Avascular necrosis (AVN) is the death of bone tissue due to a loss of blood supply. Although AVN is poorly understood, causes and risk factors for avascular necrosis of the hip include trauma (e.g. dislocation and fracture), chronic corticosteroid therapy, excessive alcohol intake, smoking, and other conditions that compromise blood circulation to the femoral head (the highest part of the thigh bone). In its early stages, AVN usually doesn’t cause symptoms. As the disease progresses, it may cause pain in the region of the affected hip, thigh, groin, and buttock. If avascular necrosis is not treated it can eventually cause the hip joint to collapse.