Chapter 4
Conclusions
Question 1: What is the relationship between each relevant patient characteristic and the presence and/or intensity of each of the patient signs, symptoms, and conditions of spinal stenosis?
- Our meta-analysis indicates that the mean canal size among patients with back pain is 0.541 standard deviation unit less than the mean canal size of patients without pain controls. While the difference between means is statistically significant, there is a 64.8 percent overlap between the distributions of the spinal canal diameters of patients with and without back pain. The overlap of the two distributions demonstrates that although there is a statistically significant relationship between spinal diameter and back pain, this relationship is not perfect. Approximately 1.7 times more patients with back pain have small spinal canals than age-matched control subjects without back pain.
- Even the modest effect mentioned in the preceding paragraph may be an overestimate of the magnitude of the relationship between pain and canal size. This is because the studies in this analysis may not distinguish a congenitally narrow canal from focal narrowing of the canal. Some of the patients in these studies may have focal spinal stenosis. If the spinal canal measurements in these patients were taken at the level of stenosis, this would lead to a lower mean canal size for that patient group. If patients with back pain are more likely to have stenosis than those without back pain, this would introduce bias toward finding smaller canals in the pain patients.
- Differences in canal diameter between patients with and without claudication were also statistically significant in our meta-analysis. The effect size for the combined groups was -1.23, and there is a 36.8 percent overlap between groups. If the results of this meta-analysis can be generalized to the population at large, a person with claudication is approximately three times more likely to have a small spinal canal than a healthy person with no claudication. However, because these data are based on only two studies, these results are not definitive and can be viewed only as reflecting trends in current data.
- We next conducted a meta-analytic evaluation of canal diameters among patients with and without sciatica or radicular pain. As in the preceding analysis, only two studies contributed data to this meta-analysis. Again, these results are not definitive and can be viewed only as reflecting trends in current data. Nevertheless, the effect size yielded by our meta-analysis was -0.597, which is statistically significant. While the difference between means is statistically significant, there is a 61.97 percent overlap between groups. These results suggest that a person with stenosis is approximately 1.78 times as likely to have a small spinal canal than a healthy person with no stenosis. Although patients with symptomatic stenosis tend to have smaller spinal canals than those without stenosis, the presence of a small canal does not necessarily predict that a patient will develop stenosis.
Question 2: Which relevant patient characteristics are associated with an increased likelihood of focal narrowing of the spinal canal?
- Some circumstantial evidence is available indicating that the development of symptomatic stenosis may be influenced by patient age, weight and occupation, and the presence or absence of osteoarthritis of the hips. However, quantitative data are not available to calculate the likelihood that a patient with a given characteristic will develop symptomatic stenosis.
Question 3: What is the relationship between degree of stenosis and the presence and/or intensity of each of the signs, symptoms, and patient conditions?
- Very little evidence exists relating the degree of narrowing of the lumbar spine with the presence or severity of the signs or symptoms of stenosis. Difficulties associated with finding such relationships include the presence of large numbers of patients with spinal narrowing and no symptoms, variations in canal size throughout the population, and lack of an accepted system for quantifying the degree of narrowing. The extent of narrowing is also likely to change with the posture of the patient. Lumbar spinal stenosis is a condition that includes both a focally narrowed spinal canal and the associated symptoms. In current clinical practice, the course of treatment depends on the severity of the symptoms, not on the degree of narrowing.
Question 4: What is the relationship between the signs and symptoms and other features of the history and physical and the results of the imaging examination?
- All the clinical trials that report data validating MRI, CT, or myelography for diagnosis of spinal stenosis had one or more flaws in design or reporting that adversely affected the reliability or applicability of the results. Each of the five trials that studied CT or MRI found that the sensitivity of the cross-sectional modality is equal to or better than the sensitivity of myelography. None concluded that myelography was superior to the cross-sectional modalities. None of the trials attempted to validate the quantitative measurements of the spinal canal made by any imaging modality.
- Clinical signs and symptoms do not appear to predict whether the results of imaging tests will show severe stenosis. The major symptoms of radiculopathy and cauda equina do not predict degree of stenosis. Lumbago and sciatica are significantly associated with disk herniation but not with stenosis. However, no trial that was relevant to the present question was prospective in design, and results of some of the trials are difficult to interpret because some patients had disk herniation. Therefore, a conclusive answer to this question awaits the results of trials of better design.
Question 5: What is the relationship between the signs and symptoms and other features of the history and physical and results of conservative treatment, and what is the relationship between the type of conservative treatment and patient outcomes?
- The proportional improvement of the groups of patients who initially have the greatest and the least ability to walk on a treadmill do not seem to be different. However, a group of the worst initial patients appears to remain the same or continue to get worse with conservative treatment. Because of the wide distribution of outcomes among patients with the worst initial status, initial status for treadmill walking distance appears to have little value in predicting the outcome of conservative treatment for individual patients.
