Spinal Cord Stimulation in the Treatment of Chronic, Intractable Pain Using the Nalu™ Neurostimulation System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Spinal Cord Stimulation in the Treatment of Chronic, Intractable Pain Using the Nalu™ Neurostimulation System (NCT04503109), a na na study. The primary outcome is Responder Rate.

2. Clinical Question

This question is about the proportion or count of participants meeting a defined response threshold, rather than the average change in pain for the group. The endpoint requires a substantial reduction from each participant’s baseline VAS pain score, but the registry record does not report how many participants met that threshold. It also does not report a response percentage, an uncertainty interval, or a statistical test for the primary outcome.

Because the study has no control group, the endpoint can describe outcomes among participants receiving the device, but it cannot by itself compare those outcomes with what would have happened under another treatment or without the device. The record identifies the intended population and endpoint, but does not report details such as baseline pain scores, participant characteristics, or the number completing the endpoint assessment. Those omissions limit how fully the clinical question can be interpreted.

3. Trial Design

The registry describes NCT04503109 as a completed, single-group device study of the Nalu Neurostimulation System. Its listed enrollment is 110. The study began on 2020-07-16, and its primary completion date is 2022-09-13. The registry lists the phase and allocation as NA, and masking as NONE. It identifies Nalu Medical, Inc. as the sponsor.

All eligible subjects were to receive the Nalu Neurostimulation System. There is no separate comparator arm, so the study is not a randomized comparison. The registry specifically describes the treatment group as the Nalu SCS System. That design can document outcomes and safety observations in participants who receive the device, but it does not estimate a comparative treatment effect against a control group.

The registry summary describes adults with chronic pain in the legs and back who have been diagnosed with failed back surgery syndrome and meet other eligibility criteria. The primary endpoint population is defined as eligible subjects who received a permanent SCS device and completed 3 months of device use per protocol. The endpoint timeframe is 3 months post device activation.

The registry marks the study completed, but this status does not supply outcome findings. It records one primary outcome measure and zero analyses. The protocol details, including the statistical analysis plan, sample-size justification, interim analyses, and handling of departures from the intended treatment or follow-up, are not reported in the registry record. A study’s planned design and its posted results are distinct: the design information specifies what was intended, while results are needed to determine what was observed. Here, the record describes the intended endpoint but does not report its observed value.

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.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Eligible subjects who received a permanent SCS device and completed 3-months of device use per protocol

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: Subjects who were implanted with a permanent SCS device and completed the 3-month timepoint per protocol

6. Primary Endpoint

The registry lists the primary outcome as Responder Rate, measured over 3 months post device activation.

The primary endpoint is the count of participants who achieved 50% or greater pain reduction from baseline on the VAS pain scale for the leg and/or back. It is assessed at 3 months post device activation, among eligible subjects who received a permanent SCS device and completed 3 months of device use per protocol.

This is a binary responder outcome: each participant either meets the specified threshold or does not. A threshold-based endpoint can be useful because it describes how many participants reached a defined level of improvement, rather than only reporting a group average that could conceal variation in individual responses. The endpoint combines pain in the leg and/or back; the registry does not report separate results for those pain locations.

The registry record does not report the number of participants meeting the response definition, the number assessed, or the proportion responding. It also does not report baseline or follow-up VAS values, an uncertainty interval, or a statistical test. Consequently, the endpoint definition alone does not establish the observed response rate or how precisely it was estimated. The restriction to participants who received a permanent device and completed device use per protocol is part of the stated endpoint population; the record does not describe how outcomes for participants who did not meet that population definition were handled in any analysis.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is a binary count: participants are classified according to whether they meet the responder definition. In this study, meeting that definition requires 50% or greater pain reduction from baseline on the VAS pain scale for the leg and/or back. The registry describes the outcome unit as participants and its parameter as a count of participants. This is different from a continuous outcome such as an average pain-score change. A count of responders can be interpreted only alongside the number of participants assessed under the endpoint definition.

What does a responder count tell us?

A responder count communicates how many assessed participants crossed a prespecified threshold. To understand how common response was in the endpoint population, readers also need the denominator. To assess precision, they need an uncertainty estimate, such as a confidence interval. General statistical explanation: a confidence interval describes the range of values compatible with the observed data under the analysis assumptions. A narrower interval generally indicates greater precision, while a wider interval indicates more uncertainty. The registry record does not report the responder count, endpoint denominator, or confidence interval, so the response frequency and its precision cannot be assessed.

Threshold outcomes simplify interpretation, but they do not convey every feature of the underlying measurements. Participants just on either side of the threshold are classified differently even if their measured changes are similar, while changes of different sizes among responders are grouped together. The registry’s endpoint also refers to the leg and/or back, rather than reporting distinct responder outcomes for each location. Separate pain-location results are not reported in the registry record.

What does the single-group design allow?

