Lack of blood supply to bone cells leading ultimately to bone demise, breakdown and eventually collapse. Symptoms range from pain with movement to pain on rest. Common causes are trauma, long use of steroids, alcohol use,smoking, radiation therapy, diabetes, HIV, and sickle cell anemia. Diagnosis is made via physical examination, history taking and MRI. Treatment can range from anti-inflammatory meds, exercise, smoking and alcohol reduction to bone graft transplant to Joint replacement.