What are the 4 Stages of Avascular Necrosis?

Avascular Necrosis: 4 Stages of Bone Damage Explained

Avascular Necrosis (AVN), also known as osteonecrosis, is a serious medical condition where your bone cells die due to an insufficient blood supply. Without adequate blood flow, your bones become brittle. This condition most commonly affects the hip joint but can also impact the knees, shoulders, and other joints.

Different Stages of Avascular Necrosis

The various stages of osteonecrosis indicate how much the disease has spread. Starting from stage 1, where there is minimal damage, it ends at stage 4, with severe damage to your bones. Let us discuss them below.

Stage 1: Early Stage of AVN

In the first stage of AVN, there are no visible changes on standard X-rays. This can make diagnosis challenging. However, you may begin to experience mild joint pain or discomfort, particularly after physical activity. This suggests that your bone is starting to suffer from a reduced blood supply, but the structural integrity remains intact.

Key features of stage 1 avascular necrosis are as follows:

1. Normal X-ray
2. Minor damage shows up in the MRI
3. Mild or no symptoms
4. No bone collapse yet

Getting diagnosed at this stage significantly improves your disease outcome.

Stage 2: Bone Changes Begin in AVN

During the second stage, the damage becomes more apparent. Although your bone has not yet collapsed, changes such as sclerosis (hardening of the bone) and the formation of small cysts may be visible on imaging scans.

You may face increased joint pain, especially with movement or pressure on the affected joint. This discomfort may start to interfere with daily activities.

Stage 2 avascular necrosis has the following features:

1. X-rays show early bone damage (sclerosis or cysts).
2. Symptoms become more noticeable
3. Bone is weakened but still maintains its shape

It is still an early stage, and treatment may help restore bone function. Doctors often recommend core decompression, which can help supply blood to your bone tissue.

Stage 3: Bone Collapse in AVN

It is an advanced stage characterised by collapsing bone cells due to regular use. Your articular surface, the smooth cartilage-covered part of the bone that forms a joint, starts to flatten or cave in. This can lead to joint stiffness, significant pain, and reduced mobility.

Here are the main features of this stage:

1. X-rays show bone collapse, often visualized as a 'crescent sign' (a subchondral fracture line), and joint surface flattening.
2. Pain is persistent and worsens with activity.
3. Joint movement becomes limited

Doctors usually recommend surgical interventions such as bone grafting or osteotomy to prevent further damage.

Stage 4: Advanced Osteoarthritis in AVN

The final stage of AVN is marked by severe joint damage. As your bones collapse and cartilage continues to deteriorate, secondary osteoarthritis sets in. It results in chronic pain, stiffness, and often a significant loss of function in the joint.

The main characteristics of the last stage of avascular necrosis are as follows:

1. X-rays reveal severe joint damage and arthritis.
2. Pain can be constant, even at rest.

Doctors usually treat stage 4 avascular necrosis with joint replacement (arthroplasty), as it significantly affects quality of life.

Avascular necrosis progresses through four distinct stages, each with its own signs and symptoms. If left untreated, it can cause irreversible damage to the bone. Therefore, early diagnosis is critical, as treatments are more effective in the initial stages.

If you are experiencing unexplained joint pain, especially in the hips or knees, consult a healthcare provider as soon as possible. Advanced imaging, such as MRI, can detect AVN even when X-rays appear normal, offering a better chance for early intervention and joint preservation.