SubQStim: A Post-market Study of Subcutaneous Nerve Stimulation in Failed Back Surgery Syndrome (FBSS) Patients: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for SubQStim: A Post-market Study of Subcutaneous Nerve Stimulation in Failed Back Surgery Syndrome (FBSS) Patients (NCT01711619), a randomized na study. The primary outcome is Effectiveness of Treatment on Reduction of Back Pain Intensity.

2. Clinical Question

This is a question about the proportion meeting a prespecified response threshold, rather than the average amount of pain change. The endpoint description specifies a 100 mm Visual Analog Scale, with 0 representing no pain and 100 representing the worst pain imaginable. A responder outcome can make a treatment contrast easier to interpret as the share of participants crossing a defined threshold, but it does not show the full distribution of changes or how far participants who respond move beyond that threshold. The registry record does not report the primary outcome estimates, so the size and precision of the contrast cannot be assessed from the posted results.

3. Trial Design

SubQStim is identified as a post-market study of subcutaneous nerve stimulation in people with FBSS. Its official description calls it interventional, prospective, multicenter, randomized, and parallel-arm. The randomized comparison assigns participants to SQS plus OMM or OMM alone. The record lists no masking, so participants and study personnel were not masked according to the registry entry. Random allocation supports a comparison of groups formed without deliberate assignment based on participant characteristics, while the absence of masking may matter for a pain outcome that participants report.

The registry lists enrollment of 162. The study start is recorded as 2012-11, and primary completion as 2016-02. Its current status is TERMINATED. The reason for termination, whether enrollment reached its intended target, and the timing and circumstances of termination are not reported in the registry record. The study is listed as phase NA.

The stated primary endpoint is a responder percentage assessed at 9 months. The secondary outcomes include average change in back pain intensity, a back-pain responder rate at 6 months using an at-least-50% threshold, and a responder rate at 9 months using an at-least-30% threshold. These outcomes address related but distinct aspects of pain response and follow-up. The record lists four outcome measures and four analyses, but does not explain how each analysis corresponds to each measure or provide the analysis results.

The registry describes an Intent-to-Treat set consisting of all subjects as randomized. It also begins to describe an As Treated set that excludes participants with major protocol deviations and classifies them according to the last treatment received before assessment; the description is incomplete. Which population was used for each reported analysis, and how the study handled departures from assigned treatment, are not reported in the registry record.

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: Patients were considered enrolled in the study upon signing an Informed Consent Form. Enrolled subjects then completed additional assessments and were provided a diary to record ther back and leg pain intensity. Upon completion of the at-home diary, eligibility was reassessed based on pain scores. Eligible subjects were then randomized.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The Intent-to-Treat patient set (ITT) consists of all subjects as they were randomized into the study. The As Treated consists of all patients of the ITT patient set, but excludes those with major protocol deviations; they are analysed according to last treatment received before the actual assessment, without replacement of missing data.

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.

6. Primary Endpoint

The registry lists the primary outcome as Effectiveness of Treatment on Reduction of Back Pain Intensity, measured over 9 months.

The primary endpoint is the percentage of participants classified as responders at 9 months. Response means at least a 50% reduction in back pain intensity from baseline, measured with a Visual Analog Scale. The scale is described as 100 mm long, with 0 representing no pain and 100 representing the worst pain imaginable. This endpoint turns a measured change into a binary classification: each participant either meets the threshold or does not.

As a general statistical concept, a responder endpoint can be useful when a threshold has a meaningful interpretation for the study question. It can express results as the proportion of participants reaching that threshold, which may be more directly interpretable than a group average alone. However, it discards information about the amount of change within each category. Participants just below the threshold and participants with no improvement are both classed as nonresponders, while responders with different degrees of improvement are grouped together.

