Study to Compare Negative Pressure Wound Therapy or Standard Dressings After Orthopedic Surgery: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Study to Compare Negative Pressure Wound Therapy or Standard Dressings After Orthopedic Surgery (NCT02064270), a randomized na study. The primary outcome is Incision Appearance Based on VAS (Incision Healing Assessment Form).

2. Clinical Question

The clinical question is about a measured appearance score at a specified follow-up, not a direct measure of every aspect of recovery or of long-term healing. The registry also lists secondary questions concerning drainage, patient user-friendliness, complications, return to the operating room, and antibiotics. These outcomes can add context, but they do not change what the primary endpoint measures.

The comparison is randomized and parallel, and the registry records no masking. Random assignment is intended to make treatment groups comparable on average, while lack of masking can matter for outcomes involving judgment or participant experience. The registry record does not report details of the assignment process or who assessed incision appearance. The posted results therefore address the registered comparison, while leaving some practical details about assessment and participant selection unavailable.

3. Trial Design

This completed study is recorded as a prospective, randomized, controlled, parallel-group comparison of single-use NPWT with standard postsurgical dressings after total knee or hip arthroplasty. The registry lists allocation as randomized and masking as none. The study phase is listed as NA. The sponsor is University of Missouri-Columbia.

The registry records an enrollment of 526. For the primary outcome, the posted arm results include 201 participants in the NPWT group and 231 in the standard-dressings group. The registry record does not explain the difference between registered enrollment and the arm sizes shown for this outcome, so those figures should not be treated as a participant-flow account. Reasons for non-inclusion in the posted outcome, if any, are not reported in the registry record.

The study start is recorded as 2014-03, and primary completion as 2017-09-07. Its status is COMPLETED. The registered primary endpoint is incision appearance based on the Visual Analog Pain Scale (VAS) Incision Healing Assessment Form, reported as a mean with a standard deviation. Despite the VAS name, the description says the score represents incision healing based on visual appearance, not pain intensity.

The primary assessment timeframe is 35 days (+/- 14 days). It could be based on an in-person visual assessment or on a standard digital photograph, according to the endpoint description. The record does not say how many assessments used each approach or whether assessors were unaware of treatment assignment. Those details matter when interpreting a visual endpoint, especially in a study with no masking.

The registry lists secondary outcomes for drainage amount, user-friendliness for the patient, participants with complications, return to the operating room, and need for antibiotics. The posted outcome summary includes a complications result. The other listed outcomes do not have result details in the record, so their patterns cannot be described. A sample-size rationale for the original study, a full statistical analysis plan, and additional details about sites and eligibility are not reported in the registry record.

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 Incision Appearance Based on VAS (Incision Healing Assessment Form), measured over 35 days (+/- 14 days).

The primary endpoint is a mean score for incision appearance on the Incision Healing Assessment Form. The registry describes a 0-100 scale: 0 represents poor incision healing and 100 represents excellent incision healing. The score is based on visual appearance, assessed in person or from a standard digital photograph, at 35 days (+/- 14 days). The result is summarized as a mean and standard deviation for each treatment arm.

This endpoint offers a standardized way to summarize an appearance assessment and compare average scores between groups. A mean captures the central tendency of the scores, while the standard deviation describes how spread out individual scores are around that mean. The endpoint description does not establish that the score captures all dimensions of wound healing, complications, or patient experience. It is one defined measure at a particular follow-up period.

Although the endpoint name includes Visual Analog Pain Scale, the registry’s description explicitly frames the total score as an assessment of incision healing based on appearance. Readers should interpret it according to that description rather than assume it is a pain score. A visual measure can be influenced by how it is assessed and by the assessor’s judgment. The record does not report assessor training, reliability testing, or masking of assessors, so those aspects cannot be evaluated from the posted information.

The primary comparison is a difference in mean scores, expressed in units on the scale. The posted means are 83.4 for NPWT and 83.5 for standard dressings. The accompanying uncertainty interval and test result are and displayed in the statistical tables.

7. Results Posted in the Registry

• Negative Pressure Wound Therapy: mean 83.40 versus 83.50 on control; difference -0.10 (95% CI -2.52 to 2.32), standardized effect d = -0.01; z-test p = 0.935.

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.

