A Comparison of Polyglactin 910 and Chromic Gut Suture in the Closure of Punch Biopsy Sites: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Comparison of Polyglactin 910 and Chromic Gut Suture in the Closure of Punch Biopsy Sites (NCT01722994), a randomized phase 4 study. The primary outcome is Presence of Scarring.

2. Clinical Question

The registry describes a comparison of two absorbable sutures used to close punch-biopsy wounds: chromic gut and polyglactin 910. The central clinical question is whether the presence of scarring differs between the groups at the reported follow-up. The primary endpoint records scarring as present or absent, rather than grading its severity. The registry also reports infection and the time until the absorbable suture fell out.

3. Trial Design

This was a completed phase 4, randomized, parallel-group study with no masking reported. The registry lists 97 participants as enrolled. Of these, 49 were assigned to punch-biopsy closure with chromic gut and 48 to closure with polyglactin 910. The study began in 2012-08, and primary completion was recorded in 2014-09. The sponsor was University of Mississippi Medical Center.

The brief summary describes patients undergoing a punch biopsy, with the closure material assigned at random. It says that the dermatologist would examine the biopsy site and ask about cosmetic satisfaction and pain at follow-up visits. The description mentions an initial return after one week and two further returns over the next two weeks. It also says patients whose sutures had fallen out before a visit would be asked when that occurred. These are descriptions of planned assessments; the registry does not establish that every participant completed every visit.

The primary outcome population was smaller than the enrollment and allocation totals. The registry reports that 42 participants were lost to follow-up or had missing data, leaving 55 who completed the study. Of those, 24 received chromic gut and 31 received polyglactin 910. The reported primary comparison therefore reflects participants with available outcome information, not an analysis of all enrolled participants.

The original sample-size justification, detailed eligibility criteria, randomization method, allocation concealment, and statistical analysis plan are not reported in the registry record. Although the brief summary likens assignment to a coin flip, procedural details beyond that description are not reported. The registry does not report masking, consistent with its designation of the study as having none.

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: Of the 97 subjects who enrolled, 49 had punch biopsy site closure with chromic gut and 48 with polyglactin 910 sutures. 42 subjects were lost to follow-up or had missing data. Of the 55 subjects who completed the study - 24 received chromic gut and 31 received polyglactin 910.

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 Presence of Scarring, measured over 1 week.

The primary endpoint is the presence or absence of scarring at a punch-biopsy closure site. The registry describes a binary scale: 0 means absent and 1 means present. It labels the primary result with a 1-week timeframe, while the outcome description says subjects were to be examined at 1 week and 3 weeks. A separate result for the later assessment is not reported in the registry record.

A binary endpoint captures whether a condition was recorded, not its degree, appearance, or importance to the participant. Scarring is relevant to the stated comparison because the study asks how biopsy-site closure outcomes differ between two suture materials. The endpoint gives a direct count of participants with scarring in each group, but it cannot by itself describe cosmetic satisfaction, pain, or the details of wound appearance.

The available primary data include one participant with scarring in each group. The denominators differ because outcome information was available for 24 participants assigned to chromic gut and 31 assigned to polyglactin 910. Interpretation should therefore focus on the comparison and its uncertainty, while keeping the missing follow-up in view. Cosmetic satisfaction and pain were mentioned in the study description, but their results are not reported in the registry record.

7. Results Posted in the Registry

• Group 2 Punch Biopsy Wound: 3.2% (1/31) versus 4.2% (1/24) on control; risk difference -0.9 percentage points (95% CI -11.1 to 9.2), risk ratio 0.77 (0.05–11.75); unadjusted two-proportion z-test p = 0.853.

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.