The registry indicates a 95% confidence interval as the measure of dispersion for the primary outcome. Such an interval generally describes uncertainty around an estimated response percentage; it does not guarantee that the true value lies within a particular interval. No primary response percentages or confidence-interval limits are reported in the registry record. Therefore, the endpoint definition is available, but the observed response rates and their precision cannot be evaluated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a randomized, parallel-arm design with no masking. It describes a binary primary endpoint: participants are classified as responders or nonresponders according to whether back pain intensity falls by at least 50% from baseline at 9 months. The displayed primary outcome unit is percentage of responders, and the stated dispersion measure is a 95% confidence interval. The record does not provide the endpoint estimates or the details of the statistical model used to produce them.

What does a responder percentage represent?

For a binary endpoint, the response percentage represents the share of assessed participants who meet the defined criterion. In this study, the criterion is based on change in a Visual Analog Scale score between baseline and the 9-month follow-up visit. The binary classification gives each participant one of two outcome states for this endpoint, even though their actual pain changes may vary substantially within either state. General statistical interpretation: a responder percentage is straightforward to communicate, but it cannot show the distribution of individual changes or the average size of change within responders and nonresponders.

A percentage depends on the denominator used. The primary description names the Intent-to-Treat patient set, but the registry record does not report the analyzed denominator for the primary outcome or explain whether every randomized participant had an observed 9-month measure. It also does not report how missing outcome values, if any, were treated. Those omissions limit the ability to reconstruct or assess the responder calculation.

How should a confidence interval be read?

The registry specifies a 95% confidence interval for the primary outcome. In general, a confidence interval communicates statistical uncertainty around an estimate under the assumptions of the method used. A narrower interval indicates greater precision than a wider interval, all else being equal. The interval is not a measure of the range of individual participants' responses, and it does not by itself establish whether an observed difference is important. The endpoint percentages and confidence-interval limits are not reported in the registry record, so the precision of the primary comparison cannot be judged.

A group-specific interval and an interval for a between-group contrast answer different questions. Separate intervals around each group's response percentage do not alone provide the same information as an interval calculated directly for the contrast. The registry information does not give a contrast estimate or state how uncertainty for the between-group comparison was calculated. It is therefore not possible to characterize the comparative precision or reproduce the primary analysis.

Why does the analysis population matter?

The Intent-to-Treat description says that all subjects are considered as randomized. As a general principle, retaining participants in their randomized groups preserves the basis of the randomized comparison, even when treatment received differs from treatment assigned. The registry also starts an As Treated definition, excluding major protocol deviations and assigning participants according to the last treatment received before assessment. That description is truncated, and the record does not identify which population was used for each outcome analysis. An analysis based on treatment received can answer a different question from one based on random assignment and may be affected by reasons for changing treatment.

What can the design tell the reader?

Random allocation is intended to reduce systematic differences between groups at assignment. A parallel-arm design compares the groups over the same general study period rather than using each participant as their own control. The record describes the study as prospective and multicenter, but details of sites, allocation procedures, concealment, and follow-up schedules beyond the stated outcome timeframes are not reported in the registry record.

The study is unmasked. General methodological explanation: when participants know their assignment, expectations may affect self-reported outcomes, and staff knowledge may influence interactions or other aspects of care. This is a potential source of measurement or performance bias, not proof that bias occurred. The registry record does not describe procedures intended to reduce such influences.

What is not established by the posted results?

The record lists four outcome measures and four analyses, but does not report their estimates, inferential results, or a complete analysis plan. No model specification, adjustment strategy, or method for handling repeated outcome measurements is reported in the registry record. The primary endpoint description identifies a 95% confidence interval but does not supply its limits. Without the numerical outcome results and analysis details, an independent reader cannot assess the treatment contrast, its uncertainty, or the robustness of the findings.

General statistical context: binary outcomes can be analyzed using methods that estimate response proportions, compare proportions, or model the probability of response while accounting for other variables. These approaches can yield different quantities and rely on different assumptions. Naming a suitable method in general does not imply that it was used in this trial; the specific statistical procedure is not reported in the registry record. No recalculated estimate is available from the reported details, and there is no basis for constructing one from the enrollment figure alone.