Number of Participants With Complications

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Negative Pressure Wound Therapy: 13.4% (27/201) versus 17.7% (41/231) on control; risk difference -4.3 percentage points (95% CI -11.1 to 2.5), risk ratio 0.76 (0.48–1.18); unadjusted two-proportion z-test p = 0.219.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Negative Pressure Wound Therapy and the control. The interval gives the range of effects that remain compatible with the data.

The registry lists secondary outcomes covering drainage amount, patient user-friendliness, complications, return to the operating room, and need for antibiotics. The posted result information includes a comparison for participants with complications. The registry record does not report result details for the other listed outcomes, so it is not possible to describe a consistent pattern across all of them.

The available complications comparison can add context to the primary incision-appearance score, because complications are a distinct outcome from visual appearance. A complication count does not measure the same construct as an average appearance score, and one result should not be treated as a substitute for the other. The complications comparison is directionally consistent with fewer participants recorded with complications in the NPWT group, but its uncertainty includes values on both sides of no difference. The table gives the endpoint-specific estimate and interval.

Secondary findings generally carry less weight than a primary result when they are not the main question or when many outcomes are examined. Each additional comparison creates more opportunities for an apparently notable result to occur by chance. This is the general statistical concern called multiplicity. The registry record does not report a multiplicity adjustment or a prespecified hierarchy among secondary outcomes, so the secondary results should be regarded as exploratory rather than as independent confirmation of the primary endpoint.

The posted secondary information is also incomplete for evaluating the wider outcome pattern. The record lists five secondary outcome topics, while the posted outcome summary includes a complications measure; results for the remaining listed topics are not reported in the registry record. There are no posted analysis entries in the record. Consequently, readers cannot determine whether unposted outcomes were measured, how they were analyzed, or whether their results agreed with the available comparison.

Overall, secondary outcomes may broaden the questions a trial addresses, but they do not resolve the uncertainty around the primary score. They should be interpreted alongside their own estimates and intervals, with attention to the number of comparisons and the completeness of reporting.

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

• Drainage Amount
• User-friendliness for Patient
• Number of Participants With Complications
• Return to the Operating Room
• Need for Antibiotics

9. Statistical Interpretation

10. Statistical Methods Explained

What is being compared?

The primary analysis compares the average incision-appearance score between the randomized NPWT and standard-dressings groups. The endpoint is continuous: each participant’s assessment is represented by a score on a 0-100 scale, and the group result is summarized with a mean and standard deviation. A mean difference expresses how far apart the two group averages are, in the same units as the scale.

The posted mean difference is defined for NPWT relative to standard dressings. A negative estimate therefore indicates a lower observed average score in the NPWT arm; a positive estimate would indicate a higher observed average score in that arm. This direction describes the estimate, not a judgment about clinical importance. The observed means are close, and the interval around their difference is shown with the comparison in the tables.

What do the mean and standard deviation describe?

In general, a mean summarizes the center of a set of measurements. A standard deviation summarizes how dispersed those measurements are around the mean. These quantities answer different questions: the mean describes the average score, whereas the standard deviation describes variability among participant scores. The posted primary results give means of 83.4 and 83.5, with standard deviations of 13.3 and 12.2, respectively.

A standard deviation is not the same as a standard error or a confidence interval. The standard deviation describes variation among observed scores. The standard error concerns uncertainty in an estimated quantity, such as a group mean or a difference in means. A confidence interval uses that uncertainty to show a range of values compatible with the observed estimate and the analysis assumptions.

How should the confidence interval and p-value be read?

General explanation: a confidence interval is a procedure for expressing estimation uncertainty. Under repeated sampling and the assumptions of the method, intervals constructed in this way would cover the underlying quantity at the stated confidence level at the stated rate. The registry summary gives the interval limits but does not name the confidence level or report the full calculation method. The interval for the primary mean difference is -2.52 to 2.32.

A p-value describes the compatibility of the observed data with a specified null model, conditional on the test’s assumptions. The posted unadjusted p-value is 0.935. It does not express the probability that the null model is true, nor does it tell readers whether a difference would be important. The word “unadjusted” indicates that this result is not presented as adjusted for multiple comparisons. The registry record does not report a complete analysis plan, including any other adjustments or model details.

Why does randomization matter?

