Spondylolisthesis is defined as the movement of adjacent vertebra relative to each other.
Although spondylolisthesis can be caused by many pathologic entities, degenerative spondylolisthesis is by far the most common. With aging, discs lose water content and ultimately height. As the vertebra on either side of the disc come closer to each other through the loss of disc height, the upper vertebra slides forward on the subadjacent vertebra producing spondylolisthesis. High stresses and motion produce degeneration of the disc and for this reason the most susceptible levels of the lumbar spine, L4-L5, followed by L3-L4 and L5-S1 are the vertebral segments most commonly involved.
Spondylolisthesis is also associated with deterioration of the facet joints connecting the two vertebra. As the facet joints become arthritic due to this deterioration, they enlarge in an attempt to confer stability. As the two rings of the vertebral segments which make up the spinal canal, slide past each other, the canal narrows in size (fig 1). The combination of canal narrowing and enlargement of the facet joints, produces the characteristic nerve compression problems found in degenerative spondylolisthesis. The nerves are compressed in two major areas at the site of a degenerative spondylolisthesis It is believed that a reduction in nerve blood flow accounts for the symptoms produced from spinal canal narrowing (Spinal stenosis).
Typically the legs ache or are painful with activity. This is called neurogenic claudication. Enlargement of the facet joints increases spinal canal narrowing by encroachment into the lateral recesses (fig 2).The enlarged facet joints separate as the vertebra moves forward producing spinal instability. Spinal instability in degenerative spondylolisthesis has important implications in the ultimate treatment of this disease Conservative therapy is always the first treatment for any degenerative spinal disorder. There is a new published in the New England Journal of Medicine finds some advantage to choosing surgery over non-invasive treatment for degenerative spondylolisthesis. View the abstract of the study.
Rarely does degenerative spondylolisthesis cause serious weakness or numbness in the legs requiring emergency surgery. Epidural steroid injections may help alleviate the the inflammation of the nerve roots producing symptomatic relief for periods of weeks or months. Physical therapy may improve the back pain associated with the slipping of the vertebra, but rarely improves the nerve compression due to spinal stenosis. Those patients whose symptoms are refractory to conservative treatments are candidates for surgery.
The goals of surgery are to alleviate nerve compression while maintaining spinal stability. If the spinal segments are rigid despite their slipped position, then microscopic decompression of the lateral recesses and nerve holes (neuroforamen) can produce significant relief of nerve pressure. This is in contradistinction to the laminectomy (see Decompressive Laminectomy) operation where stabilizing bone is removed causing the slipped segment to be at risk of further movement. In general most patients are not candidates for decompression alone because enough bone needs to be removed that the spinal segment is rendered more unstable. Because most patients present with both back and leg complaints, nerve decompression and fusion with or without spinal instrumentation is usually required to adequately treat degenerative spondylolisthesis.
During the operation, a microscope is employed to adequately remove all encroaching bone from around the affected nerves. Because the fusion operation will reestablish stability after decompression, there is no limitation to how much bone can be removed and therefore a more complete decompression can be accomplished. A posterior spinal fusion is then performed by transplanting bone from the iliac crest to the bones of the back of the spine.
The ultimate goal of this procedure is that as the fusion heals, very much like a bone heals after it is fractured, that the two vertebrae are connected by this healing fusion mass and become stabilized together. We use spinal instrumentation in degenerative spondylolisthesis for a few reasons. Adequate scientific evidence exists to indicate that fusions heal at a higher rate with the addition of spinal instrumentation. To view an animation of the surgery, click on the projector below.
Anecdotally, our patients seem to enjoy a smoother, less painful postoperative course by the addition of an “internal brace.” The instrumentation is screws connected by rods which hold the vertebra together while the fusion is healing. Postoperative care can be found in an associated description. Surgery for degenerative spondylolisthesis is one of the most gratifying spinal operations from the surgeons standpoint. Done correctly patients usually achieve excellent relief of both spinal stenosis symptoms and back pain. Function is improved allowing the individual a better quality of life.