The registry describes a single-group study in which eligible subjects receive the Nalu Neurostimulation System. An analysis of a single group can estimate the observed response frequency among participants with outcome data. It cannot directly estimate a between-group treatment effect because no separate control group is described. General statistical explanation: a randomized control group can help account for changes that might occur over time or through influences other than the study intervention. Without that comparison, a before-and-after change should not be treated as a controlled estimate of the device’s effect.

The endpoint is assessed at 3 months post device activation, but the registry does not report individual or group VAS measurements at baseline and follow-up. Nor does it report an analysis model, covariate adjustment, or method for estimating uncertainty. Those analysis details are not reported in the registry record, so they cannot be inferred from the outcome definition.

How should planning assumptions be read?

The stated sample-size assumptions describe a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They also describe detecting a stated fraction of the observed effect. These are planning assumptions, not a description of the study’s single-group allocation. The illustration is not the trial’s own design or a report of observed power. No calculated planning values or observed primary effect are included in the registry entries used for this interpretation, so the assumptions do not establish whether the study had adequate precision for its endpoint.

General statistical explanation: sample-size planning depends on the effect size being targeted, the variability or event frequency expected, the chosen error rate, and the analysis method. Planning values answer a prospective design question under stated assumptions; they do not show the probability that a completed study’s finding is true or whether a result is clinically meaningful. The record does not report a protocol-based sample-size justification, so it is not possible to determine whether the planning illustration matches the investigators’ original rationale.

Why does over-dispersion matter?

General statistical explanation: over-dispersion occurs when observed variability is greater than a statistical model assumes. If a model underestimates variability, it can produce uncertainty intervals that are too narrow or tests that are too optimistic. This issue is relevant to some count outcomes, but the registry describes this primary endpoint as a count of participants meeting a binary responder definition, not as a repeated event count. The record does not report a model or dispersion estimate, so there is no basis to state that over-dispersion was assessed or affected the analysis.

Overall, the posted methods information is enough to identify the endpoint type, threshold, assessment time, and stated endpoint population. It is not enough to reconstruct an analysis or judge its statistical precision. The missing outcome count and analysis details are essential for interpretation, not details that can be recovered from the design description alone.

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("Nalu SCS System")
n      <- c(35)
events <- c(30)
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  Nalu SCS System  35  30  85.7  69.7  95.2  70.6  93.7  70.5  93.6

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies one primary outcome measure, the responder rate, and zero analyses. It does not report whether additional outcomes were assessed outside the posted primary measure, whether multiple statistical tests were planned, or whether any adjustment for multiple comparisons was used. The statistical plan is not reported in the registry record, so the approach to multiplicity cannot be determined.

Multiplicity matters when several outcomes, time points, subgroups, or analyses are tested. General statistical explanation: as the number of statistical tests increases, the chance of at least one apparently notable result can increase if each test is considered independently without adjustment. Whether that issue applies, and how it was handled, cannot be established from the available record. No interim analyses or stopping rules are reported in the registry record.

The primary endpoint population consists of eligible subjects who received a permanent SCS device and completed 3 months of device use per protocol. This definition does not explain how the analysis handled participants who did not receive a permanent device, did not complete the stated use period, or lacked an outcome assessment. The number of participants in each situation, the amount of missing outcome data, and any imputation or sensitivity analysis are not reported in the registry record.

These omissions matter because a result based only on participants with complete follow-up may differ from one that includes all eligible participants under a prespecified analysis approach. That is a general concern about missing data, not evidence that missingness occurred or altered this study’s findings. With no reported primary result, analysis population, or missing-data method, readers cannot evaluate the impact of incomplete follow-up or determine whether the outcome analysis followed a prespecified plan.

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 3% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: copd (0.9%), drowziness (0.9%).

For the Nalu SCS System group, the registry reports 110 participants at risk for serious adverse events and 2 affected. It reports 110 at risk for other adverse events and 21 affected. The recorded number of deaths is 1. These are counts as recorded, not evidence by themselves that the device or treatment caused an event.

The registry lists COPD and Drowziness among the top serious adverse-event terms, each with a value of 0.9%. It does not provide further event-level details in the information, including timing, duration, outcome, or attribution. The record also does not clarify how the death relates to the reported adverse-event counts. Those relationships should not be inferred from the counts alone.

General statistical explanation: safety counts are descriptive and depend on the population followed and the definitions used to classify events. The number at risk gives context for the counts, but the posted figures do not provide a comparative safety estimate because the study has no control group. Nor do these summaries describe the distribution of event severity beyond the serious-versus-other classification. The registry’s safety information should therefore be read as a report of recorded counts in the study group, not as a causal comparison or a complete account of individual events.

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

The registry record establishes what the study intended to measure: whether eligible participants who received a permanent SCS device and completed 3 months of use achieved 50% or greater pain reduction from baseline on the VAS pain scale for the leg and/or back. It also records that the study was completed and lists enrollment as 110. These details describe the design and target endpoint; they do not provide the observed primary outcome.

