This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for TAP Block With Liposomal Bupivacaine Versus Bupivacaine in Robotic Hysterectomy (NCT02289079), a randomized phase 4 study. The primary outcome is Post Operative Opioid Use.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02289079 |
| Phase | Phase 4 |
| Condition | Acute Pain |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Triple |
| Enrollment | 60 |
| Arms in the primary outcome | 2 |
| Lead sponsor | University of Minnesota |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing robotic hysterectomy are the population described. The registry record does not report further eligibility criteria or participant characteristics in the primary outcome description, so the results cannot be placed in a more detailed demographic or clinical context from this record alone.
Intervention
The intervention was a subcostal transversus abdominis plane block using liposomal bupivacaine. The study description identifies the procedure as an ultrasound-guided TAP block and says the medication was injected during the block.
Comparator
The comparison group received a subcostal TAP block with bupivacaine. Both medications are described in the registry summary as standard of care in these types of surgeries; that description is not itself a comparison of trial results.
Primary question
The primary question was whether postoperative opioid use differed between the groups during the 0-72 hours after injection. Opioid use was expressed as micrograms of fentanyl equivalents, with the primary outcome reported as a median and full range. The registry record does not post a statistical test or confidence interval for this primary comparison.
3. Trial Design
The record describes a prospective randomized study with a parallel-group design. It lists triple masking, indicating the registry's recorded masking category, but does not specify which people involved in the trial were masked or how masking was maintained. The allocation method beyond randomization is not reported in the registry record.
The two treatment groups received subcostal TAP blocks with either liposomal bupivacaine or bupivacaine. The study was registered as phase 4, was sponsored by the University of Minnesota, and is marked completed. The recorded enrollment is 60. The study start is listed as 2013-06 and the primary completion as 2014-10.
The primary outcome was postoperative opioid use over the 0-72 hours after injection, expressed in micrograms of fentanyl equivalents. The registry reports a median and full range for each group. It also lists numerical rating scale, postoperative length of stay, and patient satisfaction assessed by survey as secondary outcomes. Four outcome measures are recorded overall, while three secondary outcomes are listed. The record does not provide a detailed account of the measurement schedule or analysis populations for these measures.
Although the record identifies randomization and masking, it does not report the sequence-generation method, allocation concealment, or operational masking procedures. It also does not give the protocol, a statistical analysis plan, or a sample-size justification. Those details should not be inferred from the design labels alone.
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
| Stage | Liposomal Bupivacaine TAP | Bupivacaine TAP |
|---|---|---|
| STARTED | 30 | 30 |
| COMPLETED | 28 | 29 |
| NOT COMPLETED | 2 | 1 |
Reasons for not completing this period:
| Reason | Liposomal Bupivacaine TAP | Bupivacaine TAP |
|---|---|---|
| Physician Decision | 2 | 0 |
| Lost to Follow-up | 0 | 1 |
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.
| Characteristic | Unit | Liposomal Bupivacaine TAP | Bupivacaine TAP | Total |
|---|---|---|---|---|
| Participants analysed | 28 | 30 | 58 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 20 | 25 | 45 |
| Age, Categorical: >=65 years | Participants | 8 | 5 | 13 |
| Sex: Female, Male: Female | Participants | 28 | 30 | 58 |
| Sex: Female, Male: Male | Participants | 0 | 0 | 0 |
| Region of Enrollment: United States | participants | 28 | 30 | 58 |
| weight | kilograms | 89.3 (SD 25.1) | 98.5 (SD 34.2) | 93.5 (SD 30.2) |
6. Primary Endpoint
The registry lists the primary outcome as Post Operative Opioid Use, measured over 0-72 hours after injection.
| Element | Registry entry |
|---|---|
| Result type | Median |
| Measure of spread | Full Range |
| Unit | micrograms of fentanyl equivalents |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is postoperative opioid use, measured as micrograms of fentanyl equivalents during the 0-72 hours after injection. Expressing opioid use in fentanyl equivalents allows opioid amounts to be represented on a common scale for the endpoint, rather than leaving different opioid medicines in separate units. The registry describes the endpoint as intended to assess whether liposomal bupivacaine provides decreased narcotic use compared with bupivacaine when used in a TAP block.
