Limberg-flap: Prospective Data Collection: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Limberg-flap: Prospective Data Collection (NCT00672555), a na na study. The primary outcome is Recurrence of a Pilonidal Sinus After Operation Using a Limberg-flap Procedure.

2. Clinical Question

The study also aimed to assess feasibility, results, complications, and patients’ opinions after treatment. Those aims fit a prospective evaluation of a procedure in a clinical setting, but they do not turn the design into a controlled comparison. Without a comparator, the study can describe outcomes recorded in the treated group; it cannot isolate the effect of the procedure from other influences or establish how outcomes would have differed under another approach.

3. Trial Design

This was a prospective, single-group data collection study of excision and defect coverage with a Limberg flap for pilonidal sinus. The registry lists the model as single group, the allocation as not applicable, and masking as none. It does not describe random assignment or a control arm. The listed enrollment is 70.

The record describes the primary-outcome population as per protocol: patients treated during the study period who gave informed consent, met inclusion criteria, and had no reason for exclusion. It also states that all patients were assessed at one year for recurrence. However, the record does not provide the number included in the primary analysis, explain whether any participants lacked follow-up, or give a recurrence count. Enrollment alone should not be assumed to equal the number with a recorded outcome.

The study began in 2006-08, had primary completion in 2009-01, and is listed as completed. Its phase is recorded as NA. The registry names the Cantonal Hospital of St. Gallen as sponsor. No protocol, detailed statistical analysis plan, or sample-size justification is reported in the registry record. The registry’s stated intention was to evaluate feasibility and results, with a prospective randomized study described as a possible further option if results were good. That future possibility is not a feature of the design evaluated.

Because there was no concurrent comparison group, the design is best read as descriptive. It can document what was observed among participants treated with the flap, if those outcomes are reported, but it does not provide a randomized estimate of comparative benefit or harm. The registry does not report an analysis record for the outcomes.

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.

Before assignment: 1 patient excluded because of mental handicap

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per protocol: All patients treated in the study period, who gave their informed consent and meet the inclusion criteria, as well did not have any reason for exclusion were enrolled prospectively

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 Recurrence of a Pilonidal Sinus After Operation Using a Limberg-flap Procedure, measured over 1 year.

The primary endpoint is recurrence of pilonidal sinus after operation using a Limberg-flap procedure. It is defined as a count: the number of participants with a recurrence, assessed at one year. This is a binary outcome at the participant level, because each assessed participant is classified according to whether recurrence was recorded. The registry describes the endpoint as a number of patients rather than as a time-to-event measure or a measure of recurrence severity.

Recurrence is relevant to the study’s stated purpose because the investigators were evaluating results after introducing the procedure for recurrences of the illness at their clinic. A clearly defined follow-up point gives the outcome a specified assessment horizon and makes the intended measure understandable. It does not, by itself, establish how complete follow-up was or how recurrence was determined. Those details are not reported in the registry record.

The record says patients were assessed at one year, but it does not give the recurrence count or an analysis result. Therefore, the endpoint’s definition is available, while its observed result and precision are not. Without the count and the number actually assessed, no event proportion or uncertainty interval can be interpreted from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The design determines the kinds of conclusions that can be drawn. This study is listed as single group, with allocation recorded as not applicable and masking as none. In general, a single-group study describes outcomes among people who received the studied intervention. It has no concurrent control outcome against which to estimate a treatment contrast. A prospective approach can specify the intended follow-up and collect outcomes as participants are followed, but prospective collection does not remove the need to report who was assessed and what was observed.

What does a binary endpoint mean?

The primary endpoint is a count of participants with recurrence at one year. For a binary outcome, each participant contributes a classification such as event or no event, provided the outcome is known. A count is most interpretable alongside its denominator: the count tells how many events were observed, while the denominator tells how many participants contributed outcome information. A proportion can describe the event frequency, and an uncertainty interval can show how imprecisely that frequency is estimated. The registry gives the endpoint definition and enrollment, but it does not report the recurrence count, the analyzed denominator, or an interval. No recurrence proportion or interval can therefore be read from this record.

Why does the assessment time matter?

The stated timeframe is one year. A result at a specified assessment point is tied to that follow-up horizon; it should not be treated as a lifetime outcome or as evidence about recurrence after that point. The registry says that all patients were assessed at one year, but it does not describe the assessment procedure, completeness of ascertainment, or handling of participants without a recorded assessment. Those details affect how an outcome count should be interpreted.

What does the single-group design permit?

