This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Single-Use Negative Pressure Wound Therapy for Free Flap Donor Sites (NCT03340025), a randomized na study. The primary outcome is Progression of Wound Healing.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03340025 |
| Phase | NA |
| Condition | Surgical Wound |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 20 |
| Arms in the primary outcome | 2 |
| Lead sponsor | University of Alabama at Birmingham |
| Results posted | Yes |
2. Clinical Question
Population
The registry describes free flap donor sites requiring split thickness skin grafting and lists surgical wound as the condition. It does not report further eligibility details or a fuller description of the analyzed population. The registry enrollment is 20, while the primary outcome results list 9 participants for negative pressure wound therapy and 7 for conventional dressing; the record does not explain the difference in these counts.
Intervention
The intervention was the PICO Single Use Negative Pressure Wound Therapy System, described as a single-use negative pressure wound therapy device. The trial record identifies this as a device intervention. Details about how the device was applied, duration of use, or adherence are not reported in the registry record.
Comparator
The comparison group received conventional dressing, described as traditional surgical wound dressing of xeroform gauze and padding. The registry lists xeroform gauze as a device intervention. It does not report further details about dressing changes, adherence, or other wound-care procedures in the comparator group.
Primary question
The primary question was whether wound-healing progression, assessed through percentage of skin graft take, differed between the groups. Blinded, independent raters evaluated photographs, with percentage of graft take evaluated on Day 30. The registry reports a mean of 69.9 for negative pressure wound therapy and 75.6 for conventional dressing, with full ranges of 50.0 to 90.0 and 55.0 to 95.0, respectively. No inferential comparison is posted, so these descriptive results alone do not establish whether the groups differed beyond sampling variability.
3. Trial Design
This was a randomized, parallel-group trial with single masking. The registry lists the study as completed and gives the phase as not applicable. The sponsor was the University of Alabama at Birmingham. The study began on 2018-06-15, and primary completion was recorded on 2020-04-13.
Participants were assigned to negative pressure wound therapy using the PICO Single Use Negative Pressure Wound Therapy System or to conventional dressing with xeroform gauze and padding. The registry reports enrollment of 20. For the primary outcome, the posted arm results list 9 participants in the negative pressure group and 7 in the conventional dressing group. The record does not explain why the outcome counts differ from the enrollment figure. Safety results use different at-risk counts, also without an explanation in the registry record.
The trial focused on free flap donor sites requiring split thickness skin grafting. The registry describes photographs taken at post-operative Day 5, post-operative Day 14-21, and post-operative Day 30. Percentage of skin graft take was evaluated on Day 30 by blinded, independent raters. The record does not identify who was masked, describe the randomization procedure, or report allocation concealment details. It also does not report a protocol or a statistical analysis plan, so design details beyond the listed randomized, single-masked, parallel structure are not available.
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
| Stage | Negative Pressure Wound Therapy | Conventional Dressing |
|---|---|---|
| STARTED | 11 | 9 |
| COMPLETED | 9 | 7 |
| NOT COMPLETED | 2 | 2 |
Reasons for not completing this period:
| Reason | Negative Pressure Wound Therapy | Conventional Dressing |
|---|---|---|
| Lost to Follow-up | 2 | 2 |
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.
| Characteristic | Unit | Negative Pressure Wound Therapy | Conventional Dressing | Total |
|---|---|---|---|---|
| Participants analysed | 11 | 9 | 20 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 6 | 5 | 11 |
| Age, Categorical: >=65 years | Participants | 5 | 4 | 9 |
| Sex: Female, Male: Female | Participants | 4 | 1 | 5 |
| Sex: Female, Male: Male | Participants | 7 | 8 | 15 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 1 | 0 | 1 |
| Race (NIH/OMB): White | Participants | 10 | 9 | 19 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Region of Enrollment: United States | participants | 11 | 9 | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Progression of Wound Healing, measured over Baseline through 30 days.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | percentage of skin graft take |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint was progression of wound healing, expressed as percentage of skin graft take. This measure describes the estimated portion of the graft judged to have taken at the donor site. It is a wound-healing outcome that captures the visible status of the graft, rather than a time-to-event measure or a patient-reported measure.
