The STEPS - Totalis™ Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The STEPS - Totalis™ Trial (NCT02079038), a randomized na study. The primary outcome is Percentage of Subjects With Clinically Significant Improvement in Outcomes.

2. Clinical Question

The registry describes a prospective, multicenter, randomized, double-blind trial of Totalis™ direct decompression versus a sham comparator surgical procedure in patients with lumbar spinal stenosis. The primary question concerns the percentage of participants meeting the trial’s definition of clinically significant improvement at six months, with the assessment framed from baseline to six months.

The improvement definition requires improvement in any 2 of the 3 Zurich Claudication Questionnaire domains: physical function, symptom severity, and patient satisfaction. Physical function or symptom severity must improve by at least 0.5 points from baseline; the patient satisfaction score must be below 2.5 points. In addition, the definition excludes participants with specified index-level procedures intended to treat stenosis through six months, as well as participants with unblinding. The registry reports 56.3% for Totalis and 56.0% for the Control Procedure. These are descriptive arm-specific percentages; the record does not include a statistical comparison or confidence interval for them.

3. Trial Design

The registry identifies NCT02079038 as The STEPS - Totalis™ Trial. Its official title describes a prospective, multicenter, randomized, double-blind trial evaluating the VertiFlex® Totalis™ Direct Decompression System against a sham comparator surgical procedure in patients with lumbar spinal stenosis. The design fields specify randomized allocation, double masking, and a parallel model. The listed phase is NA.

The record lists enrollment of 180. It identifies the sponsor as VertiFlex, Incorporated, the study start as 2014-05, and primary completion as 2017-01. The current status in the record is completed. The intervention listing names Totalis as a device and the Comparator Surgical Procedure as a procedure. The arm descriptions call the arms Totalis™ Direct Decompression Procedure and Comparator Procedure; the primary outcome results use the labels Totalis and Control Procedure. These naming variations refer to the intervention and comparator as recorded, and the record does not provide additional procedural detail in the outcome entry.

The trial’s brief summary describes its purpose as assessing safety and effectiveness through changes in pain, disability, patient satisfaction, and claudicatory symptoms at six months. The posted primary outcome is narrower: it is a binary composite of whether participants meet specified improvement criteria and avoid specified events through that assessment period. One primary outcome measure is listed, while the registry record contains no posted secondary outcome measures. The record does not report further details about randomization procedures, how masking was implemented or assessed, or the statistical analysis plan.

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: 180 subjects enrolled; 12 withdrew, leaving 168 subjects randomized \& treated.

Modified Intent to Treat Population

Reasons for not completing this period:

Completed 6 Months

Reasons for not completing this period:

5. Baseline Characteristics

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

Population: Randomized Population

6. Primary Endpoint

The registry lists the primary outcome as Percentage of Subjects With Clinically Significant Improvement in Outcomes, measured over Baseline and 6 Months.

The primary endpoint is the percentage of participants with clinically significant improvement in outcomes at baseline and six months. It combines patient-reported change across the Zurich Claudication Questionnaire (ZCQ) with restrictions on subsequent events. A participant must improve in any 2 of 3 domains: physical function, symptom severity, and patient satisfaction. The physical-function and symptom-severity criteria each require improvement of at least 0.5 points from baseline. The satisfaction criterion is a score below 2.5 points.

The endpoint also requires no re-operation or revision at the index level or levels intended to treat stenosis, no epidural steroid injection or selective nerve root block at those levels through six months, and no unblinding. These conditions make the endpoint more than a measure of questionnaire change alone: it classifies improvement alongside specified additional interventions and loss of masking.

