Spinal Anesthesia With Hyperbaric Levobupivacaine 0.75% for Ambulatory Knee Arthroscopy: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Spinal Anesthesia With Hyperbaric Levobupivacaine 0.75% for Ambulatory Knee Arthroscopy (NCT01881087), a randomized phase 4 study. The primary outcome is Probability of Motor Block.

2. Clinical Question

This is a dose-comparison question within a specified anesthetic approach, not a comparison of the intervention with no spinal anesthesia or with a different anesthetic. The registry lists 180 participants overall, across the three randomized dose groups. It also lists failed spinal block rate as a secondary outcome, with its measurement timeframe set at 15 minutes after dose.

Randomization and masking are relevant to how the comparison was intended to be conducted, but the record does not describe how allocation was generated or concealed, or which people were masked. Nor does it provide enough detail to assess whether participants in the registry record represent a broader clinical population. The findings should therefore be read as outcomes recorded for these three dose groups, with the endpoint definitions and analysis details available in the registry record as the boundary on interpretation.

3. Trial Design

This was a phase 4, randomized, triple-masked, parallel-group clinical trial. The registry lists an enrollment of 180 and three groups receiving a single spinal dose of hyperbaric levobupivacaine 0.75%: 7.5 mg, 9.37 mg, or 11.25 mg. Each group description specifies administration by a Whitacre needle 27G. The listed intervention is hyperbaric levobupivacaine 0.75%.

The trial began in 2006-06, reached primary completion in 2009-12, and is recorded as completed. Fundacion Clinica Valle del Lili is listed as the sponsor. The registry describes the study as a double blind randomized clinical trial in its official title, while the design information records triple masking. The record does not explain the roles included in that masking designation or reconcile the different wording.

The primary outcome is probability of motor block, with a timeframe of 200 minutes. Failed spinal block rate is the listed secondary outcome, measured 15 minutes after dose. The primary outcome is reported as a value for each arm, but the record does not include a statistical comparison, confidence interval, or reported analysis for it. The secondary outcome has pairwise comparisons against the 7.5 mg group, but no reported analyses are listed by the registry.

Important design details are not reported in the registry record. These include the eligibility criteria, allocation sequence method, allocation concealment, the precise masking procedures, the planned sample-size justification, protocol deviations, and the analysis population. The statistical analysis plan, including any planned interim analyses, is also not reported in the registry record. These omissions limit assessment of how closely the reported outcomes follow the original design and which inferential decisions were prespecified.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Probability of Motor Block, measured over 200 minutes.

The primary endpoint is named probability of motor block. Its unit is percentage of motor block, and its timeframe is 200 minutes. The description refers to the likelihood rate of motor-block persistence after a dose of spinal hyperbaric levobupivacaine 0.75%. In practical terms, the measure is intended to describe motor block over the period following administration, which is pertinent to the study’s stated interest in the clinical profile of different doses for ambulatory knee arthroscopy.

The registry reports values of 5 for the 7.5 mg group, 20 for the 9.37 mg group, and 27 for the 11.25 mg group. These are the posted primary outcome values; no uncertainty estimates or formal between-group tests accompany them. The endpoint description does not specify exactly how motor block was assessed, how often it was assessed within the 200-minute timeframe, or how the reported value was derived. It is therefore not possible to tell from the registry record whether the values represent a particular assessment time, a summary across repeated assessments, or another calculation.

In general, a motor-block measure can characterize the persistence or frequency of an effect over a defined observation period. The usefulness of comparisons depends on a clear definition, consistent assessment, and an analysis that accounts for the way observations were collected. Those methodological details are not reported in the registry record, so the primary values can be described as posted, but their measurement and statistical precision cannot be fully evaluated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

General: A randomized parallel-group design assigns participants to one of several groups, with each participant receiving the intervention assigned to that group. Randomization is intended to make treatment groups comparable on average, including with respect to measured and unmeasured characteristics. It does not guarantee identical groups in a particular trial. The registry identifies randomization and parallel groups, but does not report the sequence-generation or concealment methods, so those aspects cannot be assessed from this record.

What does masking mean?

General: Masking is intended to reduce the influence of knowledge about treatment assignment on participant experience, care, outcome assessment, or analysis. The registry records triple masking, while the official title describes the study as double blind. It does not identify the masked roles or explain the differing descriptions. The designation alone cannot establish how masking was implemented or maintained.

How should the primary values be read?

The primary endpoint is reported as an arm-level percentage measure of motor block, with a 200-minute timeframe. The registry gives values but no standard errors, confidence intervals, or formal test results. General: An estimate describes the observed data, while a confidence interval communicates the uncertainty around an estimate under a specified statistical method. Without an uncertainty measure or the analysis details that produce one, readers cannot assess the precision of these primary values from the record. The absence of a reported primary comparison also means that a formal statistical contrast among the doses cannot be attributed to the trial record.

What do the secondary comparisons show statistically?

