Spinal Cord Stimulation With Precision® System Versus Reoperation for Failed Back Surgery Syndrome: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Spinal Cord Stimulation With Precision® System Versus Reoperation for Failed Back Surgery Syndrome (NCT01036529), a randomized phase 4 study. The primary outcome is Proportion of Subjects Showing ≥50% Self-reported Leg Pain Relief From Baseline Without Request for Crossover to the Other Treatment.

2. Clinical Question

This is a comparison of two treatment strategies for pain in people who have already undergone lumbosacral spine surgery. The primary outcome combines a patient-reported change in leg pain with a treatment-decision condition: participants had to report the stated degree of relief and not request crossover. It therefore does not describe pain relief alone.

The registry record identifies the study as randomized, but the posted results do not include an analysis of the primary outcome. In particular, it does not report the proportions meeting the outcome in either arm or a statistical comparison between the arms. The clinical question is identifiable from the registered outcome definition, but the posted record does not answer it with an efficacy estimate.

3. Trial Design

The EVIDENCE trial is registered as a Phase 4, randomized, parallel-group study comparing spinal cord stimulation with reoperation for pain in people with failed back surgery syndrome. The record lists Boston Scientific Corporation as the sponsor. It reports an enrollment of 28, a start date of 2010-02, a primary completion date of 2013-05, and a status of TERMINATED.

Participants were assigned to one of two groups: Precision Spinal Cord Stimulator or Back Surgery. The registry describes the study as having no masking. In general, random allocation is intended to make treatment groups comparable at the start of a trial, while a parallel design follows different groups receiving different assigned treatments. These design features do not, by themselves, establish that the groups were balanced in this trial or show what happened after assignment.

The reoperation arm lists discectomy, laminotomy, laminectomy, foraminotomy, and fusion with or without instrumentation. The intervention arm is described as spinal cord stimulation. The registry’s brief summary defines FBSS as persistent or recurrent pain following one or more lumbosacral spine surgical procedures and describes neuropathic and nociceptive pain.

The primary outcome is the proportion of participants reporting at least 50% self-reported leg pain relief from baseline without requesting crossover to the other treatment. Its stated timeframe includes 3, 6- and 12- months post-index procedure. The registry record does not report the reason for termination, details of treatment delivery, or a fuller account of follow-up and adherence. It also contains no analysis results for the primary outcome. These gaps mean that the design can be described, but the posted record does not support a comparison of the clinical outcome between groups.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: A total of 274 subjects were screened for participation.After screening, 75 subjects were eligible for participation. Of the eligible subjects, 47 declined randomization. A total of 28 subjects were randomized.

Overall Study

Reasons for not completing this period:

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

Population: This represents the number of subjects with demographic information provided at enrollment (collected before baseline visit).

6. Primary Endpoint

The registry lists the primary outcome as Proportion of Subjects Showing ≥50% Self-reported Leg Pain Relief From Baseline Without Request for Crossover to the Other Treatment, measured over 3, 6- and 12- months post-index procedure.

The primary endpoint is a binary participant-level outcome: whether a participant showed at least 50% self-reported leg pain relief from baseline without requesting crossover to the other treatment. The registry lists the unit as the proportion of participants and specifies measurement at 3, 6- and 12- months post-index procedure.

A binary endpoint makes a clear distinction between participants who meet a prespecified response definition and those who do not. The threshold can make results easier to interpret as the proportion meeting a meaningful criterion, rather than as an average change in pain score. However, turning a continuous experience such as pain into a yes-or-no outcome also discards information about the degree of change within each group. Participants just below and well below the threshold are both counted as not meeting the response definition.

The crossover condition is part of the endpoint, not a separate detail. A participant must meet the pain-relief criterion and not request crossover. As a result, this measure reflects both reported relief and remaining on the assigned treatment rather than switching to the other option. It should not be interpreted as a measure of pain relief irrespective of crossover.

The outcome is listed across several time points, but the registry record does not post a result for any of them. It does not give the number or proportion of participants meeting the definition, nor an estimate of the difference between the arms. The endpoint definition is therefore available, but its observed performance in the trial is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record describes the allocation as randomized, the masking as none, and the model as parallel. These labels identify broad features of the design. They do not supply a detailed statistical analysis plan, and they do not tell readers how all trial procedures were carried out. Statistical explanations below are general unless explicitly tied to a feature reported in the record.

What does randomization contribute?

In general, randomization assigns participants to treatment groups using a chance-based process. Its purpose is to reduce systematic differences between groups at the point of assignment, including differences that investigators may not have measured. It does not guarantee that groups will be identical, particularly in a small trial, and it cannot prevent differences arising after assignment. The registry confirms randomized allocation but does not report the sequence-generation method, how assignments were concealed, or whether randomization used any stratification.

The record describes a parallel model, meaning the registered comparison is between groups assigned to different treatments rather than a crossover design in which each participant receives both treatments in sequence. The outcome itself includes a condition about not requesting crossover to the other treatment. The record does not provide further details on how crossover requests were handled in the analysis.

How should a binary endpoint be understood?

