Spinal fusion surgery is designed to stop the motion at a painful vertebral segment, which in turn should decrease pain generated from the joint. All lumbar spinal fusion surgery involves adding bone graft to an area of the spine to set up a biological response that causes the bone graft to grow between the two vertebral elements and thereby stop the motion at that segment.
For patients with the following conditions, abnormal and excessive motion at a vertebral segment may result in pain:
Degenerative disc disease
Isthmic, degenerative or postlaminectomy spondylolisthesis.
Other conditions that may be treated by a spinal fusion surgery include a weak or unstable spine (caused by infections or tumors), fractures, scoliosis or deformity.
At each level of the spine, there is a disc space in the front and paired facet joints in the back. Working together, these structures define a motion segment and permit multiple degrees of motion.
Two vertebral segments need to be fused together to stop the motion at one segment, so that an L4-L5 (lumbar segment 4 and lumbar segment 5) spinal fusion is actually a one-level spinal fusion.
A spine fusion surgery involves using bone grafts to cause two vertebral bodies to grow together into one long bone. Bone graft can be taken from the patient’s hip (autograft bone) during the spine fusion surgery, or harvested from cadaver bone (allograft bone).
Synthetic bone graft substitutes are also in development and one bone type called morphogenic proteins (which helps the body create bone) is currently being used for certain fusion procedures.
In general, a lumbar spinal fusion surgery is most effective for those conditions involving only one vertebral segment. Most patients will not notice any limitation in motion after a one-level spine fusion. Only in rare cases should a three (or more) level fusion surgery for pain alone be considered. Although it may be necessary in cases of scoliosis and lumbar deformity.
When necessary, fusing two segments of the spine may be a reasonable option for treatment of pain. However, spinal fusion of more than two segments is unlikely to provide pain relief because it removes too much of the normal motion in the lower back and places too much stress across the remaining joints.
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