Avascular Necrosis of the Femoral Head

Avascular necrosis (AVN) of the femoral head, also called osteonecrosis, is death of bone cells due to interruption of subchondral blood supply, leading to weakening of the trabecular bone, microfractures, subchondral collapse, articular cartilage failure, and secondary osteoarthritis. It typically affects adults aged 30-50 and is bilateral in 50-80% of cases.

Etiologies include traumatic (femoral neck fracture, dislocation) and non-traumatic causes such as corticosteroid use (most common non-traumatic cause), alcohol, sickle cell disease, lupus and other autoimmune diseases, HIV protease inhibitors, hyperlipidemia, Gaucher disease, decompression sickness (caisson disease), radiation, chemotherapy, pregnancy, organ transplantation, and idiopathic. Bilateral involvement is common and screening of contralateral hip is warranted in high-risk patients.

Staging combines clinical, radiographic, and MRI findings. The Ficat-Arlet system has stages 0-IV, while ARCO 2019 uses stages I (preradiographic, MRI positive) through IV (advanced osteoarthritis). MRI is the most sensitive modality demonstrating the double-line sign and edema. Treatment is staging-driven: early stages may benefit from non-operative management with risk factor modification, protected weight bearing, and bisphosphonates; pre-collapse disease responds to core decompression with bone marrow aspirate concentrate or vascularized/non-vascularized bone grafting; post-collapse disease requires rotational osteotomy in young patients or total hip arthroplasty in advanced cases.