Evaluating the Ease of Use of a VAC GranuFoam Bridge Dressing on Diabetic Foot Ulcers Receiving VAC Negative Pressure Wound Therapy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluating the Ease of Use of a VAC GranuFoam Bridge Dressing on Diabetic Foot Ulcers Receiving VAC Negative Pressure Wound Therapy (NCT00847730), a na na study. The primary outcome is Ease of Use Assessment.

2. Clinical Question

The study’s stated aims also included clinician-perceived ease of use and patient comfort during dressing wear. The registry description of the primary endpoint gives the three characteristics used for its composite score, but does not describe a separate comfort endpoint or report a comfort result. Thus, the central question that can be addressed from the record is limited to what the endpoint was designed to measure, rather than whether the dressing met the endpoint in practice.

Because there was one group and no control, any recorded experience would describe participants using this dressing in the study setting. It would not establish how the same participants would have rated another dressing, or whether any observed ratings were caused by the device rather than other aspects of care. Details about the care setting and concurrent treatments beyond the named negative pressure therapy system are not reported in the registry record.

3. Trial Design

This was a prospective, single-group clinical trial with an enrollment of 33 participants. The registry lists the study as completed and gives a start date of 2009-02 and a primary completion date of 2009-06. The study was listed as not applicable for phase. Allocation was not applicable, masking was none, and the model was single group. These characteristics describe a study without a randomized comparator or a masked assessment structure reported in the record.

The intervention was the V.A.C. Negative Pressure Wound Therapy System, used with a VAC GranuFoam Bridge Dressing. The arm description says the bridge dressing allowed placement away from the wound site and was designed to simplify bridging application. For each subject, the dressing was applied in compliance with the instructions for use for 48-72 hours. The primary endpoint timeframe is listed as 48-72 hours (+6 hours), so the assessment concerned a short period of dressing wear rather than a longer follow-up outcome.

The primary endpoint was an individual-level classification based on three ratings. Each characteristic—ease of dressing application, ease of conformability, and ease of dressing removal—was rated on a four-point scale from poor to excellent. The ratings were summed, and a participant was included among those with satisfactory performance only if the total and each individual rating met the stated thresholds. The analysis population is identified as intent to treat.

The registry record does not report a control group, randomization procedure, masking procedure beyond the none designation, or a detailed statistical analysis plan. It also does not report a justification for the enrollment target, planned interim analyses, or how participants with unavailable assessments were to be handled. Although one primary outcome measure is listed, the record reports zero analyses. The endpoint’s outcome value is not reported in the registry record, so the actual observed performance cannot be described from this information.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: ITT (Intent to Treat) population.

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 Ease of Use Assessment, measured over 48-72 hours (+6 hours) time period.

The primary endpoint, Ease of Use Assessment, was designed to classify participants according to ratings of three dressing characteristics: application, conformability, and removal. Each characteristic was rated from 1, poor, to 4, excellent. The three ratings were summed to give a possible total score ranging from 3-12. A participant counted as having satisfactory performance only when the total score was at least 6 and every individual characteristic score was at least 2. Higher scores indicated better outcomes.

This rule combines an overall score with a minimum standard for each characteristic. In general, a composite endpoint can summarize several related aspects of an experience, while individual minimum criteria prevent a high rating on one characteristic from fully compensating for a low rating on another. The resulting classification is not the same as reporting each characteristic separately: it reduces several ratings to a yes-or-no determination of whether the stated rule was met.

The endpoint was assessed in the intent-to-treat population during the 48-72 hours (+6 hours) period. Its unit is participants, and the outcome type is a count of participants. The threshold definition and assessment window are reported, but the number of participants meeting the rule, the percentage meeting it, and the separate rating distributions are not reported in the registry record. Consequently, the endpoint’s operational definition can be explained, but its observed result cannot be interpreted.

The stated study aims mention clinician-perceived ease and patient comfort, but the listed primary endpoint uses participant-level ratings of the three specified dressing characteristics. The record does not explain who completed each rating or provide a separate measure of patient comfort. Those details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the endpoint classify?

The outcome is a count of participants who satisfy a defined rule. Each participant receives ratings for ease of dressing application, ease of conformability, and ease of dressing removal. The scale runs from 1, poor, to 4, excellent, with higher scores indicating better outcomes. The three ratings are summed, and the total can range from 3-12. Satisfactory performance requires a total score of at least 6 and a score of at least 2 on each characteristic.

This is a binary classification derived from multiple ratings: a participant either meets the full rule or does not. In general, a threshold makes an outcome easier to describe as a frequency, but it can discard distinctions among participants who fall on the same side of the cutoff. The separate ratings and the total score could offer additional detail, but those results are not reported in the registry record.

What can a single-group count tell us?

A count in one group describes the number of participants meeting an outcome definition in that group. It does not, by itself, estimate a difference between two approaches. In general, a comparative effect requires outcome information from a comparator group and a suitable analysis of the groups. This record describes one group and no randomized comparison, so a treatment contrast is not available.