Photographs were taken at post-operative Day 5, post-operative Day 14-21, and post-operative Day 30. The percentage of graft take was evaluated on Day 30. The registry says a 10x10 grid was digitally overlain on each image, and de-identified images were randomized before review by two independent raters. The raters also graded overall graft appearance on a 1-5 scale and noted whether exposed tendon was present at each timepoint. Those additional assessments help describe the photographic review, but the posted primary result is the mean percentage of skin graft take.
Using a defined photographic assessment can make wound appearance more systematic to evaluate. Independent, blinded rating is intended to reduce the influence of knowledge about treatment assignment, although the registry does not report how agreement between raters was handled or whether their evaluations were combined in a specified way. The reported result does not include a measure of variability beyond the full range.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry reports a mean percentage of skin graft take of 69.9 for negative pressure wound therapy, with a full range from 50.0 to 90.0. For conventional dressing, it reports a mean of 75.6, with a full range from 55.0 to 95.0. These are descriptive summaries of the participants included in the posted primary outcome results. The registry does not report a standard deviation or confidence interval for either group.
The reported ranges give the lowest and highest observed values recorded for each group, but they do not show how values were distributed between those endpoints. A range can be strongly influenced by extreme observations and does not indicate how precisely a group mean has been estimated. Because no standard deviation or other detailed distribution information is posted, the spread of individual outcomes cannot be characterized fully from the registry result.
The mean in the conventional dressing group is numerically higher than the mean in the negative pressure group. That descriptive ordering is not, by itself, evidence of a reliable treatment difference. The registry record does not report a treatment-effect estimate with a confidence interval, a p-value, or a specified inferential comparison for the primary outcome. The result therefore does not establish whether the observed group means reflect a genuine difference or sampling variability.
The primary outcome counts are 9 for negative pressure wound therapy and 7 for conventional dressing. The registry enrollment is 20, and the record does not explain the relationship between enrollment and the outcome counts. The reason for any difference in the analyzed counts, such as missing photographs, exclusions, or other data availability issues, is not reported in the registry record. Without that information, the potential effect of incomplete outcome data cannot be assessed.
The trial’s stated aim was to investigate whether the device could yield superior results to simpler methods. The posted primary outcome summaries do not answer that comparative question conclusively, because no uncertainty estimate or inferential result is reported. The posted data support a description of the observed means and ranges only; they do not support a definitive claim of superiority or equivalence.
9. Statistical Methods Explained
What does the reported mean represent?
A mean is the arithmetic average of the observations included in a group’s analysis. It provides a concise description of the group’s central outcome, but it does not show the full pattern of individual results. In this trial, the reported means are 69.9 for negative pressure wound therapy and 75.6 for conventional dressing, measured as percentage of skin graft take. These values summarize the participants included in the respective posted outcome results. The registry does not report further details about how the ratings from independent reviewers were combined to produce each participant’s value.
A mean can be affected by unusually high or low observations. It is most informative when considered alongside measures of spread and uncertainty. The registry labels the dispersion as full range, reporting 50.0 to 90.0 for negative pressure wound therapy and 55.0 to 95.0 for conventional dressing. Those bounds show the span of recorded values, but they do not indicate whether most observations were clustered near the mean or distributed widely across the range.
What can a range tell readers?
A full range reports the lowest and highest observed outcome values. It is easy to interpret, but it is not a precision measure for the group mean. The endpoints may be sensitive to individual observations, especially in a study with limited outcome counts. A range also omits information about the relative frequency of values throughout the span. Without a standard deviation, interquartile range, or participant-level data, readers cannot assess the outcome distribution in more detail.
General statistical interpretation: a confidence interval expresses the uncertainty around an estimated quantity under a stated statistical method. A narrow interval generally indicates greater precision than a wide interval, though its interpretation depends on the design and assumptions. No confidence interval for the primary treatment comparison is reported in the registry record. The listed group ranges are not confidence intervals and should not be read as such.
Why does randomization matter?
Random assignment is intended to make treatment groups comparable, on average, with respect to both measured and unmeasured characteristics. It can reduce bias in a treatment comparison when assignment is implemented as planned and outcomes are analyzed appropriately. Randomization does not guarantee that groups will be alike in every feature, particularly in a study with limited enrollment, and it does not remove uncertainty from an estimate.
The registry identifies the allocation as randomized, but it does not report the sequence-generation method, concealment procedures, or any stratification factors. The record also does not state which individuals were masked under the single-masked designation. Those omissions limit assessment of how randomization and masking were implemented. The registry describes blinded, independent image raters, which is relevant to outcome assessment, but does not report how the raters’ evaluations were reconciled.
