Bone healing is a biological process and to happen properly, it needs adequate stability and blood supply. Stability could be achieved externally by mean of a cast or external fixators, or internally by mean of surface bone plating or intramedullary nailing. Blood supply delivers the important components such as oxygen, healing cells, and the body's own chemicals necessary for healing (growth factors). A broken bone also needs adequate nutrition to heal. Eating a healthy and well-balanced diet that includes protein, calcium, vitamin C, and vitamin D is the best way to ensure adequate nutrition. Nonunion occurs when the bone lacks adequate stability, blood flow, or both. Risk factors for developing nonunion are use of tobacco or nicotine in any form, older age, severe anemia, diabetes, low vitamin D level, hypthyroidism, poor nutrition, medications including anti-inflammatory drugs such as aspirin, ibuprofen, and prednisone, infection, and complicated open fractures. Some bones such as toe bones, have inherent stability and excellent blood supply, therefore expected to heal with minimal treatment. Other bones such as the femoral head and neck and small wrist bone (scaphoid), have a limited blood supply and end-on vessels, therefore they are more prone to suffer the problem of nonunion if not treated properly. Patients with nonunions usually suffer from pain at the site of the fracture long after the initial pain of the fracture disappears, limp, instability, discharge if infected, and functional impairment. Imaging studies are performed that provide detailed pictures of the bone and surrounding soft tissues. These tests may include x-rays, bone scans, computed tomography (CT) scans, and magnetic resonance imaging (MRI). A nonunion may be diagnosed if the doctor finds one or more of the following: persistent pain at the fracture site, persistent gap with no bone spanning the fracture site, no progress in bone healing when repeated imaging studies are compared over several months, or inadequate healing in a time period that is usually enough for normal healing. Treatment of nonunion could be either conservative or surgical. The most common nonsurgical treatment is a bone stimulator devices like ultrasonic or pulsed electromagnetic waves that stimulate healing. The patient places the stimulator on the skin over the nonunion from 20 minutes to several hours daily. This treatment must be used every day to be effective. Surgery is needed when nonsurgical methods fail. Surgical options include bone graft or bone graft substitute, internal fixation, and/or external fixation. Bone graft acts as a scaffold on which new bone may grow. Bone grafts also provide fresh bone cells and the naturally occurring chemicals the body needs for bone healing. The most common site of bone autograft is the "iliac crest" and "the fibula".