Improvement in Wound Healing With Negative Pressure Wound Therapy for Postoperative Total Hip Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Improvement in Wound Healing With Negative Pressure Wound Therapy for Postoperative Total Hip Arthroplasty (NCT02355691), a randomized na study. The primary outcome is Mean Wound Healing Scores by the ASEPSIS Criteria.

2. Clinical Question

The registry identifies this as a randomized, parallel-group trial with no masking. Its title frames the study around improvement in wound healing, but a title is not evidence of a treatment effect. The posted outcome values are descriptive, and the record does not report a statistical analysis that establishes how compatible the group results are with chance variation or how precisely the comparative effect is estimated.

3. Trial Design

This was a randomized, parallel-group study with no masking. Participants were assigned to the PREVENA group or the standard-dressing group. The registry lists an enrollment of 16. It reports the primary outcome for 7 participants in the PREVENA group and 9 in the standard group. The record does not explain the relationship between enrollment and the number contributing to the endpoint, or describe participant withdrawals, exclusions, or missing assessments.

The trial evaluated PREVENA negative pressure wound therapy after primary total hip arthroplasty against a standard absorptive dressing. The PREVENA arm description specifies use of the device for seven days. The primary outcome was assessed at the two-week post-surgery visit, a single evaluation time rather than a series of repeated measurements. The registry also lists “Number of Participants With Infection” as a secondary outcome, but results for that outcome are not reported in the registry record.

The study status is terminated. The registry lists a start in 2015-05 and a primary completion in 2017-05. It names the University of North Carolina, Chapel Hill as sponsor. The reason for termination, the timing of the decision, and whether the study stopped as planned or early are not reported in the registry record. The phase is listed as NA.

Important design details are absent. The registry does not report how the random sequence was generated, whether assignment was concealed, or whether the person scoring the wounds knew treatment assignment. No masking is reported, but that does not establish which individuals, if any, were aware of group assignment at the time of outcome assessment. The record also does not give a detailed statistical analysis plan or a rationale for the planned enrollment.

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: Measured outcomes for all patients that completed the treatment

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 Mean Wound Healing Scores by the ASEPSIS Criteria, measured over (Single point evaluation)-2 weeks post surgery visit.

The primary endpoint was the mean wound-healing score using the ASEPSIS criteria, assessed at the two-week post-surgery visit. ASEPSIS combines wound features relevant to infection risk, including erythema, discharge or exudate, and separation of deeper tissue. The registry describes the score as covering additional treatment, serous discharge, erythema, purulent exudate, separation of deep tissue, bacterial isolation, and duration of inpatient stay. Scores can range from 0 to 65, with most scores expected at the lower end of the scale.

The system was originally developed and validated for cardiac surgery sternal wounds. In this trial, it was used to provide a broader assessment of postoperative wound healing after total hip arthroplasty than a single wound feature could provide. The registry says higher scores indicate a greater likelihood that a surgical site infection will be present. This makes the score a measure of wound status and infection-related signs, not a direct count of infections.

The posted group values are means, and the registry gives the full range for each group. The PREVENA group mean was 0.57, with a range of 0 to 1. The standard group mean was 1.66, with a range of 0 to 16. The record does not report a confidence interval or a statistical test for the comparison. These descriptive values alone do not show how precisely the difference between groups is estimated or whether the observed pattern would be expected to persist in a larger study.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the study as randomized and parallel-group, but it does not report the statistical method used to compare the primary outcome. No analyses are listed. The discussion below distinguishes what the posted summaries describe from general statistical principles that can help interpret such results.

What does the mean describe?

The mean is a summary of the observed scores in a group. The posted means were 0.57 for PREVENA and 1.66 for the standard dressing. A mean can be useful for conveying the overall level of scores, but it does not show the full pattern of individual observations. Different sets of participant scores can have the same mean, and a small number of comparatively high or low observations can affect it. The registry reports full ranges, but not individual scores, medians, or other distribution summaries.

In general, the full range records the lowest and highest observed values. It communicates the span of observations but does not show how frequently values occurred across that span. The posted range was 0 to 1 in the PREVENA group and 0 to 16 in the standard group. Without individual data or additional summaries, the registry does not show whether observations clustered near the minimum, how the standard group’s upper value arose, or how representative each group mean is of its participants.

What would a confidence interval add?

In general, a confidence interval expresses the statistical uncertainty around an estimated quantity under a specified analysis. It can show a range of values compatible with the observed data and the method’s assumptions. A narrower interval usually indicates greater precision than a wider interval. No confidence interval is reported for the primary group summaries or their comparison, so the precision of the comparative estimate cannot be read from the registry record.

A p-value, if reported, would address the compatibility of data with a specified statistical model and null hypothesis. It would not by itself measure the size or practical importance of an effect. No p-value or test is reported. Therefore, the posted means and ranges should not be converted into a claim of statistical significance, nor can they establish that there is no difference.

