Incisional Negative Pressure Wound Therapy in High Risk Patients Undergoing Panniculectomy: A Prospective Randomized Controlled Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Incisional Negative Pressure Wound Therapy in High Risk Patients Undergoing Panniculectomy: A Prospective Randomized Controlled Trial (NCT03010137), a randomized na study. The primary outcome is Major Wound Healing Complications.

2. Clinical Question

The trial title describes a prospective randomized controlled trial. Its primary endpoint focuses on complications serious enough to meet the stated definition, rather than every possible change in wound appearance or healing. The comparison is between the assigned closure strategies; it does not establish how either approach performs in other surgical populations or settings.

The record lists 30 participants and records 15 participants in each arm. The posted primary outcome counts are 5 participants with a complication in the Standard Closure arm and 3 in the Incisional Negative Pressure Wound Therapy arm. These counts describe the observed groups. They do not, on their own, establish that the difference reflects a treatment effect rather than random variation, and the confidence interval is important for judging how uncertain the comparison remains.

3. Trial Design

The registry describes this as a randomized, parallel-group trial, with no masking. Its title identifies it as prospective. The listed enrollment is 30, and the outcome records show 15 participants in each arm. The registry status is terminated. The reason for termination is not reported in the registry record, so the status alone does not explain why the trial ended or whether that decision was related to the observed outcomes.

One group received incisional negative pressure wound therapy after closure, and the comparator group received standard closure with skin adhesive. The intervention description says the negative pressure device was applied over the entire incision in the operating room after surgical closure. The standard-closure description identifies Dermabond or topical skin adhesive as usual incision treatment. Details beyond these descriptions, including the complete device-use instructions, are not reported in the registry record.

The primary endpoint was major wound-healing complications, assessed up to 3 months after operation. The registry defines the event as abscess, hematoma or any wound complication requiring return to the operating room. Time to drain removal was listed as a secondary outcome, also with a timeframe of up to 3 months after operation.

The record does not report the randomization sequence method, allocation concealment, recruitment procedures, detailed eligibility criteria or the reason for termination. It also does not report the original sample-size justification, the trial's planned statistical methods or whether any interim analyses were planned or conducted. The trial phase is listed as not applicable. These unreported design details should not be inferred from the randomized, parallel-group label or from the results tables.

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 Major Wound Healing Complications, measured over Up to 3 months after operation.

The primary endpoint counts participants with a major wound-healing complication, rather than counting separate episodes. An event is defined as abscess, hematoma or any wound complication requiring return to the operating room. The assessment timeframe is up to 3 months after operation. The posted outcome is therefore a binary participant-level measure: each participant either met the endpoint definition or did not, as recorded in the results.

This type of endpoint can summarize clinically consequential complications in a way that is straightforward to interpret across the two groups. It also focuses on events meeting a specified threshold, rather than capturing all wound changes or the full course of healing. The registry record does not provide separate results for abscess, hematoma and other complications requiring return to the operating room, so it is not possible to identify which component contributed to the total count.

In the posted results, 5 of 15 participants in the Standard Closure arm and 3 of 15 in the Incisional Negative Pressure Wound Therapy arm had a recorded major wound-healing complication. The comparison and its confidence interval are displayed in the results tables. Because the endpoint is a count of participants and the groups are small, the observed counts should be read together with the uncertainty around the estimated difference. The endpoint definition itself does not establish that any particular closure strategy caused or prevented an event.

7. Results Posted in the Registry

• Incisional Negative Pressure Wound Therapy: 20.0% (3/15) versus 33.3% (5/15) on control; risk difference -13.3 percentage points (95% CI -44.6 to 18.0), risk ratio 0.60 (0.17–2.07); unadjusted two-proportion z-test p = 0.409.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Time to Drain Removal

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Incisional Negative Pressure Wound Therapy: mean 24.00 versus 29.00 on control; difference -5.00 (95% CI -14.88 to 4.88), standardized effect d = -0.36; z-test p = 0.321.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Incisional Negative Pressure Wound Therapy and the control. The interval gives the range of effects that remain compatible with the data.