The result is reported as a median and full range for each group. A median describes the middle observation after values are ordered; it is often useful when data are skewed or include unusually high values. The full range gives the lowest and highest reported values, but does not show how observations are distributed between those extremes. It is not a measure of uncertainty about the median.
The registry record does not report a confidence interval, hypothesis test, or adjusted estimate for this primary endpoint. Thus, the posted group summaries describe the observed opioid-use values, but do not by themselves quantify the precision of a between-group effect or establish whether the observed separation is distinguishable from sampling variation.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary results give median opioid use of 24.9 micrograms of fentanyl equivalents in the liposomal bupivacaine TAP group and 51.7 in the bupivacaine TAP group during the 0-72 hours after injection. The corresponding full ranges are 0.0 to 86.7 and 0.0 to 249.7. These are descriptive group summaries. The registry record does not post an inferential comparison for the primary endpoint, such as a confidence interval or p-value.
The medians indicate the central observed values in the two groups, while the ranges show that values extended from 0.0 in both groups to different upper endpoints. Ranges alone do not show how densely observations were concentrated, whether there were clusters or outliers, or how uncertain the difference between group medians may be. The primary outcome result should therefore be read as a summary of posted observations, not as a precise estimate of a treatment effect.
The record also posts a comparison for postoperative length of stay. The reported group means are 11.0 hours and 17.0 hours, respectively, and the unadjusted recalculated mean difference is 6.0 hours, with a 95% confidence interval from -0.079 to 12.08 and p = 0.053. This comparison is not the primary endpoint. Its confidence interval includes values on either side of zero, and the p-value is close to, but above, the conventional 0.05 threshold. Neither a threshold comparison nor the interval alone establishes a clinical interpretation. The record does not report an adjusted analysis for this result.
The secondary comparison is a simple unadjusted recalculation from posted summary statistics. It should not be mistaken for an analysis specified by the trial investigators: reported analyses are not listed in the registry record. The record indicates no discrepancy between the posted values and the recalculated comparison, but that does not substitute for a complete prespecified analysis.
For the primary outcome, there is no posted test result to interpret as statistically significant or not statistically significant. The two median values differ descriptively, but the registry record does not supply the information needed to judge the precision of that primary contrast. The conclusion must remain bounded by the posted summaries and the absence of a reported primary inferential analysis.
9. Statistical Methods Explained
Statistical interpretation depends on what each summary represents. A group median is a measure of location: after the observations are ordered, it marks the central value. It is less affected by extreme observations than a mean, which makes it useful for outcomes that may be skewed. A median does not, however, quantify uncertainty in a comparison. The full range reports only the observed minimum and maximum, and gives little information about the pattern of values between those points.
What does a confidence interval convey?
In general, a confidence interval describes the precision of an estimate under the assumptions of the method used to construct it. A wider interval indicates greater uncertainty about the estimate than a narrower interval. For the posted length-of-stay comparison, the interval runs from -0.079 to 12.08 hours around the mean difference of 6.0 hours. Because the interval includes zero, it is compatible with no mean difference as well as with differences on either side of zero under the calculation used. It is not a probability statement that the true effect lies within this particular interval.
The posted p-value for that secondary comparison is 0.053. In general, a p-value describes how unusual data at least as incompatible with a specified null hypothesis would be if that hypothesis and the test assumptions held. It does not measure the probability that the null hypothesis is true, nor does it measure clinical importance. The registry record does not say that this unadjusted comparison was prespecified or identify the test used by the investigators.
Why distinguish descriptive summaries from comparisons?
Group summaries answer what values were observed within each arm. A comparison estimates how those summaries differ between arms. For the primary endpoint, the record posts group medians and ranges but no inferential comparison. It is therefore not appropriate to attach a precision estimate or a significance conclusion to the primary result using information that is not reported in the registry record.
The length-of-stay comparison is an unadjusted recalculation from the posted means, standard deviations, and group sizes. Such a calculation uses summary statistics rather than participant-level records. It does not account for covariates, departures from the calculation's assumptions, or decisions made in the trial's own analysis. No investigator-reported analyses are listed. The record marks the discrepancy flag as false, but this does not mean that the recalculation was the sponsor's prespecified analysis.
What do the planning illustrations mean?
