Tack Optimized Balloon Angioplasty Study of the Tack Endovascular System® in Below the Knee Arteries: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Tack Optimized Balloon Angioplasty Study of the Tack Endovascular System® in Below the Knee Arteries (NCT02942966), a na na study. The primary outcome is Efficacy - Number of Participants With Freedom From MALE at 6 Months and POD at 30 Days.

2. Clinical Question

3. Trial Design

This was a prospective, multicenter, single-arm, non-blinded study of the Tack Endovascular System. The registry lists the study as completed and records 233 participants enrolled. The start date was 2017-02-08, and the primary completion date was 2019-07-11. The phase is listed as NA. The sponsor was Philips Clinical & Medical Affairs Global.

The device was intended to repair dissections after percutaneous transluminal balloon angioplasty in the mid or distal popliteal, tibial, and peroneal arteries. The registry description gives a target vessel diameter range of 1.5mm to 4.5mm. It describes implantation of a Tack using the Tack Endovascular System for repair of below-the-knee post-angioplasty dissections.

A single-arm design can describe outcomes among participants who received the device, but it does not provide a concurrent control group for estimating a treatment contrast. The allocation field is NA, and the masking field is NONE. Consequently, the record does not describe random assignment or blinded assessment. Those design features matter when interpreting outcome counts: a result from one group does not show what would have occurred to comparable participants under a different treatment or without the device.

The registry lists four outcome measures and zero analyses. It identifies secondary outcomes concerning target lesion patency and freedom from above-ankle target limb amputation at 6 months. However, their numerical results are not reported in the registry record. The record also does not report a detailed statistical analysis plan, sample-size justification, interim analyses, or a protocol for handling missing outcome data. Those details should not be inferred from the study design or endpoint wording.

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

Analysis population for the primary outcome, as defined in the registry: The number of evaluable subjects for the 6 Month Primacy Efficacy Endpoint was 209.

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 Efficacy - Number of Participants With Freedom From MALE at 6 Months and POD at 30 Days, measured over 6 months.

The primary endpoint counts participants who were free from major adverse limb events at 6 months and perioperative death at 30 days. The registry defines a major adverse limb event as above-ankle amputation of the target limb or a major re-intervention to the target lesion. The listed re-interventions are a new bypass graft, jump or interposition graft revision, and thrombectomy or thrombolysis. The endpoint therefore combines outcomes reflecting serious limb events and procedures with a perioperative death criterion.

A combined endpoint can capture more than one type of clinically important event in a single outcome measure. Its interpretation depends on the component definitions and observation periods: an overall count does not show how many participants met or failed each component separately. The registry gives 209 evaluable subjects for the 6-month primary efficacy endpoint, but the number who were free from the defined events is not reported in the registry record. Component-specific results, the number with each event, and the method for combining the 30-day and 6-month criteria are also not reported in the registry record.

The endpoint is described as a count of participants, not as a time-to-event estimate. The registry record does not give a confidence interval or an inferential comparison for this endpoint.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a binary participant outcome: a person either meets the definition of freedom from the specified events or does not. For a binary outcome, a basic descriptive analysis would report the number meeting the definition and the number evaluated. A proportion can then describe the share of evaluated participants meeting the endpoint. The registry record gives the evaluable population count but does not report the endpoint count or a resulting proportion. No such result can be reconstructed from the information recorded.

What a confidence interval would describe

In general, a confidence interval communicates the uncertainty around an estimated quantity, such as a proportion. A narrower interval indicates greater statistical precision under the assumptions of the method used; it does not remove potential bias in how participants were selected, treated, or assessed. The registry record does not report a confidence interval for the primary endpoint. Without the outcome count and interval, readers cannot assess the statistical precision of an endpoint estimate from this record.

Why the single-group design matters

In general, a single-group study can describe outcomes among participants receiving an intervention. It cannot directly estimate a contrast against a concurrent control group because none is described in the registry record. A comparison with an external benchmark, if one were made, would require details about the benchmark and assumptions that make the populations and outcome ascertainment sufficiently comparable. Such a comparison is not reported in the registry record. Statistical adjustment alone would not guarantee that differences between non-randomized groups had been removed.

The study is described as non-blinded. In general, lack of blinding can affect how treatment is delivered, how outcomes are assessed, or how decisions about further procedures are made, depending on the endpoint and study conduct. The registry record does not describe outcome adjudication or other procedures that would clarify how these possibilities were addressed. It would be inappropriate to assume either that assessment was biased or that specific safeguards were used.

