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Nonunion is a serious complication of a fracture and may occur when the fracture moves too much, has a poor blood supply or gets infected. Patients who smoke have a higher incidence of nonunion. The normal process of bone healing is interrupted or stalled. In some cases a pseudo-joint (pseudarthrosis) develops between the two fragments with cartilage formation and a joint cavity. More commonly the tissue between the ununited fragments is scar tissue.
Since the process of bone healing is quite variable, a nonunion may go on to heal without intervention in a very few cases. In general, if a nonunion is still evident at 6 months post injury it will remain unhealed without specific treatment, usually orthopedic surgery. A non-union which does go on to heal is called a delayed union.
A history of a broken bone is usually apparent. The patient complains of persistent pain at the fracture site and may also notice abnormal movement or clicking at the level of the fracture. An x-ray plate of the fractured bone shows a persistent radiolucent line at the fracture. Callus formation may be evident but callus does not bridge across the fracture. If there is doubt about the interpretation of the x-ray, stress x-rays, tomograms or CT scan may be used for confirmation.
The reasons for non-union are
- avascular necrosis (the blood supply was interrupted by the fracture)
- the two ends are not apposed (that is, they are not next to each other)
- infection (particularly osteomyelitis)
- the fracture is not fixed (that is, the two ends are still mobile)
- soft-tissue imposition (there is muscle or ligament covering the broken ends and preventing them from touching each other)
Callus is formed, but the bone fractures have not joined. This can be due to inadequate fixation of the fracture, and treated with rigid immobilisation.
No callus is formed. This is often due to impaired bony healing, for example due to vascular causes (e.g. impaired blood supply to the bone fragments) or metabolic causes (e.g. diabetes or smoking). Failure of initial union, for example when bone fragments are separated by soft tissue may also lead to atrophic non-union. Atrophic non-union can be treated by improving fixation, removing the end layer of bone to provide raw ends for healing, and the use of bone grafts.
Surgical treatment includes removal of all scar tissue from between the fracture fragments, immobilization of the fracture with metal plates, rods and or pins and bone graft. In simple cases healing may be evident within 3 months. Gavriil Ilizarov revolutionized the treatment of recalcitrant nonunions demonstrating that the affected area of the bone could be removed, the fresh ends "docked" and the remaining bone lengthened using an external fixator device. The time course of healing after such treatment is longer than normal bone healing. Usually there are signs of union within 3 months, but the treatment may continue for many months beyond that.
By definition, a nonunion will not heal if left alone. Therefore the patient's symptoms will not be improved and the function of the limb will remain impaired. It will be painful to bear weight on it and it may be deformed or unstable. The prognosis of nonunion if treated depends on many factors including the age and general health of the patient, the time since the original injury, the number of previous surgeries, smoking history, the patient's ability to cooperate with the treatment. In the region of 80% of nonunions heal after the first operation. The success rate with subsequent surgeries is less.