The planning illustrations are based on the observed length-of-stay effect and are not the trial's own design justification. The stated assumptions are a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The illustrations consider planning for 100%, 75%, and 50% of the observed effect, with participants per arm reported for 80% and 90% power. These are prospective planning scenarios. They are not observed power, do not describe the power of the completed trial, and do not establish that the chosen effect sizes are clinically meaningful.
In general, planning calculations depend on the target effect and variability assumptions. A smaller effect to detect generally requires more participants than a larger effect when other assumptions are held fixed. That general principle explains why illustrations at different fractions of an observed effect can produce different sample-size requirements; it does not validate the observed effect as a reliable planning target. The registry record does not report the trial's sample-size justification, so the planning illustrations should not be presented as the rationale used to enroll participants.
How should outcome variability be considered?
The primary endpoint uses medians and ranges, while the secondary length-of-stay endpoint uses means and standard deviations. These summaries answer different questions and should not be treated as interchangeable. In general, the mean is sensitive to extreme values, whereas the median is more resistant to them. A standard deviation describes spread around a mean under the usual interpretation; it is not the uncertainty interval for the mean difference. The registry record does not provide participant-level distributions that would allow alternative analyses or checks of assumptions.
General concerns such as skewness, unequal variability, and influential observations matter because they can affect how well a statistical method represents the data. The methods used for the investigators' primary analysis, including any handling of such features, are not reported in the registry record. No additional assumptions about the trial's analysis should be inferred from the outcome summaries alone.
10. Multiplicity, Missing Data and Analysis Populations
The registry record lists a primary outcome and secondary outcomes, but it does not report how the trial planned to control for multiple comparisons. When several outcomes are tested, the chance of at least one apparently unusual result can increase. In general, a prespecified outcome hierarchy or multiplicity adjustment can clarify how results should be interpreted, but neither is described in the registry record. The posted length-of-stay p-value is unadjusted and should be read with that limitation in mind.
The record lists zero reported analyses. That does not establish that no analyses were conducted; it means that investigator-reported analyses are not listed in this registry record. The statistical analysis plan, the primary analysis method, and any planned subgroup or sensitivity analyses are not reported in the registry record. The primary endpoint has descriptive summaries but no posted confidence interval or test.
Missing-data handling is also not reported in the registry record. The record does not describe whether any outcome values were unavailable, how missing observations were treated, or whether analyses used imputation or another approach. Without those details, the possible effect of missing data on the posted summaries cannot be evaluated.
The analysis population is not reported in the registry record. Although the record gives group sizes for the posted outcomes, it does not specify whether participants were analyzed according to randomized assignment, treatment received, or another population definition. The primary outcome groups are listed with 28 and 29 participants, while the safety groups are listed with 28 and 30 at risk. The reason for this difference is not reported in the registry record and should not be assumed.
These reporting gaps limit evaluation of prespecification, completeness, and robustness. They do not prove that the analyses were inappropriate; they mean the registry record does not provide enough information to assess those aspects.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Liposomal Bupivacaine TAP | 0 | 28 | 0.0% |
| Bupivacaine TAP | 0 | 30 | 0.0% |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Liposomal Bupivacaine TAP | 0 of 28 |
| Bupivacaine TAP | 0 of 30 |
The registry reports zero serious adverse events among 28 participants at risk in the liposomal bupivacaine TAP group and zero among 30 at risk in the bupivacaine TAP group. It also reports zero other adverse events in each group, using the same respective at-risk counts. No top serious adverse-event terms are listed.
These figures describe the events recorded in the registry for the groups and denominators shown. A zero count means that no events of the specified category are posted for those participants; it does not establish that the risk of an event is absent. The registry record does not report the safety observation period, event definitions, ascertainment procedures, or whether event collection was complete.
Deaths are recorded as null for both groups. That is not equivalent to a reported count of zero, so the registry record does not provide a death count in this entry. The safety figures should be interpreted as limited registry summaries, not as a comprehensive characterization of comparative safety.
12. What the Result Does, and Does Not, Mean
The posted primary results describe median postoperative opioid use and the full observed range for each treatment group during the 0-72 hours after injection. They show the group values recorded in the registry, but the record does not report a confidence interval or statistical test for the primary comparison. The summaries therefore do not establish the precision of a difference between the groups.
The length-of-stay comparison supplies a separate, unadjusted estimate and uncertainty interval. It is a secondary result, not a substitute for the primary analysis. Its interval and p-value should be understood as one unadjusted comparison among outcomes, with the registry's analysis plan and multiplicity approach not reported.