Time to drain removal is the one secondary endpoint posted in the results. It is a continuous measure reported as a mean in days, with a standard deviation in each arm. The table gives the endpoint-specific values and comparison; they are not repeated. There are no additional posted secondary endpoint results from which to describe a broader pattern across multiple outcomes.

This endpoint concerns a different aspect of postoperative care from the primary outcome. The primary endpoint counts participants with specified major wound-healing complications, whereas time to drain removal describes a duration. The secondary result can therefore add context, but it does not replace or resolve the primary comparison. A pattern in drain-removal timing would not, by itself, establish a pattern in major wound complications.

The secondary comparison is unadjusted, and the registry lists no reported analyses. It does not state whether this endpoint was prespecified as a key secondary outcome or how its analysis related to the primary analysis. When multiple outcomes or comparisons are considered, the chance of observing apparently notable findings can increase. This is the general reason unadjusted secondary results are usually interpreted more cautiously than a clearly prespecified primary result. The record does not report a multiplicity strategy, so it is not possible to determine whether any adjustment was planned or applied.

The registry lists six outcome measures but posts one secondary endpoint. That difference in what is listed and what is posted does not establish why other outcomes are absent, whether they were collected, or what their results were. Those details are not reported in the registry record. Accordingly, the secondary result should be treated as limited additional information, not as an independent confirmation of the primary finding.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Time to Drain Removal

9. Statistical Interpretation

10. Statistical Methods Explained

The results compare a binary primary endpoint between two randomized parallel groups. The registry defines the endpoint as the number of participants with a major wound-healing complication, and reports the event counts and group sizes. A risk difference expresses the difference between the proportion with an event in one group and the proportion in the comparison group. Here, the stated comparison is Incisional Negative Pressure Wound Therapy minus Standard Closure; a negative estimate therefore points toward a lower observed event proportion in the intervention group. This is a general explanation of the measure, not a claim about why the observed difference occurred.

What does the confidence interval communicate?

A confidence interval describes the uncertainty around an estimated effect under the method used to construct it. In repeated use of a suitable procedure, intervals constructed in that way would cover the underlying effect at the stated confidence level at the corresponding long-run rate. It is not a range that guarantees the true effect lies inside it, nor is it a probability statement about this one interval after it has been calculated. For the posted risk difference, the interval runs from -0.446 to 0.179. Because it includes zero and extends in both directions, the data are compatible with no difference as well as with differences favoring either arm.

How should the p-value be read?

The posted p-value is unadjusted. In general, a p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that null hypothesis and the test assumptions were true. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. The registry does not report enough information to identify the exact test procedure or to assess all of its assumptions. The displayed p-value should therefore be interpreted as the value posted for this comparison, not as a substitute for the effect estimate and its interval.

Why does the event count matter?

With a binary endpoint, the information in the comparison depends in part on how many participants experience the event, as well as the group sizes. When the numbers of events and participants are limited, estimates can be unstable: changing the outcome status of a small number of participants may alter the estimated difference. This is a general feature of sparse binary data. The posted result has 15 participants in each group and 5 and 3 events, so the interval provides essential context for the point estimate. No additional model details or adjusted estimates are reported in the registry record.

What can be said about randomization and masking?

The record labels the allocation randomized and the model parallel, and lists masking as none. Randomization is intended, in general, to help make groups comparable with respect to factors that could influence outcomes. It does not ensure that every factor is balanced in a small trial, and the record does not describe the randomization sequence or allocation concealment. With no masking, participants and study personnel were not recorded as masked, but the record does not specify which people assessed or adjudicated the endpoint. Details of outcome adjudication are not reported in the registry record.

What analysis details are unavailable?

The registry record does not report a full statistical analysis plan, the trial's original sample-size justification, an analysis population definition, handling of missing outcome data, or planned interim analyses. It reports no analyses in the analysis listing. The posted comparison is unadjusted, and no adjustment for covariates is described. It is not possible from the record to determine whether the displayed comparison corresponds to a prespecified primary analysis or whether any other planned analyses were omitted.

