This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Study to Evaluate the Effectiveness of DRG Stimulation for Discogenic Low Back Pain (NCT02587637), a na na study. The primary outcome is Percentage of Subjects With 30% or Greater Reduction in Back Pain at 6 Months.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02587637 |
| Phase | NA |
| Condition | Chronic Pain |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 20 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Abbott Medical Devices |
| Results posted | Yes |
2. Clinical Question
Population
The study concerned people with chronic discogenic low back pain who were refractory to other available treatments. The registry summary says selected participants were not suitable candidates for lumbar spinal surgery and would meet the study centre’s routine selection process for dorsal root ganglion stimulation. The primary endpoint description specifies implanted subjects; its population statement says 15 patients were implanted with the DRG Axium system. The registry record does not provide further eligibility details or describe the characteristics of the participants.
Intervention
The intervention was dorsal root ganglion (DRG) stimulation, identified as a device intervention. The study was a prospective post-market observational pilot study intended to evaluate DRG stimulation in the management of chronic discogenic pain. The record does not report additional details about device settings, treatment delivery, or participant follow-up beyond the outcome timeframes it names.
Comparator
There was no separate comparator group in the recorded design. The study is listed as a single-group study, with allocation and masking listed as not applicable and none, respectively. The registry summary says results were intended to inform clinical practice and future comparative studies, but the record does not describe a concurrent control group or a randomized treatment comparison.
Primary question
The primary question was how many implanted subjects had a sustained, clinically meaningful reduction in low back pain at the six-month follow-up visit compared with baseline. The endpoint description defines this as a reduction of at least 30% or 2 points on a numerical pain rating scale. The registry record does not report the observed number or percentage meeting that definition, or an analysis estimating the result.
3. Trial Design
This was a prospective post-market observational pilot study evaluating DRG stimulation for chronic discogenic low back pain. The registry lists a single-group model, an allocation value of not applicable, and no masking. Those features describe a study that follows participants receiving the device intervention rather than assigning participants to a randomized comparison between treatment groups. The registry record does not report a separate control arm, a randomization procedure, or a masking procedure.
The record lists enrollment of 20 and describes a single device arm. Its primary endpoint population statement says 15 patients were implanted with the DRG Axium system. These figures refer to different parts of the study description: enrollment is not the same as the stated implanted population for the primary endpoint. The record does not explain why the number implanted differs from total enrollment, nor does it report how many implanted participants contributed data at the six-month visit.
The study is marked completed. Its primary endpoint is assessed at six months, while the listed secondary outcomes include global impression of change at six and 12 months and the proportion with at least 50% reduction in back pain at six and 12 months. The record names six outcome measures in total, but does not give result values for the primary endpoint or the listed secondary outcomes.
The registry summary describes participants as refractory to other available treatments and not suitable candidates for lumbar spinal surgery. It also says participants would meet the selection process routinely used at the study centre. Further eligibility criteria, recruitment details, follow-up procedures, and the study’s statistical plan are not reported in the registry record. The record describes the study’s intended role as informing current clinical practice and future comparative studies; it does not establish a comparative treatment effect.
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
| Stage | All Subjects |
|---|---|
| STARTED | 20 |
| Received Intervention | 15 |
| COMPLETED | 14 |
| NOT COMPLETED | 6 |
Analysis population for the primary outcome, as defined in the registry: 15 patients were implanted with the DRG Axium system.
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.
| Characteristic | Unit | All Subjects |
|---|---|---|
| Participants analysed | 20 | |
| Age, Customized | years | 45 (22 to 71) |
| Sex: Female, Male: Female | Participants | 13 |
| Sex: Female, Male: Male | Participants | 7 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| Race (NIH/OMB): Asian | Participants | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 19 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 1 |
| Region of Enrollment: Netherlands | participants | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Percentage of Subjects With 30% or Greater Reduction in Back Pain at 6 Months, measured over 6 months.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number and percentage of implanted subjects who achieved a sustained, clinically meaningful reduction in low back pain at the six-month follow-up visit compared with baseline. The registry defines qualifying reduction as at least 30% or 2 points on a numerical pain rating scale. This is a binary outcome: each participant either meets the endpoint definition or does not, and the result can be expressed as a count and percentage.