Length of Time Till Absorbable Suture Fall Out

• 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:
  • Group 2 Punch Biopsy Wound Using Polyglactin 910 Suture: mean 20.20 versus 15.70 on control; difference 4.50 (95% CI 1.37 to 7.63), standardized effect d = 0.81; z-test p = 0.005.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically higher for Group 2 Punch Biopsy Wound Using Polyglactin 910 Suture than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Presence of Infection

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Group 2 Punch Biopsy Wound Using Polyglactin 910 Suture: 3.2% (1/31) versus 16.7% (4/24) on control; risk difference -13.4 percentage points (95% CI -29.6 to 2.7), risk ratio 0.19 (0.02–1.62); unadjusted two-proportion z-test p = 0.086.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Group 2 Punch Biopsy Wound Using Polyglactin 910 Suture and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes add context about wound infection and the time until absorbable suture fall-out. Their directions do not form a single result that can be used to settle the primary scarring question: the outcomes measure different aspects of the wound and its closure. The registry does not report a combined analysis linking infection or suture retention to scarring, so these measures should be read as separate observations rather than as explanations for the primary result.

The reported secondary comparisons are unadjusted. When several outcomes are examined, the chance of encountering an apparently notable result can increase, even if there is no underlying effect on any outcome. The registry does not report whether the secondary outcomes were prespecified as key confirmatory tests or whether any adjustment for multiple comparisons was planned. A secondary p-value therefore carries less weight than a result from a clearly specified, multiplicity-aware analysis.

The secondary data may be useful for describing what was observed in these participants, but they cannot compensate for the primary endpoint’s limited precision or for missing follow-up. Nor do they establish that a difference in one outcome causes a difference in another. The registry’s assessment schedule includes additional visits, but separate results at every described visit are not reported in the registry record.

The brief summary also mentions participant satisfaction and pain assessments. Results for those assessments are not reported in the registry record. Their absence means the reported secondary outcomes do not provide a full account of every experience described in the study summary. The overall secondary pattern should therefore be treated as exploratory context, not as a substitute primary conclusion.

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

• Length of Time Till Absorbable Suture Fall Out
• Presence of Infection
• Presence of Infection

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports the primary endpoint as a count of participants with scarring and a comparison expressed as a risk difference. For a binary outcome, a risk is the proportion of participants in a group who have the event. A risk difference subtracts one group’s risk from the other group’s risk. In this comparison, the negative estimate of -0.009 indicates a lower observed proportion in the polyglactin 910 group than in the chromic gut group. It is an estimate from the available participants, not a direct measurement of the true difference in every eligible patient.

What does a binary outcome capture?

A binary measure classifies each participant as having or not having the recorded event. Here, scarring was coded as absent or present. This approach makes the outcome straightforward to count and compare, but it does not distinguish degrees of scarring. It also does not capture whether participants considered a scar acceptable or how it affected satisfaction. Those dimensions would require other reported measures; results for cosmetic satisfaction are not reported in the registry record.

The primary event counts are one in each group. Their denominators are 24 for chromic gut and 31 for polyglactin 910. Since the denominators differ, comparing counts alone would be misleading; the risk difference uses each group’s event frequency relative to its own denominator. The registry reports group proportions of 0.042 and 0.032, respectively, and an estimated risk difference of -0.009.

How should the p-value be understood?

The unadjusted p-value for the primary comparison is 0.853. In general, a p-value describes how compatible the observed data are with a specified null model, assuming that model and the analysis method apply. It is not the probability that the null hypothesis is true, and it does not quantify the chance that the finding is due to chance in a general sense. A large p-value does not prove that there is no difference. The registry does not report the full test specification or an analysis plan, so the reported p-value should be read as the posted unadjusted result rather than as evidence of a particular unreported modeling choice.

Unadjusted means that the reported p-value is not presented as corrected for multiple outcome comparisons or other adjustments. The registry record does not report a multiplicity procedure, an adjusted primary analysis, or a detailed account of covariate adjustment. The confidence interval and p-value should be considered together: the p-value does not show clear evidence against a no-difference model, while the interval makes the range of plausible directions and sizes more visible.

Why is the risk difference useful?

