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Fusion is a surgical procedure in which two or more spinal vertebrae are joined together by bone. Spinal fusion may be necessary in the low back or the neck. There are several indications for spinal fusion, and there are several different types of spinal fusions.
The classic indication for spinal fusion in the low back is instability, which means that there is abnormal motion between the vertebrae. The most common cause of instability that we see is spondylolisthesis, but instability can also occur after a wide laminectomy. Fusion is also indicated for scoliosis, curvature of the spine that is severe, progressive, or very painful. However, there are other indications for spinal fusion, some of which remain controversial. These include fusion for disc pain, prophylactic fusion after wide decompression especially if the facet joint is removed, and fusion for neck pain.
For all types of fusion, bone is used. For some types of fusions, bone bank bone works as well as the patients own bone, but for other types, the patients own bone leads to a higher fusion rate.
Low Back Fusions
Intertransverse fusion: the bone is placed to join the bones that stick out from the body of the vertebrae (transverse processes). In this type of fusion, the patients own bone works better.
Posterior fusion: this is done only rarely now. Bone is placed in the back of the laminae.
Facet fusion: the facet joints are fused together. It is not usually done without an accompanying interbody fusion.
Interbody fusion: Bone is placed between the vertebral bodies. It is probably the strongest type of fusion. It places the load along the spine in the way nature intended the spine to work. Interbody fusion can be performed from the back (posterior lumbar interbody fusion) or from the front (anterior interbody fusion). The choice is made according to the patients problem and the skills and experience of the surgeon. Interbody fusions can be done with cages made of bone or titanium, bone dowels, or bone rings. When interbody fusion is done with bone rings or dowels, it is best to use screws and bars in the back of the spine to get the highest success rate.
We use screws and bars frequently because we feel patients feel better faster, they do not need a brace, and there is a higher rate of fusion. In experienced hands, there is a low complication rate from the use of this type of fixation.
The current standard of fusion for one-level disc pain is the use of cages made of titanium. The cages are filled with bone, placed between the vertebrae, and then the bone grows through the cage making one solid piece of bone. We find this technology very good for single level fusions, but not as successful for fusions of two or more levels, where a two-stage procedure appears to work better and faster.