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Long-Term Results of Surgery Compared With Nonoperative Treatment for Lumbar Degenerative Spondylolisthesis in the Spine Patient Outcomes Research Trial (SPORT)

Abdu, William A. MD, MS∗,†; Sacks, Olivia A. BA; Tosteson, Anna N.A. ScD∗,‡,§; Zhao, Wenyan PhD, MS∗,†; Tosteson, Tor D. ScD∗,§; Morgan, Tamara S. MA∗,§; Pearson, Adam MD, MS∗,†; Weinstein, James N. DO, MS†,§; Lurie, Jon D. MD, MS∗,‡,§

Author Information
doi: 10.1097/BRS.0000000000002682


Degenerative spondylolisthesis (DS) with lumbar stenosis is commonly treated with lumbar decompression and fusion.1 Prior studies have compared outcomes of surgical or nonoperative treatment for spinal stenosis but included mixed groups of patients with and without DS2–5 or were limited by small sample sizes and a lack of validated outcome measures.6–9

Spine patient outcomes research trial (SPORT) demonstrated that DS patients treated surgically had significantly greater improvements in pain and function compared with those treated nonoperatively through 4 years of follow-up.9 However, several studies have found that the early advantage of surgery compared with nonoperative treatment narrowed over time.2–12 In this study, we sought to compare surgical and nonoperative outcomes out to 8 years for DS patients and also to compare results among different fusion techniques.


Study Design

SPORT was conducted at 13 US medical centers with multidisciplinary spine practices across 11 states. The study included a randomized trial and an observational cohort of patients who declined randomization.13

Patient Population

The population has been described in detail previously.9,14 Briefly, all patients had neurogenic claudication or radicular leg symptoms for at least 12 weeks, cross-sectional imaging demonstrating spinal stenosis, DS on a standing lateral radiograph, and physician confirmation that they were surgical candidates. Patients with adjacent levels of stenosis were eligible, while patients with spondylolysis and isthmic spondylolisthesis were not. Enrollment took place from March 2000 to February 2005.

Study Interventions

The protocol surgery consisted of a standard, posterior decompressive laminectomy with or without fusion using autogenous iliac crest bone-graft. The use of pedicle screw instrumentation or interbody fusion was at the discretion of the treating surgeon.13 Fusion surgeries were classified into the following groups: (1) decompression with posterolateral in situ fusion (PLF); (2) decompression with instrumented posterolateral fusion with pedicle screws (PPS); and (3) decompression with interbody fusion plus instrumented posterolateral fusion with pedicle screws (360°). The nonoperative protocol was individualized by the treating physician, but included, at a minimum, physical therapy, education and counseling with instructions for exercising at home, and nonsteroidal anti-inflammatory agents if tolerated by the patients.13,15

Outcome Measures

The primary end points were the Short Form-36 (SF-36) bodily pain and physical function scores16–19 and the Oswestry Disability Index (ODI; American Academy of Orthopaedic Surgeons/Modems version)20 measured at 6 weeks, 3 months, 6 months, and yearly out to 8 years. Secondary outcomes included patient self-assessed global improvement, satisfaction with current symptoms and care,21 the stenosis bothersomeness index,2,22 low back pain bothersomeness,2 and leg pain bothersomeness.2

SF-36 scores range from 0 to 100, with lower scores indicating more severe symptoms; the ODI ranges from 0 to 100, with lower scores indicating less severe symptoms; the stenosis bothersomeness index ranges from 0 to 24, with lower scores indicating less severe symptoms. Low back pain and leg pain bothersomeness ranges from 0 to 6, with lower scores indicating less severe symptoms. Surgical treatment effect was defined as the mean changes from baseline in the surgical group minus that in the nonoperative group (difference-in-difference).

Statistical Methods

The statistical methods for the analysis of this trial have been reported in detail in previous publications.1,9,12,14,23 Data from the randomized trial was initially analyzed on an intent-to-treat basis. Due to crossover, subsequent analyses were based on treatments actually received, as described previously.11,23

Follow-up times were measured from enrollment for the intent-to-treat analyses and from the beginning of treatment for the as-treated analyses (i.e., the time of surgery for the surgical group and the time of enrollment for the nonoperative group). All changes from baseline before surgery were included in the estimates of the nonoperative treatment effect and all changes after surgery were included in the estimates of the surgical effect.