The risk difference expresses the comparison on the scale of the outcome proportions. A value of zero represents equal observed risks, while a negative or positive value indicates which group has the lower or higher observed risk according to the comparison’s direction. Unlike a relative measure, the risk difference stays in the same units as the proportions. It can therefore communicate the absolute size of the estimated contrast. Its uncertainty still matters: the interval from -0.111 to 0.092 crosses zero and permits differences in either direction.

Other relative measures are also present in the registry comparison, including a risk ratio and an odds ratio. Relative measures express a comparison as a ratio rather than an absolute difference. With very few events, relative measures can be unstable and may have broad intervals. The primary interpretation relies on the reported risk difference and its confidence interval, which directly describe the absolute contrast in scarring proportions.

What limits the analysis population?

The registry reports 97 enrolled participants, with 49 assigned to chromic gut and 48 to polyglactin 910. The primary outcome data are reported for 24 and 31 participants, respectively. The record states that 42 participants were lost to follow-up or had missing data. This reduction in available observations lowers precision and can also create bias if the participants with missing outcomes differ systematically from those whose outcomes were recorded.

In general, randomization helps create comparable groups at assignment, but incomplete outcome data can weaken that protection in the analyzed sample. The registry does not report whether the primary analysis followed an intention-to-treat approach, how missing data were treated, or whether sensitivity analyses were conducted. Those omissions prevent a fuller assessment of the impact of missingness.

Statistical methods can describe the observed comparison and its uncertainty, but they cannot recover unobserved outcomes without additional assumptions. Any analysis that accounts for missing outcomes would need a stated method and assumptions; these are not reported in the registry record. Consequently, the primary estimate should be understood as the reported comparison among participants with available data, not as a definitive estimate for all enrolled participants.

11. Confidence Intervals and Precision

The primary risk-difference estimate is -0.009. Its confidence interval extends from -0.111 to 0.092, so it includes zero and allows effects in either direction. The point estimate is close to zero, but the interval is broad enough that the data do not pin down the underlying difference precisely. The unadjusted p-value of 0.853 is consistent with the absence of clear evidence against a no-difference model, but it does not establish equivalence.

A confidence interval describes uncertainty around an estimated effect under the statistical method used. It is not a range containing every plausible individual outcome, and it does not mean that all values inside the interval are equally likely. The interval’s inclusion of zero indicates that the available data are compatible with no difference; its extension on either side also indicates compatibility with differences favoring either group.

The small number of scarring events and the available sample size contribute to limited precision. Outcome information was available for 55 participants, despite 97 enrolled, with 42 lost to follow-up or missing data. Missingness may affect precision and may also affect the validity of the estimate if the observed participants differ from those without data. The registry does not report an analysis of that possibility.

The confidence interval should therefore be read alongside the event counts, group denominators, and follow-up information. The estimate summarizes the observed contrast, but it does not support a finely resolved claim about the size or direction of a broader effect. A confidence interval or p-value alone cannot determine whether a difference would matter in practice.

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 planning figures are illustrations based on the observed effect, not the trial’s original design calculation. The original sample-size assumptions are not reported in the registry record. For the reported binary and continuous outcomes, the planning figures represent participants per arm, rather than total events. The registry’s general planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The calculations consider effects set at the stated fraction of the observed effect.

The 80% power column describes the number of participants per arm that the illustration estimates would be needed for an 80% chance of detecting the chosen effect under the stated assumptions, if that effect were the true one and the analysis assumptions held. The 90% power column applies the same idea with a higher target chance of detection. These are planning targets, not guarantees about the outcome of a future study.

Rows that plan for a smaller fraction of the observed effect require more participants per arm. Smaller differences are harder to distinguish from sampling variation, so a study generally needs more information to detect them with the same target power. The figures also depend on the observed effect used as their starting point; that estimate is uncertain, especially when outcome events are few.

These figures are not observed power. They do not describe the probability that the completed trial detected an effect after its results were known. They are hypothetical planning illustrations under stated assumptions, and they should not be treated as the trial’s original target or as evidence that a future study of a particular size would necessarily reach a conclusion.

