Effect of Platelet Rich Plasma and Keratinocyte Suspensions on Wound Healing: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Effect of Platelet Rich Plasma and Keratinocyte Suspensions on Wound Healing (NCT00856934), a randomized phase 1 study. The primary outcome is Complete Wound Healing.

2. Clinical Question

The clinical question is therefore about the comparative wound-healing outcomes associated with two biological preparations and standard dressings in this trial population. The randomized allocation supports comparisons between the groups, while the open-label design means masking was absent. The registry record does not report further detail about how the wound assessments were performed or whether assessors were independent of treatment assignment.

3. Trial Design

This was a prospective randomized trial with a parallel-group design. The registry identifies it as Phase 1 and lists the status as completed. Enrollment was 45. The sponsor was Centre Hospitalier Universitaire Vaudois. The recorded start was 2005-06, and primary completion was 2006-03.

Participants were assigned to one of three groups: control, PRP, or PRP+K. Each group had 15 participants in the posted primary-outcome results. Control wounds received standard dressings. In the PRP group, PRP was sprayed onto the wound bed with Calcium Choride, followed by the same standard dressings. In the PRP+K group, keratinocytes suspended in PRP were applied with Calcium Choride, followed by those dressings.

Masking is recorded as none. The registry does not report allocation concealment, the randomization sequence method, or whether outcome assessors were masked. It also does not report further operational details, such as how participants were recruited or whether any changes to the study design occurred.

The primary outcome was complete wound healing, expressed as a mean number of days. The stated assessment schedule began on post operative day 5 and continued every other day thereafter. Pain, measured as a VAS Pain Score on post operative day 5, was the posted secondary outcome. The record lists two outcome measures and two analyses. The registry record does not report a fuller statistical analysis plan, a protocol, or the original sample-size rationale. These omissions mean that the design can be described from the recorded features, but not reconstructed in all procedural or analytical detail.

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 Complete Wound Healing, measured over Post operative day 5 and every other day thereafter.

The primary endpoint, Complete Wound Healing, measures the time required for complete epithelialization, in days. The registry describes assessment on post operative day 5 and every other day thereafter. The posted results are means and standard deviations for each group, so the endpoint is presented as a continuous measure of healing time.

Time to complete healing is used to describe how quickly wounds reached the specified healing state. Comparing group means gives a summary of average healing time in the trial groups. A mean difference expresses the contrast between two group averages in the original unit, days. A negative difference in the recalculated comparisons indicates that the intervention group's reported mean was lower than the control group's mean.

This summary does not describe every participant's healing trajectory. The registry record does not report individual observations, the distribution of healing times, or details of how incomplete healing or unavailable assessments were handled. Since assessments were scheduled at intervals rather than continuously, the precise timing of epithelialization between assessment visits is not available in the posted results. The endpoint is therefore interpreted as recorded: mean days to complete healing under the trial's assessment schedule, rather than a more detailed account of each wound's course.

7. Results Posted in the Registry

• PRP: mean 7.20 versus 13.90 on control; difference -6.70 (95% CI -7.79 to -5.61), standardized effect d = -4.40; z-test p = <0.001.
• PRP+K: mean 5.70 versus 13.90 on control; difference -8.20 (95% CI -9.27 to -7.13), standardized effect d = -5.47; z-test p = <0.001.

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.

Pain

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • PRP: mean 1.50 versus 7.20 on control; difference -5.70 (95% CI -6.28 to -5.12), standardized effect d = -7.07; z-test p = <0.001.
  • PRP+K: mean 0.40 versus 7.20 on control; difference -6.80 (95% CI -7.30 to -6.30), standardized effect d = -9.71; z-test p = <0.001.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for PRP than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for PRP+K than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Pain is the posted secondary outcome, recorded as a VAS Pain Score on post operative day 5. Across the three groups, the reported means follow the same broad ordering as the primary outcome: the control group has the highest mean, PRP is lower, and PRP+K is lowest. The recalculated comparisons also point in the same general direction as the primary-outcome comparisons. This consistency across the two posted outcomes offers a related, but not independent, perspective on the trial's group pattern.

Pain and time to complete healing measure different aspects of the post-operative experience. Agreement in their broad group ordering does not establish that one outcome explains the other, nor does it confirm that the same underlying mechanism accounts for both. The registry record does not report a joint analysis relating pain scores to healing times.

The registry reports an ANOVA for the secondary outcome, with p = 0.05, and the recalculated pairwise comparisons are unadjusted. Secondary findings generally carry less weight than a prespecified primary analysis because they are additional opportunities to observe group differences. When several outcomes or contrasts are examined, the chance of at least one apparently notable result can increase unless the analysis plan addresses multiplicity. The registry record does not report how secondary comparisons were selected or whether any multiplicity adjustment was used.

