You may find the information presented through the SPORT studies helpful in answering this question. SPORT stands for Spine Patient Outcomes Research Trial. It is an ongoing long-term study conducted at 13 medical centers across 11 states in the United States. These medical centers provide multidisciplinary treatment to patients with spinal disorders including degenerative spondylolisthesis. Patients are followed at regular intervals and outcomes are measured in terms of pain, function, and disability.
Degenerative spondylolisthesis occurs with aging most often affecting the L4-L5 level in people over 50 years old. Women are affected six times more often than men. Spondylolisthesis alters the alignment of the spine. In this condition, degeneration of the disc and facet (spinal) joints can lead to one of the vertebral bones to slip forward over the one below it. As the bone slips forward, the nearby tissues and nerves may become irritated and painful. The spinal canal narrows (a condition called stenosis) putting pressure on the spinal nerves.
Previous SPORT studies have shown that patients have more improvement with surgery compared with a conservative (nonoperative) approach for the problem of degenerative spondylolisthesis with multilevel stenosis. Patients enrolled in a recent SPORT study who had leg pain or discomfort and other neurologic symptoms for at least three months were diagnosed with single-level degenerative spondylolisthesis and single or multi-level lumbar stenosis. This was the first study to compare the results of surgery for single-level degenerative spondylolisthesis accompanied by multilevel stenosis. The patients were divided into two groups. One group (130 patients) had a decompression procedure at more than one level (for the stenosis) and a fusion at one level (for the spondylolisthesis). The second group (77 patients) had the same multilevel decompression but only a single-level fusion.
Because SPORT is an ongoing data collecting type of study, many different pieces of information are collected about the patient, symptoms, insurance, clinical observations and test results, levels and severity of dysfunction, operative problems and results, and so on. This makes it possible to present tables of comparisons for patient demographics, comorbidities, fusion levels, and outcomes.
Although the multilevel fusion procedures took longer and the patients had more blood loss, there were no differences between the two groups in terms of blood replacement, complications during or after the surgeries, or number of reoperations required. Most other comparisons were similar between the two groups. The only real trend was for greater improvement of physical function in the single-level fusion group compared with the patients who had multilevel fusion. But that was only seen after the third year and the benefit evened out between the two groups after the fourth year of follow-up.
This study offers the additional information that surgical results are very similar when treating patients who have single-level degenerative spondylolisthesis and multilevel lumbar stenosis using different surgical approaches. Whether performing a single-level fusion procedure or a multiple-level fusion, the outcomes (measured as bodily pain and function) were about the same (i.e., not significantly different).
Therefore, given that surgery is often very beneficial for this condition, surgeons may want to limit fusion to just the spinal level where instability from the degenerative spondylolisthesis is present. In this way, patients are not exposed to longer operative times. And they are saved from higher levels of blood loss. This is an important consideration for older adults with multiple medical problems. It may be argued that fusing additional levels prevents future adjacent-segment disease but this remains under investigation.