Repeated measures of outcomes were used as the dependent variables. The treatment received was included as a time-varying covariate. To evaluate the two treatment arms across all time periods, a global significance test was based on the time-weighted average of the outcomes (area under the curve) and compared using a Wald test.24 Kaplan–Meier estimates of reoperation rates at 8 years were computed for the observational and randomized cohorts and compared via the log-rank test.

Comparisons among fusion groups were done in a hierarchical fashion and are described in detail in previous publications.9,14 At each assessment interval, the first step was to test for any differences among the three fusion groups. If a difference was detected at P < 0.10, the next step evaluated differences between the three groups based on pair-wise comparisons. For these comparisons, Type I error was set at 0.05. Since these comparisons represent the most basic approach for evaluating for treatment differences they were considered planned comparisons and, as such, no adjustments were made for multiple comparisons.

To adjust for potential confounding, baseline variables associated with missing data or treatment received were included as adjusting covariates in longitudinal regression models.24 Computations were performed using SAS software (PROC MIXED for continuous data with normal random effects and PROC GENMOD for binary and non-normal secondary outcomes; SAS software, version 9.1, Cary, NC).


A total of 607 participants out of 892 eligible participants (304 in the randomized trial and 303 in the observational cohort) with DS were enrolled. In the randomized cohort, 159 patients were assigned to surgery, and 145 patients were assigned to nonoperative treatment. Of those 159 assigned to the surgical cohort, 64% (101) underwent surgery by 2 years, 66% (105) by 4 years, and 72% (115) by 8 years. Of those 145 assigned to nonoperative care, 49% (71) underwent surgery by 2 years and 54% (79) by 4 years, but no additional patients underwent surgery between 4 and 8 years (Figure 1).

Figure 1
Figure 1:
Exclusion, enrollment, randomization, and follow-up of trial participants. The values for surgery, withdrawal, and death are cumulative over 8 years. For example, a total of eight patients died during the follow-up period. [Data set March 9, 2013].

Of the 303 patients enrolled in the observational cohort, 173 initially chose surgical treatment, and 130 chose nonoperative treatment. In the surgery group, 97% (168) underwent surgery by 2 years, and one additional patient underwent surgery between 4 and 8 years. Of those 130 patients in the observational cohort initially in the nonoperative group, 25% (33) underwent surgery by 2 years and 38% (49) underwent surgery by 8 years.

A total of 601 patients out of 607 enrolled (99%) had at least one follow-up visit and were included in the analysis. In the combined cohort, 412 of 607 (68%) patients had undergone surgery by 8 years, with 84% of these (345) being within the first year (Figure 1).

Patient Characteristics

In the combined as-treated cohort, the surgery patients were younger and more likely to be receiving compensation (Table 1 ). The surgery group also reported SF-36 BP (31.6 vs. 36.9, P = 0.001) and PF (32 vs. 39.3, P < 0.001), ODI (43.9 vs. 36.5, P < 0.001), stenosis bothersomeness (15.3 vs. 13.3, P < 0.001), and leg pain bothersomeness (4.6 vs. 4.3, P = 0.05) scores indicative of significantly more severe baseline symptoms compared with the nonoperative group.

Patient Baseline Demographic Characteristics, Comorbidities, and Health Status Measures According to Diagnosis and Treatment Received
TABLE 1(Continued)
TABLE 1(Continued):
Patient Baseline Demographic Characteristics, Comorbidities, and Health Status Measures According to Diagnosis and Treatment Received

At 8 years, 264 of 601 patients were lost to follow-up, with 337 (56%) of the original enrollees remaining in the study. Table 2  compares the baseline characteristics of those who remained in the study with those who dropped out of the study. Patients retained in the study were younger, had more formal education, and were more likely to be employed and/or receiving compensation (Workman's Compensation or Social Security Benefits) at baseline. These same patients were less likely to have diabetes or heart problems. With respect to 2-year outcomes, patients in the surgical group who were subsequently lost to follow-up had significantly worse outcomes except on the ODI, while the results for those in the nonoperative group subsequently lost to follow-up were similar to those retained in the study. As a result, the surgical treatment effect at 2 years was greater among those retained in the study; this difference was statistically significant for BP and stenosis bothersomeness (Table 3).