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, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.042; treatment proportion p₁ = 0.032; average p̄ = 0.037.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.2668 = 0.5230.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.2667 = 0.2245.
4. n = (0.5230 + 0.2245)² / (-0.0094)² = 6,311.2, rounded up to 6,312 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
p0 <- 0.0416666666666667                          # control proportion
p1 <- 0.032258064516129                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^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 (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1722994)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 6,312 (80% power), 8,449 (90% power)
 75% of observed effect: n per arm = 11,564 (80% power), 15,480 (90% power)
 50% of observed effect: n per arm = 26,790 (80% power), 35,863 (90% power)
power.prop.test: 6311.2 
Simulated power at n = 6,312 per arm: 0.802 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The study reports a primary scarring outcome and secondary outcomes that include infection and time until suture fall-out. The registry lists infection twice among its secondary outcome names, while the reported results include infection and suture fall-out. It does not explain whether the repeated listing reflects separate assessments or a registry-entry duplication. Results for all planned assessments, including separate scarring results at each described visit, are not reported in the registry record.

When several outcomes or time points are tested, there are multiple opportunities to observe a small p-value by chance. Statistical approaches can control this multiplicity, for example by adjusting the testing threshold or by designating a limited set of confirmatory outcomes in advance. The registry record does not report a multiplicity adjustment, a hierarchy of outcomes, or a prespecified strategy for interpreting multiple tests. The reported secondary p-values are unadjusted and should be interpreted with that limitation in mind.

Missing data are a substantial feature of the reported primary outcome. The registry states that 42 participants were lost to follow-up or had missing data. Among those with primary outcome data, 24 received chromic gut and 31 received polyglactin 910. The registry does not report the reasons for missingness by group, the timing of loss to follow-up, or the characteristics of participants with missing outcomes.

The record also does not report how missing outcomes were handled statistically, whether participants were analyzed according to their randomized assignment, or whether any sensitivity analysis assessed alternative assumptions about missing data. These details matter because missingness can affect both the precision and the validity of a comparison. The analysis population and missing-data method are not reported in the registry record.

Without a stated analysis plan, multiplicity procedure, and missing-data approach, the reported estimates remain useful descriptions of the available observations but have important limits as confirmatory evidence. The registry record does not report interim analyses or a detailed statistical analysis plan.

15. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

The registry’s safety record lists zero serious adverse events among 49 participants at risk in the chromic gut group and zero among 48 at risk in the polyglactin 910 group. It also lists zero other adverse events in each group among those same numbers at risk. No serious adverse-event terms are listed.

These figures describe what was recorded in the registry; they should not be taken to establish that no adverse events occurred outside the recorded information or that the groups have identical safety profiles. The primary outcome population is smaller than the safety population listed, and the registry does not explain the completeness of adverse-event collection or provide further event detail. Deaths are not reported in the registry record.

Zero recorded events in these groups provide limited information about uncommon harms. The safety counts are descriptive and do not establish comparative safety with precision. They should be interpreted in light of the study’s recorded follow-up and the registry’s limited detail.

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

The primary data show one recorded case of scarring in each group among participants with available outcome information. The estimated risk difference is -0.009, and the confidence interval ranges from -0.111 to 0.092. This is an uncertain estimate: it includes no difference and also allows differences in either direction. The unadjusted p-value does not provide clear evidence of a difference, but it does not prove that the sutures produce the same outcome.

The result applies to the reported participants and assessment, not automatically to every patient undergoing a punch biopsy. The study enrolled 97 participants, but primary outcome data were available for 55, with 42 lost to follow-up or missing data. The record does not report an analysis resolving how those missing outcomes might affect the comparison. This limits confidence in extending the observed comparison to all enrolled participants.

The endpoint is the presence or absence of scarring, not a detailed measure of scar appearance, participant satisfaction, or pain. Although the study summary describes satisfaction and pain questionnaires, their results are not reported in the registry record. The registry’s primary outcome is labeled at 1 week, while its description mentions assessment at 1 week and 3 weeks; a distinct later result is not reported.