Why can score distributions matter?

In general, statistical methods for means often rely on assumptions about the distribution of the outcome or the sampling behavior of the mean. A wound score bounded from 0 to 65 and expected by the registry to be concentrated at lower scores may not follow a symmetric, unbounded distribution. The observed ranges are also quite different between groups. These features make it important to understand the individual observations and the planned analysis. The record does not report a diagnostic assessment, a transformation, a nonparametric approach, or another method chosen to address the score’s distribution.

General methods may also need to account for over-dispersion: variability greater than a model expects. When over-dispersion is ignored, model-based uncertainty can be understated. That principle is relevant to count or score outcomes when their observed variability exceeds model assumptions, but the registry does not report a model or enough detail to determine whether over-dispersion was assessed in this trial. No claim can be made about whether it affected the analysis.

What is known about the analysis population?

The registry describes measured outcomes for patients who completed treatment. It lists outcome counts of 7 for PREVENA and 9 for the standard group, but does not report participant flow or explain whether those numbers correspond to everyone randomized, everyone treated, or everyone with an available score. It also does not report whether the primary analysis followed assigned groups, included only treatment completers, or used another population definition. Such distinctions matter because excluding participants after randomization can affect how well a comparison preserves the randomized design.

How should planning illustrations be read?

In general, a sample-size calculation is a planning exercise: it estimates how many participants may be needed to detect a chosen effect under specified assumptions. It is not an outcome of the trial and is not observed power. The registry’s planning assumptions describe a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect set as a stated fraction of the observed effect. The record does not report the trial’s own design justification. Specific planning counts are not reported in the registry record. Any such illustration should therefore be understood as conditional on its assumptions, not as evidence that the completed trial had adequate power.

These general principles do not substitute for the absent trial analysis. The registry does not report the statistical plan, handling of missing outcomes, multiplicity strategy, model assumptions, or inferential results. Readers can describe the observed summaries, but cannot independently verify an adjusted comparison or reproduce a prespecified analysis from the record.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary ASEPSIS mean wound-healing score and one secondary outcome, the number of participants with infection. It also reports that there are two outcome measures, but only one secondary outcome is named in the record. The infection outcome’s results are not reported in the registry record. This means the posted results do not give a complete account of all listed outcomes.

When a study evaluates more than one outcome or makes multiple comparisons, the chance of at least one apparently notable result can increase. In general, a statistical plan may specify which outcome is primary and how to interpret additional analyses, including whether any adjustment for multiple testing is planned. The registry identifies a primary outcome but does not report a multiplicity strategy or a detailed statistical analysis plan. No claim can be made about whether multiplicity was addressed in an analysis outside the posted record.

The primary endpoint is described as measured among patients who completed treatment. The group outcome counts are 7 and 9, while enrollment is listed as 16. The record does not provide a participant-flow diagram or explain whether any randomized participants lacked a score, did not complete treatment, or were excluded. It does not report an imputation method, a missing-data sensitivity analysis, or a rule for handling incomplete assessments.

These omissions matter because a comparison restricted to treatment completers can differ from a comparison that retains all randomized participants in their assigned groups. The registry does not state which analysis population was used or whether the reported endpoint summaries include all randomized participants with available data. Thus, the completeness and consequences of missing outcome data cannot be assessed from the registry record.

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 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events for 0 of 7 participants at risk in the PREVENA group and 0 of 9 participants at risk in the standard group. It reports 0 deaths in each group. These are the posted serious-event and death counts; they do not establish that the treatments have equivalent safety or that serious events could not occur.

For other adverse events, the record reports 0 of 7 participants affected in the PREVENA group and 1 of 9 affected in the standard group. The event term for that other adverse event is not reported in the registry record. The registry also lists no top serious-event terms. The absence of a listed term should not be interpreted as an exhaustive narrative of safety observations.

In general, adverse-event counts are descriptive. Small group counts provide limited information about uncommon harms, and a zero count in a trial does not imply zero risk beyond the observed participants and follow-up. The record does not give detailed event descriptions, timing, severity grading, relatedness assessments, or follow-up duration for these adverse-event summaries. The primary wound score is an efficacy-related endpoint and should not be treated as a substitute for a complete safety assessment.

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

The posted data describe a randomized comparison of PREVENA negative pressure wound therapy with a standard absorptive dressing after primary total hip arthroplasty. At the two-week visit, the PREVENA group had a mean ASEPSIS score of 0.57 and a full range of 0 to 1. The standard group had a mean of 1.66 and a full range of 0 to 16. The registry’s description associates higher scores with a greater likelihood of surgical site infection.