Why is over-dispersion relevant in general?
General statistical explanation: over-dispersion occurs when outcome variation is greater than a statistical model expects. If a model assumes less variability than the data contain, standard errors may be too small and confidence intervals may be too narrow. This is a general concern for analyses of outcomes whose values vary substantially across participants, but the registry does not report a model-based analysis or enough distributional detail to assess over-dispersion for this endpoint.
What inferential results are available?
The registry posts group means and full ranges, but it does not report an inferential treatment comparison, p-value, or confidence interval for the primary outcome. The record lists zero posted analyses. That does not establish that no analysis was conducted; it means that an analysis result is not reported in the registry record. No adjusted estimate or covariate-adjusted model is reported either.
The trial record describes planning illustrations based on a stated fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such calculations are planning illustrations and are not observed power. They are also not evidence of the trial’s original sample-size justification. The registry does not report the protocol’s sample-size justification or actual planning illustration values. Since no primary comparison estimate is reported, a reader should not treat a planning calculation as a substitute for a trial result.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one primary outcome measure, progression of wound healing, and reports no secondary outcomes. It lists zero analyses. The absence of posted analyses does not mean that no analyses were performed; it means that results of inferential analyses are not reported in the registry record. No statistical analysis plan is reported, so it is not possible to determine which comparisons were planned, whether any were prespecified, or whether an adjustment for multiple comparisons was intended.
Multiplicity arises when several outcomes, timepoints, subgroups, or analytical choices are examined. Repeated testing can increase the chance of finding an apparently notable result by chance. General statistical practice may address this through a prespecified hierarchy or an adjustment, but the registry does not report such a plan. The description mentions photographs at post-operative Day 5, post-operative Day 14-21, and post-operative Day 30, while the primary endpoint description specifies percentage of graft take evaluated on Day 30. The record does not report inferential results for the other assessments described.
Missing-data handling is not reported in the registry record. The enrollment figure is 20, while the primary outcome results list 9 participants for negative pressure wound therapy and 7 for conventional dressing. Safety results list 11 and 9 participants at risk, respectively. The registry does not explain these differences or state whether missing outcomes were imputed, excluded, or handled by another method. It also does not identify an intention-to-treat, per-protocol, or other analysis population. Consequently, the posted summaries cannot establish how the analyzed participants were selected or whether missingness could have affected the group results.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Negative Pressure Wound Therapy | 0 | 11 | 0.0% |
| Conventional Dressing | 0 | 9 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Negative Pressure Wound Therapy | 0 of 11 |
| Conventional Dressing | 0 of 9 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Negative Pressure Wound Therapy | 0 of 11 |
| Conventional Dressing | 0 of 9 |
The registry lists zero serious adverse events in the negative pressure wound therapy group among 11 participants at risk and zero in the conventional dressing group among 9 participants at risk. It also lists zero other adverse events in each group, using the same respective at-risk counts. The deaths field is zero for both groups. No serious adverse event terms are listed.
These figures describe what is recorded in the registry; they should not be read as proof that no adverse experiences occurred outside the recorded categories or reporting period. The adverse-event observation period and the methods for collecting events are not reported in the registry record. The record also does not explain why these at-risk counts differ from the primary outcome counts.
Zero recorded events can occur when events are absent, but interpretation also depends on the number of people observed, the duration and completeness of follow-up, and how events were defined and collected. Those details are not reported. The safety figures therefore provide a limited description of recorded events and do not establish comparative safety.
12. What the Result Does, and Does Not, Mean
The primary result describes percentage of skin graft take in the participants included in the posted outcome summaries. The mean was 69.9 for negative pressure wound therapy and 75.6 for conventional dressing. The full ranges were 50.0 to 90.0 and 55.0 to 95.0, respectively. These figures give a descriptive account of the observed results, not a complete estimate of the treatment effect.
The result does not establish that one dressing strategy is superior. No confidence interval, p-value, or inferential comparison is reported for the primary outcome. A numerical difference between sample means can arise from a treatment effect, from sampling variability, or from other factors. Without an estimate of uncertainty and information about the analyzed population, the registry summaries cannot distinguish among those possibilities.
