Osteonecrosis

Osteonecrosis, also known as avascular necrosis (AVN), is the death of bone tissue caused by reduced or interrupted blood flow. It most commonly affects the femoral head but can involve the femoral condyles, humeral head, and bones of the ankle and knee.

Causes include traumatic injury that disrupts blood supply, and nontraumatic risk factors such as prolonged corticosteroid use, excessive alcohol, sickle cell disease, Gaucher disease, hypercoagulable states, decompression (caisson) disease, and radiation therapy. It can be associated with organ transplantation and chemotherapy.

Pathophysiology: ischemia decreases osteocyte survival; microfractures and collapse of subchondral bone may occur; eventual collapse of the articular surface leads to joint incongruity and osteoarthritis.

Clinical features: insidious joint pain, typically in the hip, groin or thigh, with reduced range of motion; pain worsens with weight bearing and activity. Diagnosis: X-rays may be normal in early disease; MRI is the most sensitive test; CT and bone scans can aid assessment; evaluation for risk factors and exclusion of infection or tumor.

Staging and treatment: management depends on stage. Early disease may be treated with protected weight bearing, physical therapy, and procedures to restore blood supply such as core decompression or bone grafts. Advanced disease often requires joint replacement; osteotomies and vascularized grafts are additional options.

Prognosis varies with stage and etiology; without treatment, femoral head collapse and secondary arthritis commonly develop.