These results do not establish whether one block medication is better or worse in clinical practice. Statistical summaries alone do not settle clinical importance, and the registry record does not provide the trial protocol, detailed participant characteristics, or full analysis methods needed for a comprehensive assessment. The record's statement that both medications are standard of care is background text, not a conclusion drawn from the trial comparison.
Nor do the posted adverse-event counts show that either approach is free of risk. The recorded counts are zero for serious and other adverse events in the groups shown, but event definitions, follow-up details, and death counts are not available in the record. The appropriate interpretation is limited to what is posted: descriptive outcome summaries, a secondary recalculated comparison, and sparse safety counts, with important analytic details not reported.
13. Why This Trial Matters Statistically
This trial illustrates why outcome summaries and inferential evidence are not interchangeable. The primary endpoint is presented as medians and full ranges, which describe the observed data but do not provide an estimate of uncertainty in the between-group contrast. Readers may see different central values, yet still need an interval or a suitable test to assess how precisely the contrast is estimated.
It also shows the importance of keeping primary and secondary outcomes distinct. The registry posts a quantitative secondary comparison for length of stay, but does not post a corresponding inferential analysis for the primary opioid-use outcome. A secondary result cannot fill that reporting gap, particularly when a multiplicity plan and prespecified analysis are not available.
The planning illustrations demonstrate another statistical distinction: sample-size planning is a prospective design exercise, whereas power calculated after observing results is not evidence that a trial was adequately designed. The registry's planning scenarios are based on the observed secondary effect and stated assumptions; the trial's own sample-size justification is not reported. Those illustrations should not be read as the original design rationale or as observed power.
Finally, the record makes visible how registry reporting can constrain interpretation. Missing methods, analysis populations, missing-data handling, and safety follow-up details do not prove a flaw in the trial, but they prevent readers from checking important features of the evidence. Careful statistical interpretation means distinguishing observed summaries from tested comparisons and reported details from details that remain unavailable.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
Several limitations are specific to the information in this trial record. The primary outcome is reported with group medians and full ranges, but no confidence interval, test, or adjusted comparison is posted. The primary results therefore permit descriptive reading but not a registry-based assessment of the precision of the between-group contrast.
The record provides limited detail about participants. It identifies patients undergoing robotic hysterectomy, but does not report further eligibility criteria or participant characteristics in the primary outcome description. The primary endpoint group sizes are listed as 28 and 29, while the safety at-risk counts are 28 and 30. The reason for the differing counts is not reported in the registry record.
There is also limited information about secondary outcomes. Numerical rating scale and patient satisfaction are listed, but their numerical results are not reported in the registry record. The length-of-stay comparison is an unadjusted recalculation rather than a listed investigator-reported analysis. The record does not give the statistical analysis plan, multiplicity approach, analysis population, or missing-data procedures.
Safety reporting is similarly bounded: the adverse-event counts are posted, but event definitions and the observation period are not. Death values are null rather than reported as zero. These are limitations of the available record and should not be converted into assumptions about how the study was conducted or what unreported results would have shown.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: TAP Block With Liposomal Bupivacaine Versus Bupivacaine in Robotic Hysterectomy — NCT02289079.
- Registry record last updated 2023-05-10; status last verified 2023-05.
- Results first posted 2016-01-18.
- 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.
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18. Record Summary
NCT02289079 is a completed phase 4 randomized, parallel-group study titled “TAP Block With Liposomal Bupivacaine Versus Bupivacaine in Robotic Hysterectomy.” The official title describes an ultrasound-guided subcostal TAP block study. The record lists triple masking, enrollment of 60, sponsorship by the University of Minnesota, a study start of 2013-06, and primary completion in 2014-10.
The primary outcome is postoperative opioid use in micrograms of fentanyl equivalents during the 0-72 hours after injection, summarized by median and full range. The record also lists numerical rating scale, postoperative length of stay, and patient satisfaction assessed by survey as secondary outcomes.
The posted primary endpoint summaries are descriptive and are not accompanied by an inferential comparison in the registry record. A secondary length-of-stay comparison is available as an unadjusted recalculation. Key details, including the statistical analysis plan, missing-data handling, and analysis population, are not reported in the registry record.