The endpoint is described as a count of participants with an event, not as a rate per unit of follow-up. The posted result therefore does not account for differing follow-up duration through a time-to-event method. The registry states a timeframe of up to 3 months after operation; it does not provide individual follow-up durations, censoring information or time-to-event analyses for the primary endpoint.

These methodological explanations are general context for reading the posted statistics. They do not fill gaps in the trial record. The appropriate interpretation rests on the event counts, the estimated difference and its uncertainty, while recognizing that additional analytic and conduct details are not reported.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.133, with a 95% confidence interval from -0.446 to 0.179. This interval is wide and spans zero. In practical terms, the posted data do not pin down the direction or size of the underlying difference with precision: they are compatible with fewer events in the intervention group, little or no difference, or more events in that group. The interval should be read as uncertainty around the estimated comparison, not as a range of outcomes that were observed among participants.

The group sizes are 15 participants per arm, with 5 recorded events in Standard Closure and 3 in Incisional Negative Pressure Wound Therapy. For a binary endpoint, relatively few events can limit how precisely a difference in event proportions is estimated. The point estimate is therefore not enough to characterize the evidence; its interval shows that estimates of meaningful differences in either direction remain compatible with the data.

The posted unadjusted p-value is 0.409. It does not resolve the uncertainty expressed by the interval. In general, a p-value and a confidence interval summarize related but different aspects of a comparison: the p-value addresses compatibility with a specified null hypothesis, while the interval conveys a range of effect estimates compatible with the data and method. The registry record does not report details of the test procedure or a prespecified precision target.

These results should not be read as demonstrating equivalence. A conclusion of equivalence would require an appropriate design and a defined margin, neither of which is reported in the registry record. The present interval is an imprecise estimate rather than evidence that the two approaches have the same effect.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size table and curve are planning illustrations based on the observed effect, not the trial's original design calculation. The listed assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The table shows planning for 100%, 75% and 50% of the observed effect. For the binary primary outcome and the continuous secondary outcome, the figures are participants per arm. The note about total events applies to time-to-event tables; neither posted endpoint is presented as a time-to-event sample-size table.

The 80% power column describes the planned number of participants per arm under the stated assumptions to give an 80% chance of detecting the selected effect if that effect were the true one. The 90% power column uses a higher target chance of detecting that effect, and therefore lists a larger planned number of participants per arm. These are planning concepts, not guarantees that a future study will detect an effect. The table’s rows show that planning for a smaller fraction of the observed effect requires more participants. This is not observed power.

For the primary comparison, the listed figures increase from 172 participants per arm when planning for 100% of the observed effect to 318 for 75% and 741 for 50% at the 80% power target. At the 90% target, the corresponding figures are 230, 425 and 991 participants per arm. These illustrations depend on using the observed estimate as their starting point. Since that estimate is uncertain, the table should not be treated as a precise prediction of what another study would need.

For the secondary endpoint, the table likewise reports participants per arm. The curve is a visual aid for the planning relationship represented by the table; it is not a record of participants enrolled or an outcome of the trial. The trial's own sample-size assumptions and justification are not reported in the registry record.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.333; treatment proportion p₁ = 0.200; average p̄ = 0.267.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6254 = 1.2257.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6182 = 0.5203.
4. n = (1.2257 + 0.5203)² / (-0.1333)² = 171.5, rounded up to 172 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.333333333333333                          # control proportion
p1 <- 0.2                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(3010137)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 172 (80% power), 230 (90% power)
 75% of observed effect: n per arm = 318 (80% power), 425 (90% power)
 50% of observed effect: n per arm = 741 (80% power), 991 (90% power)
power.prop.test: 171.5 
Simulated power at n = 172 per arm: 0.809 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists six outcome measures, while one secondary endpoint is posted in the results. The primary endpoint is major wound-healing complications, and the posted secondary endpoint is time to drain removal. The record does not explain the status of the other listed outcome measures or whether they were assessed, collected or omitted from the results. Their absence from the posted results should not be interpreted as evidence that no such outcomes occurred or that they were not measured.

