Intraoperative Trocar Slippage Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Intraoperative Trocar Slippage Study (NCT01476748), a randomized phase 3 study. The primary outcome is Trocar Slippages With LaproStop.

2. Clinical Question

3. Trial Design

The registry identifies NCT01476748 as a randomized study with single masking and a single-group model. It lists three trocar arms: Covidien Versaport, Ethicon Xcel, and Storz Reusable. Each listed arm has 5 participants. The record gives overall enrollment as 15. It does not explain how the single-group model label relates to the three arm entries.

The official title calls the study a pilot study, and the primary outcome population is also described as a pilot study. The registry nevertheless lists the phase as phase 3. The record does not explain this combination of labels. It describes random assignment to trocar groups and says LaproStop was assigned to one of two trocars by chance. However, the arm descriptions associate LaproStop with all three listed trocar groups. This leaves the device allocation structure unclear from the registry record.

The primary outcome concerns participant counts with slippage when using LaproStop. A secondary outcome is named for slippages without LaproStop. The record identifies two outcome measures but posts numerical results only for the primary outcome. It lists no analyses. The masking designation is single, but who was masked and what information was masked are not reported in the registry record.

The record gives the study status as completed. It does not report the randomization method, allocation concealment, study protocol, statistical analysis plan, or sample-size justification. These omissions limit how fully the planned design and the relationship between the reported arms and comparisons can be assessed.

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: All enrolled participants were included in the trial

Overall Study

Analysis population for the primary outcome, as defined in the registry: Pilot 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 Trocar Slippages With LaproStop, measured over During the hysterectomy procedure, up to 2 hours and 32 minutes.

The primary endpoint is the number of participants with trocar slippages while using LaproStop. The unit is participants, and the outcome is recorded as a count of participants with an event. Its stated timeframe is during the hysterectomy procedure, up to 2 hours and 32 minutes. This endpoint focuses on whether a participant experienced a slippage, rather than reporting the number of slippage episodes per participant or the distance a trocar moved.

Participant-level event counts can describe how often the recorded event occurred within each group. In this study, the posted counts are 1 for Covidien Versaport, 2 for Ethicon Xcel, and 3 for Storz Reusable, with 5 participants in each listed arm. The registry does not provide a definition of slippage, a measurement procedure, or information about how events were adjudicated. Those details are important for understanding what qualifies as an event and whether the outcome was assessed consistently across groups.

The brief summary also names the broader aim of assessing slippage without LaproStop. That is reflected in the named secondary outcome, but numerical results for it are not reported in the registry record. Accordingly, the primary endpoint alone cannot describe the effect of LaproStop relative to its absence.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What do the posted counts represent?

The primary outcome is a count of participants who had a slippage with LaproStop. The posted arm results are 1 for Covidien Versaport, 2 for Ethicon Xcel, and 3 for Storz Reusable. The corresponding listed arm size is 5 for each group. These values are event counts, not percentages, rates, or model-based estimates. Converting them into other quantities would require calculations not reported in the registry record, so the interpretation should remain with the posted counts.

A binary outcome records whether an event occurred for a participant. When participant-level information is reduced to a group count, details such as event timing, repeated episodes, and participant characteristics are not visible. The registry does not report those details for this outcome. It also does not describe the operational definition of slippage or the measurement process, which limits assessment of how consistently events were identified.

Why would an interval estimate matter?

General statistical explanation: a confidence interval expresses uncertainty around an estimate. It indicates which values remain reasonably compatible with the data under the model used to calculate it. A point estimate alone does not convey that uncertainty. With few observations, uncertainty can be considerable, so interval estimates can help distinguish a stable estimate from one that could plausibly vary widely.

No confidence interval or other uncertainty measure is reported for the posted counts. The record also lists no statistical analyses. Therefore, it is not possible to assess the precision of group comparisons, or to determine from the registry whether a formal hypothesis test was planned or performed. The absence of a reported p-value is not evidence that groups are equivalent or that there is no difference.

What does random allocation contribute?

General statistical explanation: random allocation can reduce systematic differences between groups at the point of assignment, on average, when implemented as planned. It does not guarantee that groups will be alike in every characteristic, particularly in a study with limited enrollment. Interpretation also depends on knowing what was randomized and how allocation was conducted.

The registry labels allocation randomized and says patients were randomly assigned to trocar groups. Its brief summary also describes assigning LaproStop to one of two trocars by chance. However, the arm descriptions list LaproStop with each trocar group. The method of sequence generation, concealment, and the intended allocation of the device are not reported in the registry record. The single-masking designation is recorded, but the identity of the masked party is not reported.

