“…11,36 Conditions known to cause avascular necrosis include trauma, alcoholism, infections, medications (including corticosteroids, bisphosphonates, and highly active antiretroviral therapy), dysbaric trauma, marrow infiltration disorders, hypercoagulability states, autoimmune diseases, and idiopathic etiology. 4,27,31 These causes may be divided into three categories: (a) conditions resulting in external blood vessel compression near or within the bone, (b) disorders resulting in blood vessel occlusion because of thickening of the vessel wall, and (c) disorders resulting in blood vessel blockage from a thromboembolic process (Box 11-1). 12 For conditions resulting in external blood vessel compression, the mechanism is either marrow edema causing compression of the vessel in an enclosed region or excessive packing of the marrow through the deposition of abnormal tissue or material (e.g., fat in steroid administration or hyperlipidemia).…”