Multiplicity arises when several outcomes, time points, subgroups or analyses are examined. In general, considering many comparisons can make apparently unusual results more likely, even when there is no underlying effect. Researchers may address this through prespecified outcome hierarchies, adjustment procedures or careful interpretation. The registry record does not report whether any multiplicity strategy was planned or used. It also does not report a complete analysis plan that would show which comparisons were prespecified.

The record reports no analyses in its analysis listing. This does not provide enough information to establish whether the posted comparisons were the only analyses conducted or whether additional analyses were planned. The posted p-values are unadjusted, and no adjustment method is described. The secondary result should therefore be treated as exploratory in interpretation unless further documentation clarifies its status; the registry record does not identify it as exploratory or confirmatory.

Missing-data procedures and analysis populations are also not reported in the registry record. It is not stated whether all randomized participants were included in each outcome analysis, how missing observations were handled, or whether any participants were excluded after randomization. The arm records show 15 participants in each group, but this alone does not establish the analysis population for every endpoint. The record does not report individual-level follow-up completeness or reasons for missing data.

These gaps limit assessment of whether the posted comparisons fully reflect the planned analyses and whether outcome reporting is complete. They do not justify assuming that data were missing or that selective reporting occurred. They mean that readers cannot verify those aspects from the registry record.

15. 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.

The posted adverse-event summary lists 15 participants at risk for serious adverse events in each arm and records 0 affected participants in each. It also lists 15 participants at risk for other adverse events in each arm and records 0 affected participants in each. Deaths are recorded as 0 in both arms. No serious adverse-event terms are listed.

These figures describe what is recorded in the registry summary. They do not establish that no adverse events of any kind occurred outside the categories or definitions used for this summary. The record does not provide further detail about adverse-event definitions, collection procedures, severity grading or follow-up completeness. It also does not identify whether the zero counts reflect complete ascertainment for every participant.

Safety results should be read alongside the small number of participants and the stated follow-up timeframe. Zero recorded events in these groups is not proof that an event cannot occur, nor is it a comparison precise enough to characterize uncommon risks. The posted figures are descriptive and do not warrant a broader safety conclusion beyond the registry record.

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

The posted primary result is a comparison of major wound-healing complications up to 3 months after operation. The event count was lower in the Incisional Negative Pressure Wound Therapy arm than in the Standard Closure arm, and the estimated risk difference was negative. The confidence interval is broad and includes zero, while the posted unadjusted p-value does not provide strong evidence against a no-difference null hypothesis. Taken together, the result is an uncertain estimate rather than a definitive demonstration of a difference.

The result does not establish that the two approaches are equivalent. It also does not demonstrate that one approach is superior, because the uncertainty is substantial and the record does not report an equivalence or noninferiority design. A numerical direction in a small randomized comparison is not enough to establish a causal effect with precision, even though randomization is intended to support fair comparisons.

The endpoint is limited to the registry's combined definition of abscess, hematoma or a wound complication requiring return to the operating room. The posted data do not separate these components, and the timeframe is up to 3 months after operation. The result therefore does not address other wound outcomes, longer-term healing or outcomes outside that definition and timeframe.

The trial record identifies a high-risk population undergoing panniculectomy in preparation for renal transplant. The finding should not automatically be extended to other types of surgery, patient groups or care settings. The registry does not provide detailed eligibility criteria or the reason for trial termination, and several aspects of the statistical plan, missing-data handling and analysis populations are not reported.

The appropriate conclusion is narrow: the posted groups had the reported event counts, and the estimated comparison remains imprecise. The result does not establish a treatment effect, rule out potentially important differences, or provide a basis for medical decisions. It is one trial's posted evidence, with limitations that matter when considering how much can be inferred.