What can be said about sample-size planning?

The registry record describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It also says the effect to detect is expressed as a fraction of the observed effect. Such an illustration concerns a hypothetical future design; it is not a measure of the probability that this completed study detected an effect.

General statistical explanation: a sample-size calculation depends on assumptions about the effect to be detected, variability, allocation, and the decision rule. If those assumptions change, the planning result can change. A calculation based on an observed effect is especially dependent on the stability of that estimate. The registry record does not report numerical planning outputs or a design justification for this trial, so no particular required sample size can be interpreted from the record.

Sample-size planning should not be confused with observed power. Observed power is not a substitute for an effect estimate and its uncertainty. The registry’s planning description refers to illustrations, not to a reported analysis of the trial’s ability to detect an effect.

What is not documented?

The registry lists no analyses and does not report a statistical analysis plan. It does not specify whether analyses were intended to be descriptive, whether comparisons were adjusted, how missing outcomes would be handled, or which analysis population would be used. These omissions prevent reconstruction of an inferential analysis from the posted information. General statistical principle: model choice and analysis rules should be defined in relation to the outcome, design, and estimand; they cannot be inferred reliably from the outcome counts alone.

Because the primary result is a participant count and no inferential analysis is posted, there is no basis in the registry record for evaluating model assumptions, over-dispersion, or adjustment for covariates. General statistical explanation: over-dispersion occurs when observed variation exceeds what a chosen statistical model expects; addressing it matters when a model is used to estimate uncertainty. It is not possible to assess that issue from the aggregate counts without a reported model or analysis.

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("Covidien Versaport Trocars", "Ethicon Xcel Trocars", "Storz Reusable Trocars")
n      <- c(5, 5, 5)
events <- c(1, 2, 3)
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  Covidien Versaport Trocars  5  1  20.0  0.5  71.6  3.6  62.4  4.3  64.1
ARM  Ethicon Xcel Trocars  5  2  40.0  5.3  85.3  11.8  76.9  11.8  77.7
ARM  Storz Reusable Trocars  5  3  60.0  14.7  94.7  23.1  88.2  22.3  88.2

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary outcome, “Trocar Slippages With LaproStop,” and names a secondary outcome, “Trocar Slippages Without LaproStop.” It lists two outcome measures, but numerical results are posted only for the primary outcome. Results for the secondary outcome are not reported in the registry record.

When a study considers multiple outcomes or comparisons, the chance of a false-positive finding can depend on how many tests are conducted and how the analysis is planned. General statistical principle: multiplicity procedures can control that risk, but the appropriate approach depends on the hypotheses and testing strategy. The registry record does not report a multiplicity plan, a hierarchy of tests, or any testing procedure. It also lists no analyses, so the use of any such approach cannot be established from the posted information.

The record does not report how missing outcome data were defined or handled, whether participants could be excluded after randomization, or what analysis population was planned. It does not describe a missing-data imputation method or sensitivity analysis. These are not details that can be inferred from the arm counts alone.

General statistical principle: missing data can affect estimates when the availability of an outcome is related to participants’ characteristics or event status. Reporting how many outcomes were assessed and how absent data were handled helps readers judge possible bias. Those details are not reported in the registry record. The record’s randomized designation does not by itself establish that an intention-to-treat analysis was conducted; no analysis population is specified.

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 0% reporting threshold.

The serious adverse event entries list 5 participants at risk and 0 affected in each of the Covidien Veraport, Ethicon Xcel, and Storz Reusable groups. The entries for other adverse events also list 5 participants at risk and 0 affected in each group. These are the safety figures recorded in the registry; they should be read as reported counts for the listed groups, not as proof that no events could occur.

The deaths field is null for each group. A null entry is not the same as a reported count of zero. The registry record therefore does not report death counts for these groups. No serious adverse event terms are listed.

General statistical explanation: a zero count in a study group does not establish that the underlying risk is zero. Limited observation can leave substantial uncertainty about uncommon events, and safety interpretation depends on the observation period, definitions, completeness of reporting, and follow-up. The registry gives the primary outcome timeframe, but does not provide additional detail about safety ascertainment or follow-up. The safety entries should therefore be understood as recorded event counts, not as a comprehensive estimate of safety.

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

The registry reports participant counts with trocar slippages while using LaproStop: 1 in the Covidien Versaport group, 2 in the Ethicon Xcel group, and 3 in the Storz Reusable group. Each listed group has 5 participants. These results describe what was recorded in this pilot study during the hysterectomy procedure. They do not, by themselves, show whether the differences among the groups are meaningful or would persist in another study.

