In patients with imaging-confirmed spinal stenosis without spondylolisthesis and leg symptoms persisting for at least 12 weeks, surgery was superior to nonsurgical treatment in relieving symptoms and improving function. In the as-treated analysis, the treatment effect for surgery was seen as early as 6 weeks, appeared to reach a maximum at 6 months, and persisted for 2 years; it is notable that the condition of patients in the nonsurgical group improved only moderately during the 2-year period. The intention-to-treat results must be viewed in the context of the substantial rates of nonadherence to assigned treatment. The pattern of nonadherence was striking because both the surgical and the nonsurgical groups were affected, unlike the results of many studies involving surgical procedures.30
The mixing of treatments owing to crossover can be expected to create a bias toward the null.31
The large effects seen in the as-treated analysis and the characteristics of the crossover patients suggest that the intention-to-treat analysis underestimated the true effect of surgery.
This study provides an opportunity to compare results involving patients who were willing to participate in a randomized study (randomized cohort) and those who were unwilling to participate in such a study (observational cohort).13-16
These two cohorts were remarkably similar at baseline. Other than treatment preference, the only significant differences were small ones in signs of nerve-root tension and the location of stenosis. The two cohorts also had similar outcomes, without significant differences in the as-treated analyses. Given these similarities, the combined analyses are well justified. Although these analyses are not based on randomized treatment assignments, the results are strengthened by the use of specific inclusion and exclusion criteria, the sample size, and adjustment for potentially confounding baseline differences.32
The characteristics of the patients were similar to those in previous studies, even though the latter involved mixed-cohort patients (i.e., those with or without spondylolisthesis). In our study, the functional status of the patients at baseline was similar to that of patients in the Maine Lumbar Spine Study7,8
(SF-36 score, 34.8 and 35.0, respectively) but worse than that in the study by Malmivaara et al.10,11
(Oswestry Disability Index, 42.4 and 35.0, respectively).
In the as-treated analysis, the functional improvement in the surgical group at 1 year was very similar to that in the Maine Lumbar Spine Study (26.5 and 27.0, respectively) but greater than in the study by Malmivaara et al. (Oswestry Disability Index, −21.4 and −11.3, respectively). Functional improvement in the nonsurgical group was greater in our study than in the previous studies, with a change of 10.5 in the SF-36 physical function score at 1 year, as compared with 1.0 in the Maine Lumbar Spine Study, and a change of 9.3 in the Oswestry Disability Index at 2 years, as compared with 4.5 in the study by Malmivaara et al. The greater improvements in our study, compared with those in the study by Malmivaara et al., may be related to differences in the selection of patients. In the study by Malmivaara et al., patients with moderate spinal stenosis were specifically selected, whereas in our study, we attempted to enroll patients with spinal stenosis who were surgical candidates.
In the as-treated analysis, we can directly compare the estimates of treatment effect with those of the previous studies. The estimated 1-year treatment effects for surgery were smaller in our study than in the Maine Lumbar Spine Study (changes in bodily pain of 14.6 and 30.4, respectively, and in physical function of 15.9 and 25.5, respectively). However, in the Maine Lumbar Spine Study, treatment effects for baseline differences between the study groups were not adjusted, which probably explains these discrepancies. At 1 year, the estimated treatment effects were similar in our study and the study by Malmivaara et al.: Oswestry Disability Index, −12.5 and −11.3, respectively; leg pain, 17% (on a 7-point scale) and 15% (on an 11-point scale); and back pain, 14% (on a 7-point scale) and 21% (on an 11-point scale).
It is interesting that among patients who underwent surgery, the magnitude of the mean changes in patients with spinal stenosis was nearly identical to that in the patients with degenerative spondylolisthesis at 2 years: bodily pain, 26.9 and 29.9, respectively; physical function, 23.0 and 26.6; Oswestry Disability Index, −20.5 and −24.2; and bothersomeness of symptoms, −7.8 and −8.9.16
The treatment effects in these studies of spinal stenosis were larger than those in the observational study of patients with inter-vertebral disk herniation because of strong improvements in the nonsurgical group of patients with intervertebral disk herniation that were not seen in either stenosis group.14-16
There was little evidence of harm from either treatment. Often patients fear they will get worse without surgery, but this was not the case for the majority of patients in the nonsurgical group, who, on average, showed small improvements in all outcomes. The 1-year rate of reoperation for recurrent stenosis was 1.3%, a rate similar to those reported by Malmivaara et al. (2%) and by the Maine Lumbar Spine Study (1.2%). At 2 years, mortality was nearly the same in the two study groups and was lower than actuarial projections. The postoperative death rate of 0.3% and the overall postoperative complication rate of 12% were slightly better than the reported Medicare rates in patients with spinal stenosis who did not undergo spinal fusion (death rate, 0.8%; rate of complications, 14%).1
However, higher rates of complications have been reported with increasing age and coexisting medical conditions.33
The primary limitation of our study was the marked degree of nonadherence to randomized treatment. This factor reduced the power of the intention-to-treat analysis to show treatment effects, though there was still a significant treatment effect for the measure of bodily pain at 2 years. The as-treated analyses do not share the strong protection from confounding that exists for the intention-to-treat analyses. However, these analyses were carefully adjusted for important baseline covariates and yielded results similar to those of previous studies. The characteristics of the crossover patients were as one might expect: those with severe symptoms and a preference for surgery crossed over into the surgical group, and vice versa.
Another limitation was the heterogeneity of the nonsurgical treatments. Given the limited evidence regarding efficacy of most nonsurgical treatments for spinal stenosis and individual variability in response, the creation of a limited, fixed protocol for nonsurgical treatment was neither clinically feasible nor generalizable. The flexible treatment protocols allowed for individualization of nonsurgical treatment plans, reflect current practice among multidisciplinary spine practices, and were consistent with published guidelines.34,35
However, we did not assess the effect of surgery versus any specific nonsurgical treatment.
In conclusion, in the as-treated analysis, if we combine the randomized and observational cohorts, carefully adjusting for potentially confounding baseline factors, patients with spinal stenosis without degenerative spondylolisthesis who underwent surgery showed significantly greater improvement in pain, function, satisfaction, and self-rated progress than did patients who were treated nonsurgically.