A binary endpoint presents the proportion meeting the full definition, rather than the average change in a questionnaire score. Such a composite can combine outcomes that matter to the trial’s question, but its interpretation depends on all included criteria. A participant who improves in questionnaire domains but has an excluded intervention or unblinding does not meet the stated composite definition. The registry does not report component-specific results, so the posted percentage cannot show which domain or exclusion most affected classification. Nor does the primary outcome entry provide uncertainty estimates or a formal between-arm test.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Randomization is a design method intended to make treatment assignment independent of participants’ prognostic characteristics on average. It supports a comparison between assigned groups, but it does not guarantee identical groups in every respect, and it does not replace a clearly reported analysis. The registry identifies randomized allocation, double masking, and a parallel design. The detailed sequence-generation, concealment, and masking procedures are not reported in the registry record.

What does the primary percentage represent?

For a binary endpoint, each participant is classified as meeting or not meeting the endpoint definition. The arm-level percentage expresses the share classified as meeting it among the group represented in that outcome record. Here, the endpoint classification is composite: it depends on the ZCQ improvement criteria and the absence of specified additional procedures and unblinding through six months. The registry posts 56.3% for Totalis and 56.0% for Control Procedure, alongside arm records with n=103 and n=50. The record does not state the detailed numerator or how missing assessments were classified.

Percentages give an accessible summary, but they do not convey precision by themselves. A confidence interval is a statistical range designed to express uncertainty around an estimate under a specified method and assumptions. A narrower interval generally indicates greater precision, while a wider interval indicates less precision. No confidence interval is posted for this primary outcome. Without one, readers cannot assess the range of estimates compatible with the observed data using the registry entry alone.

Why distinguish descriptive and inferential comparisons?

A descriptive comparison reports the observed results in the trial arms. An inferential comparison applies a statistical procedure to estimate uncertainty or test a stated hypothesis. A p-value, confidence interval for an arm contrast, or adjusted model result may be part of that inferential assessment. None is reported for the primary endpoint in the registry record. The percentages should therefore be read as descriptive values, not as a formal test of whether the interventions differ.

Randomization does not make an unadjusted difference automatically precise or clinically meaningful. Precision depends in part on the amount of outcome information and variability, while clinical interpretation depends on the endpoint’s meaning and the prespecified context. The record does not report an inferential estimate, a clinically meaningful difference threshold, or a formal hypothesis for the posted percentages. No new difference or ratio is calculated from the arm values.

What does the composite add?

Composite outcomes combine multiple criteria into one endpoint. This can represent a broader definition of improvement than any individual measure, but the overall result can be affected by the frequency of each component and by how the components are defined. A participant may satisfy some improvement criteria but not meet the whole endpoint because another required condition is not met. In this trial, the endpoint includes change in two of three ZCQ domains, a satisfaction threshold, avoidance of specified index-level procedures, and no unblinding. The registry does not provide results for each component separately, so it is not possible to determine which elements account for the posted composite percentages.

How should planning calculations be understood?

A sample-size calculation is a planning exercise: it estimates the amount of information a future study might need under specified assumptions. The record describes planning illustrations based on a fraction of the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such illustrations are not observed power and do not establish what the trial was designed to detect. The registry record does not report the trial’s own sample-size justification or confirm that these illustration assumptions were used in the original design.

Power is a design concept relating to the probability of detecting a specified effect under a model and assumptions. Calculating power after observing trial results from the observed effect does not supply a useful substitute for a confidence interval or prespecified test. The posted sample-size assumptions should therefore be understood as planning context, not as evidence that the primary result is conclusive. No planning values are cited in the registry record excerpt.

What is not documented about analysis?

The registry record lists no analysis entries for the primary result. It does not identify an analysis population, an adjustment strategy, a statistical test, or a missing-data method. For a binary outcome, analysts may use methods that estimate arm proportions, compare proportions, or model the probability of meeting the endpoint. Different methods can address different estimands and assumptions. The chosen method and its justification are not reported, so an independent reconstruction of the sponsor’s inferential analysis is not possible.

These limitations do not mean that no analysis was conducted; they mean that analysis details are not available in the registry record. The primary endpoint values remain descriptive registry results. If a sponsor analysis is reported elsewhere in the posted results, that analysis takes precedence over a simple recalculation from summary statistics; the registry record does not flag a discrepancy for this result.

