Feasibility Study of The Use of FLEX HD® Surgical Implant or STRATTICE® Reconstructive Tissue Matrix in The Closure of Abdominal Wall Defects With Component Separation in Clean or Contaminated Cases: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Feasibility Study of The Use of FLEX HD® Surgical Implant or STRATTICE® Reconstructive Tissue Matrix in The Closure of Abdominal Wall Defects With Component Separation in Clean or Contaminated Cases (NCT01597128), a non-randomized na study. The primary outcome is Hernia Recurrence.

2. Clinical Question

3. Trial Design

This was a completed, non-randomized, parallel study of FLEX HD and STRATTICE in abdominal wall defect closure with component separation. The registry lists enrollment as 35. It identifies the interventions as devices and the study phase as not applicable. Masking is listed as none. The study began in 2011-03, reached primary completion in 2015-05, and has a completed status.

Because allocation was non-randomized, these groups should not be treated as a like-for-like control comparison. In a randomized study, assignment is designed to distribute measured and unmeasured factors across groups by chance. Here, the registry does not describe the assignment process or report whether the groups were comparable at baseline. Differences in patient characteristics, case complexity, surgical practice, or other factors could therefore influence any observed group difference; whether those factors differed is not reported in the registry record.

The record identifies 10 outcome measures and 0 analyses. It gives a primary endpoint and its assessment timeframe, but does not report the result, analysis population, statistical model, or handling of missing outcome data. The brief summary describes the purpose as examining the feasibility of using either device in hernia repair. The registry record does not define a specific feasibility threshold or report a feasibility result. The listed design and status describe how the study was registered, but completion alone does not establish what the outcome findings were.

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

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 Hernia Recurrence, measured over 12 months.

The primary endpoint is hernia recurrence, measured as the percentage of patients with recurrence at 12 months. The registry states that recurrence is assessed by physical examination and/or CT scan. This is a binary outcome at the participant level: a participant is classified according to whether recurrence is identified under the study’s assessment approach. The record does not provide further criteria for deciding what counts as recurrence or how the physical examination and imaging assessments are combined when they differ.

As a general statistical matter, recurrence is relevant to a repair study because it describes whether the repaired hernia has returned during the stated follow-up period. Reporting the percentage with recurrence makes the outcome interpretable as a proportion of participants, provided the denominator and the handling of unavailable assessments are clear. Those details, along with the actual recurrence results, are not reported in the registry record.

The endpoint specification alone does not establish a result. No group-specific recurrence percentages, event counts, comparison estimate, confidence interval, or statistical test are reported. The registry therefore describes what was intended to be measured, not how often recurrence occurred or how precisely any difference between devices was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry classifies the primary outcome as a binary percentage outcome and gives its unit as percentage of patients. In general, a binary endpoint records whether an event occurred for each participant, rather than measuring a continuously varying quantity. A percentage is an event count expressed relative to an eligible denominator. For this study, the event is hernia recurrence assessed at 12 months by physical examination and/or CT scan. The registry does not report the event counts or percentages, so no primary outcome calculation can be described from the posted record.

What does an effect estimate describe?

In general, a group comparison can be expressed as a difference in percentages, a ratio of percentages, or another measure suited to the endpoint and analysis. These measures answer related but distinct questions. A difference describes separation on the percentage scale; a ratio describes the event frequency in one group relative to the other. The choice should be stated alongside the estimate and its uncertainty. No such estimate is reported for recurrence, so it would be inappropriate to infer one from the enrollment or adverse-event information.

How should uncertainty be read?

In general, a confidence interval describes uncertainty around an estimate under the statistical model and assumptions used. A narrow interval indicates greater precision than a wide interval, but neither width nor statistical compatibility with a null value answers whether an effect matters clinically. The interval also cannot correct problems in study design. There is no recurrence estimate or interval in the registry record. No statistical test or p-value for the primary outcome is reported either.

The binary outcome classification also makes the denominator important. Participants without an assessment may not be classifiable as having or not having recurrence unless the analysis specifies how missing observations are handled. An analysis restricted to participants with available examinations can differ from an analysis that uses another missing-data method. The registry does not report the number assessed at 12 months, the amount of missing outcome data, or the method used to address it.

What does non-randomized allocation change?

In general, randomization aims to make comparison groups similar in expectation with respect to measured and unmeasured prognostic factors. Non-randomized allocation does not provide that design protection. A valid analysis may need to account for measured differences, but adjustment cannot guarantee removal of confounding, especially from factors not measured or not included in the model. The registry labels the allocation as non-randomized and explicitly notes that the arms are not a like-for-like control comparison. It does not describe the allocation procedure, baseline balance, covariate adjustment, or a model for the primary endpoint.