The primary outcome is not a direct comparison of LaproStop with no LaproStop. Although the study description and named secondary outcome concern slippages without LaproStop, numerical results for that outcome are not reported in the registry record. The available counts therefore do not establish an effect attributable to the device. The record also does not clarify the device allocation structure, which further limits interpretation of comparisons involving LaproStop.

No inferential analysis, uncertainty interval, or p-value is reported. The counts cannot establish the precision of an estimate, and they should not be treated as evidence of equivalence between trocar groups or as evidence that a difference is absent. The record does not report a definition of slippage, a detailed assessment procedure, or participant-level data that would permit a more complete evaluation.

The results are specific to the listed groups and the stated procedure timeframe. The registry record does not report participant characteristics or enough details to judge how closely the study population represents other settings. The study is described as a pilot, but the record does not report its design rationale or sample-size justification. Its phase is listed as phase 3; the record does not explain that designation alongside its pilot-study description.

The appropriate reading is narrow: the registry posts descriptive primary-outcome counts and limited adverse-event counts, while leaving key design and analysis details unreported. These data alone do not support medical advice or a broader conclusion about the performance of a trocar or device.

14. Why This Trial Matters Statistically

This record illustrates the distinction between descriptive results and inferential evidence. Participant counts can show what was recorded in each study group, but comparisons require an analysis that accounts for uncertainty. Here, the registry posts counts for the primary outcome but lists no analyses, effect estimates, confidence intervals, or p-values. Readers therefore cannot assess the precision of a comparison from the registry results.

The study also highlights why a clearly defined estimand matters. The primary endpoint concerns slippage with LaproStop, while the stated broader aim includes slippage without the device. A secondary outcome is named for the latter, but its numerical results are not reported in the registry record. The record’s difference between the brief summary’s allocation description and the arm descriptions adds uncertainty about which contrasts the posted data represent.

General statistical principle: a randomized design is most interpretable when the randomized units, treatment conditions, comparator, outcome, and analysis population are clearly documented. Randomization alone does not resolve ambiguity in how the intervention was assigned or how outcomes were analyzed. The registry identifies random allocation, but does not report the allocation method, masking details, analysis plan, or missing-data approach.

The record is also a useful reminder that safety counts need context. Zero recorded serious or other adverse events in the listed groups does not establish absence of risk, and null death entries should not be read as zero. Clear distinctions among zero, missing, and unreported values are important for statistical interpretation.

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.

Several limitations arise from the registry record itself. Although the trial is labelled randomized, the allocation method and concealment procedures are not reported. The record describes random assignment to trocar groups and chance assignment of LaproStop to one of two trocars, but its arm descriptions associate the device with all three listed groups. This leaves the treatment structure unclear. The model is labelled single-group even though the record lists three arms, and it does not explain that classification.

The primary outcome is a participant count, but the record does not define slippage or describe how it was measured and adjudicated. No participant characteristics or participant-level outcome data are reported. Numerical results for the named secondary outcome are not reported in the registry record. The registry lists no analyses, and does not provide an analysis plan, uncertainty estimates, or comparison results.

There is also a naming difference: the outcome arm calls the Covidien group “Versaport,” while the arm description uses “Veraport.” The record does not explain whether these labels refer to the same trocar. The phase is listed as phase 3, while the official title and primary outcome description identify the study as a pilot; no explanation is reported.

The safety entries report zero serious and other adverse events in each group, but death values are null. Safety definitions, ascertainment details, and follow-up information beyond the primary outcome timeframe are not reported. Finally, the record does not report a sample-size justification or the numerical results of its planning illustration. These omissions constrain interpretation of both efficacy-related outcomes and safety.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Intraoperative Trocar Slippage Study — NCT01476748.
• Registry record last updated 2014-09-17; status last verified 2014-09.
• Results first posted 2014-08-29.
• 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

NCT01476748 is listed as a completed randomized study with single masking and a single-group model. The registry reports enrollment of 15 and lists three trocar arms, each with 5 participants. The study is described as a pilot study and is listed as phase 3.

The primary outcome is the number of participants with slippages with LaproStop during the hysterectomy procedure, up to 2 hours and 32 minutes. The posted counts are 1 for Covidien Versaport, 2 for Ethicon Xcel, and 3 for Storz Reusable. A secondary outcome concerns slippages without LaproStop, but numerical results for it are not reported in the registry record. The record lists no analyses.

The registry records zero serious and other adverse events in each listed group; death values are null. It does not report inferential results, a detailed statistical plan, or key details about allocation and outcome measurement. The posted results are descriptive and do not provide a formal estimate of comparative effects.