Electrical Stimulation for the Treatment of Back Pain Using Peripheral Nerve Stimulation (PNS): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Electrical Stimulation for the Treatment of Back Pain Using Peripheral Nerve Stimulation (PNS) (NCT03179202), a na na study. The primary outcome is Number of Subjects That Experienced ≥30% Reduction in Average Low Back Pain Intensity.

2. Clinical Question

This question is framed around the proportion of participants who met a prespecified response threshold, rather than around an average change in pain score. Daily diaries captured average pain intensity over a 7-day period at baseline and at end of treatment. The underlying pain item came from Brief Pain Inventory-Short Form Question 5, which uses an 11-point scale from “No Pain” to “Pain as bad as you can imagine.” The registry record defines success as a reduction of at least 30% in the participant’s mean score.

Because the study had one group and no separate control, the question is descriptive: it asks how many participants in the study met the response definition. It does not, by itself, estimate how outcomes would differ under another treatment or under no stimulation. The number of participants meeting the threshold and the corresponding statistical uncertainty are not reported in the registry record. Therefore, the clinical question can be described, but the posted record does not show its numerical answer.

3. Trial Design

This was a completed post-market study of the SPRINT Peripheral Nerve Stimulation System for back pain. The registry record lists the study as single-group, with no allocation and no masking. It reports enrollment of 166 and identifies SPR Therapeutics, Inc. as the sponsor. The study started on 2017-06-23, and primary completion was 2021-05-11. The phase is listed as NA.

All participants in the described group were to have up to four leads placed in the low back, use the PNS system, and receive electrical stimulation. The brief description explains that leads were placed through the skin into the low-back muscles and attached to stimulators worn on the body. The registry record does not describe a randomized assignment or a concurrent control group. Consequently, comparisons between treatment strategies are not part of the design described in the record.

The primary endpoint compares baseline with end of treatment, which the record defines as 8-weeks after treatment began. Participants recorded average pain intensity in daily diaries during 7-day periods. The registry record also lists secondary outcomes covering worst pain intensity, Oswestry Disability Index, health-related quality of life, Beck Depression Inventory, Patient Global Impression of Change, and pain interference.

The registry record identifies eight outcome measures, but it does not provide analysis entries. Detailed information about the planned statistical model, sample-size justification, interim analyses, or analysis population definitions beyond “Protocol Population” is not reported in the registry record. The design therefore supports a description of outcomes within the enrolled group, while the available record leaves important details about the analysis and the numerical endpoint results unspecified.

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: After obtaining informed consent, subjects were evaluated for eligibility.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Protocol Population presented. EOT data were not available for eight subjects.

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 Number of Subjects That Experienced ≥30% Reduction in Average Low Back Pain Intensity, measured over Baseline and End of Treatment (EOT= 8-weeks post-start of treatment).

The primary endpoint counts participants who achieved at least a 30% reduction in average low back pain intensity between baseline and end of treatment. For each participant, diary scores from the baseline and end-of-treatment 7-day periods were averaged, and the percentage reduction was determined. The endpoint is therefore a binary response at the participant level: a participant either met the threshold or did not.

The pain item was excerpted from Brief Pain Inventory-Short Form Question 5. Its 11-point numerical rating scale runs from 0, representing “No Pain,” to 10, representing “Pain as bad as you can imagine.” The endpoint uses this repeated diary information to classify participants according to change from their own baseline rather than treating each diary entry as an independent participant.

A threshold-based endpoint can be easier to interpret than a change in a group average: it expresses the result as a count of people reaching a defined degree of improvement. However, reducing a continuous score to two categories also discards information about the size of changes within each category. Participants just below the threshold and participants with little change are grouped together as nonresponders, while participants at or above it are grouped as responders.

The endpoint definition and timing are reported, but the number meeting the threshold is not reported in the registry record. Without that count and the relevant denominator, the endpoint’s observed response rate and its precision cannot be described.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a single-group result estimate?

In a single-group study, the observed outcome describes participants who received the intervention under the study conditions. For this study, the primary outcome was a count of participants meeting the defined pain-reduction threshold. A count becomes easier to interpret when its denominator is clear, because the same count can represent different response frequencies in groups of different sizes. The registry record reports enrollment of 166, but it also notes unavailable end-of-treatment data for eight subjects. The endpoint denominator and the handling of those missing observations are not reported in the registry record.

A single-group design does not directly estimate a treatment contrast. In a randomized comparison, the difference between groups can be used to assess how outcomes differed under the assigned strategies, subject to the assumptions and limitations of that trial. Here, there is no separate comparator group described. A change from baseline can be measured, but attributing that change to the intervention requires caution because time trends, co-interventions, expectations, and other influences are not separated by a concurrent control.

What does a response threshold retain and discard?

The endpoint classifies each participant according to whether the reduction in average pain intensity reached at least 30%. Thresholds have an intuitive interpretation: they distinguish participants who meet a stated response criterion from those who do not. This can be useful when a study is interested in the number of people reaching a particular level of change.

