Avascular Necrosis of the Hip: Why Early Diagnosis Saves Joints

Avascular necrosis (AVN) of the femoral head — also called osteonecrosis — is the death of bone tissue at the top of the thigh bone because its blood supply has been compromised. It is a condition that strikes young adults, often in their 20s, 30s and 40s, and can progress from a small painless lesion to a collapsed femoral head requiring hip replacement within months if left unchecked. The most important fact about AVN is also the most often missed: early diagnosis radically changes the treatment options and the long-term outcome. A patient diagnosed at stage 1 or 2 has joint-preserving options. A patient diagnosed at stage 3 or 4 usually needs hip replacement. The window matters.

What causes AVN?

The blood supply to the head of the femur is delicate — a single small artery supplies most of it. Anything that compromises that vessel can cause bone tissue to die. The most common causes we see:

• Steroid use (long courses of oral corticosteroids — for asthma, autoimmune disease, or after COVID-19 hospitalisation)
• Alcohol excess (heavy chronic consumption)
• Trauma (femoral neck fracture, hip dislocation)
• Sickle cell disease
• Caisson disease (decompression sickness)
• HIV antiretroviral therapy
• Idiopathic — no identifiable cause

In our Bengaluru practice, post-steroid AVN has become more common after the COVID-19 pandemic — a clear pattern emerged in patients who received high doses of corticosteroids during severe respiratory illness.

Symptoms

The classic early symptom is groin pain that worsens with weight bearing. Patients often describe a deep ache that is initially intermittent and progresses to constant pain. Range of motion gradually reduces, particularly internal rotation. As the disease progresses to femoral head collapse, mechanical symptoms — catching, giving way — develop. By this point, the joint surface has changed shape and arthritis is established.

How AVN is diagnosed and staged

Plain X-rays appear normal in the earliest stages — a key reason AVN is missed. MRI is the diagnostic test of choice and is sensitive enough to pick up changes long before X-ray changes appear. Any young adult with persistent unexplained groin pain — particularly if they have a risk factor — should have an MRI rather than an X-ray as the first imaging.

The disease is staged most commonly by the Ficat–Arlet system:

• Stage 1 — pre-radiographic. MRI shows changes. Treatable.
• Stage 2 — radiographic changes without femoral head collapse. Treatable.
• Stage 3 — femoral head collapse (the curve of the head is lost). Joint preservation difficult.
• Stage 4 — established arthritis. Hip replacement required.

Joint-preserving treatments

The aim in early-stage AVN is to halt progression and preserve the patient’s native hip. Three approaches are used:

Core decompression

A small drill is used to remove a core of bone from the femoral neck, relieving the pressure inside the dead area and stimulating new blood vessel growth. Best results are in stage 1 and small stage 2 lesions. Often combined with bone graft or marrow concentrate. Outcomes: 60–80% successful at preventing progression to replacement in early stages, falling sharply once collapse has begun.

Bone grafting

Structural bone graft — vascularised fibula or non-vascularised — can be used in larger lesions to support the femoral head architecture while healing occurs. Technically demanding; results vary.

Pharmacological treatment

Bisphosphonates have a small role in slowing progression. Statins may help in steroid-induced AVN. Adjuvant rather than definitive treatment.

When hip replacement is the answer

Once the femoral head has collapsed (stage 3) or arthritis is established (stage 4), joint preservation is rarely successful and total hip replacement becomes the right answer. The good news is that hip replacement is an excellent operation, and modern implants and bearings perform extremely well in younger patients with AVN — many last more than two decades.

Activity recommendations

In early AVN, weight bearing restrictions are usually advised — partial weight bearing on crutches for several weeks during the joint-preservation phase. After joint preservation, swimming, cycling, and walking are encouraged; high-impact activities and contact sports are discouraged. After hip replacement, the same long-term guidelines apply as for other hip replacement patients.

What can be done to prevent AVN?

Where possible, the underlying risk factor should be addressed: minimising steroid dose and duration, treating alcohol use, managing sickle cell disease aggressively. Patients on high-dose steroids should be aware of the warning sign of new hip pain.