Patient Baseline Demographic Characteristics, Comorbidities, and Health Status Measures According to Patient Follow-Up Status
TABLE 2 (Continued)
TABLE 2 (Continued):
Patient Baseline Demographic Characteristics, Comorbidities, and Health Status Measures According to Patient Follow-Up Status
Time-Weighted Average of Treatment Effects at 2 According to Treatment Received and Patient Follow-Up Status

The final as-treated models controlled for the following covariates: age, sex, race, work status, body mass index, neuroforaminal stenosis, depression, osteoporosis, joint problems, duration of current symptoms, reflex deficit, number of moderately or severely stenotic levels, treatment preference, other comorbidities (see Table 3 footnote), baseline SF-36 and ODI scores, baseline stenosis bothersomeness score, and center.

Randomized Controlled Trial—Intention to Treat Analysis

In the ITT analysis, the group randomized to nonoperative care improved significantly more on the ODI than the patients randomized to surgery in years 6, 7, and 8 (Supplemental Table 1, The nonoperative group also improved significantly more on the SF-36 PF at year 7. The magnitude of these differences was relatively low (i.e., approximately 5 points on the ODI and 7 points on the SF-36 PF). The nonoperative group improved significantly more than the surgery group in the global 8 years ITT analysis on the ODI (P = 0.039, Figure 2). There were no significant differences in the global 8-year analyses for the other primary outcome measures.

Figure 2
Figure 2:
Main outcomes surgery versus nonoperative combined cohort.

As Treated Analyses

The as-treated analysis demonstrated that patients treated surgically improved significantly more than those treated nonoperatively in the randomized, observational, and combined groups on all outcome measures at years 6, 7, and 8. In the combined analysis, the surgical group showed little degradation in outcomes from years 5 through 8 (Supplemental Table 1, At 8 years, the treatment effects of surgery were 11.8 (95% confidence interval [CI], 7.2–16.4) for SF-36 BP; 10.3 (95% CI, 5.9–14.7) for SF-36 PF; and –10.3 (95% CI, –13.6 to –6.9) for the ODI. The surgery group improved significantly more than the nonoperative group in the global 8-year as-treated analysis on all outcome measures (Figure 2).

Surgical Treatment and Complications

Among surgery patients with complete surgical data (n = 406), 7% (n = 29) underwent decompression alone, 21% (n = 84) had PLF, 55% (n = 222) had PPS, and 17% (n = 71) had 360° fusion. The 8-year reoperation rate was 22% (91/406), with recurrent stenosis/progressive listhesis being the most common indication for re-operation.

At 8 years, there were 33 deaths in the surgical group, compared with 53 expected deaths and 17 compared with 37 expected deaths in the nonoperative group based on age and sex-specific mortality data.25 The hazard ratio based on a proportional-hazards model adjusted for age was 1.2 (95% confidence interval, 0.63–2.1; P = 0.64). Of the 50 deaths observed in both groups, two were considered probably related to treatment: one patient died of respiratory distress 32 days after surgery, and the other died of sepsis 82 days after surgery.

Fusion Technique

Baseline characteristics of the three fusion groups are also summarized in Table 1 . Comparison between the PLF and 360° treatment groups revealed the most pronounced differences. The 360° patients were younger, more likely to be employed and had less severe stenosis, with moderate/severe stenosis more likely to be localized to one stenotic level. The PLF patients reported more severe baseline neurologic deficits and were more likely to have multiple levels of moderate/severe central stenosis. A greater percentage of PPS patients had radiographic instability (>10° of rotation of 4 mm of translation on flexion-extension radiographs).

The mean operation time was shortest for PLF (157.6 min), in contrast to PPS (212 min) and 360° (273.7 min) (Table 4). Mean estimated blood loss was highest for PPS and lowest for PLF (654 mL vs. 507 mL). Patients undergoing 360° fusion had the lowest rate of dural tear (PLF = 11%; PPS = 11%; 360° = 1%; P = 0.039). There were no significant differences between the groups in postoperative complications. Eight-year reoperation rate was 24% for PLF, 20% for PPS, and 24% for 360° (P = 0.61).

Operative Treatments, Complications and Events by Fusion Group

The time-weighted average outcomes from baseline through 8 years demonstrated that PPS patients improved significantly more on the SF-36 physical function score compared with the 360° group (PPS = 24.5 [95% CI 21.7–27.3]; 360° = 18 [95% CI 11.6–24.4]; P = 0.022) (Figure 3). There was a trend towards the PLF group improving more on the SF-36 physical function score compared with the 360° patients, but the difference was not statistically significant (PLF = 26.8 [95% CI 21.6–32]; 360° = 18 [95% CI 11.6–24.4] P = 0.062).