The secondary comparisons are risk differences between each higher-dose group and the 7.5 mg group. The registry supplies estimates, confidence intervals, and unadjusted p-values. General: A risk difference expresses the difference in outcome frequency between groups on the absolute scale. A confidence interval describes a range of values compatible with the data and statistical model, subject to its assumptions. A p-value measures how unusual the observed data, or more extreme data, would be under a specified null hypothesis and model. It is not the probability that the null hypothesis is true, and it does not measure clinical importance.

The posted intervals for both risk differences include zero, and the posted unadjusted p-values are 0.675 and 0.549. In general, these results do not establish a difference, but they also do not show that the groups are equivalent. Demonstrating equivalence requires a prespecified margin and a suitable analysis; neither is reported in the registry record. The estimates are based on small counts of failed blocks, which means the available data provide limited precision about the comparison.

Why does a low event count matter?

General: With sparse binary outcomes, a small change in the observed event count can have a substantial influence on the estimated contrast. Standard errors and confidence intervals may be large relative to the estimated effect, and some statistical methods can perform poorly if their assumptions are not met. The registry does not identify the method used for the reported risk differences or provide a fuller statistical analysis plan. The results should therefore be understood as the posted unadjusted analyses rather than as a complete account of the trial’s statistical approach.

How should the planning illustrations be interpreted?

The sample-size illustrations are based on the observed secondary effect, with assumptions of a two-sided significance level of 0.05, equal allocation between two groups, and a normal approximation. They show participants per arm for 80% and 90% power under scenarios that target the observed effect or a stated fraction of it. General: Such calculations describe planning requirements under assumptions; they are not the trial’s observed power, do not establish that the original trial was adequately powered, and do not replace a protocol-based sample-size justification. The registry does not report the trial’s own sample-size justification, and the illustrations should not be treated as evidence about the primary endpoint.

The record lists no reported analyses for the primary outcome and no reported analyses under its general analyses listing. It also does not report an interim-analysis plan, a multiplicity strategy, a missing-data method, or the populations included in the analyses. These are consequential omissions: the interpretation of estimates can depend on endpoint handling, group inclusion, model choice, and whether multiple comparisons were anticipated. Statistical details beyond the posted secondary comparisons are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The registry record does not report whether the trial planned adjustment for multiple testing. This matters because the study has three dose groups and the posted secondary analyses compare two of them against the 7.5 mg reference group. When several hypotheses are tested, the likelihood of at least one small p-value under a collection of null hypotheses can rise. General: Multiplicity procedures can control a chosen error rate or define a testing hierarchy, but the appropriate approach depends on the prespecified scientific questions and analysis plan. No such plan is reported in the registry record.

The secondary p-values are unadjusted. They therefore describe each comparison on its own and should not be interpreted as multiplicity-adjusted evidence across outcomes or dose comparisons. The record does not report whether the primary outcome was intended to be tested first, whether secondary comparisons were exploratory, or how the primary endpoint would be analyzed statistically. It also does not report interim analyses or any adjustment associated with repeated looks at accumulating data.

Missing-data handling and analysis populations are not reported in the registry record. The listed enrollment and arm sizes do not specify how many participants were included in each outcome analysis, whether all randomized participants were retained in their assigned groups, or how unavailable outcome data were handled. General: Missingness can affect interpretation when participants with missing outcomes differ systematically from those with observed outcomes. The risk depends on why data are missing and on the analysis used; no assumption or method can be assigned from this record.

The registry also does not describe protocol deviations, exclusions after randomization, or sensitivity analyses. These omissions do not establish that problems occurred, but they prevent readers from evaluating how robust the posted estimates are to alternative assumptions. For the primary endpoint, the lack of a reported test and uncertainty interval is especially important: multiplicity cannot be assessed without knowing the planned inferential framework, and the result cannot be judged as confirmatory or exploratory from the record alone.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

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

The registry reports no serious adverse events and no deaths in any of the three dose groups. The number at risk for serious adverse events and other adverse events is listed as 59 for the 7.5 mg group, 61 for the 9.37 mg group, and 60 for the 11.25 mg group. These are the posted safety counts; the registry lists no serious adverse event terms.

General: Zero recorded events in a study group means that no events of that category were reported among the participants counted in that group. It does not prove that the true risk is zero or rule out uncommon harms. The degree of reassurance depends on the amount of observation, completeness of reporting, definitions, and follow-up, details that are not fully described in the registry record. These counts should be read as registry safety reporting rather than as a comprehensive assessment of all possible adverse effects.

The record does not give detailed definitions for serious or other adverse events, follow-up duration for safety outcomes, or a narrative account of event ascertainment. It also does not list non-serious event terms. As a result, the absence of posted events cannot be generalized beyond the categories and reporting recorded for this trial. These figures are descriptive and do not establish comparative safety between doses.

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

The registry records a randomized comparison of three single doses of spinal hyperbaric levobupivacaine 0.75% and posts arm-level values for the primary motor-block outcome. Those values rise across the listed dose groups, but no primary confidence intervals or formal comparisons are reported. The secondary failed-block comparisons are unadjusted and based on few events, with uncertainty that does not establish a clear difference.