A threshold endpoint can make a result easier to interpret than a change in a pain score alone: it describes the proportion of participants who reached a prespecified level of improvement. That is a general explanation of this type of endpoint, not a claim about the study’s observed results. The registry record does not state how the two qualifying thresholds were applied when a participant met one but not the other, or provide further details about how sustained reduction was defined or assessed.
The record identifies the endpoint timeframe as six months and the endpoint population as implanted subjects. It says 15 patients were implanted, but does not report the number assessed at follow-up, the number meeting the endpoint, or the percentage. It also does not report a confidence interval or inferential test for this outcome. The endpoint definition is therefore available, while its result and precision are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes a single-group observational study and identifies a clear primary outcome: the number and percentage of implanted subjects with a sustained, clinically meaningful reduction in low back pain at six months compared with baseline. It defines that reduction as at least 30% or 2 points on a numerical pain rating scale. However, the posted results do not report the observed count or percentage for this primary outcome. They also do not report an estimate of uncertainty, such as a confidence interval, or an inferential analysis. The outcome’s numerical result and precision are therefore not reported in the registry record.
The distinction between enrollment and the primary endpoint population matters. The study lists 20 enrolled participants, while the endpoint description says 15 patients were implanted. The primary outcome is described for implanted subjects, but the record does not state how many of those subjects contributed six-month outcome data. Without that follow-up denominator and the number meeting the definition, a reader cannot interpret the primary endpoint as a rate or determine how much information underlies it.
The study design also limits what can be inferred. A single-group observational study can describe outcomes among participants receiving the device intervention, but it does not provide a concurrent comparison group in the recorded design. Consequently, a change from baseline, even if its numerical value were available, would not by itself distinguish the intervention’s contribution from other possible explanations for change. This is a general design consideration, not a conclusion about what caused any participant’s outcome.
The registry lists secondary outcomes involving global impression of change and a threshold of at least 50% reduction in back pain at six and 12 months. It does not report their results. The record also lists zero analyses. No p-value, confidence interval, adjusted estimate, or method for handling repeated outcome assessments is reported in the registry record. Without those details and the outcome data, it is not possible to evaluate statistical evidence for the primary or secondary outcomes from the registry information.
The safety entry reports zero serious adverse events among 20 subjects at risk, zero deaths, and five events in the separate “other” category among 20 at risk. These are descriptive registry figures. The record does not provide serious adverse event terms, and it does not define the “other” category in the material available. The safety counts should not be interpreted as a complete account of event types, timing, or causal relationship to the intervention.
Overall, the record establishes the intended endpoint, study structure, and some safety counts, but it does not report the primary outcome result or statistical analyses. The absence of a reported result is not evidence that participants did or did not meet the endpoint. It means that the registry record does not permit a quantitative assessment of the primary outcome’s observed frequency or precision.
9. Statistical Methods Explained
The registry describes a binary primary outcome and a single-group observational design. Statistical concepts can clarify what such an endpoint and design would ordinarily mean, but the registry record does not report a detailed statistical analysis plan or an analysis of the primary outcome.
What does a binary endpoint represent?
General statistical explanation: a binary endpoint classifies each participant into one of two categories, such as meeting or not meeting a stated response threshold. The study’s primary endpoint is framed as a count and percentage of participants reaching a defined pain-reduction threshold by six months. To interpret that percentage, a reader needs both the number meeting the definition and the number assessed for the endpoint. The record gives the implanted population statement as 15 patients, but does not report the number assessed at six months or the number who met the definition.
The endpoint description uses the phrase “at least 30% or 2 points” on a numerical pain rating scale and calls the reduction sustained and clinically meaningful. Those terms indicate the intended threshold-based classification, but the record does not give operational details for sustained response, missing visits, or the use of the two alternatives in classifying participants. Such details matter because different classification rules can change which observations count as endpoint events. The rules used are not reported in the registry record.
