What is avascular necrosis of the hip?

Avascular necrosis (AVN), also known as osteonecrosis, occurs when the blood supply to the femoral head, the ball of the hip joint, is disrupted. Without adequate blood flow, bone cells die and the structural integrity of the femoral head is progressively lost. Over time, the necrotic bone weakens, the articular surface collapses, and severe hip osteoarthritis develops.

AVN follows a predictable staging progression:

• Stage 1 (early): swelling inside the bone. Only visible on MRI; usually fully reversible.

• Stage 2: bone scarring and cysts begin to form. Visible on MRI and some X-rays.

• Stage 3: a small fracture forms under the joint surface, signaling that a collapse is near.

• Stage 4 (late): the hip bone collapses, causing permanent damage that usually requires a hip replacement.

Bilateral AVN: up to 80% of people with AVN in one hip will develop it in the other. This is why we always check both hips, even if only one side hurts.

Symptoms of avascular necrosis of the hip

AVN symptoms are often absent in the earliest stages, when treatment is most effective. As the condition progresses, common signs include:

• Deep, aching pain in the groin, hip, or thigh, often initially intermittent and activity-related

• Progressive worsening of pain over weeks to months, eventually becoming present at rest

• Night pain disturbing sleep

• Stiffness and reduced range of motion in the hip

• A limp developing as pain worsens with weight bearing

• In advanced collapse: severe pain, marked stiffness, and functional disability comparable to end-stage osteoarthritis

The most important clinical signal is hip or groin pain in someone with a known risk factor for AVN, particularly long-term corticosteroid use, alcohol excess, or a recent hip injury or fracture.

AVN results from any condition or event that disrupts blood flow to the femoral head. Common contributing causes include:

• Corticosteroid use is the most common non-traumatic cause, responsible for approximately 35% of cases. Steroids cause fat cell enlargement within the femoral head that compresses intraosseous blood vessels.

• Alcohol excess is the second most common non-traumatic cause, causing fat accumulation and vascular damage within bone.

• Trauma including hip fracture or dislocation directly disrupts the arterial supply to the femoral head. Post-traumatic AVN can develop months to years after the original injury.

• Sickle cell disease causes vascular occlusion from sickling red blood cells within the bone's blood vessels.

• Systemic lupus erythematosus is associated with AVN both from the disease itself and from the corticosteroid treatment it requires.

• Coagulopathies and thrombophilia cause small vessel thrombosis within bone, reducing perfusion.

• Decompression sickness in divers causes nitrogen bubble formation in bone vasculature.

• Idiopathic a significant proportion of AVN cases have no identifiable cause.

How is avascular necrosis of the hip detected?

AVN is primarily detected through MRI, which can spot the condition long before symptoms appear or X-rays show damage. Blood tests help identify why the bone's blood supply was interrupted.

MRI is the gold standard for AVN. It can detect Stage 1 changes, like bone swelling, when the hip still looks normal on an X-ray. Elfcare’s full-body MRI images both hips at once, which is vital since AVN often affects both sides. Catching it early (stage 1 or 2) is the only way to save the joint and avoid a hip replacement.

Blood tests cannot detect AVN directly but identify the systemic conditions most commonly driving it and assess the impact of associated conditions. Relevant markers in Elfcare's panel include:

• CRP: measures inflammation from underlying conditions like lupus that can cause AVN.

• Lipid profile (cholesterol and triglycerides): high fat levels in the blood are linked to tiny blockages in bone vessels, especially for those on steroids.

• HbA1c and glucose: assesses if diabetes-related vascular issues are starving the bone of blood.

• Vitamin D and calcium: checks your baseline bone health to see how well your skeleton can recover.

• Full blood count: screens for blood disorders that can cause "clumps" in small bone arteries.

• Ferritin: looks for iron storage issues that can affect blood vessels.

• Albumin: a marker of nutrition; low levels can hinder the body's ability to heal damaged bone.

Why early detection matters

The difference between stage 1 and stage 4 AVN is the difference between a preserved, functioning joint and a total hip replacement. At stage 1, core decompression surgery, a minimally invasive procedure that relieves intraosseous pressure and stimulates new blood vessel formation, can halt progression and allow healing in a significant proportion of cases. Bisphosphonates and protected weight bearing provide additional joint-preserving benefit at early stages. Once the femoral head has collapsed, none of these options apply. Because AVN is frequently bilateral, identifying and staging both hips simultaneously through MRI ensures that early disease in the asymptomatic hip is not missed until it too reaches an irreversible stage.

How Elfcare can help

Elfcare's full body MRI images both hips as standard, providing simultaneous bilateral assessment of the femoral heads. This is the most clinically important tool for AVN detection, identifying bone marrow changes at the earliest reversible stage before structural damage has occurred. For someone with known risk factors including long-term corticosteroid use, excess alcohol, or a previous hip injury, proactive hip MRI is one of the most valuable assessments available.

Our blood panel covers the metabolic, inflammatory, and haematological markers most relevant to AVN risk and associated conditions.

If our MRI or blood tests identify findings consistent with AVN or related bone pathology, we take care of further diagnostics or refer you to the appropriate specialist.