General explanation: random assignment is used to reduce systematic differences between treatment groups at the point of assignment. It can support a causal comparison when the assignment process is implemented as intended and the analysis appropriately accounts for the trial design. Randomization does not guarantee that every feature is balanced in a particular trial, and it does not remove concerns about missing outcomes, measurement, or departures from assigned treatment.

This study is listed as randomized, parallel, and unmasked. The registry record does not describe sequence generation, allocation concealment, adherence, crossover, or the analysis population. It is therefore possible to describe the registered design, but not to verify these implementation details from the posted information.

What can be inferred about the analysis method?

The primary outcome is reported as a mean and standard deviation, and the comparison is presented as a mean difference with a confidence interval and an unadjusted p-value. The registry record does not report the named statistical test, whether the comparison was adjusted for other variables, or how distributional assumptions were checked. It would be inappropriate to infer a particular model from the summary statistics alone.

The sample-size illustration is a separate calculation based on the observed effect and stated planning assumptions. It uses a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. It shows participants per arm for the specified effect fractions. These planning calculations do not describe the original trial’s design rationale; that rationale is not reported in the registry record.

For a continuous endpoint, the assumptions behind a normal approximation relate to how the estimate behaves across repeated samples. General explanation: if data are strongly skewed or contain influential outliers, a mean-based analysis may require careful checking or a method suited to the distribution. The registry summary does not provide score distributions, diagnostic checks, or alternative analyses, so those features cannot be assessed.

Finally, the presence of a p-value does not establish that every methodological choice was prespecified. The registry record reports no posted analysis entries. It does not provide enough information to determine whether the endpoint analysis was prespecified in a detailed statistical analysis plan, how multiple outcomes were handled, or whether interim analyses took place. Those points remain unreported in the registry record.

11. Confidence Intervals and Precision

The primary mean-difference estimate is -0.1 units on the incision-appearance scale. Its confidence interval extends from -2.52 to 2.32. The interval includes zero and also includes values in both directions. This means the posted estimate is uncertain: the observed data do not pin down the direction of the underlying difference with precision.

Precision concerns how narrowly the data locate an effect estimate. A narrow interval would indicate greater precision, while a wider interval would leave more possible values compatible with the data and analysis. Here, the interval spans effects on both sides of zero. The p-value of 0.935 is consistent with the absence of a clear statistical distinction in this comparison, but it is not a substitute for looking at the interval or judging what differences might matter.

The interval should not be read as a range that contains every plausible effect, nor as a probability statement about this specific treatment difference. General explanation: a confidence interval has its usual repeated-sampling interpretation when the method’s assumptions hold. The registry record does not name the confidence level or report the full interval calculation, which limits how completely the precision calculation can be checked.

Statistical precision and clinical importance are separate. The record does not provide a threshold for a meaningful change in the appearance score. Without such a threshold, the interval cannot be classified as excluding all clinically important differences. It also cannot establish equivalence. The safest reading is that the posted average scores are close, while the interval leaves uncertainty about the size and direction of the underlying mean difference.

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 a record of the trial’s original sample-size justification. The calculations use a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. For these continuous-outcome planning rows, the figures are participants per arm, not total participants or total events.

The table shows planning for 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The 80% power column gives the modeled number of participants per arm for an 80% chance of detecting the stated effect under the planning assumptions, if that effect were the true one. The 90% power column gives the modeled number per arm for a 90% chance under those same assumptions. Power is a long-run property of a planned study under a specified effect and analysis; it is not a probability that this particular result is correct.

Smaller effects are harder to distinguish from random variation, so the illustration requires more participants per arm as the target effect becomes smaller. The very large figures in the table reflect planning around fractions of the observed mean difference, which is close to zero. They should not be interpreted as a recommendation or as evidence that the original study was designed with these assumptions. This is not observed power.

The registry record does not report the original sample-size assumptions, target effect, or calculation method. The posted enrollment is 526, while the primary outcome table shows arm sizes of 201 and 231. The planning illustration is distinct from both those observed outcome counts and the study’s recorded enrollment. It helps readers see how sample size depends on the effect one aims to detect, but it does not explain the trial’s recruitment or outcome reporting.

