Avascular Necrosis of the Hip: The Silent Bone Disease

Avascular necrosis (AVN) of the hip — also called osteonecrosis — is the death of bone tissue in the femoral head (the hip's ball) caused by interruption of its blood supply. Starved of blood, the bone quietly dies from the inside; months later it weakens, cracks, and finally the ball collapses, destroying the joint. It's called the silent disease for two reasons: early stages may cause little or no pain, and early X-rays look completely normal while the damage is already underway.

A young patient's disease

Unlike osteoarthritis, AVN typically strikes adults between 25 and 50 — people at the peak of career and family life. It affects both hips in 40-70% of cases, often at different stages. That combination — young age plus a joint-destroying disease — is exactly why catching it before collapse matters so much: everything we can do to save the natural joint only works in the early stages.

What cuts off the blood supply: the main causes

1. Corticosteroid (cortisone) use

The most common identifiable cause. Prolonged or high-dose cortisone — for asthma, autoimmune disease, kidney conditions, or taken casually without prescription, which remains a real problem in Egypt — disturbs fat metabolism inside the bone and its microcirculation. Risk rises with dose and duration, but susceptible patients can develop AVN even after shorter courses. Any young adult with groin pain and a cortisone history needs AVN excluded.

2. Heavy alcohol intake

The second classic cause worldwide, through similar fat-embolism and microcirculation mechanisms.

3. Sickle cell disease — relevant in Egypt

Sickled red cells block the fine vessels feeding the femoral head, making AVN one of the most common orthopedic complications of sickle cell disease — often bilateral and appearing distressingly young. Egypt has meaningful sickle cell prevalence, particularly in certain governorates and in families with roots in the oases, Upper Egypt, and Nubia. Every sickle cell patient with hip or groin pain deserves a low threshold for MRI.

4. Other causes — and 'no cause at all'

Hip trauma (fracture or dislocation can tear the blood vessels), diving/decompression sickness, some clotting disorders, chemotherapy and radiotherapy, lupus (both the disease and its steroid treatment) — and in roughly 20-30% of cases, no cause is ever identified (idiopathic AVN).

The stages: a race against collapse

AVN progresses through recognizable stages. Stage 1: bone is dying but X-rays are normal — only MRI shows it. Stage 2: X-rays begin showing patchy density changes; the ball is still round. Stage 3: the 'crescent sign' — a fracture line under the joint surface — appears, and the ball begins to flatten. Stage 4: collapse and secondary arthritis of the whole joint. The line between stages 2 and 3 is the most important boundary in this disease: before collapse, joint-preserving treatment is possible; after collapse, the joint is on an irreversible path.

Why early MRI changes everything

A normal X-ray does NOT exclude early AVN — X-rays can stay normal for months while bone is already dead, because they show mineral density, not blood supply. MRI detects AVN at the earliest stage with over 95% sensitivity, often before symptoms are significant. The practical rule: a young adult with persistent groin or deep hip pain, plus any risk factor (cortisone, sickle cell, heavy alcohol) and a normal X-ray, needs an MRI — not reassurance and painkillers. In Egypt in 2026 a hip MRI costs EGP 3,000-6,000; a delayed diagnosis costs a hip joint.

Treatment: core decompression vs hip replacement

Before collapse: core decompression

In early-stage AVN (before the ball deforms), core decompression drills one or more tracks into the dead segment to relieve pressure inside the bone, stimulate new blood vessels, and allow living bone to rebuild — sometimes combined with bone graft or biologic augmentation. Done at the right stage, it can halt progression and preserve the natural hip in a substantial proportion of patients, especially with small lesions. It's a limited operation with crutch use for around 6 weeks.

After collapse: total hip replacement

Once the ball has collapsed, no procedure restores it — total hip replacement becomes the reliable solution, and results in AVN patients are excellent for pain and function. Because AVN patients are young, surgeons favor cementless implants and low-wear bearings (ceramic) designed for decades of use. Modern implants make THR a very good operation even at 35 — but preserving your own joint for another decade first, when possible, is better still.

When to see a specialist

See an orthopedic specialist promptly if you have persistent groin or deep hip pain and any AVN risk factor — especially a history of cortisone treatment or sickle cell disease. Insist on discussing MRI if the X-ray is normal but pain persists beyond 4-6 weeks. If you already have AVN in one hip, the other should be imaged too: silent disease on the opposite side is common and most treatable exactly when it's silent.

AVN is the diagnosis I most hate making late. At stage 1 or 2, I can offer a young patient an operation that may save his own hip. Six months later, after the head collapses, the honest conversation becomes about which implant — not whether. If there's one message: young patient, groin pain, cortisone or sickle cell history, normal X-ray — get the MRI. — Prof. Dr. Mohamed Kamal, Bone Art Clinic