The parallel model means the interventions are assigned to separate groups rather than being described as sequential treatments for each participant. In this study, the record lists a FLEX HD group and a STRATTICE group. The parallel designation does not mean the groups were randomized or comparable. The absence of masking is also recorded. The registry does not describe who knew which device was used or how outcome assessors applied the recurrence criteria.

What do the planning assumptions mean?

The registry describes a planning illustration based on a fraction of an observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such an illustration is distinct from an analysis of observed trial outcomes. In general, sample-size planning asks how many participants might be needed under stated assumptions to detect a target effect with a chosen statistical operating characteristic. It does not show that a study had that level of power after data collection, and it does not establish that the assumed effect is true.

The record does not report the primary endpoint effect needed to interpret that planning description, nor does it provide numerical planning results in the registry record for this account. The trial’s listed enrollment of 35 is not, by itself, evidence that the study could reliably detect a particular difference. The registry record also does not report the original sample-size justification. Planning illustrations should therefore be understood as assumption-dependent rather than as an observed result or a statement about the study’s actual power.

Finally, the registry lists 10 outcome measures and 0 analyses. This does not identify which outcomes were analyzed, whether analyses were conducted but not entered, or how the primary endpoint was handled. The record does not report a statistical analysis plan, interim analyses, multiplicity procedures, model specification, or analysis population. Without those details and the outcome data, the methods cannot be reconstructed beyond the registered endpoint definition and the broad design characteristics.

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("Flex HD", "Strattice")
n      <- c(18, 17)
events <- c(2, 2)
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  Flex HD  18  2  11.1  1.4  34.7  3.1  32.8  3.4  33.1
ARM  Strattice  17  2  11.8  1.5  36.4  3.3  34.3  3.6  34.7

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 10 outcome measures and 0 analyses. It does not report which outcomes were designated as secondary, whether any were tested inferentially, or whether a multiplicity procedure was used. When several outcomes are tested, general statistical practice considers how the number of comparisons affects the interpretation of chance findings. The record does not provide enough information to determine whether or how that issue was addressed. The primary endpoint is identified as hernia recurrence at 12 months, but no analysis result is posted.

Missing data are also not described. The registry record does not state how many participants completed a 12-month assessment, whether any examination or CT information was unavailable, or what rule was used when assessment methods disagreed. In general, missing outcome data can affect both the denominator and the interpretation of a percentage. The effect depends on how much information is missing and whether the missingness is related to outcome status or other participant characteristics; neither is reported.

The analysis population is not reported in the registry record. It is therefore unclear whether the endpoint was intended to be analyzed among all enrolled participants, only those with available follow-up, or another defined group. The record also does not describe exclusions, protocol deviations, or any approach to analysis after non-randomized allocation. These omissions limit reproducibility and make it impossible to assess how the posted endpoint definition would translate into an analysis.

12. Safety Results

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

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: abdominal abscess (5.9%), abdominal wound/mesh infection (5.9%).

The registry reports serious adverse events for 18 participants at risk in the FLEX HD group: 0 were affected. For STRATTICE, 17 participants were at risk and 2 were affected. These are the reported serious-event counts and denominators; they do not describe the primary endpoint of hernia recurrence. The registry also lists Abdominal Abscess and Abdominal Wound/Mesh Infection among the top serious terms, each at 5.9%. It does not assign those term percentages to a particular group in the information.

Other adverse events were reported for 14 of 18 participants at risk in the FLEX HD group and 14 of 17 in the STRATTICE group. Event counts can overlap: one participant may have experienced more than one event or event term. They should not be added to infer a number of unique participants. The registry does not report the number of deaths. It also does not provide event-level timing, severity detail beyond the serious classification, or a causal assessment connecting events to a device.

As a general statistical point, raw adverse-event counts are descriptive and do not establish that an intervention caused an event. The non-randomized design further limits a direct safety comparison because the groups may differ in factors affecting event risk. These figures should be read as recorded safety counts, not as a controlled estimate of comparative risk.

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

The registry record establishes that a completed, non-randomized study examined FLEX HD and STRATTICE for abdominal wall defect closure with component separation. It identifies hernia recurrence at 12 months as the primary endpoint and specifies physical examination and/or CT scan as the assessment basis. It also provides group-level counts for serious and other adverse events. These registry entries describe the study’s question, design, and some safety reporting.