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, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -0.100; pooled standard deviation σ = 12.723.
2. n = 2 × (1.96 + 0.842)² × 12.723² / -0.100² = 254,125.6, rounded up to 254,126 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
delta <- -0.0999999999999943                      # observed difference in means
sigma <- 12.7234630359783                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^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 (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2064270)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 254,126 (80% power), 340,203 (90% power)
 75% of observed effect: n per arm = 451,779 (80% power), 604,804 (90% power)
 50% of observed effect: n per arm = 1,016,503 (80% power), 1,360,809 (90% power)
power.t.test: 254126.5 
Simulated power at n = 254,126 per arm: 0.799 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-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 identifies a primary outcome and several secondary outcome topics. Examining more than one outcome raises a general statistical issue: with repeated tests, the chance of at least one result appearing unusually strong by chance can increase. Common responses include prespecifying an outcome hierarchy, adjusting the threshold for multiple comparisons, or clearly labeling secondary analyses as exploratory. The registry record does not report a multiplicity strategy, a hierarchy among secondary outcomes, or adjusted secondary results.

The primary p-value is described as unadjusted. The record does not say whether any adjustment was planned for the set of outcomes, whether interim looks at accumulating data occurred, or whether the primary analysis was specified before results were examined. These details are not reported in the registry record, so the posted results cannot establish how multiplicity was addressed in the study’s full analysis.

Missing-data handling is also not reported in the registry record. The primary outcome has posted arm sizes of 201 and 231, while registered enrollment is 526. These figures alone do not show why the participant counts differ, whether outcomes were unavailable, or how any such cases were handled. The record does not provide a participant flow, reasons for missingness, an imputation method, or sensitivity analyses for missing outcomes. It would therefore be inappropriate to assume that all randomized participants were included or that missingness had no effect.

The analysis population is not reported in the registry record. The posted summary does not identify whether the analysis followed an intention-to-treat approach, a per-protocol approach, or another definition. Nor does it explain how participants who did not receive their assigned dressing, if any, were treated in the analysis. These omissions matter because different population definitions can produce different estimates.

In general, complete reporting of prespecified outcomes, participant flow, analysis populations, missing-data methods, and multiplicity handling helps readers distinguish planned analyses from exploratory ones. Those details are not available in the registry record. The posted estimates can still be described, but their relation to a complete prespecified analysis plan cannot be verified.

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.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: deep infection requiring additional surgery (2.6%).

The registry reports serious adverse events for both arms: 5 among 201 participants in the NPWT group and 6 among 231 participants in the standard-dressings group. It reports other adverse events for 3 participants in the NPWT group and 5 in the standard-dressings group. Deaths are recorded as 0 in each arm.

These figures should be read as counts with their corresponding group sizes, not as a complete account of the nature, timing, duration, or severity of every event. The registry lists “Deep Infection Requiring Additional Surgery” as the top serious adverse event term, at 2.6%. The record does not establish which arm that term refers to or give further event-level detail.

Comparisons of adverse-event counts can be imprecise, especially when events are uncommon. The figures do not by themselves establish a difference in safety between the interventions, and they should not be interpreted as proof that events outside the listed categories did not occur. The registry information does not report a detailed safety analysis or an attribution of events to treatment.

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

The primary result is an estimate of the difference in mean incision-appearance scores at the registered follow-up. The posted means are close, and the estimated difference is -0.1 units. Its confidence interval, from -2.52 to 2.32, includes zero and values in both directions. The result therefore does not provide a precise estimate of the direction or size of the underlying mean difference.

This does not demonstrate that the interventions are equivalent. A conclusion of equivalence requires an explicit margin defining differences small enough to count as equivalent, and an analysis designed for that purpose. Neither is reported in the registry record. Conversely, the result does not establish that one dressing produces a meaningfully better appearance score. The posted evidence is best described through its estimate and uncertainty, not a binary claim that there is or is not an effect.

The endpoint is a visual assessment at 35 days (+/- 14 days). It is not a complete measure of wound healing over time, patient experience, or all possible complications. The registry lists additional secondary outcomes, but results for several of them are not reported in the registry record. The available secondary complications comparison is a separate outcome and should not be collapsed into the primary appearance score.

The design is randomized, which supports a group comparison, but the registry records no masking. Since the primary endpoint is based on visual appearance, assessment procedures and assessor awareness could matter. The record does not report whether assessors were masked, how measurements were standardized in practice, or how missing outcomes were handled. Those unknowns are relevant to confidence in the estimate.

