Nonunion is a term which refers to the paucity and failure of the normal bone healing process after a fracture.
For bone healing to happen, the bone needs adequate stability, blood supply and good nutrition.
The basic principle of the treatment of fractures is that the broken pieces must be put back into position and prevented from moving out of place until they heal. Some fractures can be held in position with a cast while some others require surgical fixation with implants like screws, plates and nails or with external fixator frames.
Blood delivers oxygen, healing cells, and the body's own chemicals necessary for healing (growth factors) to the fracture site. If the blood supply to the fracture site is compromised, the bone doesn't get the necessary substances for healing. Nonunions are more likely to happen if the injured bone has a limited blood supply.
Some bones, such as toe bones, have inherent stability and excellent blood supply. They can be expected to heal with minimal treatment. Some bones, such as the upper thighbone (femoral head and neck) and small wrist bone (scaphoid), have a limited blood supply. The blood supply can be destroyed when these bones are broken. Some bones, such as the shinbone (tibia), have a moderate blood supply, however, an injury can disrupt it. For example, a high-energy injury can damage the skin and muscle over the bone and destroy the external blood supply. In addition, the injury can destroy the internal blood supply found in the marrow at the center of the bone.
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; dietary supplements that go beyond the daily requirements are not effective. (The rare exception is the severely malnourished patient with many injured organs. In this case, the doctor will discuss dietary guidelines and make recommendations for adding dietary supplements.)