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("Control Procedure")
n      <- c(50)
events <- c(28)
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  Control Procedure  50  28  56.0  41.3  70.0  42.3  68.8  42.2  68.9

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity concerns arise when a study evaluates multiple outcomes, time points, subgroups, or statistical tests. Testing many questions can increase the chance of a positive result arising by chance unless the analysis plan addresses that issue. The registry lists one primary outcome measure and no posted secondary outcome measures. It does not report whether additional analyses, time points, subgroups, or exploratory outcomes were examined, so the overall multiplicity strategy is not reported in the registry record.

Missing outcome data can affect a binary endpoint if participants with absent assessments are excluded, counted as not meeting the endpoint, imputed, or handled through another method. Those choices can change the interpretation and may require sensitivity analyses. The registry record does not report the amount or pattern of missing primary outcome data, how missing observations were handled, or whether sensitivity analyses were performed. The arm-specific n values shown with the outcome do not establish the analysis population or explain any difference from the enrollment entry.

Analysis populations also matter. An intention-to-treat analysis generally compares participants according to randomized assignment, while other populations may restrict inclusion according to treatment received or protocol adherence. The registry record does not identify which population underlies the posted endpoint percentages. It also does not report a statistical plan, prespecified testing hierarchy, or multiplicity adjustment. Accordingly, the primary percentages can be described as posted, but their role in a confirmatory testing strategy cannot be determined from the registry record.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: heart failure (3.6%), urinary tract infection (2.7%), coronary artery disease (1.8%), trauma from fall (1.8%), non-alcoholic cirrhosis (1.8%).

The safety record lists serious adverse events for the Totalis and Control Procedure groups, with at-risk counts of 112 and 56, respectively. It records 19 serious events in the Totalis group and 11 in the Control Procedure group. Other adverse-event counts are 98 and 42, respectively. The record lists 1 death in the Totalis group and 0 in the Control Procedure group. These entries are counts, not adjusted comparisons, and the record does not provide confidence intervals or a statistical test for them.

The most frequent serious-event terms listed are Heart failure (3.6%), Urinary Tract Infection (2.7%), Coronary Artery Disease (1.8%), Trauma from Fall (1.8%), Non-alcoholic cirrhosis (1.8%), and Dehydration (1.8%). These percentages are reported as event terms in the registry; the entry does not supply further information about event timing, severity grading, relatedness, or whether an individual could contribute more than one event.

Serious adverse events are not necessarily caused by the intervention. The record does not provide attribution details, and the at-risk counts differ from the primary endpoint arm records. These safety figures therefore should not be directly compared with the primary outcome percentages or treated as a complete causal assessment of safety. They describe the events recorded under the registry’s safety fields.

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

The registry’s primary result describes the proportion meeting a specific composite definition of clinically significant improvement at six months: 56.3% in the Totalis arm and 56.0% in the Control Procedure arm. The definition combines improvement in ZCQ domains with a satisfaction threshold and the absence of certain procedures and unblinding. These figures answer a descriptive question about the recorded endpoint, not every question a reader might have about pain, disability, satisfaction, or claudicatory symptoms separately.

The figures do not, on their own, show whether a difference between arms is statistically distinguishable from chance. The registry record does not report a confidence interval, p-value, adjusted estimate, or analysis method for the primary outcome. Nor do the close displayed percentages prove equivalence or establish that the interventions have identical effects. Equivalence or non-inferiority conclusions require appropriate prespecified margins and analyses, which are not reported in the registry record.

The result also does not reveal the extent to which each endpoint component influenced classification. Component-specific outcome data and details about missing observations are not reported. The record does not state which analysis population was used, making it difficult to assess how the endpoint percentages relate to all randomized participants or to those with observed six-month assessments.