The result also does not settle whether a difference of any particular size matters to patients. The registry record does not report a minimally important difference for the scale. Statistical uncertainty and clinical importance must be considered separately: a confidence interval describes uncertainty in an effect estimate, while a meaningfulness threshold requires clinical context. The posted summary supplies the former but not the latter.

17. Why This Trial Matters Statistically

This trial is statistically useful as an example of why a point estimate should not be read in isolation. The observed mean scores are close, but the confidence interval conveys the range of uncertainty around their difference. Looking at both the estimate and interval avoids turning a nonsignificant p-value into a claim of no effect, or treating a small observed difference as proof of an important one.

The trial also illustrates the distinction between an endpoint’s name and its operational definition. The primary outcome includes the phrase Visual Analog Pain Scale, but its registry description says it assesses incision healing based on visual appearance. Accurate interpretation depends on the measure’s stated meaning, scale, timing, and assessment method, rather than on a label alone.

Randomized allocation is an important design feature, but it does not answer every question about measurement and analysis. The endpoint involves visual judgment, masking is recorded as none, and the registry does not report assessor masking or the full statistical analysis plan. These details show why design labels need to be considered alongside how outcomes were collected and how uncertainty was calculated.

The posted secondary complications result and safety counts provide additional context, while the unreported results for other listed outcomes limit broader conclusions. This is a reminder that a trial’s evidential picture depends not only on the primary comparison but also on complete reporting, multiplicity handling, and transparent participant accounting.

Finally, the sample-size illustration makes clear that planning depends on the effect one wants to detect. When the observed effect is close to zero, planning around smaller fractions of it requires very large participant counts under the stated assumptions. Those calculations are illustrations, not a reconstruction of the original design. The original sample-size rationale is not reported in the registry record.

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.

Several trial-specific limitations in the registry information affect interpretation. First, the primary endpoint is based on visual appearance, but the record does not report whether assessors were masked to treatment assignment, how assessors were trained, or whether the in-person and photograph-based assessments were handled consistently. Masking is recorded as none for the study, and the endpoint description permits either assessment approach. The balance between those approaches is not reported.

Second, the outcome follow-up is centered on 35 days (+/- 14 days). This provides a defined assessment window, but the posted primary result does not describe later incision appearance. The registry record does not provide additional primary follow-up results in the information, so the result should not be extended to other time periods.

Third, the enrollment is recorded as 526, while the primary outcome reports 201 participants in the NPWT arm and 231 in the standard-dressings arm. The record does not explain this accounting or provide a participant flow. It does not report the analysis population, missing-data methods, or reasons for any absent outcome data. This prevents a full assessment of how the posted outcome sample relates to enrollment.

Fourth, the registry does not report the original sample-size justification, full statistical analysis plan, multiplicity strategy, or details of any interim analyses. It also does not give the clinical threshold for a meaningful difference in the appearance score. These gaps limit interpretation of the planned status of analyses and the practical importance of the confidence interval.

Finally, the record does not report detailed participant characteristics, eligibility criteria, or site information beyond the sponsor. These omissions limit assessment of how the enrolled participants and care setting compare with other clinical contexts. They do not invalidate the posted comparison, but they narrow what can be concluded from this registry summary.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Study to Compare Negative Pressure Wound Therapy or Standard Dressings After Orthopedic Surgery — NCT02064270.
• Registry record last updated 2018-04-17; status last verified 2018-04.
• Results first posted 2018-04-17.
• 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 completed randomized, parallel-group study compared single-use incisional NPWT with standard postsurgical dressings after total knee or hip arthroplasty. The registry records no masking and an enrollment of 526. The primary endpoint was mean incision appearance on a 0-100 scale at 35 days (+/- 14 days).

The posted primary means were 83.4 for NPWT and 83.5 for standard dressings. The estimated mean difference was -0.1, with a confidence interval from -2.52 to 2.32 and an unadjusted p-value of 0.935. The interval includes zero and effects in either direction, so the result remains uncertain about the underlying difference.

The registry also lists secondary outcomes and adverse-event counts. Result details for several listed secondary outcomes, the full statistical plan, missing-data handling, and the original sample-size rationale are not reported in the registry record. The available data support a careful description of the posted comparisons, but not claims of equivalence or a clinically meaningful difference.