The classification also compresses information. It does not show the full distribution of score changes, and it treats all participants on the same side of the threshold alike, even if their changes differ substantially. A continuous outcome analysis can preserve more information about the size and spread of changes, while a binary endpoint answers a narrower question. The registry record lists the binary primary endpoint but does not report its count or the underlying distribution of pain changes.

Why does uncertainty matter?

An observed count is an estimate from the participants who contributed outcome data, not a perfectly precise description of every person to whom the findings might be relevant. A confidence interval is a range of values compatible with the observed data under a specified statistical procedure. It communicates sampling uncertainty around an estimate; it does not account for every possible source of bias, such as missing data or the absence of a comparator.

No confidence interval for the primary outcome is reported in the registry record. No p-value or other inferential test for that endpoint is reported either. Without the observed result and its uncertainty, readers cannot assess whether the estimate is precise or whether it is compatible with a wide range of underlying response frequencies.

How should planning illustrations be read?

Sample-size calculations are planning exercises, not results from participants. The stated planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect to detect set as a stated fraction of the observed effect. Time-to-event calculations are described as total event counts; other calculations are described as participants per arm. These are general planning conventions, and the resulting sample sizes depend on assumptions about the effect and design.

The registry record describes those calculations as planning illustrations and says they are not the trial’s own design. In particular, a two-arm planning illustration does not change the actual study into a randomized or controlled comparison: the record describes a single-group study. Such illustrations should not be read as observed power, as evidence that a particular effect occurred, or as proof that the study was adequately or inadequately sized. The numerical planning outputs are not stated in the registry record.

What can be learned from adverse-event counts?

Adverse-event counts describe events recorded in the study group. They do not, without a comparator and additional information, establish whether an event was caused by the intervention or whether the event rate differs from another treatment. Serious and other adverse events are distinct categories in the registry record, and their counts should be read with their stated at-risk group sizes. The record does not report the methods used to assess causal relationship or provide enough detail to infer causation from the counts alone.

In general, statistical methods are most informative when the endpoint definition, denominator, missing-data approach, analysis population, and uncertainty estimates are all clear. Some of those details are present, including the diary-based endpoint definition and the note about unavailable end-of-treatment data. The planned model, missing-data procedure, and inferential results are not reported in the registry record, so the numerical analyses cannot be independently evaluated from the record.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Protocol Population")
n      <- c(83)
events <- c(58)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Protocol Population  83  58  69.9  58.8  79.5  59.3  78.7  59.3  78.7

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists a primary outcome and several secondary outcome domains, and it reports eight outcome measures. When a study examines multiple outcomes, the chance of at least one apparently unusual result can increase if each is tested separately without accounting for multiplicity. Methods such as prespecifying a primary endpoint, adjusting for multiple tests, or treating secondary analyses as exploratory can address different aspects of this issue. The multiplicity approach for this study is not reported in the registry record, so it is not possible to determine whether or how the listed outcomes were adjusted or prioritized in analysis.

The registry record says end-of-treatment data were unavailable for eight subjects. Missing outcomes can affect both the denominator and the estimate, especially if participants without measurements differ systematically from those with measurements. The record identifies the presented primary population as the Protocol Population, but does not report the endpoint denominator, the reasons for missing data, or whether any imputation or other missing-data method was used. No particular assumption about the missing outcomes can therefore be justified from the record.

The analysis population and the treatment of participants who did not complete the end-of-treatment diary are important for interpreting a participant count. The registry record does not specify whether all enrolled participants were included in the primary analysis, how incomplete diary periods were handled, or whether sensitivity analyses assessed alternative assumptions. Those details are not reported in the registry record.

The record lists no analysis entries. Accordingly, it does not provide the numerical primary or secondary outcome analyses needed to evaluate multiplicity, missing-data sensitivity, or the precision of estimates.

12. Safety Results

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

Deaths

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: shoulder procedure (1.0%), heart attack (1.0%), breast cancer (1.0%), heart procedures (1.0%), melanoma (1.0%).

The registry record lists an adverse-event group titled “Enrolled/Received Leads,” with 99 participants at risk for serious adverse events and 4 affected. It reports 99 participants at risk for other adverse events and 49 affected. One death is recorded. These counts are presented as registry safety figures; the record does not provide enough information to determine from the counts alone whether events were caused by the device or procedure.

The listed serious-event terms include Shoulder procedure, Heart attack, Breast Cancer, Heart procedures, Melanoma, and Liver/Lymph node metastases, each reported as 1.0%. These terms describe events recorded in the registry and should not be treated as evidence that the intervention caused them. The record does not describe the causal-assessment methods or provide event-level timing and clinical context in the registry record reported.

Counts and percentages answer different descriptive questions, and the stated at-risk group matters when reading a count. The figures should not be converted into comparisons with another treatment: the study is single-group and no comparator group is reported. Nor do the listed terms establish the overall safety profile beyond the events captured and reported in the registry. Serious-event and other-event counts are distinct categories; they should be read separately and without assuming that one category includes or excludes any particular participant from the other.