The responder count, endpoint denominator, response percentage, uncertainty interval, and primary statistical analysis are not reported in the registry record. As a result, the posted information cannot quantify how often the defined response occurred or how precisely it was estimated. It cannot support a conclusion that participants did or did not meet the response threshold.

Even with a reported response frequency, the single-group design would describe outcomes among participants receiving the device, not a controlled difference against another treatment or no device. General statistical explanation: changes from baseline can be influenced by factors other than the intervention, so a within-group observation does not isolate the intervention’s contribution. This is a limitation of the design’s interpretation, not a finding that any particular alternative explanation occurred.

The safety figures describe recorded counts in the Nalu SCS System group: 2 affected by serious adverse events, 21 affected by other adverse events, and 1 death, with 110 at risk for each adverse-event category. The registry record does not establish causation or provide enough event detail to make a comparative safety assessment.

Accordingly, the record is informative about the intended population, device, endpoint definition, and some safety counts. It is not sufficient to determine the primary outcome result, its uncertainty, or a comparative treatment effect. Those conclusions require outcome and analysis reporting that is not present in the registry record.

14. Why This Trial Matters Statistically

This study illustrates why a clearly defined endpoint and a reported result are both necessary for statistical interpretation. The responder definition specifies the pain-reduction threshold, assessment time, and target population. However, without the number meeting that definition and the number assessed, readers cannot determine the observed response frequency. Without an uncertainty interval, they cannot judge the estimate’s precision.

The design also matters. A single-group study can describe outcomes in participants who received the device, but it does not provide a control-group contrast. Statistical interpretation must distinguish a within-group outcome from evidence about a comparative effect. That distinction remains important even when the outcome is expressed as a clinically understandable responder threshold.

The registry records enrollment of 110 and marks the study completed, but neither fact supplies the primary endpoint result. Completion describes study status; enrollment describes the listed study size. Neither shows how many participants contributed to the endpoint or what outcomes they experienced. The registry also records safety counts, which can be read descriptively but do not establish causality.

Finally, the record’s zero analyses and lack of reported details on missing data, multiplicity, and the analysis plan illustrate the limits of registry information when results are not posted. Readers need more than a protocol-style outcome definition to evaluate statistical evidence: they need the observed data summary, the analysis population, and a clear account of uncertainty. These distinctions help prevent a design description from being mistaken for a result.

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 main limitation for interpreting this study’s clinical outcome is that the registry record does not report the primary responder result. The number of responders, number assessed, response percentage, confidence interval, and primary statistical test are not reported. The registry also does not give baseline or follow-up VAS scores, so the distribution of pain measurements cannot be examined.

The single-group design has no separate control arm. As a result, outcomes among participants receiving the Nalu Neurostimulation System cannot be contrasted with outcomes under another condition using this study’s design. This constrains interpretation of changes from baseline and prevents a controlled estimate of comparative effect.

The stated endpoint population is restricted to eligible subjects who received a permanent SCS device and completed 3 months of device use per protocol. The record does not report how many participants met that definition, how many did not complete follow-up, or whether missing outcomes were handled using an analysis population different from the stated endpoint population. The resulting risk of bias from missing or incomplete data cannot be evaluated.

The registry describes pain in the leg and/or back in a combined responder definition. Separate results by pain location, participant characteristics, or other clinically relevant subgroups are not reported in the registry record. The statistical analysis plan, sample-size justification, interim analyses, and multiplicity approach are also not reported. These are limits on what can be assessed from the registry, not evidence that the investigators did or did not conduct particular analyses.

Safety reporting is limited to group counts and a short list of serious-event terms. Details on event timing, severity beyond the classification, outcomes, and attribution are not reported. The recorded counts therefore cannot establish whether an event was caused by the device or treatment.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Spinal Cord Stimulation in the Treatment of Chronic, Intractable Pain Using the Nalu™ Neurostimulation System — NCT04503109.
• Registry record last updated 2026-11-04; status last verified 2026-10.
• Results first posted 2026-11-04.
• 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

NCT04503109 is a completed, single-group study of the Nalu Neurostimulation System sponsored by Nalu Medical, Inc. The registry lists enrollment of 110, a start date of 2020-07-16, and a primary completion date of 2022-09-13. The phase and allocation are recorded as NA, and masking is NONE.

The primary outcome is a count of participants with 50% or greater pain reduction from baseline on the VAS pain scale for the leg and/or back at 3 months post device activation. The endpoint population is eligible subjects who received a permanent SCS device and completed 3 months of device use per protocol. The registry record does not report the primary outcome result or an analysis.

For the Nalu SCS System group, the record lists 2 participants affected by serious adverse events and 21 affected by other adverse events, with 110 at risk in each category, and 1 death. COPD and Drowziness are each listed at 0.9% among the top serious-event terms. The record does not establish event causation.