Avascular Necrosis of the Femoral Head

Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

 

Avascular Necrosis of the Femoral Head: Staging, Diagnosis, and Treatment Approach

Key Points

1. Overview

• Avascular necrosis is the death of bone tissue in the femoral head due to reduced blood supply.
• It is a progressive condition that can lead to collapse of the hip joint if untreated.
• The exact cause is not always clear, but several risk factors are known.

2. Risk Factors

• Risk factors can be broadly categorized into direct and indirect causes.

Direct Causes

• Trauma and radiation exposure.
• Blood-related disorders such as leukemia, lymphoma, and sickle cell disease.
• Metabolic and genetic conditions.

Indirect Causes

• Long-term steroid use.
• Excessive alcohol consumption.
• Chronic kidney disease.
• Organ transplantation.
• Autoimmune disorders.
• Coagulation disorders.

3. Bilateral Involvement

• Both hips may be affected in a large proportion of patients.
• The opposite hip should always be evaluated, even if there are no symptoms.

4. Importance of Early Diagnosis

• Early detection improves the success of joint-preserving procedures.
• Delayed diagnosis increases the risk of femoral head collapse.

5. Imaging and Diagnosis

• X-rays:
  • May be normal in early stages.
  • Later stages show structural changes and collapse.
• Magnetic Resonance Imaging:
  • Most sensitive investigation for early disease.
  • Shows characteristic signal changes in the femoral head.

Key Imaging Signs

• Crescent sign: indicates subchondral fracture.
• Double-line sign:
  • Inner bright line represents vascular tissue.
  • Outer dark line represents sclerotic bone.

6. Prognostic Factors

• Size of the lesion is the most important factor affecting progression.
• Smaller lesions with defined margins have better outcomes.
• Bone marrow edema indicates higher risk of progression.

7. Staging of Disease

• A commonly used staging system divides the disease into four stages:

Stage One

• Normal X-ray findings.
• Abnormal magnetic resonance imaging or bone scan.

Stage Two

• X-ray shows bone density changes.
• No collapse of the femoral head.

Stage Three

• Presence of crescent sign indicating subchondral fracture.
• Early collapse may be seen.

Stage Four

• Advanced collapse and deformity.
• Secondary degenerative changes in the joint.

8. Risk of Collapse

• Determined using combined necrotic angle measured on imaging.
• Larger angles are associated with higher risk of collapse.

9. Transient Osteoporosis

• A separate condition that can mimic osteonecrosis.
• Symptoms may be severe despite minimal changes on X-ray.
• Magnetic resonance imaging shows bone marrow edema.
• Does not require surgical treatment and usually resolves.

10. Treatment Strategies

1. Early Stages (Before Collapse)

• Aim is to preserve the femoral head.
• Options include:
  • Core decompression.
  • Bone grafting or graft substitutes.
  • Vascularized bone grafts.
  • Use of biological therapies such as stem cells.

Core Decompression

• Involves drilling into the affected area to reduce pressure.
• Can be performed using a single large channel or multiple small channels.
• Promotes healing and reduces pain.

1. Medical Management

• Bisphosphonates may reduce pain and risk of collapse.
• Their use is still considered under evaluation.

1. Advanced Stages (After Collapse)

• Joint preservation is usually not possible.
• Total hip replacement is the treatment of choice.
• Provides reliable pain relief and improved function.

11. Surgical Options

• Bone Grafting Techniques
  • Non-vascularized grafts.
  • Vascularized fibular grafts, especially in younger patients.
• Total Hip Replacement
  • Preferred in advanced disease.
  • Cementless implants are commonly used.

12. Special Considerations

• In patients with sickle cell disease:
  • Higher risk of disease progression.
  • Surgical procedures may be technically more challenging.
• Younger patients may have slightly less favorable outcomes after joint replacement compared to those with osteoarthritis.

13. Key Takeaways

• Avascular necrosis is a progressive condition requiring early diagnosis.
• Magnetic resonance imaging is essential for early detection.
• Treatment depends on disease stage and severity.
• Joint-preserving procedures are effective in early stages.
• Total hip replacement is the definitive treatment in advanced cases.