Those observations do not establish that PREVENA caused a lower score. The registry reports no inferential comparison, confidence interval, or p-value, and it does not report the primary statistical analysis method. The means and ranges cannot show how precisely a comparative effect is estimated. They also do not establish whether a difference is clinically important. No threshold for a clinically meaningful difference is reported in the registry record.

The study’s registered secondary outcome was the number of participants with infection, but its results are not reported. Therefore, the posted ASEPSIS summaries should not be represented as infection counts or used to infer the secondary infection result. The score incorporates several wound findings, whereas infection is a separate outcome in the registry.

The registry reports enrollment of 16 and marks the study as terminated. It does not report the reason for termination, provide detailed participant disposition, or describe how missing outcomes were handled. It also does not state whether the wound assessors were masked. These limitations make it difficult to assess completeness of follow-up, the potential influence of outcome assessment, and the extent to which the posted groups represent the randomized population.

The appropriate conclusion is limited: the registry reports the group summaries and adverse-event counts for this small trial, but it does not provide enough analysis or outcome information to draw a firm comparative conclusion. The results are neither proof of benefit nor proof of no effect. They are descriptive observations from the participants whose outcomes were posted.

13. Why This Trial Matters Statistically

This trial illustrates why descriptive summaries and inferential evidence should be kept separate. The posted means differ numerically, and the group ranges also differ. Those summaries describe observed wound scores, but without an inferential analysis they do not quantify uncertainty about the comparison. A statistical interpretation must distinguish the pattern in the observed participants from conclusions about a broader population.

The ASEPSIS endpoint also highlights the importance of understanding what an outcome measures. It combines multiple wound features associated with infection risk, rather than recording only infection status. Its use can provide a broader wound assessment, but the score’s meaning depends on its measurement properties and its application in the target surgical setting. The registry notes that the system was originally developed and validated for cardiac surgery sternal wounds; it does not report further validation details for this trial population.

The record also demonstrates the value of complete outcome reporting. Infection was a registered secondary outcome, but its results are absent. The lack of participant-flow information, a reported statistical plan, and an inferential comparison makes it harder to determine how the observed summaries should be interpreted. Even a randomized design does not by itself answer questions about missing outcomes, measurement, analysis choices, or precision.

Finally, a small terminated study can generate useful descriptive information while remaining insufficient for a firm estimate of comparative effect. The trial record supports examination of the reported wound-score and adverse-event observations, but it leaves key uncertainty unresolved. These are statistical limits on interpretation, not a clinical recommendation.

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 registry record contains limited information about trial conduct and analysis. It identifies randomization, parallel groups, and no masking, but does not describe the randomization procedure or allocation concealment. It does not report whether outcome assessors were masked, which is relevant because the primary endpoint involves scoring wound features. The reason for termination is not reported, and the record does not establish whether termination affected follow-up or data collection.

The posted primary results are means and full ranges. Individual scores, standard deviations, medians, distributions, confidence intervals, and a comparative test are not reported. The outcome counts are 7 for PREVENA and 9 for the standard group, but participant flow and the relationship between those counts and the randomized population are not explained. Although the primary endpoint description refers to patients who completed treatment, the record does not report how many did not complete treatment or how missing scores were handled.

The secondary outcome of participants with infection is listed but its results are not reported. The record gives no detailed statistical analysis plan, multiplicity approach, covariate adjustment strategy, or sensitivity analysis. It also does not state a clinically meaningful threshold for interpreting ASEPSIS score differences. The score’s original validation context was cardiac surgery sternal wounds, and additional information on its measurement performance after total hip arthroplasty is not reported in the registry record.

The safety summaries are similarly brief: serious-event and death counts are reported, and one other adverse event is listed in the standard group, but its term and detailed event characteristics are not reported. These omissions constrain assessment of both efficacy-related outcomes and safety. They do not show that unreported events or analyses did not occur; they mean those details are not available in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Improvement in Wound Healing With Negative Pressure Wound Therapy for Postoperative Total Hip Arthroplasty — NCT02355691.
• Registry record last updated 2018-04-17; status last verified 2018-03.
• 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.

18. Record Summary

The registry describes a randomized, open-label, parallel-group trial of PREVENA negative pressure wound therapy versus a standard absorptive dressing after primary total hip arthroplasty. PREVENA was described as being used for seven days. The primary endpoint was mean ASEPSIS wound-healing score at the two-week post-surgery visit.

The posted mean scores were 0.57 for PREVENA and 1.66 for the standard group, with full ranges of 0 to 1 and 0 to 16, respectively. No inferential analysis is reported. The registered secondary outcome, number of participants with infection, has no results reported in the registry record.

Enrollment was 16, the study status is terminated, and the reason for termination is not reported. The record does not provide participant-flow details, a statistical analysis plan, or information on missing-data methods. Serious adverse events and deaths were reported as 0 in both groups; one other adverse event was reported in the standard group, without a reported event term.