Spinal fusion surgery for isthmic spondylolisthesis

In most cases non-surgical treatment is successful in relieving the patient’s pain, but if not surgery can be considered. Spinal fusion [4] surgery for spondylolisthesis [5] is generally quite effective, but because it is a large procedure with a lot of recovery, it usually is not considered until a patient has failed six months of concerted non-surgical treatment. A spondylolisthesis above the L5-S1 level is more likely to need surgery because of the amount of motion in the upper vertebral segments. It is less likely that a spondylolisthesis at L5-S1 will need surgery.

However, because the incidence of spondylolisthesis is so much higher at L5-S1, most surgeries will still be a L5-S1. This segment at the bottom of the spine is not a major motion segment as it is deep in the pelvis and is not really designed to move much. This is an important point because if this level is fused it does not transfer a lot of stress to the other levels of the spine. After an L5-S1 fusion, the spine is still biomechanically much the same as it was preoperatively, and most patients will not perceive any difference in their motion after a one-level lumbar fusion.

Pre-operative considerations

The preoperative workup will include x-rays and a MRI scan. Some physicians will also require a patient to undergo a discogram prior to a spinal fusion, although the usefulness of this study is still a matter of fierce debate among surgeons. Some surgeons believe that discograms are a good indicator of whether or not a disc space is a pain generator and can help determine the number of levels requiring a fusion. Other surgeons believe this study is far too subjective and lacks specificity and sensitivity. Unfortunately, there is little literature that indicates whether or not a preoperative discogram leads to a more successful surgical outcome.A recent study by Carraggee in Spine indicated that discograms were predictive of a good outcome in only 50% of cases. Whether or not the study is used is more a matter of philosophical bias than true science.

Type of surgical approaches

A posterior fusion (approached from the back) with pedicle screw instrumentation is generally considered the gold standard of spinal fusion for spondylolisthesis. However, there is also an increasing acceptance that an accompanying fusion of the disc space can lead to a better fusion and increased stability. About 80% of the stress goes through the disc space, so supporting the anterior column (the disc space in the front of the spinal column) with a fusion greatly increases the stiffness of the fusion construct. The manner in which the disc is fused is largely guided by the surgeon’s preference.

Some surgeons prefer accessing the disc space through an anterior incision in the abdomen, called an anterior lumbar interbody fusion (ALIF). An anterior approach affords the best exposure to the disc space. It allows a large device to be used for the fusion, increasing the surface area for a fusion to set up and allowing for more postoperative stability. Another added benefit of an anterior approach is that a better reduction of the deformity caused by the spondylolisthesis is often possible. Jacking the disc open in the front re-establishes the patient’s normal sagittal alignment, giving them a more normal inward curve to their low back. This approach does require an extra incision in the abdomen, in addition to an incision in the low back. There is also the added risk of a great vessel injury, as the aorta and vena cava lie in front of the spine. However, with an experienced vascular and spine surgeon team, the risk of a vessel injury should be very low, and the benefits of added stability and fusion area very often outweigh the risks of the extra surgery. For male patients having an ALIF at L5-S1, there is a risk of retrograde ejaculation, in which the ejaculation goes into the bladder.

Another technique for accessing the disc space for a fusion is through an incision in the low back in a posterior approach, called a posterior lumbar interbody fusion (PLIF), or a transforaminal interbody fusion (TLIF). Approaching the disc space from posterior has the benefit over an ALIF of requiring only one incision in the low back. The drawbacks are that only a limited portion of the disc space can be accessed from the back as the dural sac that contains the nerve roots is in the way. This limits the size of interbody fixation device that can be used, and therefore can limit the added stability and fusion area. Also, placing a device from the posterior into the disc space puts both the exiting and traversing nerve root at risk.

Postoperative care

After a spinal fusion surgery, the patient will be hospitalized for 1 to 5 days. Early ambulation is encouraged as walking helps limit the chances of postoperative complications, such as deep venous thrombosis or pneumonia. It is also very gentle on the spine and can enhance healing. With modern stabilization procedures the need for postoperative bracing is now very limited, and most patients will not require a brace. Surgeons have different preferences as to how fast a patient is mobilized and how soon rehabilitation is started. Between 6 to 12 weeks after the spinal fusion, stabilization exercises to redevelop core strength can be useful. These strengthening exercises, along with hamstring stretching and conditioning, will be encouraged to allow the patient to become more functional.

After three to six months, the fusion is usually set, and the patient will be allowed to resume normal activities. In the early postoperative course, most surgeons will limit the patient’s activity. After the fusion is set, the more the patient uses their fusion the stronger it will get. Bone is a live tissue, and it will respond to stress by increasing the strength of a fusion. Generally speaking, permanent activity restrictions are not necessary after a one-level fusion at L5-S1, but may be considered in cases of multilevel fusions.