The enrollment of 33 is not itself the number meeting the endpoint. The record names the intent-to-treat population for the primary measure, but does not report the number with a completed assessment or the endpoint count. It is therefore not possible to recover an outcome estimate from the enrollment figure alone.

How should uncertainty be understood?

In general, a confidence interval gives a range of values compatible with the observed data under the assumptions of the method. A narrow interval indicates greater precision than a wide interval, while an interval for a single-group proportion would still not create a comparison with an alternative dressing. No primary endpoint estimate or confidence interval is reported in the registry record. The registry also lists zero analyses, so no inferential result for the primary outcome is available to discuss.

For a binary outcome, uncertainty depends on both the number assessed and the number meeting the endpoint. Without those outcome counts, no interval can be interpreted. A p-value would address a specified statistical test, not the practical meaning or precision of a result on its own. No primary endpoint p-value or test is reported in the registry record.

What does a planning illustration represent?

In general, a sample-size planning illustration estimates the number of participants that might be needed under stated assumptions to detect a chosen effect with a chosen error rate and power. It is not an observed result and does not describe the probability that a completed study has found a true effect. The planning assumptions listed for this record specify a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a stated fraction of the observed effect. The listed guidance says that non-time-to-event planning values are participants per arm.

Those assumptions describe a hypothetical two-arm planning calculation, whereas the actual study is single group. No planning values or sample-size justification are reported in the registry record. The illustration should therefore not be read as the study’s design rationale, as a basis for inferring observed power, or as evidence that the trial was planned around a particular effect. Interim analyses and the trial’s own statistical plan are not reported in the registry record.

Why might over-dispersion matter in other analyses?

In general, over-dispersion means that outcome variability is greater than expected under a statistical model’s assumptions. It can make standard errors too small if a model does not account for the extra variation, which can make intervals appear too narrow and tests too optimistic. This is a general consideration for count-data analyses; it is not a reported feature of this study. The listed primary endpoint is a participant count, and no analysis model or dispersion estimate is reported in the registry record.

What is the scope of the available statistical evidence?

The record gives a study design, an enrollment figure, an endpoint definition, and safety counts. It does not give the primary outcome count, individual ratings, uncertainty interval, or analysis details. Consequently, statistical methods can clarify what the endpoint was intended to quantify and what kinds of inference would be needed, but cannot supply an estimate of the endpoint result. No recalculated primary outcome estimate is available from the reported information.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one outcome measure and zero analyses. It does not describe a multiplicity-adjustment procedure or explain whether multiple endpoints, time points, or subgroup analyses were planned. The primary endpoint definition includes three characteristic ratings that contribute to a composite classification, but the record does not report separate analyses for those ratings. A multiplicity strategy is therefore not reported in the registry record.

In general, multiplicity arises when several statistical tests or outcomes are examined, because the chance of at least one apparently unusual result can increase as more tests are considered. Adjustment methods can address that issue when a testing plan is specified. No such plan is available, and the absence of reported analyses means there are no primary endpoint tests to evaluate for multiplicity.

The primary analysis population is identified as intent to treat. The record does not state how missing ratings, incomplete assessments, or participants without an endpoint classification were handled. It also does not report the number with observed endpoint data. These details are not reported in the registry record; missing outcomes should not be assumed to have been counted as either satisfactory or unsatisfactory.

In general, an analysis population and missing-data approach affect what a reported estimate represents. An intent-to-treat label identifies the stated population, but without participant flow and missing-data rules it does not establish how the endpoint was analyzed in practice. The registry record does not provide enough information to assess attrition, deviations from the intended assessment, or sensitivity to missing data.

11. 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 5% reporting threshold.

Most frequent non-serious adverse event terms

The safety counts are reported for the VAC GranuFoam Bridge Dressing group. Among 33 participants at risk, 0 serious adverse events were recorded; among 33 participants at risk, 8 other adverse events were recorded; and 0 deaths were recorded. These are counts, not estimates of comparative risk, because the study has no control group.

The serious-event listing does not name any serious adverse-event terms. The other-event count indicates that 8 participants were affected, but the registry record does not describe the events, their severity, timing, duration, or whether investigators considered them related to the dressing or therapy. The counts should not be interpreted as a complete account of all possible harms beyond what the record reports.

In general, an observed count of zero serious events means none were recorded among the participants at risk during the reported observation, not that the possibility of such events is absent. A single-group safety summary also cannot show whether event frequency differs from another treatment. The short primary assessment period was 48-72 hours (+6 hours); the duration of safety follow-up is not reported in the registry record. The safety figures do not answer the missing primary ease-of-use result.

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

The record is useful for understanding how the study defined satisfactory performance. It specifies three ease-of-use characteristics, a four-point rating scale, and a rule that combines a minimum total with minimum ratings on every characteristic. It also identifies the intended analysis population and the period in which the assessment was made. These details make the endpoint definition clear enough to distinguish it from a general statement of perceived ease.

However, the registry record does not report the number of participants who met the endpoint rule, the percentage meeting it, or the underlying ratings. The main clinical-performance result therefore cannot be read from this record. The listed enrollment of 33 does not reveal the endpoint result, and the absence of analyses means that no statistical uncertainty estimate or test is available for the primary measure.