Accordingly, the findings describe an imprecise comparison in the available records. They neither establish that one suture is superior nor demonstrate equivalence. The reported secondary outcomes provide separate observations and are unadjusted; they do not resolve the uncertainty in the primary scarring comparison. No treatment recommendation follows from these registry results alone.

17. Why This Trial Matters Statistically

This trial illustrates how the amount of observed information can matter as much as the point estimate. The primary estimate is close to zero, but the confidence interval is broad and crosses zero. A reader who focuses only on the estimate or p-value could miss that the data remain compatible with a range of differences in either direction. Statistical interpretation requires both the direction of the estimate and the precision with which it is measured.

The study also highlights the difference between enrollment and an outcome-specific analysis population. Although 97 participants enrolled and the registry reports assignment to both groups, primary outcome information was available for 55. Missing outcomes can reduce precision and can challenge the comparability created by randomization if those missing differ from those observed. The registry does not report methods to evaluate or address this issue.

Finally, multiple outcomes make a clear analysis plan important. Scarring is the primary outcome, while infection and suture fall-out provide additional information. Because the secondary tests are unadjusted and the registry does not report a multiplicity strategy, those findings should be treated as context rather than as independent confirmation. These are general statistical concerns that apply whenever studies compare groups on several outcomes and have incomplete follow-up.

The registry record is useful for seeing what was enrolled, what outcomes were recorded, and how uncertain the primary comparison is. Its limitations also show why transparent reporting of planned analyses, missing-data handling, outcome timing, and safety collection is important for interpreting clinical research.

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 are specific to this record. The primary result is based on 55 participants, while the registry reports 97 enrolled and 42 lost to follow-up or with missing data. The number and reasons for missing outcomes by group are not reported. This leaves uncertainty about whether the observed participants represent the randomized groups as a whole.

The primary result is labeled with a 1-week timeframe, but the outcome description says assessments were conducted at 1 week and 3 weeks. A separate result for the later assessment is not reported in the registry record. This makes the timing of the posted primary comparison less fully documented than the outcome description suggests.

The registry’s terminology for the polyglactin group is not fully consistent: the intervention entry names polyglactin 910, while the brief summary and arm description refer to PDS. The record does not clarify this naming difference. Eligibility criteria, detailed randomization procedures, allocation concealment, the original sample-size justification, and the statistical analysis plan are also not reported.

The primary endpoint records scarring only as present or absent, and results for cosmetic satisfaction and pain described in the study summary are not reported. The secondary results are unadjusted, and the registry does not describe a plan for multiple comparisons. Adverse-event details are limited, and deaths are not reported in the registry record. These limitations constrain interpretation of both the outcome comparisons and their applicability beyond the recorded participants.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: A Comparison of Polyglactin 910 and Chromic Gut Suture in the Closure of Punch Biopsy Sites — NCT01722994.
• Registry record last updated 2016-03-02; status last verified 2016-02.
• Results first posted 2016-03-02.
• 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

NCT01722994 is a completed phase 4 randomized parallel-group study comparing absorbable sutures for punch-biopsy wound closure. The registry reports 97 enrolled participants, with 49 assigned to chromic gut and 48 to polyglactin 910. The primary endpoint is presence of scarring, with a reported 1-week timeframe.

Primary outcome information was available for 55 participants: 24 in the chromic gut group and 31 in the polyglactin 910 group. The risk-difference estimate is -0.009, with a confidence interval from -0.111 to 0.092 and an unadjusted p-value of 0.853. The interval includes zero and effects in either direction. The registry also reports infection and time until suture fall-out as secondary outcomes.

Missing follow-up, unresolved suture naming, limited outcome detail, and the absence of a reported analysis plan constrain interpretation. The registry does not report the original sample-size justification or methods for handling missing data and multiple comparisons.