How should a percentage be interpreted?
General statistical explanation: a percentage is a sample estimate of how common an outcome was in the participants included in its denominator. It describes the observed study group; it does not automatically describe all people with the condition or establish why the outcome occurred. The denominator is essential. For this study, total enrollment is 20, while the endpoint population statement identifies 15 implanted patients. The record does not state how many of those patients had an observed six-month outcome. It also does not provide the numerator. Therefore, the primary endpoint percentage cannot be read or reconstructed from the registry record.
A confidence interval is a way to express the uncertainty around an estimated quantity, under the assumptions of the method used. General statistical explanation: for a proportion, an interval reflects the fact that a finite group of participants may not precisely represent the underlying population. Its width depends on the data and the chosen method. No confidence interval or method for calculating one is reported for the primary endpoint, so the precision of the study’s response proportion cannot be assessed from the registry record.
What does the single-group design allow?
General statistical explanation: an observational single-group study can describe outcomes recorded in a group that received an intervention. A before-and-after outcome can also describe the pattern of change within participants when both baseline and follow-up measurements are available. However, without a concurrent comparator, the design does not directly estimate how outcomes would have differed under another treatment or no intervention. Changes over time may have explanations other than the intervention, and the study design alone cannot separate those explanations.
For this study, the endpoint is defined by comparison with baseline, but the registry does not report the actual baseline and follow-up observations, the endpoint count, or an analysis comparing those measurements. Nor does it report a control group. The record therefore supports describing the study question and design, but not a causal or comparative estimate of the intervention’s effect.
What analyses are reported?
The registry records zero analyses. It does not report a statistical test, model, adjustment, confidence interval, or analysis population for the primary endpoint. The statistical plan, including any prespecified handling of incomplete observations, is not reported in the registry record. In the absence of these details, no inferential result should be attributed to the study, and no unreported analysis should be assumed.
General statistical explanation: an analysis population identifies which participants are included in a particular calculation. In a study with enrollment, implantation, and follow-up stages, those groups can differ. Clear reporting of the population and missing observations helps readers understand the denominator and the limits of an estimate. Here, the record identifies 20 enrolled and 15 implanted, but does not report the six-month analysis population or the handling of participants without outcome data.
How do the planning assumptions differ from observed results?
The record describes sample-size planning illustrations based on an observed effect, not the study’s own design. The stated illustration assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is described as a stated fraction of the observed effect. The record notes that time-to-event illustrations give a total number of events, while other illustrations give participants per arm.
These are planning assumptions, not evidence that the study used a two-arm design. The recorded study is single-group, and the record does not report the protocol’s sample-size justification. Planning illustrations do not describe the number of participants actually observed meeting the endpoint, nor do they constitute observed power. No numerical planning outputs or observed effect estimate are reported in the registry record. The illustration assumptions therefore should not be used as a substitute for a reported primary outcome analysis.
General statistical explanation: over-dispersion is relevant when observed variability exceeds what a statistical model assumes. It can affect standard errors and uncertainty estimates in analyses of some count outcomes. The primary endpoint is described as a participant count meeting a binary criterion, but the record does not report a model or an analysis that would permit assessing over-dispersion. No conclusion about its presence or relevance in this study can be drawn from the registry record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary endpoint and several secondary outcomes. The primary endpoint is the percentage of subjects with at least 30% reduction in back pain at six months, with the endpoint description also allowing a reduction of 2 points on a numerical pain rating scale. Secondary outcomes include global impression of change at six and 12 months and at least 50% reduction in back pain at six and 12 months. The record states that there are six outcome measures in total, but does not report results for these measures.