The design also limits interpretation. A single group can describe experience under the study conditions but cannot establish how that experience compares with another dressing or approach. No random allocation or comparator is reported. Thus, the record cannot support a controlled estimate of relative performance. The title and stated aims identify ease of use and comfort as motivations, but a separate comfort result is not reported in the registry record.

The planning assumptions describe a hypothetical two-arm calculation, including a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such assumptions are not observed findings and do not show that a study had adequate power. No actual planning results or design justification are reported in the registry record. Any sample-size illustration should be understood as planning information, not as evidence about what participants experienced.

The adverse-event figures are separate descriptive counts: 0 serious adverse events, 8 other adverse events, and 0 deaths among the stated group at risk. The record does not report event details or a comparison group. These counts neither establish a comparative safety profile nor fill the gap in the primary endpoint reporting. The appropriate overall reading is that design and measurement criteria are documented, while the central outcome result and important analysis details remain unreported.

13. Why This Trial Matters Statistically

This study illustrates why an endpoint definition and an endpoint result are distinct pieces of evidence. The registry describes a concrete rule for satisfactory performance: ratings on application, conformability, and removal are combined, with a minimum requirement for both the total and each characteristic. That definition allows a reader to understand what would count as success according to the study’s criterion. But without the number meeting that criterion, the actual result remains unknown.

The case also shows the limits of a single-group design for comparative questions. A one-group assessment can describe participants’ reported or recorded experience during the specified use period, but it cannot show what would have happened under an alternative dressing. A comparator and an appropriate comparative analysis would be needed for that type of claim. The registry identifies no randomized comparison, so the result, even if reported, would need to be interpreted as descriptive of the study group.

Statistical reporting matters beyond a headline count. Information on the number assessed, missing outcomes, individual ratings, and uncertainty would help readers judge how complete and precise the endpoint estimate was. Those details are not reported in the registry record. The listing of zero analyses makes the distinction especially important: an endpoint may be prespecified and fully defined, yet still lack a posted outcome analysis.

Finally, planning calculations and observed results answer different questions. The listed planning assumptions concern a hypothetical two-arm design, while the actual study is single group. A planning illustration cannot replace a reported outcome or be treated as observed power. The record therefore offers a useful example of how to read study structure, endpoint rules, and safety counts without treating design descriptions as evidence of an unreported result.

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 limitation for interpretation is that the registry record does not report the primary endpoint result. It gives the scoring rule and timeframe but not the number meeting the satisfactory-performance criteria, the number assessed, or the distribution of ratings. The central ease-of-use outcome therefore cannot be quantified or assessed for precision.

The study is single group, with no comparator and no random allocation. This prevents a direct assessment of relative performance and leaves no basis for separating an observed experience from other influences. Masking is listed as none. The record does not provide detail on who assigned the ratings or whether the assessor was independent, so the risk of measurement influences cannot be evaluated from the registry entry.

The registry identifies an intent-to-treat population but does not report participant flow, missing-data handling, or the number contributing observed endpoint data. It does not explain whether all three characteristics were available for every participant or how incomplete assessments were classified. These omissions make it difficult to evaluate completeness and the practical application of the endpoint rule.

The stated aims include patient comfort, but a separate comfort measure or result is not reported in the registry record. Details about participant characteristics, ulcer features, study setting, eligibility criteria, and concurrent care beyond the named therapy system are also not reported. The primary assessment is limited to the 48-72 hours (+6 hours) timeframe; longer-term outcome and safety follow-up are not described.

Safety reporting is limited to aggregate counts, without event descriptions or relationship assessments. No analysis plan, interim analyses, or sample-size justification is reported in the registry record. Together, these gaps restrict interpretation to the stated study design, endpoint definition, and recorded safety counts rather than the actual ease-of-use outcome or comparative conclusions.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Evaluating the Ease of Use of a VAC GranuFoam Bridge Dressing on Diabetic Foot Ulcers Receiving VAC Negative Pressure Wound Therapy — NCT00847730.
• Registry record last updated 2024-10-16; status last verified 2024-10.
• Results first posted 2019-07-16.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

18. Record Summary

NCT00847730 is a completed, prospective, single-group clinical trial of a VAC GranuFoam Bridge Dressing used with the V.A.C. Negative Pressure Wound Therapy System for diabetic foot ulcers. Enrollment was 33. The listed start date is 2009-02, and the primary completion date is 2009-06. The study was not applicable for phase, had no masking, and did not report a randomized comparison.

The primary measure was a participant count based on an ease-of-use assessment of dressing application, conformability, and removal. Satisfactory performance required a total score of at least 6 and a score of at least 2 for each characteristic. The assessment period was 48-72 hours (+6 hours), and the stated analysis population was intent to treat. The primary outcome result is not reported in the registry record, which lists zero analyses.

Safety counts were 0 serious adverse events, 8 other adverse events, and 0 deaths among the stated group at risk. The record does not provide details about the other events or a comparator for interpreting those counts.