The primary measure is a proportion: participants are classified according to whether they meet the response definition. In general, a proportion summarizes the frequency of an event within a group. Comparing proportions can describe a difference in response rates, but the estimate is most informative when accompanied by a measure of uncertainty, such as a confidence interval. A confidence interval gives a range of values compatible with the observed data and the statistical method used; it is not a guarantee that the true value lies within that range.

The response definition combines a threshold for leg pain relief with a condition about crossover. That makes the endpoint interpretable as meeting the complete registered definition, not as a general summary of pain. Different choices about time point, crossover, or missing responses can change what a calculated proportion represents. The registry record provides the endpoint definition and its timeframe, but not the analysis rules for those choices.

What can the posted analysis tell us?

The registry lists zero analyses for the primary outcome. It provides no arm-specific response proportions, comparison estimate, confidence interval, or p-value. Accordingly, there is no posted efficacy analysis to interpret. A p-value, in general, measures how compatible data are with a specified statistical model under a null hypothesis; it does not measure the size or clinical importance of an effect. Because no p-value is reported for this endpoint, none can be assessed.

The outcome is specified at 3, 6- and 12- months post-index procedure. Repeated assessment over time can raise questions about which time point is primary for inference and how several comparisons are handled. The registry record does not report an analysis plan identifying a single time point, a model for repeated observations, or a method for accounting for multiple comparisons. No particular approach should be assumed.

What do the sample-size illustrations represent?

The sample-size section presents planning illustrations based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. These are illustrations about sample sizes under stated assumptions. They are not the trial’s own sample-size justification, which is not reported in the registry record, and they are not observed power. The stated fraction of the observed effect refers to the effect size used in a planning scenario. The record does not provide a trial-specific justification or sufficient primary-outcome results to assess the assumptions against the posted endpoint analysis.

In general, a planning calculation estimates the sample size that would be required under chosen assumptions about the effect, variability or event rate, significance level, and power. Changing those assumptions changes the illustration. Such calculations do not establish what a completed trial actually found, and they cannot substitute for its observed estimates and uncertainty. The planning values should therefore be read as design illustrations, not as evidence about treatment performance or as a retrospective measure of the trial’s power.

Why does the record’s status matter?

The registry marks the study TERMINATED, but does not report why. That status is not itself a statistical result. Without the reason for termination, participant flow, outcome completeness, and analysis details, readers cannot determine from this record whether termination affected follow-up or the availability of primary-outcome data. In general, those details help assess how an analysis relates to the randomized groups and how precisely the outcome has been estimated. They are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is listed at 3, 6- and 12- months post-index procedure. Analysing outcomes at multiple time points can create a multiplicity question: repeated opportunities to test or emphasize a difference may affect how results should be interpreted. In general, a protocol or statistical analysis plan can specify a primary time point or a method for handling multiple comparisons. The registry record does not report such a plan or describe any adjustment for multiplicity. The listed time points alone do not show that a particular adjustment was required or used.

The registry record contains no primary-outcome analysis, and it does not report the analysis population. It is therefore not possible to establish whether the analysis followed the randomized assignment, included only participants who completed treatment, or used another population definition. These are different analysis choices; the record does not identify one as the approach used.

Missing-data handling is also not reported in the registry record. The primary outcome depends on self-reported leg pain and on whether participants requested crossover, but the record does not describe what happened when a pain report or crossover information was unavailable. In general, excluding participants with missing data, imputing values, or using other assumptions can lead to different estimates. No particular method should be attributed to this trial from the posted record.

The record does not provide participant flow by arm, the number with outcome data at each time point, or reasons for missing observations. It also does not report an interim-analysis plan or stopping rule; neither should be inferred from the TERMINATED status. These omissions limit assessment of how complete and comparable the outcome data were and how the results, if reported elsewhere, should be interpreted.

11. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: radicular pain (7.7%), upper respiratory tract infection (6.7%), urinary tract infection (6.7%), back pain (6.7%), urinary retention (6.7%).

The registry lists serious and other adverse-event figures separately for each treatment group. For the Precision Spinal Cord Stimulator group, 1 of 13 participants at risk is listed as affected by a serious adverse event, and 3 of 13 are listed as affected by other adverse events. For the Back Surgery group, the corresponding figures are 4 of 15 for serious adverse events and 2 of 15 for other adverse events. These are the posted counts and denominators, not an adjusted comparison.

The registry also lists Radicular Pain at 7.7%, Upper respiratory tract infection at 6.7%, Urinary Tract Infection at 6.7%, Back Pain at 6.7%, Urinary Retention at 6.7%, and Sternal Fracture at 6.7% among the top serious-event terms. The record does not specify an arm attribution for these terms in the registry record. They should not be assumed to have occurred in a particular group or interpreted as a complete account of all events.

In general, adverse-event counts describe events recorded under the registry’s reporting definitions; they do not by themselves establish that a treatment caused an event. The record does not report deaths, and it does not provide further detail about event timing, severity beyond the serious-versus-other grouping, or how participants with multiple events were counted. These safety entries should be read as descriptive information, not as a substitute for a full safety analysis.