When a study examines multiple outcomes or time points, there are general statistical considerations about multiplicity: the more questions tested, the greater the opportunity for chance findings if each is treated as a separate confirmatory test. A prespecified analysis plan can describe which outcome is primary and how secondary analyses are to be interpreted. The registry identifies a primary outcome, but the statistical plan, any multiplicity adjustment, and the intended status of secondary analyses are not reported in the registry record. No analysis results are listed.
The record does not report how missing outcome data were handled, whether all implanted participants completed follow-up, or how participants without six-month measurements were classified. The endpoint population statement gives 15 implanted patients, but the number with observed primary endpoint data is not stated. The analysis populations for the primary and secondary outcomes are also not reported in the registry record.
These omissions affect interpretation, not just technical detail. A reported percentage needs a clear denominator, and the treatment of missing observations can influence that percentage. Without the analysis population and missing-data approach, readers cannot assess how complete the outcome data were or whether the reported analysis, if any, included all participants defined for the endpoint. The registry record does not supply a basis for assuming that missing observations were absent or handled in a particular way.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| All Subjects | 0 | 20 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| All Subjects | 0 of 20 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| All Subjects | 5 of 20 |
Most frequent non-serious adverse event terms
| Event term | Organ system | All Subjects |
|---|---|---|
| Increased Pain | General disorders | 5 of 20 |
| Pain at pocket | Skin and subcutaneous tissue disorders | 3 of 20 |
The safety entry is for “All Subjects” and lists 20 subjects at risk for serious events, with zero affected. It also lists 20 subjects at risk in the other adverse event category, with five affected, and zero deaths. These are the counts recorded in the registry; they are not estimates of comparative risk because the study has no separate control group in its recorded design.
The serious event count should be read as a registry summary, not as proof that no safety events of any kind occurred. The record does not list serious adverse event terms, so the types and circumstances of serious events are not described. It also does not report event timing, duration, severity definitions, relationship to the device, or a more detailed accounting of the other events. The meaning and scope of the “other” category are not reported in the registry record.
General statistical explanation: safety counts are easier to interpret when the population at risk, event definitions, observation period, and method for collecting events are clear. A count of participants affected is not necessarily the same as a count of all event episodes if participants can have more than one event. The registry entry gives participants affected, but does not provide event-level detail. These figures describe what the registry reports and do not support broader conclusions about safety beyond the recorded counts.
12. What the Result Does, and Does Not, Mean
The result described by the registry is primarily a study question, not a reported estimate. The primary endpoint asks how many implanted subjects had a sustained, clinically meaningful reduction in low back pain at six months compared with baseline, using a threshold of at least 30% or 2 points on a numerical pain rating scale. The registry does not give the count or percentage meeting that endpoint. As a result, it does not show the observed frequency of response or the precision of that frequency.
The study’s structure is important to what its results could mean. It is a prospective, single-group observational pilot study, not a randomized comparison in the record. In general, a descriptive result from a single group can characterize outcomes among the participants observed. It cannot by itself show what would have happened to those same participants under an alternative intervention or without the intervention. No comparative treatment effect is reported.
The listed secondary outcomes extend the questions to global impression of change and a larger pain-reduction threshold at six and 12 months. Their results are also not reported in the registry record. No inferential analyses are listed, and no confidence intervals or p-values are reported. Thus, the record does not provide a basis for judging whether an outcome estimate is statistically precise or how it would compare with another group.
The study’s intended role was to inform current clinical practice and future comparative studies in this specific population. That aim is consistent with a pilot observational design, which can describe a clinical experience and raise questions for later research. It does not remove the limitations of having no recorded control group or of lacking reported outcome values.
The safety counts have a separate, limited meaning: the registry records zero serious adverse events among 20 at risk, five affected in the other category among 20 at risk, and zero deaths. The record does not provide more detailed event descriptions or a causal assessment. These counts should not be expanded into conclusions that the intervention is safe or unsafe. They are the reported counts, with their scope limited by the detail available in the registry record.
In short, the record specifies what the study set out to measure and reports selected safety counts, but it does not report the primary or secondary outcome results. It therefore cannot establish whether participants reached the specified pain-reduction threshold, how consistently outcomes were observed, or whether any changes were caused by the intervention.