10. Multiplicity, Missing Data and Analysis Populations

The record lists multiple outcomes: average change in back pain intensity, responder outcomes at different follow-up times and thresholds, and a primary responder endpoint at 9 months. Considering multiple endpoints or time points raises a general statistical issue: if many hypotheses are tested, the chance of at least one apparently notable result can increase. Methods such as prespecifying a testing hierarchy or adjusting inference can address that issue, but the statistical plan, any multiplicity procedure, and any interim analyses are not reported in the registry record. The list of outcomes alone does not establish how multiplicity was handled.

The record identifies the Intent-to-Treat population as all subjects as randomized, and begins an As Treated description. It does not report which population was used for each analysis, whether all randomized participants contributed outcome data, or how participants with missing follow-up measurements were handled. There is no reported imputation method, missingness assumption, or sensitivity analysis in the registry information. As a general principle, missing-data methods can affect estimates when the availability of an outcome is related to participant characteristics or response; without details, the direction or extent of any such effect cannot be evaluated.

The record also does not report a complete protocol-deviation procedure or explain the treatment of participants who discontinued or switched treatment. These gaps prevent a full assessment of how the randomized groups were represented in the endpoint analysis. A sample-size justification and details of any interim monitoring are not reported in the registry record. The enrollment count alone does not establish the planned statistical power or the precision achieved for the primary endpoint.

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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: device stimulation issue (3.6%), therapeutic product ineffective (3.6%), implant site infection (3.6%), back pain (3.6%), diaphragmatic hernia (1.8%).

The registry reports serious adverse-event figures for SQS+OMM and OMM Alone. For serious events, the record lists 19 affected participants among 55 at risk in SQS+OMM, and 9 among 60 at risk in OMM Alone. For other adverse events, it lists 18 among 55 at risk in SQS+OMM, and 17 among 60 at risk in OMM Alone. These are counts of participants recorded as affected and the corresponding at-risk group counts, not a complete description of event timing, duration, severity beyond the serious classification, or causal attribution.

The listed leading serious-event terms include Device stimulation issue, Therapeutic product ineffective, Implant site infection, and Back pain, each reported as 3.6%. Diaphragmatic hernia and Drug withdrawal syndrome are each reported as 1.8%. The denominator and event-counting details for these term percentages are not reported in the registry record, so they should not be converted into participant counts or treated as direct measures of comparative risk.

Deaths are not reported in the registry record. The adverse-event figures are descriptive registry entries; they do not by themselves establish whether an event was caused by an intervention or whether groups differ statistically. Interpretation also depends on consistent definitions, comparable follow-up, and complete ascertainment, details not reported in the registry record.

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

The registry record establishes the question the trial was designed to address: whether the proportion meeting a defined back-pain response threshold at 9 months differed between SQS plus OMM and OMM alone. It also identifies the randomized, prospective, multicenter, parallel-arm design and the lack of masking. These details explain the intended comparison and its context, but do not supply the result of that comparison.

The primary outcome percentages, contrast estimate, confidence-interval limits, and test result are not reported in the registry record. Therefore, the posted information does not show which group had a higher response percentage, how large any difference was, or how precisely it was estimated. The named secondary outcomes likewise cannot be interpreted without their results. The study's enrollment of 162 should not be mistaken for the number contributing to the primary analysis, because the analyzed denominator is not reported.

The endpoint itself also has a defined scope. It records whether participants cross the at-least-50% reduction threshold, rather than describing every participant's pain trajectory. Average change and other responder thresholds appear among the secondary outcomes, but their results are not reported in the registry record. Even if a primary estimate were available, it would answer the stated responder question and would not, by itself, describe all dimensions of pain or establish why participants changed.