The result also does not establish that the approaches are equivalent. Demonstrating equivalence requires a prespecified framework and an analysis designed to assess whether any difference is sufficiently small under defined criteria. Such a framework is not reported in the registry record. A failure to report an inferential comparison is not evidence that the groups have the same outcome.
The trial addresses a clinically relevant wound-healing measure at free flap donor sites, but conclusions are constrained by the limited posted outcome information. The registry does not report how the difference between enrollment and outcome counts arose, the handling of missing data, the analysis population, or the planned statistical methods. Readers can describe the reported means, ranges, and adverse-event counts, but should not infer a definitive treatment effect or broader applicability from these summaries alone.
13. Why This Trial Matters Statistically
This trial is statistically informative as an example of the distinction between descriptive results and comparative evidence. Group means and ranges let readers see the observed outcome summaries, but they do not by themselves quantify uncertainty in the contrast between treatments. Without an inferential estimate, the numerical ordering of the means cannot answer whether an underlying treatment difference is distinguishable from sampling variability.
The registry also illustrates why denominators and analysis populations matter. Enrollment is reported as 20, while the primary outcome and safety summaries use different group counts. The record does not explain the differences. Such count information is essential for understanding which participants contribute to each result and whether missing outcomes might influence interpretation. Reporting the counts clearly alongside methods for missing data would make the evidence easier to assess.
Outcome assessment is another statistical consideration. The primary outcome was derived from photographs reviewed by blinded, independent raters, with a grid-based assessment and additional judgments about graft appearance and exposed tendon. These procedures are relevant to measurement quality. However, the registry does not report how rater assessments were combined or how agreement was evaluated. Measurement definitions and reproducibility matter because uncertainty in outcome assessment can affect the precision and credibility of a treatment comparison.
Finally, the trial record’s stated planning assumptions should be distinguished from the trial’s own design rationale and from observed evidence. Planning illustrations based on an observed effect do not show that the study had adequate power, and they do not replace a reported treatment-effect estimate. The record does not report a sample-size justification or inferential findings. These limitations make transparent reporting of analysis plans and results especially important.
14. 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 primary outcome summaries include 9 participants for negative pressure wound therapy and 7 for conventional dressing, while the registry reports enrollment of 20. The reason for the difference is not reported in the registry record. Safety results use at-risk counts of 11 and 9, and the relationship between those counts and the primary outcome counts is also unexplained. This makes it difficult to determine which participants contributed to each reported result.
The registry does not report a standard deviation or confidence interval for percentage of graft take, nor does it provide a treatment-effect estimate or p-value. The full ranges describe the endpoints of observed values but do not show the distribution within either group or the precision of the group means. No participant-level outcome information is reported.
The record does not report the randomization method, allocation concealment, the identity of the person or people masked, or a statistical analysis plan. Although it describes blinded, independent image raters, it does not explain how their assessments were combined or whether agreement was assessed. Details of adherence, treatment delivery, co-interventions, and missing-data handling are not reported in the registry record.
Follow-up for the primary endpoint is described through Day 30, but the registry does not report the adverse-event observation period. It also does not provide inferential results for the photographic assessments at other listed timepoints. The record describes a specific donor-site setting, but further eligibility criteria and participant characteristics are not reported. These limitations restrict assessment of precision, bias, and the extent to which the posted results may apply beyond the analyzed participants.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Single-Use Negative Pressure Wound Therapy for Free Flap Donor Sites — NCT03340025.
- Registry record last updated 2021-07-30; status last verified 2021-07.
- Results first posted 2021-07-30.
- 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.
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Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
The registry record describes a completed, randomized, parallel-group, single-masked trial sponsored by the University of Alabama at Birmingham. It compares the PICO Single Use Negative Pressure Wound Therapy System with conventional dressing using xeroform gauze and padding for free flap donor sites requiring skin grafting. The recorded enrollment is 20.
The primary outcome is progression of wound healing, measured as percentage of skin graft take and evaluated on Day 30 from photographs reviewed by blinded, independent raters. The registry reports means of 69.9 and 75.6, with full ranges of 50.0 to 90.0 and 55.0 to 95.0, respectively. It does not report an inferential comparison or confidence interval.
The record lists zero serious adverse events, zero other adverse events, and zero deaths in each group. It does not explain differences between enrollment and the outcome or safety counts, or report a statistical analysis plan, missing-data methods, or analysis populations.