A descriptive event count can characterize the experience of participants in the study, if the outcome and analysis denominator are available. It cannot by itself show that the procedure caused the observed outcome or that it performs better or worse than an alternative. In comparative trials, random allocation is used to support a fair comparison by balancing, on average, measured and unmeasured factors across groups. This study has no randomized comparison. The registry therefore does not support an estimate of a between-treatment effect.

Masking is recorded as none. In general, knowledge of the treatment can influence subjective outcome assessment or participant-reported outcomes, depending on how those outcomes are collected. Recurrence may involve clinical judgment, while satisfaction, body image, and cosmetic scores are inherently patient-centered measures. The registry record does not explain who assessed recurrence, how subjective outcomes were measured, or whether assessors were independent. The effect of the absence of masking cannot be quantified from the record.

What can confidence intervals and significance tests tell readers?

In general, a confidence interval expresses the statistical uncertainty around an estimate under the assumptions of the analysis. A narrow interval indicates greater precision than a wide interval, while neither an interval nor a significance test addresses every source of bias. A p-value, if reported, assesses how compatible the data are with a specified statistical model and null hypothesis; it is not a measure of clinical importance or the probability that a treatment works. The registry record contains no analysis records and does not report a primary-outcome estimate, confidence interval, or p-value. No inferential conclusion can be drawn from a significance test that is not reported.

How should planning calculations be read?

Sample-size illustrations are planning calculations, not observed results and not evidence of achieved power. The stated planning assumptions describe two-sided significance level 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. They are not the design of this single-group study, which has no two-arm allocation. The registry record does not report the trial’s own sample-size justification. Any planning illustration should be read as hypothetical rather than as a description of the study’s enrollment rationale or an observed treatment effect. Because the registry record does not report the primary recurrence result, the observed effect that such an illustration would use is not available for clinical interpretation.

General statistical methods can clarify what a complete result would need to communicate: the outcome count, the number assessed, the method used to handle missing observations, and an estimate with an appropriate measure of uncertainty. These details are not reported for the primary endpoint in the registry record. The endpoint’s definition is not a substitute for those results, and enrollment by itself does not supply them.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Pilonidal Sinus Treated With Limberg Flap")
n      <- c(70)
events <- c(1)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Pilonidal Sinus Treated With Limberg Flap  70  1  1.4  0.0  7.7  0.3  7.7  0.3  7.6

11. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures and identifies recurrence at one year as the primary outcome. Listed secondary outcomes include minor wound complications, reoperations for treatment of complications, overall satisfaction with the procedure, body image score, and cosmetic score. Multiple outcomes create a multiplicity issue: when many outcomes are examined, the chance of at least one apparently notable result can increase. In general, a statistical plan may specify which outcome is primary and whether any adjustment or hierarchy will be used. No multiplicity strategy is reported in the registry record, and the record lists no analysis records.

The record does not report results for the primary endpoint or the listed secondary outcomes. It also does not describe a missing-data method, imputation, sensitivity analysis, or how participants without a recorded outcome would be handled. Although the primary-outcome description says all patients were assessed at one year, no follow-up accounting or analyzed denominator is reported. A statement about intended assessment does not establish that all outcome information was available or analyzed.

The primary population is described as per protocol, consisting of treated patients who consented, met inclusion criteria, and had no exclusion reason. The registry does not report how many participants met that definition for analysis or whether any enrolled participants were excluded from the primary analysis. It does not describe an intention-to-treat analysis. These omissions limit assessment of whether the analyzed population matches the enrolled population and whether missing outcomes could affect the findings.

12. 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 1% reporting threshold.

Most frequent non-serious adverse event terms

The registry’s adverse-event record separates serious events from other events. It records 0 serious adverse events among 70 at risk and 18 other adverse events among 70 at risk for the group treated with a Limberg flap. These are counts, not comparative estimates. The registry does not provide event descriptions for the other category in the registry record, nor does it report a comparison group.

A count of 0 serious events in this study should be read as no serious events recorded in the registry category for this group, not as proof that serious events are impossible or that the risk is absent. General interpretation of uncommon events depends on the amount and duration of observation, definitions, and completeness of reporting. The record does not provide enough detail to assess those features or to calculate an uncertainty interval.

The deaths field has no numerical result reported in the registry record. The adverse-event counts also do not answer the primary recurrence question. They should be interpreted separately from recurrence and from the listed patient-reported outcomes.

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

The record establishes what the study set out to examine: prospective outcomes after excision and coverage of a pilonidal sinus defect with a Limberg flap, including recurrence at one year. It also records enrollment of 70 and adverse-event counts for the treated group. These registry entries describe the design and selected recorded outcomes, but they do not provide the primary recurrence result.