The termination status is recorded, but the reason for termination is not reported. Status alone cannot show whether the study stopped because of enrollment, operational, safety, efficacy, or other considerations. Similarly, the adverse-event counts describe reported events but do not establish causal effects or a comprehensive comparison of harms. Overall, the registry record provides design and endpoint definitions, while leaving the efficacy estimates, their uncertainty, and key analysis details unavailable for interpretation.

13. Why This Trial Matters Statistically

This trial illustrates why a registry record needs to be read at two levels: the study question and the reported evidence. The design and endpoint description are specific enough to identify a randomized comparison of a device-plus-management strategy with management alone, and to understand that the primary endpoint is a threshold-based pain response at 9 months. Those details are useful for interpreting what an eventual estimate would represent.

At the same time, outcome definitions are not outcome findings. The registry record does not report the primary response percentages, comparative estimate, confidence interval, or test result. That distinction is central to statistical interpretation: a well-defined endpoint cannot establish the magnitude or precision of a group difference when its estimates are absent. It also prevents readers from checking whether the reported analysis aligns with the stated endpoint.

The record highlights design considerations common to patient-reported outcomes. Randomization addresses group assignment, while open-label conduct can leave expectations and reporting behavior relevant to interpretation. The primary outcome is binary, so the selected response threshold determines how continuous pain-score changes are summarized. The secondary outcomes include other thresholds and average change, but no results are reported to show how these measures relate to one another.

Finally, the registry's termination status and safety counts underscore the value of complete reporting. A status label does not explain the reason for stopping, and adverse-event counts without fuller analytical context cannot settle comparative safety questions. For biostatisticians and clinical researchers, the central lesson is to distinguish documented design features from unreported analytical decisions and results, and to state the limits of inference when key estimates are unavailable.

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 principal limitation for interpreting this trial record is that the primary and secondary outcome estimates are not reported in the registry information available for analysis. There is no reported primary response percentage by group, between-group contrast, confidence-interval limit, or test result. The primary endpoint is described, but its observed magnitude and precision cannot be assessed.

The analysis information is incomplete. The record names the Intent-to-Treat population and begins an As Treated definition, but the latter is truncated. It does not state which population was used for each analysis, the analysis denominators, or how missing outcome data, discontinuations, and treatment changes were handled. The statistical model, covariate adjustment, multiplicity approach, interim analyses, and sample-size justification are not reported in the registry record.

The study is listed as TERMINATED, but the reason for termination is not reported. The registry information does not explain whether termination affected enrollment, follow-up, or analysis completion. Although enrollment is listed as 162, that figure does not establish how many participants had evaluable 9-month data.

The primary endpoint uses a participant-reported pain measure in an unmasked study. This is a design consideration rather than evidence that the outcome was biased. Further details about assessment procedures and steps to limit measurement influence are not reported. The adverse-event entries include group counts and selected terms, but the registry record does not provide the fuller event definitions, timing, attribution, or comparative analysis needed for a comprehensive safety interpretation.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: SubQStim: A Post-market Study of Subcutaneous Nerve Stimulation in Failed Back Surgery Syndrome (FBSS) Patients — NCT01711619.
• Registry record last updated 2018-10-22; status last verified 2018-01.
• Results first posted 2018-10-22.
• 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

SubQStim is a post-market, prospective, multicenter, randomized, parallel-arm study comparing subcutaneous peripheral nerve stimulation plus optimized medical management with optimized medical management alone in people with back pain due to FBSS. The registry lists no masking, enrollment of 162, study start in 2012-11, primary completion in 2016-02, and status TERMINATED.

The primary endpoint is the percentage of participants with at least a 50% reduction in back pain intensity at 9 months, measured using a Visual Analog Scale. Secondary outcomes include average change and responder outcomes at other thresholds or follow-up times. Primary and secondary outcome estimates are not reported in the registry record. The reason for termination, analysis methods, missing-data handling, and multiplicity procedures are also not reported. Serious and other adverse-event counts are listed, but the registry information does not provide a full comparative safety analysis.