12. What the Result Does, and Does Not, Mean

This registry record is useful for identifying the question the trial was designed to address: whether spinal cord stimulation or reoperation was associated with a different proportion of participants meeting a specified leg-pain response definition without requesting crossover. It also documents the randomized, parallel-group design, the two treatment groups, the listed follow-up time points, and the study’s terminated status.

It does not report the primary-outcome results. There is no posted proportion meeting the response definition in either group, no comparison estimate, and no confidence interval or p-value. As a result, the record cannot show the direction or size of any difference, how precisely it was estimated, or whether the results were consistent across the listed time points. The absence of an analysis in the registry should not be mistaken for evidence that the treatments had equal outcomes.

The definition itself should guide interpretation. It concerns self-reported leg pain relief from baseline at a stated threshold and also requires that the participant did not request crossover. It is not a general measure of all pain, function, quality of life, or overall treatment success. The registry record does not provide results for those other domains.

The posted safety figures describe affected participants and selected serious-event terms, but they do not establish causation or provide a complete comparative safety assessment. Likewise, the sample-size section’s planning illustrations are not observed power and do not fill the gap left by missing primary-outcome estimates.

In short, the record supports a description of the trial’s registered question and some design and safety details. It does not support a conclusion about which strategy performed better, the magnitude of a treatment effect, or the uncertainty around such an effect. Those conclusions would require primary-outcome results and information about the analysis population, missing data, and methods that are not reported in the registry record.

13. Why This Trial Matters Statistically

This trial raises several statistical issues that matter when reading clinical research. First, the primary outcome is a threshold-based response rather than an average pain score. That makes the result potentially easy to express as a proportion meeting a definition, but the threshold conceals variation among participants who do not meet it. The exact definition—including the crossover condition—therefore determines what the measure represents.

Second, the outcome is listed at 3, 6- and 12- months post-index procedure. Multiple time points can make it important to distinguish a prespecified primary time point from supportive or repeated assessments. The registry does not report how this was handled. Without the analysis plan and time-specific results, readers cannot assess whether the chosen time point was clear in advance or whether patterns differed over follow-up.

Third, the record gives a small enrollment of 28 but no primary-outcome estimates or uncertainty intervals. In general, limited data can produce imprecise estimates, but the precision of this trial’s treatment comparison cannot be determined from enrollment alone. The actual number contributing endpoint data is not reported in the registry record. A sample-size illustration can explore assumptions, but it cannot replace the observed estimate or establish the precision achieved.

Finally, the trial is marked TERMINATED, while the reason, participant flow, and analysis details are not reported. This highlights why study status, outcome results, and analysis methods should be considered together rather than treating any one registry field as a finding. The posted record is statistically informative about the question and endpoint, but incomplete for evaluating the treatment contrast.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The most consequential limitation of the registry record is that it does not include an analysis of the primary outcome. Although the endpoint and its timeframe are specified, no arm-specific response proportions or between-group estimate are reported. The record therefore does not permit an assessment of the efficacy question it identifies.

The record does not explain why the study was terminated or provide participant flow by group. Enrollment is reported as 28, but the number assessed at each follow-up time point and the number included in any analysis are not reported in the registry record. It is consequently unclear how complete the primary-outcome data were.

The absence of a reported statistical analysis plan limits assessment of the intended handling of the multiple listed time points, missing responses, crossover requests, and analysis populations. The record also does not report methods for the randomization sequence or allocation concealment. No particular method can be assumed, and the available design labels do not answer these questions.

The primary endpoint is a combined response definition: self-reported leg pain relief meeting a threshold and no request for crossover. It does not capture all aspects of pain or treatment experience. In addition, the listed surgical procedures include several types of back surgery, but the record does not report how those procedures were distributed or analysed. These features limit what can be learned from the registered endpoint and intervention descriptions alone.

The safety entries are descriptive and do not provide a full account of event timing, causal assessment, or a detailed analysis. The selected serious-event terms are not linked to an arm in the registry record. Overall, the record offers a limited view of design and safety information, but lacks the outcome estimates and methodological detail needed for a complete statistical evaluation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Spinal Cord Stimulation With Precision® System Versus Reoperation for Failed Back Surgery Syndrome — NCT01036529.
• Registry record last updated 2020-11-16; status last verified 2020-11.
• Results first posted 2013-10-28.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

The registry record describes a Phase 4 randomized, parallel-group trial with no masking, comparing the Precision Spinal Cord Stimulator with Back Surgery for pain in people with failed back surgery syndrome. Enrollment is 28; the listed study status is TERMINATED. The primary endpoint is the proportion reporting at least 50% self-reported leg pain relief from baseline without requesting crossover, at 3, 6- and 12- months post-index procedure.

The record lists one outcome measure and zero analyses. It does not report primary-outcome results, the reason for termination, the analysis population, or missing-data methods. Serious and other adverse-event counts are posted by group, along with selected serious-event terms. The planning illustrations are not observed power. The record defines the trial question and some design features, but does not provide the efficacy analysis needed to estimate or interpret the primary treatment comparison.