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

The registry record describes a post-market evaluation of a peripheral nerve stimulation system and specifies a primary response definition based on diary-reported average low back pain intensity. The study enrolled 166 participants and used a single-group design. End of treatment was defined as 8-weeks after treatment began, and the record notes that end-of-treatment data were unavailable for eight subjects.

Those details explain the intended outcome and the structure of the study, but the numerical primary result is not reported in the registry record. There is no reported count of participants achieving at least a 30% reduction, no endpoint denominator, and no confidence interval. The posted record therefore does not establish the observed response frequency or how precisely it was estimated. The intervention description alone does not answer the outcome question.

Even if a response count were available, a single-group result would describe what happened among participants in the study, not the difference attributable to treatment compared with an alternative. With no separate comparator, the design cannot directly distinguish intervention-associated change from other explanations for change over time. The registry record also does not report the analysis methods needed to assess how missing end-of-treatment data were handled.

The safety information is similarly descriptive. It records serious and other adverse-event counts, the at-risk group sizes, one death, and several serious-event terms. These entries do not by themselves establish causation or provide a comparative safety estimate.

Thus, the record allows readers to understand the study question, intervention, timing, and some safety counts. It does not report enough outcome analysis to determine the magnitude or precision of the primary result, compare the intervention with another strategy, or draw a causal conclusion. The absence of a reported result should be distinguished from a result showing no change: the registry record does not state either conclusion.

14. Why This Trial Matters Statistically

This study illustrates how trial design determines the kind of statistical question that can be answered. The primary endpoint is a participant-level response count, based on a defined threshold applied to diary-based pain scores. That is different from comparing average pain changes between groups. Keeping the estimand clear—the quantity the analysis is intended to describe—helps prevent a descriptive count from being mistaken for a treatment effect relative to a control.

The record also demonstrates why outcome definitions and outcome results are separate pieces of evidence. It explains the pain scale, diary periods, response threshold, and end-of-treatment timing. Yet it does not report the primary response count, its denominator, or an uncertainty interval. A well-defined endpoint is essential, but it cannot replace the estimate needed to understand what was observed.

Missing data are another central statistical issue. The record identifies eight participants without end-of-treatment data, but does not describe the method used to handle them. When outcomes are missing, both the denominator and the assumptions behind an estimate can matter. Without that information, readers cannot assess the sensitivity of a result to alternative handling of missing observations.

Finally, the registry record distinguishes the actual single-group design from planning illustrations based on two-arm assumptions. This distinction matters because a hypothetical sample-size calculation does not create a comparator, and a planning figure is not evidence of observed power. The study is a useful case for reading endpoint definitions, study structure, missingness, and safety counts separately rather than allowing one element to imply conclusions that the record does not report.

15. 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 important limitation for statistical interpretation is that the registry record does not report the numerical primary outcome. It gives the response threshold and measurement timing but not the number meeting that threshold, the analysis denominator, or a measure of precision. The registry record also lists no analysis entries, so numerical primary and secondary analyses cannot be reviewed.

The study has a single group, no allocation, and no masking. There is no concurrent control group described, limiting the ability to interpret baseline-to-end-of-treatment change as an effect attributable to the intervention. The record does not report analysis methods that might address confounding or other alternative explanations, and it would not be appropriate to assume that such methods were used.

End-of-treatment data were unavailable for eight subjects. The missing-data reasons, handling method, and sensitivity analyses are not reported in the registry record. The primary population is named as the Protocol Population, but the record does not define its relationship to the full enrolled group or state which participants contributed to the endpoint calculation.

The registry record lists several secondary outcome domains and eight outcome measures, but does not report a multiplicity strategy or the numerical results for those measures. The protocol’s sample-size justification, statistical plan, interim analyses, and endpoint-specific uncertainty estimates are also not reported in the registry record. These gaps limit evaluation of how analyses were planned and how robust any estimates may be.

The safety record includes counts and event terms but does not establish causality. The absence of comparative safety data and detailed event context means those counts should remain descriptive.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Electrical Stimulation for the Treatment of Back Pain Using Peripheral Nerve Stimulation (PNS) — NCT03179202.
• Registry record last updated 2022-08-05; status last verified 2022-07.
• Results first posted 2022-08-05.
• 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.

19. Record Summary

The registry record describes NCT03179202, a completed post-market, single-group study of the SPRINT Peripheral Nerve Stimulation System for back pain. It reports enrollment of 166, no allocation, no masking, and sponsor SPR Therapeutics, Inc. The study started on 2017-06-23, with primary completion on 2021-05-11.

The primary endpoint counted participants achieving at least a 30% reduction in average low back pain intensity from baseline to end of treatment, defined as 8-weeks after treatment began. The record says end-of-treatment data were unavailable for eight subjects, but does not report the primary endpoint result or its analysis.

Secondary outcome domains include pain intensity, disability, health-related quality of life, depression, global impression of change, and pain interference. Safety entries report 4 serious adverse events among 99 at risk, 49 other adverse events among 99 at risk, and one death. The registry record does not establish causation or provide a comparator-based estimate.