13. Why This Trial Matters Statistically
This study is statistically informative in part because it makes the distinction between a study objective and an analyzed result visible. The primary endpoint is defined in concrete terms: a sustained reduction in low back pain at six months, assessed against baseline and expressed as a participant count and percentage. Yet the registry record does not report the count, percentage, or an analysis. A clear endpoint definition is useful, but it cannot replace the outcome data needed to estimate the result.
The difference between enrollment and the primary endpoint population is another important statistical point. The record lists 20 enrolled participants and states that 15 patients were implanted. It does not report how many had six-month data. Readers need to know the denominator for a percentage and which participants contributed to it; otherwise, the magnitude and completeness of an outcome cannot be evaluated. The endpoint population statement alone does not tell how many observations were available at follow-up.
The design also clarifies why a future comparative study could address a different question. This study is prospective and observational, with a single group. It may describe outcomes among participants receiving the device, but it does not provide a concurrent comparator for separating intervention-associated change from other influences. The registry summary explicitly presents the pilot as intended to inform future comparative studies in this population.
Finally, the record illustrates that safety counts and efficacy outcomes are distinct kinds of information. It reports selected adverse event counts, but no primary or secondary outcome results. It also records zero analyses. Keeping those details separate avoids treating a completed study status or a defined endpoint as if it were an outcome estimate. The statistical value of the record is in identifying the design, target population, endpoint, and reporting gaps that would matter when interpreting or planning further research.
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 direct limitation is that the registry record does not report the primary endpoint result. It defines the six-month threshold outcome, but gives neither the number meeting the definition nor the percentage. The six-month analysis denominator, confidence interval, and inferential analysis are also not reported. The same absence of outcome values applies to the listed secondary outcomes.
The design is single-group and observational, with no separate comparator recorded. Accordingly, the study cannot provide a randomized comparison between DRG stimulation and another treatment. Any within-group outcome description, if reported, would not by itself establish that the intervention caused the observed changes. This limitation follows from the design and is separate from the missing result values.
The participant counts require careful distinction. The record lists 20 enrolled and says 15 patients were implanted, but does not explain the difference or report how many implanted participants had six-month data. The analysis populations and missing-data methods are not reported in the registry record. Without them, the completeness and denominator of the primary outcome cannot be assessed.
The registry does not report detailed eligibility criteria, participant characteristics, device delivery details, or operational definitions beyond the wording of the primary endpoint. It does not explain the application of the endpoint’s two alternative thresholds or how sustained reduction was determined. These omissions limit the ability to assess reproducibility and applicability to populations beyond the study group described.
The statistical plan, sample-size justification, any interim analyses, and methods for multiple outcomes are not reported in the registry record. The available planning illustration assumptions are not the trial’s own design and do not supply the missing endpoint analysis. Safety reporting is also limited: serious event terms are absent, and the other adverse event category is not further defined. These gaps prevent a fuller assessment of outcome precision, data completeness, and event details.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Study to Evaluate the Effectiveness of DRG Stimulation for Discogenic Low Back Pain — NCT02587637.
- Registry record last updated 2024-09-19; status last verified 2024-09.
- Results first posted 2024-09-19.
- 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.
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18. Record Summary
The registry describes a completed prospective post-market observational pilot study of DRG stimulation for chronic discogenic low back pain. It lists a single-group design, enrollment of 20, and 15 implanted patients in the primary endpoint population statement. The primary endpoint is the count and percentage of implanted subjects with a sustained reduction in back pain at six months compared with baseline, defined as at least 30% or 2 points on a numerical pain rating scale.
The primary and listed secondary outcome results are not reported in the registry record, and the record lists zero analyses. It does not report the analysis population, missing-data methods, or statistical plan. Safety entries report zero serious adverse events among 20 at risk, five affected in the other category among 20 at risk, and zero deaths; further event details are not reported. The single-group design does not provide a concurrent treatment comparison.