17. Why This Trial Matters Statistically

This trial illustrates a central challenge in biostatistics: a randomized design can support a comparative question, yet a small number of participants and events can leave the estimated effect uncertain. The primary table gives both the observed counts and an estimated difference, but the confidence interval shows why the point estimate alone is not an adequate summary. A result that points in one direction can remain compatible with materially different possibilities.

The trial also offers a useful example of how endpoint definition shapes interpretation. The primary measure combines several types of major wound complication into a participant-level count. That makes the endpoint direct to summarize, but the registry does not post component-specific outcomes. Readers therefore need to distinguish the overall endpoint from claims about any one type of complication.

Another statistical lesson is the separation between a study's observed result and planning illustrations. The sample-size table uses the observed effect to illustrate requirements under stated assumptions. It is not a record of the trial's original design justification, and its estimates depend on a potentially uncertain observed effect. Clear labeling prevents planning numbers from being mistaken for evidence that the trial was adequately powered or for a measure of what the trial actually achieved.

Finally, the record shows why registry completeness matters. It identifies the trial as randomized and lists outcomes, but does not report the original sample-size rationale, analysis populations, missing-data methods or multiplicity strategy. These omissions do not invalidate the posted data, but they constrain how fully readers can assess the analysis and reporting. The combination of numerical results and transparent recognition of uncertainty is essential for a careful statistical reading.

18. 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 total enrollment is 30, with 15 participants recorded in each arm. The small group sizes and limited event counts constrain precision, as reflected in the wide confidence interval for the primary comparison. The result cannot sharply distinguish between several possible underlying differences.

The registry status is terminated, but the reason is not reported in the registry record. The record does not state whether termination was related to recruitment, feasibility, administrative decisions or any other cause, so no explanation should be inferred. The original sample-size justification and design assumptions are also not reported, which prevents comparison of the actual enrollment with the trial's intended target.

The trial is listed as having no masking. The record does not describe who assessed the endpoint, whether events were adjudicated using independent review, or whether outcome assessors knew the assigned group. The randomization sequence and allocation concealment methods are not reported. These missing details limit evaluation of potential sources of bias, without establishing that bias occurred.

The primary endpoint combines abscess, hematoma and qualifying wound complications requiring return to the operating room. Component-specific results are not posted. Follow-up is stated as up to 3 months after operation, so the record does not provide evidence on longer-term outcomes. The registry also does not report missing-data procedures, analysis populations or the completeness of follow-up by arm.

The record lists six outcome measures but posts one secondary endpoint, and it does not explain the status of the other measures. No multiplicity strategy or full statistical analysis plan is reported. The secondary result is unadjusted, and there are no analyses listed in the registry. Finally, the stated population is specific to high-risk patients undergoing panniculectomy, described as preparation for renal transplant; the findings may not apply to other populations or procedures.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Incisional Negative Pressure Wound Therapy in High Risk Patients Undergoing Panniculectomy: A Prospective Randomized Controlled Trial — NCT03010137.
• Registry record last updated 2020-06-09; status last verified 2020-05.
• Results first posted 2020-06-09.
• 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.

22. Record Summary

This registry record describes a prospective randomized, parallel-group trial with no masking, comparing incisional negative pressure wound therapy with standard closure after panniculectomy in high-risk patients. Enrollment is listed as 30, and the primary outcome records 15 participants per arm. The registry status is terminated; the reason is not reported in the registry record.

The primary endpoint was major wound-healing complications up to 3 months after operation, defined as abscess, hematoma or any wound complication requiring return to the operating room. The posted counts were 5 participants in the Standard Closure arm and 3 in the Incisional Negative Pressure Wound Therapy arm. The estimated risk difference was -0.133, with a 95% confidence interval from -0.446 to 0.179 and an unadjusted p-value of 0.409.

Time to drain removal is the one secondary endpoint posted. The record does not report the original sample-size rationale, a full statistical analysis plan, multiplicity methods, missing-data procedures or analysis populations. The findings should therefore be read as an imprecise comparison from this trial, not as definitive evidence of a difference or equivalence.