Avascular Necrosis

Definition/diagnostic criteria Avascular necrosis (AVN), also known as osteonecrosis, refers to the death of bone tissue due to a lack of blood supply. This condition can lead to bone collapse and pain, particularly in the hip and shoulder joints. Diagnostic criteria include a combination of clinical assessment and imaging findings. MRI is considered the gold standard for diagnosis, being able to detect early changes before they appear on X-rays.

Epidemiology AVN predominantly affects individuals between 30 and 50 years of age and has a variety of risk factors, including long-term steroid use, excessive alcohol consumption, trauma, and certain medical conditions like sickle cell disease. The exact incidence in the UK is unknown.

Diagnosis
Clinical features: Patients typically present with joint pain, which initially occurs only with movement but can progress to constant discomfort. The hip is the most commonly affected joint, followed by the shoulder, knee, and ankle.

Investigations: Early diagnosis is crucial for effective management.

• X-rays: initial imaging, though changes may only be visible in later stages.
• MRI: highly sensitive in detecting early bone changes and marrow oedema.
• CT scans: useful in assessing the extent of bone collapse.
• Bone scans: can detect changes in blood flow to the bone but are less specific than MRI.

Typical abnormalities include subchondral lucency, sclerosis and eventual collapse of the joint surface.

Treatment Treatment of AVN aims to prevent further bone loss and collapse and relieve pain. Interventions can be pharmacological or surgical.

Pharmacological:

• Analgesics for pain management, including paracetamol and NSAIDs.
• Bisphosphonates may be used to slow the progression in early-stage disease.

Surgical:

• Core decompression in early stages to reduce intraosseous pressure and promote revascularisation.
• Osteotomy may be considered to redistribute load on the affected bone.
• Joint replacement, particularly total hip or shoulder arthroplasty, in advanced cases with significant joint destruction.

Prognosis The prognosis of AVN varies depending on the stage at diagnosis and the underlying cause. Early-stage disease (particularly pre-collapse) has a better prognosis with conservative or surgical intervention. Without treatment, most cases of AVN progress to joint destruction and severe arthritis within two to four years, necessitating joint replacement surgery.