A fusion can be indicated for multiple reasons such as instability of the spine, when severe, painful arthritic/degenerative changes exist, when there is a concern of the patient developing postoperative instability or other reasons. If any of these conditions exist, a fusion is typically recommended as the course of treatment. Sometimes the fusion is done at the first operation and sometimes the fusion is done at a later operation.
In a fusion, an attempt is made to get two or more spinal vertebrae to grow together into one, solid bone. This can be done with the patient's own bone (taken from the back of the pelvis at about the belt level), using bone bank bone (from another person's body) or various synthetic bone substitutes. Metal hardware is also typically inserted in the form or screws with rods and/or plates to increase the chances that the fusion will grow successfully.
Once the bone chips and hardware are in place, it is up to your body to unite the fragments together and to heal into a solid fusion. This does not always occur. Sometimes the body will not form a good solid fusion and sometimes the bone chips will be absorbed by the body and thus no fusion will result. If this happens it may be necessary in the future to repeat the operation and attempt the fusion again.