Spinal fusion is a surgical procedure which aims to bring together two or more spinal vertebrae so that in time they fuse into one solid, bony unit. Generally, the intervertebral disk is removed and replaced with grafted bone or bone substitutes. The bones are held in place with hardware, such as screws, plates, wires and rods, allowing the fixed bones to grow together.
Cervical
The cervical vertebrae are the uppermost bones of the spine. There are seven cervical vertebrae and according to the Chicago Institute for Neurosurgery and Neuroresearch, the most common cervical fusions occur at sixth and seventh vertebrae. They also state the the most rare location is at the third and fourth vertebrae. A main reason for cervical spine fusion is discectomy, or vertebral disk removal. The disk is usually removed from the front, or anterior aspect. The cervical bones can be fused from the front in a process known as anterior fusion. Usually bones taken from the patients' pelvis are used to fill the gap left by the disk. In time, the vertebrae grow together and become one continuous bone. More rarely, a posterior fusion is used. The difference is that posterior fusions require bone graft placement on the back side of the vertebrae.
Thoracic
The twelve thoracic vertebrae compose the middle segment of the vertebral column, below the cervical segments. According to Medscape Today, the thoracic vertebrae are less vulnerable to degenerative instability and more resistant to trauma due to their stabilization with the ribs. This means if a force is enough to destabilize the vertebrae, the result is often associated with spinal cord injury. Fusion to re-stabilize thoracic vertebrae requires slightly different hardware than in other vertebral segments. As described in Spineuniverse, wires and hooks instead of screws are usually preferred due to the anatomy of the thoracic vertebrae. Bone graft material is place intravertebrally and packed into the facet joints of the vertebrae.
Lumbar
Below the thoracic segments lie the five lumbar vertebrae. Anterior, posterior and posterolateral lumbar spinal fusion describe approaches to the lumbar spinal column. The fusion process is similar to that in other vertebrae. As with other vertebral segments, the disk material is first removed and the space is packed with transplanted bone. The unstable bones are then fixed in place using hardware. The lumbar vertebrae are larger than other vertebrae, with thicker and more robust walls. This allows the surgeon to use screws and plates more aggressively to stabilize the bones.
Lumbosacral
There are five sacral vertebrae and they normally are fused in maturity. Therefore, they are naturally stable by virtue of such fusion. However, it is not uncommon that the last lumbar and first sacral vertebrae require fusion. This is called lumbosacral interbody fusion. The process is similar to other vertebral fusions. However, eOrthopod reports that fusion between these two segments can lead to sacroiliac pain. This might be a result of the shifting forces following fusion.