Because the recurrence count and analyzed denominator are not reported in the registry record, the primary endpoint cannot be quantified or assessed for precision. The absence of that result does not mean there were no recurrences; it means the registry record does not state how many were observed. Likewise, the study’s stated aim to evaluate feasibility, complications, and patient opinion is not evidence that those outcomes were favorable. Results for the secondary outcomes are not reported in the registry record.

Even if a complete single-group outcome count were available, it would describe the participants treated in this study and would not establish a comparative treatment effect. No concurrent comparator was included, and the study was not randomized. A difference from outcomes reported elsewhere, if one were considered, would not by itself be a controlled estimate because the populations, care settings, outcome definitions, and follow-up could differ.

The adverse-event figures document the registry categories and counts, but they do not establish comparative safety or rule out unrecorded events. They also do not provide detail about event severity beyond the serious-versus-other categorization. The appropriate conclusion is therefore narrow: this registry record describes a prospective single-group evaluation and reports certain adverse-event counts, while leaving the central recurrence result and secondary-outcome results unavailable for interpretation.

14. Why This Trial Matters Statistically

This study is statistically useful as an example of the distinction between a clearly stated clinical question and a result that can be quantitatively interpreted. The registry defines a specific primary outcome, a recurrence count at one year, and describes a prospective population treated with the procedure. Those details identify what the investigators intended to measure. However, an endpoint definition cannot replace the event count, denominator, and uncertainty estimate needed to characterize the observed outcome.

The single-group design also makes the limits of descriptive evidence visible. A prospective cohort can document outcomes in the clinical setting where treatment is introduced. It may help describe feasibility and generate questions for later research. But without a concurrent comparator, it cannot estimate how outcomes differ under another treatment. The registry itself describes a randomized study as a possible future option; that possibility should not be confused with the design of this completed study.

The entry also illustrates why outcome reporting and analysis transparency matter. Recurrence, wound complications, reoperations, satisfaction, body image, and cosmetic score address different aspects of experience. Without the results and analysis details, readers cannot assess the observed patterns, precision, or potential impact of missing data and multiple outcomes. The adverse-event counts add some descriptive safety information, but they do not fill those gaps.

For biostatistical interpretation, the key distinction is between study aims, recorded design features, and reportable results. The first two are present in the registry record; the primary outcome result is not. Keeping those categories separate prevents a design description or a planning illustration from being mistaken for evidence of an observed treatment effect.

15. 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 principal limitation for interpreting this registry entry is the absence of the primary recurrence count. Although recurrence at one year is clearly identified as the primary outcome, no estimate, denominator, or uncertainty measure is reported. The stated enrollment of 70 does not establish how many participants contributed to the endpoint analysis. The record’s statement that all patients were assessed does not provide participant-level follow-up accounting.

The single-group design has no concurrent comparator and no random allocation. Consequently, the study cannot estimate a controlled difference between the Limberg-flap procedure and another approach. The absence of masking is recorded, but the registry does not describe outcome assessors or assessment procedures. This leaves uncertainty about how recurrence and subjective outcomes were determined.

Results for the listed secondary outcomes are not reported in the registry record. The record also does not describe multiplicity handling, missing-data procedures, an analysis plan, or a sample-size justification. The per-protocol population is defined in words, but the number analyzed and any exclusions are not stated. These gaps prevent assessment of analysis-population selection and the possible influence of missing observations.

Finally, adverse-event reporting is limited to counts in serious and other categories. Details of the other events, duration of safety follow-up, and numerical death information are not reported in the registry record. The adverse-event counts therefore offer only a restricted description and do not support comparative safety conclusions.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Limberg-flap: Prospective Data Collection — NCT00672555.
• Registry record last updated 2011-06-29; status last verified 2011-06.
• Results first posted 2011-06-29.
• 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.

19. Record Summary

NCT00672555 is listed as a completed, prospective, single-group study of excision and Limberg-flap coverage for pilonidal sinus. The sponsor is Cantonal Hospital of St. Gallen. The recorded start is 2006-08, primary completion is 2009-01, and enrollment is 70. Allocation is listed as not applicable, masking as none, and phase as NA.

The primary endpoint is the number of participants with pilonidal sinus recurrence at one year. The registry record describes a per-protocol population and says patients were assessed at that time, but does not report the recurrence count or analysis denominator. Secondary outcomes concern wound complications, reoperations, satisfaction, body image, and cosmetic score; their results are not reported in the registry record.

The adverse-event record lists 0 serious events among 70 at risk and 18 other events among 70 at risk. No analysis records are listed. The record does not report a sample-size justification, missing-data method, or multiplicity strategy.