- Many conservative methods have been proposed for treating patients with lumbar spinal stenosis. Our search of the literature uncovered only one randomized controlled trial that compared a conservative treatment to placebo treatment specifically in lumbar spinal stenosis patients. That study indicated that local anesthetic block provides temporary relief from neurogenic claudication for up to 3 months. No evidence is available for effectiveness beyond 3 months. Evidence for the efficacy of other conservative treatments in lumbar spinal stenosis patients is lacking. However, the lack of evidence for effectiveness does not prove that these treatments are not effective. The lack of evidence is an indication of the failure to design adequate clinical trials to show effectiveness.
- Evidence for the efficacy of other conservative treatments in lumbar spinal stenosis patients is lacking. However, the lack of evidence for effectiveness does not prove that these treatments are not effective. The lack of evidence is an indication of the failure to design adequate clinical trials to show effectiveness.
Question 6: What is the relationship between the signs, symptoms, and other features of the history and physical and the success or failure of surgical treatment?
- Poor study quality, especially the lack of pretreatment measurements of patient condition, reduce the usefulness of available data to answer the question of whether patient signs, symptoms, and other characteristics determine the success of surgery for degenerative lumbar stenosis. The few studies that do stratify outcomes by patient characteristics, especially those that examined degree of stenosis, did not find a connection between successful treatment and specific patient characteristics. Regression analysis from two studies suggests that patients in poor health due to comorbidity may have inferior outcomes after surgery compared to healthier patients.
- The lack of comparable patient groups and pretreatment data is a common problem in evaluating studies that examined both surgical and nonsurgical treatment groups. Typically, the two patient groups differ in the extent to which lumbar spinal stenosis affects their signs and symptoms and their pretreatment outcome measurements. This leads to treatment selection based on the extent of disease, and patients are not randomly assigned to treatment groups. Less severe cases may tend to receive conservative treatment, and more severe cases may tend to receive surgery. Data are lacking on the effect of conservative treatment on patients with severe stenosis, since these patients seem to receive surgery shortly after diagnosis. One study suggests that patients who do not fare well with conservative treatment tend to have greater stenosis, but data on spinal canal diameter are not reported, and this trend cannot be verified. A single randomized controlled trial offers the best available evidence that patients with severe symptoms benefit more from surgery than conservative treatment. In this trial, the apparent superiority of surgery in moderate patients may be an artifact caused by inclusion of severe patients. The failure of these patients to respond to conservative therapy supports the benefits of surgery for patients with severe symptoms. Two studies suggest that patients with moderate stenosis may improve after receiving only conservative treatment. However, data from a single cohort study suggest that at one year after treatment, patients with moderate pain will benefit more from surgery than from conservative treatment. The statistical significance of the observed long-term effects in this study (four years) was not robust to a worst-case sensitivity analysis of dropouts.
Question 7: What is the relationship between the results of the imaging examination and the success or failure of surgical treatment?
- No published trials provided the data necessary to determine whether a group of lumbar spinal stenosis patients with particular results on a diagnostic imaging test will have better results after surgery than another group. The one controlled surgical trial that reported imaging results did not differentiate between surgical and nonsurgical patients in its published imaging results.
- Nine uncontrolled trials reported surgical outcomes as a function of degree of stenosis, as measured by myelography. All nine of these studies used different scales to categorize stenosis. Two trials reported better outcomes among patients with more severe stenosis, and three reported worse outcomes among patients with more severe stenosis. Four studies reported no significant difference between the groups. Most of the studies failed to report preoperative data that would allow us to determine whether the observed differences between groups resulted from surgery or were preoperative differences.
- Sufficient information was not provided in any of the articles we examined to permit us to demonstrate an association between imaging findings and surgical results.
- We are unable at this time to use imaging results to identify patient groups that would be more or less likely to benefit from surgery. One trial found that patients with normal myelograms did not benefit from surgery, but there is a question as to whether those patients even had spinal stenosis.
Question 8: What is the relationship between the type of surgery received and the success or failure of surgical treatment?
- Taken at face value, the results of two randomized controlled trials would seem to suggest that instrumentation (eg., pedicle screws) in addition to fusion does not improve surgical outcomes among patients with spondylolisthesis compared to fusion alone. However, both trials may have had too few patients (and, therefore, insufficient statistical power) to render any such conclusion definitive.
- One trial provided evidence that fusion is beneficial compared to decompressive surgery alone in these patients.
- Drawing conclusions from just one or two trials is problematic, however. This is because such conclusions have a rather high potential to be influenced by publication bias (the potential that trials with negative findings are not published) or the "file drawer" problem (the tendency of investigators to not report findings that are not statistically significant). Until data from larger and well-designed randomized controlled trials comparing surgical interventions are available, reliable conclusions are not possible.
Question 9: What costs are associated with nonsurgical and surgical treatment ofspinal stenosis?