Figure 3
Figure 3:
Outcomes for different fusion techniques.


Long-term surgical and nonoperative outcomes from 5 to 8 years were similar to earlier outcomes for DS patients, with the as-treated analysis demonstrating significantly better outcomes for surgery compared with nonoperative treatment. The ITT analysis showed significantly better outcomes on the ODI and SF-36 PF for the group randomized to nonoperative care at some of the later time points. However, this result is difficult to interpret due to the lack of consistency among outcomes and the high cross-over rates. Given that 54% of the patients randomized to nonoperative treatment underwent surgery, while 28% of the patients randomized to surgery never had surgery, the results of the as-treated analysis, which were carefully controlled for potential confounders, may better reflect the comparative effectiveness of surgery.26

There are few studies with long-term outcomes comparable to SPORT. Outcomes were collected at 8 and 10 years on patients in the Maine Lumbar Spine Study (MLSS).4 For this mixed cohort of spinal stenosis patients with and without DS, the benefit of surgery at 4 years narrowed at 8- and 10-year follow-up. The surgery group maintained a significant advantage on leg pain and disability, but not on back pain or patient satisfaction at the long-term follow-up. Slatis et al27 performed an RCT comparing surgery to nonoperative treatment for stenosis with and without degenerative spondylolisthesis in 94 patients. At 6 years, the benefit of surgery was maintained for the ODI (treatment effect = 9.5) but not for leg and back pain. In contrast, the SPORT as-treated analysis showed a persistent advantage for surgery on all outcome measures out to 8 years. The 10 years 23% reoperation rate in MLSS was consistent with the 8 years 22% reoperation rate in SPORT.

In SPORT, surgical technique had minimal effect on clinical outcomes or reoperation rates. These findings at 8 years were similar to the findings at 4 years.28 To date, few other studies have focused on fusion techniques specific to patients with DS. Fischgrund et al7 randomized DS patients to decompression and fusion with or without pedicle screw instrumentation and found no difference in 2-year clinical outcomes between the two fusion groups, though there was a higher pseudoarthrosis rate in the uninstrumented group. Campbell et al's29 systematic review compared interbody fusion plus posterolateral instrumented fusion to posterolateral instrumented fusion alone for DS using the ODI and visual analog scale as the primary outcomes. No statistically significant differences were found between techniques. Although these studies do not provide direct comparison to our study, they suggest no advantage to more complex approaches to fusion in DS patients.

Two recent randomized controlled trials comparing decompression alone to decompression with posterolateral instrumented fusion reported conflicting results. Ghogawala et al30 found better patient reported outcomes and a lower reoperation rate for patients treated with decompression and fusion. In contrast, Forsth et al31 found no differences in patient reported outcomes or reoperation rates between the two surgical techniques. The decompression only group in SPORT was too small to allow for statistically robust comparison to fusion, so no direct comparison to these studies is possible.


Non-adherence to the randomized treatment group is a major limitation of this study, reducing the power of the intent-to-treat analysis to demonstrate a treatment effect. Although the as-treated analysis was subject to confounding due to baseline differences between the groups, rigorous analyses controlled for these differences and yielded results similar to prior studies.2,8,14 However, confounding by unmeasured variables is not possible to control and could have affected the results. Patients who were lost to follow-up were older, less-well educated, sicker, and had worse surgical outcomes over the first 2 years. Loss to follow-up of patients in the surgery group with worse short-term outcomes than those lost to follow-up in the nonoperative group raises concerns for overestimation of the surgical treatment effect. Additionally, the fusion types in the SPORT were not randomly assigned and selection bias may have affected these results.


This trial demonstrated a long-term advantage of surgical treatment for DS patients who presented with neurogenic claudication or radiculopathy consistent with imaging demonstrating spinal stenosis at the level of the listhesis. Fusion technique did not affect long-term outcomes.

Key Points

  • A persistent advantage for surgery for DS was maintained at 8 years.
  • At 8 years, outcomes data were available for 56% of original enrollees.
  • Loss to follow up of patients with worse early outcomes in the surgery group could lead to overestimation of long-term outcomes.
  • Fusion techniques were compared and did not affect outcomes


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degenerative spondylolisthesis; nonoperative; outcomes; randomized trial; spinal stenosis; spine patient outcomes research trial; surgery

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