Avascular Necrosis (AVN), also known as Osteonecrosis, is a serious orthopedic condition that occurs when the blood supply to a bone is reduced or completely interrupted. Without adequate blood flow, bone tissue begins to die, eventually leading to the collapse of the affected bone and damage to the surrounding joint.

The hip joint is one of the most commonly affected areas. Following the COVID-19 pandemic, orthopedic specialists across the world observed an increase in AVN cases, particularly among patients who received prolonged or high-dose steroid therapy during their COVID treatment.

In this article, Dr. Balaraju Naidu, Senior Robotic Orthopedic Surgeon at ONUS Robotic Hospitals, explains the causes, symptoms, stages, diagnosis, and treatment options for AVN of the hip.

What is Avascular Necrosis (AVN)?

Avascular Necrosis is a condition where the blood supply to a portion of the bone is disrupted. Since bone tissue requires a constant blood supply to remain healthy, a lack of circulation causes the bone cells to die.

Over time, the weakened bone structure may collapse, leading to severe pain, restricted movement, arthritis, and disability.

The femoral head—the ball-shaped upper part of the thigh bone (femur) that fits into the hip socket—is particularly vulnerable to AVN because of its delicate blood supply.

Why Did AVN Cases Increase After COVID-19?

During the COVID-19 pandemic, steroids played a crucial role in managing severe respiratory complications. While these medications helped save lives, excessive or prolonged steroid use was associated with several complications, including AVN.

How Steroids Contribute to AVN

Steroids can:

• Affect blood circulation to bones
• Increase fat deposits within blood vessels
• Cause blockage of small blood vessels supplying the femoral head
• Reduce the bone’s ability to repair itself

Not everyone who receives steroids develops AVN, but patients who received high doses or prolonged treatment may be at a higher risk.

Other Causes of AVN

Apart from steroid use, AVN can develop due to:

• Hip injuries or fractures
• Joint dislocations
• Excessive alcohol consumption
• Blood clotting disorders
• Autoimmune diseases
• Sickle cell disease
• Certain medications
• Radiation therapy
• Unknown causes (Idiopathic AVN)

Early Symptoms of AVN

One of the biggest challenges with AVN is that symptoms may be absent in the early stages.

As the condition progresses, patients may experience:

Common Symptoms

• Deep pain in the groin region
• Hip pain while walking
• Pain while climbing stairs
• Stiffness in the hip joint
• Limping while walking
• Difficulty sitting cross-legged
• Reduced range of motion
• Pain radiating to the thigh or buttock

Initially, pain may occur only during activity but later becomes persistent even at rest.

Stages of Avascular Necrosis (AVN)

Orthopedic surgeons classify AVN into four stages based on imaging findings and the extent of bone damage.

Stage 1 – Early AVN

• X-rays may appear normal
• MRI can detect early changes
• Mild or occasional pain
• No collapse of the femoral head

At this stage, treatment aims to preserve the natural hip joint.

Stage 2 – Bone Damage Begins

• Structural changes become visible
• Bone tissue starts deteriorating
• Increased pain during movement
• Joint surface remains intact

Early intervention is highly effective during this stage.

Stage 3 – Collapse of Femoral Head

• The weakened bone begins to collapse
• Joint shape becomes irregular
• Significant pain and stiffness
• Daily activities become difficult

Joint-preserving procedures may still be possible in selected patients.

Stage 4 – Advanced Arthritis

• Severe collapse of the femoral head
• Joint cartilage damage
• Advanced arthritis develops
• Severe pain and restricted mobility

Hip replacement surgery is often the most effective treatment at this stage.

How is AVN Diagnosed?

Early diagnosis is critical for preserving the hip joint.

Clinical Evaluation

Your orthopedic surgeon may assess:

• Walking pattern
• Hip movement
• Pain location
• Joint flexibility

Imaging Tests

X-Ray

Useful for detecting advanced stages of AVN.

MRI Scan

The most sensitive test for detecting AVN in its earliest stages.

CT Scan

May help evaluate the extent of bone collapse in certain cases.