What the evaluable count can and cannot show

The registry identifies 209 evaluable subjects for the 6-month primary efficacy endpoint and reports 233 enrolled participants. In general, the distinction between enrolled and evaluable populations matters because a complete-case analysis can differ from an analysis that includes all enrolled participants under a prespecified missing-data approach. The registry record does not explain why some participants were not included in the evaluable count, whether endpoint status was unavailable for them, or how missing outcomes were handled. The count by itself does not establish that all missing outcomes were excluded, nor does it show whether missingness could affect the endpoint estimate.

The primary endpoint refers to events over more than one stated period: freedom from major adverse limb events at 6 months and perioperative death at 30 days. In general, a composite endpoint needs an explicit analysis rule for combining its components and observation windows. The record defines the relevant events but does not report component-level counts or a detailed analysis rule. It therefore does not show whether one component was more frequent than another or how each contributed to the endpoint result.

Multiplicity and planning

In general, when a study evaluates several outcomes or performs several statistical tests, multiplicity can raise the chance of finding at least one apparently notable result by chance. A prespecified testing hierarchy or adjustment may address that issue, but the registry record does not describe a multiplicity plan. It lists four outcome measures and zero analyses, so there is no reported inferential testing strategy to evaluate.

The record does not report a sample-size justification or the assumptions used to plan enrollment. Any sample-size planning illustration based on a stated fraction of an observed effect is a planning exercise, not an observed result or observed power. Here, the registry record does not report the primary effect estimate needed to interpret such an illustration. General sample-size methods can describe how assumed effect size, significance level, allocation, and variability influence a planning calculation, but those general principles cannot fill in missing study-specific assumptions or results.

Finally, statistical significance and clinical importance are distinct concepts in general. A p-value, if reported, would address compatibility of data with a specified statistical model and null hypothesis; it would not establish causation or importance by itself. The registry record does not report a p-value, model-based estimate, or confidence interval for the primary endpoint. The available statistical account is therefore descriptive of the planned endpoint and study structure, not a quantitative efficacy analysis.

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("Tack Endovascular System (4F)")
n      <- c(209)
events <- c(200)
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  Tack Endovascular System (4F)  209  200  95.7  92.0  98.0  92.0  97.7  92.0  97.7

11. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, including the primary efficacy endpoint and secondary outcomes concerning target lesion patency and freedom from above-ankle target limb amputation at 6 months. It records zero analyses. No multiplicity procedure, testing hierarchy, or prespecified strategy for interpreting multiple outcomes is reported in the registry record. In general, examining multiple endpoints can increase the chance of a seemingly notable result arising by chance; a planned approach to multiplicity helps readers understand how results were to be interpreted. The registry record does not give enough information to determine whether such an approach was specified elsewhere.

The primary endpoint description identifies 209 evaluable subjects, compared with 233 enrolled participants. The record does not report why the endpoint-evaluable count differs from enrollment, the number of missing observations, or the handling of missing endpoint data. It does not describe an intention-to-treat population or another analysis population beyond the stated evaluable subjects. Those terms should not be inferred from the participant counts alone.

In general, missing data can affect an estimate when the likelihood of an outcome being unavailable is related to participant characteristics or outcome status. Statistical approaches may make different assumptions about missingness, and sensitivity analyses can examine how conclusions change under alternative assumptions. No missing-data method or sensitivity analysis is reported in the registry record. The primary endpoint result itself is also not reported, so its robustness to missing data cannot be assessed.

The registry record does not report the statistical analysis plan, interim analyses, or a sample-size justification. These omissions leave the intended analysis procedures and planning assumptions unclear; they do not establish that no such procedures existed outside 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 0% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: peripheral vascular disease (3.9%), claudication (3.4%), gangrene toe (2.1%), anemia (1.7%), osteomyelitis of the foot (1.7%).

For the Tack Endovascular System (4F) group, the registry records 233 participants at risk for serious adverse events and 179 affected. It also records 233 participants at risk for other adverse events and 137 affected. The record lists 63 deaths. These are safety counts as recorded; the registry information described does not specify the death observation period or attribute the deaths to the device. The counts alone do not establish causation.

The most frequently listed serious adverse event terms and their recorded percentages are Peripheral vascular disease, 3.9%; Claudication, 3.4%; Gangrene toe, 2.1%; Anemia, 1.7%; Osteomyelitis of the foot, 1.7%; and Pneumonia, organism unspecified, 1.7%. These are event-term entries, not a breakdown of the primary efficacy endpoint. The record does not explain whether participants could contribute more than one event term, or provide further detail about timing, severity grading, or attribution for these entries.

In general, safety counts should be read alongside their observation periods, event definitions, and attribution rules. Those details are not reported in the registry record. The figures therefore describe recorded safety experience in this single group; without a comparison group, they do not estimate excess risk relative to another treatment or to no device treatment.