The secondary outcome should therefore be considered supportive descriptive context rather than a stand-alone confirmation of the primary result. The record lists pain as the secondary outcome but does not report the analysis population, missing-data handling, or further prespecification details. Those omissions limit assessment of how the secondary result should influence the overall interpretation.

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

• Pain

9. Statistical Interpretation

10. Statistical Methods Explained

The registry's reported primary analysis is an ANOVA involving the control, PRP, and PRP+K groups. ANOVA is a general method for assessing whether group means differ, while accounting for the variation observed within groups. Its overall result does not automatically identify which groups differ from one another. The registry reports p = 0.05 for this analysis, but does not provide its estimated group contrasts or confidence intervals.

What does a mean difference express?

A mean difference subtracts one group mean from another, preserving the measurement unit. For the recalculated comparisons, the contrast is intervention group minus control. The negative estimates therefore correspond to lower mean days to complete healing in the intervention group than in control. The recalculated estimates are -6.7 days for PRP versus control and -8.2 days for PRP+K versus control. These are unadjusted comparisons based on the posted means and standard deviations.

Unadjusted means that the recalculation does not account for additional variables or a more complex model. The registry does not report covariate-adjusted estimates. The recalculated comparisons are useful for expressing the observed contrasts in days, but they are not evidence that the sponsor used the same method. The sponsor's own analysis takes precedence when describing the analysis reported by the trial.

What does a p-value communicate?

In general, a p-value describes how incompatible the observed data are with a specified null model, assuming the model and its assumptions apply. It is not the probability that the null hypothesis is true, and it does not measure the size or importance of an effect. The registry's overall ANOVA p-value is 0.05. The recalculated, unadjusted pairwise p-values are p < 0.001 for each intervention-versus-control contrast. These p-values arise from different analyses, so they answer different questions and should not be conflated.

Statistical significance is not a substitute for considering the effect estimate, its uncertainty, and the trial's conduct. The registry does not report whether the sponsor prespecified a significance threshold or how multiplicity was handled. A small p-value in a recalculation does not fill those gaps.

Why does variability matter?

Standard deviations describe how spread out individual measurements are around a group mean. General statistical interpretation depends on both the difference in group means and the variability of measurements. With less variation, a given mean difference can be estimated more precisely; with greater variation, it is generally harder to distinguish a group contrast from sampling variation. The posted standard deviations are 2.0 days for control, 0.8 days for PRP, and 0.7 days for PRP+K. The recalculation uses the posted group summaries and does not use participant-level data.

General methods for continuous outcomes often rely on assumptions about the outcome distribution and the sampling behavior of group means. The registry record does not report diagnostic checks or detailed assumptions for the ANOVA. No claim about whether those assumptions were checked can be made from the record.

What is the role of randomization?

In general, randomized assignment aims to make groups comparable in expectation, which can support causal comparisons when the trial is conducted and analyzed appropriately. It does not guarantee that small groups will be identical on every characteristic. The registry identifies randomized allocation, but does not report the sequence generation or allocation concealment methods. Masking is recorded as none, which means the study is described as open-label. The record does not explain whether outcome assessment could have been masked separately.

The recalculated confidence intervals quantify uncertainty for the simple pairwise mean differences under the calculation used. They do not address every source of uncertainty, such as possible measurement bias, missing observations, model departures, or unreported analytic choices. Those issues require information beyond the posted aggregate results.

11. Confidence Intervals and Precision

Confidence intervals express the range of effect estimates compatible with the data and the calculation's assumptions. In general, a narrower interval indicates greater statistical precision, while a wider interval indicates more uncertainty about the effect's size. An interval is not a guarantee that the true effect lies within its limits, and it does not account for biases that are not represented in the calculation.

For PRP compared with control, the recalculated mean difference is -6.7 days, with a confidence interval from -7.79 to -5.61 days. For PRP+K compared with control, the recalculated mean difference is -8.2 days, with a confidence interval from -9.272 to -7.128 days. Both intervals lie on the negative side of zero, consistent with lower mean healing times in the intervention groups in these unadjusted comparisons. The posted tables present these intervals alongside the corresponding estimates.

The precision should be read in the context of 15 participants per group. The intervals are calculated from posted summary statistics and are not the sponsor's reported intervals; the registry does not report intervals for its ANOVA result. The record also does not provide participant-level observations, so the recalculation cannot examine distribution shape or other features that might affect inference.