The record does not report the primary endpoint results. Without recurrence counts, percentages, a group comparison, or uncertainty estimates, it is not possible to describe whether recurrence was more or less frequent in either group or how precisely a difference was estimated. The study’s completed status should not be mistaken for evidence that the endpoint result was reported or that a prespecified feasibility objective was met.

Even if a comparative recurrence estimate were available, non-randomized allocation would require cautious interpretation. Differences could reflect factors other than the device, and the registry does not report baseline characteristics or adjustment methods. The event counts likewise do not establish a causal relationship to either device. They are descriptive entries in a study that is not identified as a like-for-like control comparison.

In general, statistical evidence is most informative when the endpoint definition, analysis population, missing-data handling, effect estimate, and uncertainty are all reported. Those details are absent or incomplete in the registry record. The listed enrollment and safety denominators cannot substitute for those missing elements. The defensible conclusion is therefore limited: the record specifies what the study intended to examine and some adverse-event counts, but it does not provide the primary result needed to characterize recurrence or make a comparative statistical interpretation.

14. Why This Trial Matters Statistically

This study illustrates a common challenge in clinical research: a registry can identify a focused outcome and a completed study without presenting the outcome analysis needed to assess the central question. The endpoint is clearly named as hernia recurrence at 12 months, with physical examination and/or CT scan as the assessment approach. Yet the recurrence counts and comparison estimate are not reported. Without them, readers cannot assess the observed effect or its precision.

The non-randomized design is also statistically consequential. Device groups in a non-randomized study may differ in clinical factors related to outcome. A comparison of their results, if reported, would need to be interpreted in light of possible confounding and the methods used to account for it. The registry record notes that the arms are not a like-for-like control comparison, making it particularly important not to treat any raw contrast as a causal device effect.

The record further shows why endpoint reporting and analysis transparency matter. The primary outcome definition does not reveal the number assessed, the handling of unavailable follow-up, or the analysis population. The registry lists 10 outcome measures and 0 analyses, leaving multiplicity and analysis choices unclear. This is not evidence about the quality or conduct of analyses outside the registry; it is a limit on what the registry record allows readers to evaluate.

The statistical lesson is that a study’s design, outcome definition, and completion status are not substitutes for reported results. Interpretation depends on transparent outcome data and methods, especially when allocation is not randomized.

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 is that the registry record does not report the primary outcome results. There are no recurrence counts or percentages at 12 months, no comparison estimate, and no uncertainty interval. As a result, the primary question cannot be answered from the posted record.

The non-randomized allocation limits causal interpretation. The registry does not describe how participants were allocated, provide baseline characteristics, or report adjustment for prognostic differences. Its note that the arms are not a like-for-like control comparison reinforces that an unadjusted contrast should not be treated as a device effect.

Important details of endpoint ascertainment are not reported. Although recurrence is based on physical examination and/or CT scan, the record does not provide operational criteria, assessor procedures, or a rule for reconciling assessments. It also does not report follow-up completeness, missing-data handling, analysis populations, or exclusions. The listed adverse-event counts do not address these gaps in the primary endpoint.

The registry lists 10 outcome measures but 0 analyses. It does not report a statistical analysis plan, multiplicity approach, endpoint model, interim analyses, or original sample-size justification. The planning description is assumption-based and does not provide a reported primary endpoint result. Finally, the record does not report deaths. These limitations concern what can be established from the registry record and should not be taken as evidence about information that may exist outside it.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Feasibility Study of The Use of FLEX HD® Surgical Implant or STRATTICE® Reconstructive Tissue Matrix in The Closure of Abdominal Wall Defects With Component Separation in Clean or Contaminated Cases — NCT01597128.
• Registry record last updated 2017-03-16; status last verified 2016-10.
• Results first posted 2017-03-16.
• 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

NCT01597128 is a completed, non-randomized, parallel device study of FLEX HD and STRATTICE for abdominal wall defect closure with component separation. The registry lists enrollment as 35, no masking, and a study phase of not applicable. The study began in 2011-03, with primary completion in 2015-05.

The primary endpoint is hernia recurrence at 12 months, assessed by physical examination and/or CT scan. The registry record does not report recurrence results, a comparative estimate, or an analysis. It lists 10 outcome measures and 0 analyses. Serious adverse-event counts are reported for both groups, as are counts for other adverse events, but deaths are not reported. Non-randomized allocation and the absence of reported outcome analyses limit interpretation of comparative effects.