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

The registry record establishes that a prospective, multicenter, non-blinded, single-arm study of the Tack Endovascular System was completed, with 233 participants enrolled. It specifies the intended use in repairing post-angioplasty dissections below the knee and defines a primary efficacy endpoint involving freedom from major adverse limb events at 6 months and perioperative death at 30 days. It also states that 209 subjects were evaluable for the 6-month primary efficacy endpoint.

The registry record does not report how many participants met the primary endpoint. Nor does it report numerical results for the secondary outcomes listed, a confidence interval, or a statistical comparison. The design and endpoint definitions therefore explain what the study set out to evaluate, but the available record does not quantify the observed efficacy outcome or its precision.

Even a reported favorable event count in a single-arm study would describe outcomes in that study group; it would not by itself establish a causal treatment effect. Without a concurrent comparison group, differences from another setting could reflect differences in participants, care, follow-up, or assessment. This general limitation should not be mistaken for evidence that the device did or did not affect outcomes.

The safety information records participants affected by serious and other adverse events and a death count, along with selected serious-event terms. It does not provide all details needed to interpret timing or attribution, and the counts do not establish that the device caused an event. Taken together, the record supports an account of study design, intended use, outcome definitions, and recorded safety counts. It does not support a quantitative conclusion about efficacy, comparative benefit, or causation.

14. Why This Trial Matters Statistically

This study is statistically notable for the gap between a clearly described endpoint and the absence of its numerical result in the registry record. The endpoint definition and evaluable population are essential context, but they are not sufficient to estimate the observed frequency of the outcome. Without the number meeting the endpoint, a reader cannot calculate or assess its precision from the registry information.

The single-arm design also defines the type of inference available. Such a study can provide descriptive evidence about outcomes among enrolled participants, but it does not provide a randomized estimate of how outcomes compare with another treatment. This distinction is important whenever a study is described in terms of efficacy: an endpoint may be intended to measure efficacy, while the design still limits causal interpretation.

The difference between the enrolled population and the stated evaluable population raises a separate reporting issue. The registry record does not explain how the endpoint-evaluable group was formed or how unavailable outcomes were handled. Transparent reporting of analysis populations and missing data is important because readers need to understand who contributed to an estimate and what assumptions might affect it.

Finally, the study lists multiple outcomes but no analyses. The registry record does not describe a multiplicity plan, a statistical analysis plan, or a sample-size justification. These omissions limit assessment of how the outcomes were to be analyzed and interpreted. They do not prove that no such plans existed, but they mean that the statistical evidence cannot be fully evaluated from the registry record alone.

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 direct limitation of the available registry information is that it does not report the primary endpoint count or numerical results for the listed secondary outcomes. The record therefore does not allow readers to estimate the observed endpoint frequency or its precision. Although 209 subjects are identified as evaluable for the 6-month primary efficacy endpoint, the reason this differs from the 233 enrolled participants is not reported in the registry record.

The study is single-group and non-blinded, with no concurrent comparator described. This means the registry information cannot establish a randomized treatment contrast. The record does not describe endpoint adjudication, detailed follow-up procedures, or measures used to address potential differences in outcome assessment.

The primary endpoint combines major adverse limb events and perioperative death, but the record does not report separate component counts or a detailed rule for combining the stated observation periods. The secondary outcome results are also unavailable. Without those details, the relative contribution of different types of events cannot be assessed.

The registry record does not report a statistical analysis plan, multiplicity approach, sample-size justification, interim analyses, or missing-data method. It also does not explain the endpoint-evaluable population. These gaps limit evaluation of prespecification and analysis choices. They should be understood as limitations of the information reported in the registry record, not proof that the procedures were absent from the full study documentation.

Safety counts are recorded, but additional context about timing and event attribution is not given. In a single-group study, these counts cannot be interpreted as comparative risks. No conclusion about causation follows from the recorded counts alone.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Tack Optimized Balloon Angioplasty Study of the Tack Endovascular System® in Below the Knee Arteries — NCT02942966.
• Registry record last updated 2022-01-31; status last verified 2021-04.
• Results first posted 2021-07-28.
• 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 a completed, prospective, multicenter, non-blinded, single-arm study of the Tack Endovascular System for repairing post-angioplasty dissections in below-the-knee arteries. It records 233 participants enrolled and identifies 209 subjects as evaluable for the 6-month primary efficacy endpoint.

The primary endpoint concerns freedom from major adverse limb events at 6 months and perioperative death at 30 days. The record defines the events but does not report the number meeting the endpoint, a confidence interval, or an analysis estimate. Numerical results for the listed secondary outcomes are also not reported in the registry record.

Safety entries include serious and other adverse event counts, a death count, and selected serious-event terms. The single-group design does not provide a concurrent treatment comparison, and the registry record does not report detailed analysis methods, missing-data handling, or multiplicity procedures. The available information describes the study design and outcomes of interest but does not permit a quantitative efficacy assessment.