These intervals address sampling uncertainty under the calculation's assumptions. They do not capture uncertainty from the absence of masking, incomplete reporting, choices made after examining data, or possible problems in outcome measurement. A precise-looking estimate is not, by itself, proof that an estimate is free of bias or applies beyond the trial population.

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 figures are planning illustrations based on the observed effect, not a reconstruction of the trial's original design. For these continuous outcomes, the figures are participants per arm, not total events. The calculations assume a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row uses the stated fraction of the observed effect as the effect to detect. The trial's own original design assumptions and sample-size justification are not reported in the registry record.

The 80% power column gives the calculated number of participants per arm for a planning scenario designed to have an 80% chance of detecting the specified effect under those assumptions. The 90% power column gives the corresponding number per arm for a 90% chance. These are design-planning quantities, not descriptions of what happened in the completed trial.

Rows that plan for a smaller fraction of the observed effect generally require more participants than rows planning for the full observed effect. The observed effects in this trial are large relative to the posted standard deviations, so the illustrative figures can be very small. That should not be read as a recommendation for a future study: planning from effects observed in a small trial can be optimistic, and other considerations may affect a study's design.

This is not observed power. It does not estimate the probability that the completed trial detected an effect after its results were known. The registry record does not report the assumptions used when the trial was originally designed, so the illustrations should be understood only as calculations based on the posted results and the stated planning assumptions.

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 = -6.700; pooled standard deviation σ = 1.523.
2. n = 2 × (1.96 + 0.842)² × 1.523² / -6.700² = 0.8, rounded up to 1 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 <- -6.7                      # observed difference in means
sigma <- 1.52315462117278                     # 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(856934)
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 = 1 (80% power), 2 (90% power)
 75% of observed effect: n per arm = 2 (80% power), 2 (90% power)
 50% of observed effect: n per arm = 4 (80% power), 5 (90% power)
power.t.test: 2.3 
Simulated power at n = 1 per arm: NA (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. Analyses Reported by the Sponsor

The sponsor's reported primary analysis is an ANOVA across the control, PRP, and PRP+K groups, with p = 0.05. The registry does not report an estimate or confidence interval from that analysis. It also does not provide pairwise results from the sponsor's analysis, so the ANOVA result cannot be used to identify the size or direction of a particular pairwise contrast.

The recalculated results are simple, unadjusted comparisons of each intervention group's posted mean with the control mean. They give mean differences of -6.7 days for PRP versus control and -8.2 days for PRP+K versus control, with the corresponding confidence intervals and p-values displayed alongside those estimates. These calculations are not the sponsor's reported analysis and should not be presented as if they were.

There is no reported discrepancy between the posted sponsor analysis and the recalculation. Even so, they are distinct analyses: the sponsor's ANOVA considers all three groups in an overall test, while the recalculation estimates specific intervention-versus-control contrasts. The sponsor's own analysis takes precedence when describing what the trial reported. The recalculation can provide an additional, transparent summary of the posted group means, but it cannot establish which analysis was prespecified or whether other analyses were conducted.

15. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and a secondary outcome, and reports analyses across three groups for both. The recalculated results additionally present two intervention-versus-control comparisons for each outcome. Looking across multiple outcomes and contrasts raises the general issue of multiplicity: when several statistical tests are conducted, some may appear notable by chance even if no true differences exist. Whether and how to address this depends on the prespecified analysis plan and the aims of the comparisons.

The registry record does not report a multiplicity strategy, such as a testing hierarchy or adjustment to account for multiple comparisons. It also does not report whether the pairwise comparisons were prespecified. The recalculated pairwise p-values are unadjusted and should be read as such. The reported ANOVA p-values are overall tests and do not reveal whether follow-up comparisons were performed by the sponsor.

Missing-data reporting is also limited. The posted results give 15 participants in each group, but the registry record does not explain whether all randomized participants contributed to each outcome, whether any assessments were missing, or how unavailable outcomes were handled. It does not identify an analysis population, such as all randomized participants or only those with a completed assessment. Therefore, the group counts alone do not establish the handling of every participant's data.

The registry record does not report a detailed statistical analysis plan, protocol deviations, sensitivity analyses, or the methods used to check model assumptions. These details matter because they help readers distinguish prespecified analyses from exploratory ones and understand how robust findings are to alternative reasonable choices. Their absence does not show that such procedures were not performed; it means they are not reported in the registry record.

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

The posted results show lower mean time to complete healing in the PRP and PRP+K groups than in the control group. The recalculated, unadjusted pairwise contrasts quantify those differences in days, and their confidence intervals indicate the sampling uncertainty under the calculation used. Pain scores also follow a similar broad ordering among the three groups. These statements describe the results recorded for this trial.

