Avascular necrosis of the femoral head — also called osteonecrosis or aseptic necrosis — is the death of bone in the femoral head caused by interruption of its blood supply. Untreated, the necrotic segment collapses, the overlying cartilage fails and secondary arthritis follows, frequently in patients in their thirties and forties.
The commonest associations are prolonged or high-dose corticosteroid therapy and excessive alcohol intake. Trauma — femoral neck fracture or hip dislocation — disrupts the blood supply directly. Other recognised causes include sickle cell disease and other haemoglobinopathies, coagulation disorders, systemic lupus erythematosus, decompression sickness in divers, radiotherapy, chemotherapy and organ transplantation. In a proportion of patients no cause is identified. Both hips are affected in a substantial number of cases, so the asymptomatic side should always be imaged.
Early necrosis is often silent. The first symptom is usually groin pain, worse on weight-bearing and at the extremes of movement, sometimes of surprisingly sudden onset. Because plain radiographs remain normal for months, a normal X-ray does not exclude the diagnosis. Any patient with unexplained hip pain and a risk factor should have an MRI, which detects the lesion at a stage when treatment can still preserve the joint.
The Ficat–Arlet classification is widely used. Stage I has a normal radiograph with changes visible only on MRI. Stage II shows sclerosis and cystic change with a preserved spherical head. Stage III is marked by subchondral collapse — the crescent sign — and flattening of the head. Stage IV shows joint space narrowing and established secondary arthritis. The critical threshold is collapse: before it, the femoral head can potentially be saved; after it, it cannot.
In pre-collapse disease, core decompression reduces intraosseous pressure and stimulates revascularisation by drilling channels into the necrotic segment, sometimes combined with bone graft or biological augmentation. Results are best for small, medially located lesions treated early. Protected weight-bearing and treatment of the underlying cause are adjuncts, but no medication reliably reverses established necrosis.
Once the femoral head has collapsed or arthritis is established, total hip replacement gives predictable and durable pain relief. Modern uncemented implants with hard bearing surfaces perform well in this typically younger patient group, and the ASI minimally invasive approach allows rapid return to work and activity.
The interval between the first symptom and collapse can be short. Prompt MRI in an at-risk patient with hip pain is the single most useful step in preserving the joint. Contact the practice if you have hip pain and any of the risk factors described above.
to guide you about your condition, to choose the best possible treatment.
