before starting high-dose bisphosphonates or denosumab for cancer.

Frequently asked questions

What is avascular necrosis?

Avascular necrosis is the death of bone tissue caused by a loss of blood supply. It most often affects the hip. The dead bone weakens and can collapse, causing pain and arthritis. It is also called osteonecrosis.

What are the first symptoms of avascular necrosis of the hip?

Early AVN may cause no symptoms. The first symptom is usually a deep, aching pain in the groin, buttock or thigh, worse with walking or standing. Over time pain may occur at rest, and you may develop a limp and stiffness.

What causes avascular necrosis?

Common causes are hip fractures and dislocations, long-term or high-dose steroid medicines, heavy alcohol use and sickle cell disease. Lupus, radiation, organ transplants, decompression sickness and some blood disorders also raise the risk. Sometimes no cause is found.

Can avascular necrosis heal on its own?

Small, early lesions occasionally stabilize or heal, particularly in children with Perthes disease. In adults, larger lesions in weight-bearing joints usually progress without treatment. Early diagnosis with MRI gives the best chance of saving the joint.

Is avascular necrosis serious?

It can be, because it often leads to collapse of the joint and arthritis, especially in the hip. With early treatment some joints can be preserved, and late-stage disease is treated very effectively with joint replacement. It is not life-threatening.