They do not establish that either intervention will have the same result in other populations, clinical settings, or wound-care circumstances. The registry record describes 45 participants in a randomized, open-label, parallel-group Phase 1 trial. It does not report sufficient participant characteristics or setting details to judge how closely other populations resemble this trial population. The relatively small groups and unmasked design are relevant when considering the scope of the findings.

The results do not establish that PRP+K is superior to PRP. The posted recalculations compare each intervention separately with control; they do not include a direct PRP+K-versus-PRP contrast. Comparing the separate estimates against a shared control is not a substitute for testing that direct contrast.

The registry's overall ANOVA result and the recalculated pairwise results are different statistical summaries. Neither p-values nor confidence intervals settle questions about clinical importance, measurement quality, or bias. The registry does not report a threshold for a clinically important difference, and no such threshold can be inferred from the posted means alone.

These data also do not establish how the treatments should be used in practice. The trial record provides outcome summaries, not individualized guidance. Its results are best understood as findings from the enrolled participants under the described procedures, with uncertainty and reporting gaps kept in view.

17. Why This Trial Matters Statistically

This trial illustrates why a statistical reading should distinguish the sponsor's overall analysis from pairwise effect estimates. The ANOVA p-value addresses a three-group question, while the recalculated mean differences compare each intervention group with control. These are related but not interchangeable questions. Reporting both perspectives makes clear that an overall test does not itself communicate the size of each contrast.

The outcome is expressed in days, so the estimated differences retain an interpretable measurement unit. Alongside each mean difference, a confidence interval communicates the precision of the unadjusted estimate. Reading the estimate and interval together is more informative than treating a p-value as the whole result.

The trial also highlights the importance of comparing the primary and secondary outcomes without treating agreement as independent confirmation. Both outcomes have a broadly similar group ordering, but multiple outcomes and comparisons raise questions about prespecification and multiplicity. The registry record does not report the information needed to resolve those questions.

Finally, the very small planning figures generated from the observed effects demonstrate a broader design lesson: post-trial planning illustrations are not a substitute for a prospective sample-size rationale. The original design assumptions are not reported, and planning based on an observed effect can be optimistic. These distinctions help readers separate what the study observed, what the sponsor formally reported, and what a recalculation can add.

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 limitations specific to this trial affect interpretation. The registry records no masking. Since wound healing and pain assessments may involve judgment or participant reporting, the absence of masking is relevant to the possibility of measurement or expectation effects; the record does not say whether outcome assessors were separately masked. The description of randomization is also limited: the sequence-generation and allocation-concealment methods are not reported.

Each group included 15 participants in the posted primary-outcome results. Estimates from groups of this size may remain sensitive to individual observations. The registry does not post participant-level data, so the distribution of healing times, outliers, or the influence of individual participants cannot be examined from these summaries.

Complete wound healing was assessed on post operative day 5 and every other day thereafter. The registry does not explain how the exact healing day was assigned between scheduled assessments, or how wounds that had not healed by the end of observation were handled. Further details on follow-up, missing assessments, exclusions, and analysis populations are not reported in the registry record.

The sponsor's ANOVA is reported with a p-value but without an estimate or confidence interval. The posted registry results therefore do not provide the sponsor's effect-size summary or pairwise test details. The original sample-size rationale, a detailed statistical plan, multiplicity procedures, and sensitivity analyses are also not reported. These are reporting limitations; they do not establish whether related procedures were or were not used.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Effect of Platelet Rich Plasma and Keratinocyte Suspensions on Wound Healing — NCT00856934.
• Registry record last updated 2009-03-06; status last verified 2009-02.
• Results first posted 2009-03-06.
• 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

NCT00856934, titled “Effect of Platelet Rich Plasma and Keratinocyte Suspensions on Wound Healing,” is recorded as a completed, randomized, open-label, parallel-group Phase 1 trial sponsored by Centre Hospitalier Universitaire Vaudois. Enrollment was 45, with 15 participants in each of the control, PRP, and PRP+K groups.

The primary endpoint was mean days to complete wound healing, assessed from post operative day 5 and every other day thereafter. The registry also reports pain measured by VAS Pain Score on post operative day 5. The sponsor's reported analysis was an ANOVA across the three groups for each outcome. The record does not report the original sample-size justification, detailed analysis plan, or further information about missing data and analysis populations.

The posted group means and the unadjusted recalculations describe lower average healing times and pain scores in the intervention groups than in control. Those results should be read alongside the small group sizes, absence of masking, unreported analysis details, and distinction between sponsor-reported and recalculated analyses.