What is avascular necrosis?

Avascular necrosis (AVN), also known as osteonecrosis, is a condition where the blood supply to a bone is disrupted, leading to the death of bone tissue. While AVN can affect several joints, the hip joint—specifically the femoral head—is the most commonly involved site.

If you want to learn more about this topic, you can watch Amie Coombs' lecture here:

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But why is the hip so prone to this condition? Let’s break it down.

1. Unique Blood Supply of the Femoral Head

● The femoral head has a very delicate and limited blood supply.

● The main vessels, called the retinacular arteries, travel along the femoral neck to reach the head.

● These arteries are end arteries – meaning they do not have significant backup (collateral circulation).

● If these small vessels are injured or blocked, the blood flow to the femoral head is drastically reduced, making it extremely vulnerable to ischemia.

2. Vulnerability to Trauma

● The blood vessels of the femoral head are particularly at risk during hip injuries.

● Femoral neck fractures or hip dislocations can easily damage the retinacular arteries.

● Even with proper fracture fixation, once the blood supply is lost, the femoral head often undergoes necrosis.

● This is why young patients with hip fractures are closely monitored for signs of AVN.

3. High intraosseous Pressure and Mechanical Stress

● The femoral head is enclosed in a tough, compact structure and covered with cartilage.

● This makes the environment inside the bone high-pressure with limited space for new vessels to form if blood flow is disrupted.

● On top of that, the hip bears significant mechanical load during walking, running, and daily activities, which accelerates bone collapse once necrosis sets in.

What are the risk factors of avascular necrosis of the hip?

1. Traumatic risk factors

     ● Femoral head neck fractures

     ● Acetabular fractures

     ● Failed DHS surgery

     ● Hip dislocation or contusion

2. Atraumatic risk factors

     ● Alcohol

     ● Corticosteroids

     ● Autoimmune diseases - Lupus/RA

     ● Sickle cell

     ● Smoking

     ● Obesity

     ● Diabetes

     ● COVID - 19

What are the stages of avascular necrosis?

The ARCO Classification (Association Research Circulation Osseous) is one of the most widely used systems to stage avascular necrosis (AVN) of the femoral head. It combines radiographic, MRI, CT, and clinical findings to give a clear picture of disease progression.

Here is a breakdown of the stages:

What are the symptoms to watch for?

     ● Deep, dull pain in the groin, buttock, or thigh

     ● Pain worsens with weight-bearing

     ● Stiffness and reduced hip range of motion

     ● Limping as the condition progresses

What are the treatment options?

Medications

     ● Alendronate and Bisphosphonates are used in the initial stages.

     ● In terms of regenerative medicine, stem cell treatment is also used.

Operative management:

     ● Total hip replacement is commonly done.

     ● Rotational osteotomy

     ● Moving the area affected by AVN to a non-weight bearing portion

     ● Core decompression

        Drilling of the area affected to decompress the area

        It uses vascularised bone grafts or biological agents that promote bone repair

If you want to learn more about this topic, you can watch Amie Coombs' lecture here:

Click here

Sources:

From the lecture ‘Avascular Necrosis of the Hip’ by Amie Coombs