Should Fusion for Degenerative Spondylolisthesis Include the Sacrum?Low back pain from degenerative spondylolisthesis is often treated with spinal fusion when conservative (nonoperative) care fails to improve symptoms or function. But spinal fusion often results in the need for a second (revision) surgery. One common problem that develops is adjacent segment disease (ASD). The question this study attempted to answer is whether or not extending an L5-S1 fusion to include the sacrum can reduce the risk of adjacent segment disease.
Before we go any further exploring this topic, let's clear up a few terms. First, what is degenerative spondylolisthesis? In this condition, one of the vertebrae (spine bones) slips forward over the one below it.
Normally, the bones of the spine (the vertebrae) are neatly stacked on top of one another. Ligaments and joints support the spine. Spondylolisthesis alters the alignment of the spine and creates a narrowing of the spinal canal. As the bone slips forward, the nearby tissues and nerves may become irritated and painful. Low back pain and leg pain are the main symptoms but there can be sensory changes with numbness, tingling, and loss of sensation as well.
The degenerative aspect of spondylolisthesis tells us the condition develops over time as we age. Adults over age 50 are affected most often. There are degenerative changes in all parts of the spine including the joints, discs, and soft tissues. Slippage at the L4-L5 segment is the most common in this age group with this condition.
Without the normal alignment, spacing, and proper shock absorption, increased load is transferred through the spine. The disc at the L5S1 spinal level takes the brunt of it, so this is the area where degenerative disc disease is the worst in many patients.
Removal of the disc between L4-L5 with fusion of the same segment is referred to as a lumbar floating fusion or LFF. LFF is separate from a lumbrosacral fusion (LSF) where the L5 segment is fused to the main body of the sacral bone. So with this information in mind, we come back to the original question. Does extending the L4-L5 fusion down to also include the L5-S1 level yield a better result? And are there fewer cases of adjacent segment disease (ASD)?
By following 107 patients for five years or more, surgeons from the UCLA Comprehensive Spine Center at the University of California (Los Angeles) gained some new perspective on this issue. They found that the extended fusion did NOT improve results. There is no need to fuse the L5-S1 segment as a preventive measure against developing adjacent segment disease. The authors suggest that lumbosacral fusion should be used for patients with instability at the L5-S1 level (not just for disc degeneration).
Outcomes used to measure final results included X-rays, clinical presentation (signs and symptoms), and function. Function was measured using two well-known and commonly used tests: the Oswestry Disability Index (ODI) and the modified Brodsky criteria.
Careful records were kept of before and after results, age and sex (male versus female) of the patients, and spinal levels operated on.
Results were analyzed taking all of these additional factors into consideration.
How good are the results of a lumbar fusion that does not go past the L5 level? For the most part, clinical results (improved pain and function) and patient satisfaction were good-to-excellent in 82 per cent of the patients. The incidence of adjacent segment disease (ASD) was actually less in this group (the lumbar floating fusion group) compared with the (extended) lumbosacral fusion (LSF) group.
The higher rate of adjacent segment disease in the lumbosacral fusion (LSF) group may be the direct result of a longer fused rigid segment. With a longer area fused, there is an increased load and stress on the
normal segments above. Some researchers have concluded from their studies that increasing age is a risk factor for ASD but age was not statistically significant in this study.
In summary, extending spinal fusion to include the sacrum for patients with degenerative spondylolisthesis is not helpful. In fact, the extended fusion increases the risk of adjacent segment disease above the start of the fusion. Without this extension, the surgery is shorter and with less blood loss. There is also the advantage of less bone graft and a lower risk of pseudoarthrosis (failed fusion with spine motion still present) with the lumbar floating fusion.
Jen-Chung Liao, MD, et al. Surgical Outcomes of Degenerative Spondylolisthesis With L5-S1 Disc Degeneration. In Spine. September 1, 2011. Vol. 36. No. 19. Pp. 1600-1607.
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