The safety counts and event terms add a separate descriptive view, but they do not establish that an event was caused by a procedure, and they are not a complete benefit-harm comparison. Overall, the record documents a randomized, double-blind trial and its posted arm-level primary percentages. The available registry entry does not provide enough statistical detail to turn those percentages into a formal estimate of comparative effect with quantified uncertainty.

14. Why This Trial Matters Statistically

This trial is statistically informative as an example of how the definition of an endpoint shapes what a reported percentage means. The primary measure is not simply a change in pain or a questionnaire score. It combines improvement in selected ZCQ domains, a patient satisfaction threshold, avoidance of specified index-level procedures, and no unblinding through six months. Readers need to understand these elements before interpreting the arm percentages as a broad measure of improvement.

The randomized, double-blind, parallel design establishes a framework for comparing the groups, but transparent reporting of the analysis is also essential. Arm-level percentages are useful descriptions; confidence intervals, an explicit comparison, an analysis population, and a missing-data approach would show how much uncertainty surrounds the comparison and how the reported data were handled. Those details are not reported for this primary result in the registry record.

The trial also illustrates why a composite endpoint benefits from component reporting. A single overall percentage is compact, but it can conceal different patterns across physical function, symptom severity, satisfaction, and subsequent procedures. Reporting the components would help readers understand what kinds of outcomes contributed to the composite without changing the endpoint’s overall summary.

Finally, safety data need their own context. Counts and named serious-event terms describe what was recorded, but without attribution, timing, and comparative analysis they do not resolve causation. The registry entry allows a careful description of the trial’s design, endpoint, and posted results while also making clear where statistical interpretation is limited by absent analysis details.

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 registry record leaves several trial-specific details unresolved. Although it identifies randomized allocation, double masking, and a parallel design, it does not report the randomization procedure, allocation concealment, or how masking was maintained or evaluated. The description calls the comparator a sham comparator surgical procedure, but further details about the comparator procedure are not reported in the registry record.

The posted primary endpoint is measured at baseline and six months, but the record does not explain the analysis population, provide endpoint numerators, or describe the handling of missing measurements. It does not report confidence intervals, a p-value, an adjusted result, or the statistical test used. It also does not provide component-specific results for the ZCQ domains or the endpoint’s additional procedure and unblinding conditions. These omissions restrict assessment of both precision and the makeup of the composite result.

The registry reports enrollment of 180, while the primary outcome records list n=103 and n=50 for the two arms. Safety at-risk counts are also reported separately as 112 and 56. The record does not explain how these different counts relate to enrollment, outcome availability, or safety follow-up. They should not be reconciled by assumption.

The registry does not provide a sample-size justification for the original study, a full statistical analysis plan, multiplicity procedures, or details of interim analyses. It lists no secondary outcome measures and no analysis entries. The brief summary refers to pain, disability, satisfaction, and claudicatory symptoms, but further posted results for those domains are not included in the registry record. Thus, the available information supports a description of the posted primary percentages and safety entries, but not a full reconstruction of trial conduct or confirmatory analysis.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The STEPS - Totalis™ Trial — NCT02079038.
• Registry record last updated 2020-08-07; status last verified 2020-07.
• Results first posted 2020-08-07.
• 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

NCT02079038 is a completed, prospective, multicenter, randomized, double-blind, parallel trial comparing Totalis™ direct decompression with a sham comparator surgical procedure for lumbar spinal stenosis. The record lists enrollment of 180, a study start of 2014-05, and primary completion of 2017-01.

The primary outcome is the percentage meeting a composite definition of clinically significant improvement at six months. The record reports 56.3% for Totalis, with n=103, and 56.0% for the Control Procedure, with n=50. No confidence interval, formal comparison, or analysis method is reported for these percentages. Safety entries include serious and other adverse-event counts and deaths, but do not provide attribution or a statistical comparison.

The registry record lists one primary outcome measure, no secondary outcome measures, and no analysis entries. Details on missing data, analysis populations, multiplicity, and the trial’s own sample-size justification are not reported.