osteonecrose

Osteonecrosis, also known as avascular necrosis, is the death of bone tissue caused by reduced or interrupted blood supply. It most commonly affects the femoral head but can involve any bone that relies on a limited blood supply. When the necrotic area involves the joint surface, there is a risk of progressive joint collapse and secondary osteoarthritis.

Causes and risk factors include both traumatic and nontraumatic factors. Trauma can disrupt vessels supplying a bone. Nontraumatic causes common in adults are prolonged high-dose corticosteroid use, excessive alcohol intake, sickle cell disease, decompression sickness, radiation therapy, autoimmune disorders, pancreatitis, and lipid disorders. Often multiple risk factors are present.

Pathophysiology involves failure of blood flow to bone tissue, leading to death of osteocytes and marrow. The necrotic bone weakens and may fracture under load, causing subchondral collapse and irregular joint surfaces. Over time, this can lead to painful arthritis and reduced joint function.

Clinical presentation typically includes joint pain that worsens with weight bearing, reduced range of motion, and sometimes a limp. Symptoms may be insidious and progress over months to years. The hip is most commonly affected; pain can be referred to the groin, thigh, or knee.

Diagnosis relies on imaging. X-rays may be normal in early disease; magnetic resonance imaging is the most sensitive test for early detection. CT provides detailed bone anatomy, while bone scintigraphy can be used in certain cases. Staging systems (such as ARCO or Ficat) help assess extent and guide treatment decisions.

Treatment depends on stage and joint involved. Early disease may be managed with activity modification, analgesia, and physical therapy; bisphosphonates or lipid-lowering therapies are used variably. Surgical options include core decompression, bone grafting, and vascularized grafts to preserve the joint. In advanced disease with femoral head collapse or secondary arthritis, total hip arthroplasty is common. Prognosis varies; preservation strategies are more successful in smaller, less advanced lesions. Prevention focuses on minimizing risk factors when possible.