These findings do not show that one dose is superior, equivalent, or inferior on the primary outcome. An ordered set of arm-level values is not by itself evidence of a dose-response relationship: uncertainty, a defined analysis, and appropriate comparisons are needed to judge whether a pattern is distinguishable from random variation. The record also does not describe the calculation of the primary measure in enough detail to determine precisely what each value represents.

General: A non-significant result does not prove that two groups are the same. It may reflect a small effect, imprecise estimates, limited information, or a combination of these. Equivalence requires a prespecified acceptable difference and an analysis designed to assess that question. No equivalence or non-inferiority framework is reported in the registry record.

The trial’s scope is also bounded by its design and documentation. It addresses the listed doses in the described spinal technique for ambulatory knee arthroscopy; the record does not report enough participant characteristics or eligibility details to assess how broadly the findings apply. The outcome timeframes are specific, and safety reporting is limited to the recorded event counts. The results should therefore be understood as a limited description of these randomized groups, not as general evidence about other procedures, techniques, populations, or doses.

No treatment recommendation follows from these registry results. Their main interpretive value is to make clear what was recorded and where the evidence is uncertain: primary outcome values without reported inferential analysis, and secondary comparisons with sparse events and unadjusted tests.

13. Why This Trial Matters Statistically

This trial illustrates why a reported outcome value and a statistical conclusion are not the same thing. The registry gives primary arm-level motor-block values, but without uncertainty estimates, a comparison test, or a detailed definition of the endpoint. A visible pattern across groups can prompt a scientific question, but it cannot quantify how precisely the pattern is estimated or establish whether it exceeds chance variation.

The contrast between the primary and secondary reporting is also instructive. The secondary endpoint includes pairwise estimates and unadjusted p-values, while the primary endpoint has no reported inferential analysis. A reader should not let the presence of secondary statistics create the impression that the central dose question has been fully analyzed. Endpoint priority, measurement definition, and a prespecified analysis plan all shape what conclusions can be drawn.

General: Sparse events make it especially important to interpret effect estimates together with confidence intervals, rather than treating a p-value as a complete summary. Wide or zero-inclusive intervals can reflect limited information; they do not establish equivalence. Likewise, sample-size illustrations based on an observed effect are planning scenarios and are not retrospective evidence of adequate power.

The record also demonstrates the importance of complete trial reporting. Details about the primary outcome calculation, missing data, analysis populations, multiplicity, and sample-size justification would help readers assess precision and robustness. Their absence does not prove that the original investigators did not consider these issues, but those considerations are not reported in the registry record. For biostatisticians and clinical researchers, this is a useful example of separating the posted numerical pattern from the strength and completeness of the statistical evidence.

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 specific to this record affect interpretation. First, the primary outcome is described as a probability or likelihood rate of motor-block persistence, with percentage of motor block as its unit, but the registry does not define the calculation or explain the assessment schedule within the 200-minute timeframe. Without that detail, readers cannot confidently map the posted values to a particular clinical or statistical quantity.

Second, the primary results are arm-level values without reported uncertainty estimates or inferential comparisons. The record does not give the number of participants contributing primary outcome data in each group, nor does it explain how incomplete assessments were handled. Overall enrollment and listed arm sizes do not answer those outcome-specific questions.

Third, the secondary endpoint has sparse event counts, and its comparisons are unadjusted. The record does not state whether these comparisons were prespecified, whether there were other planned analyses, or how multiplicity was addressed. The secondary findings therefore have limited precision and should not be treated as definitive evidence of similarity or difference.

Finally, key design and analysis details are not reported in the registry record: eligibility criteria, participant characteristics, randomization procedures, allocation concealment, masking roles, analysis populations, missing-data methods, the statistical analysis plan, and the trial’s own sample-size justification. The registry uses different masking descriptions in its official title and design information without explaining the difference. These reporting gaps limit appraisal of potential bias, generalizability, and the robustness of the results.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Spinal Anesthesia With Hyperbaric Levobupivacaine 0.75% for Ambulatory Knee Arthroscopy — NCT01881087.
• Registry record last updated 2017-07-12; status last verified 2017-04.
• Results first posted 2017-07-12.
• 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.

18. Record Summary

NCT01881087 is a completed phase 4 randomized parallel-group trial sponsored by Fundacion Clinica Valle del Lili. It lists an enrollment of 180 and compares single spinal doses of hyperbaric levobupivacaine 0.75%: 7.5 mg, 9.37 mg, and 11.25 mg. The record describes triple masking, while the official title says double blind.

The primary outcome is probability of motor block over 200 minutes. Arm-level values are reported, but no primary statistical analysis or uncertainty estimates are listed. The secondary outcome is failed spinal block rate at 15 minutes after dose; pairwise comparisons against the 7.5 mg group are unadjusted. No serious adverse events or deaths are reported in the listed groups.

The record does not report the primary endpoint calculation, the trial’s sample-size justification, analysis populations, missing-data methods, multiplicity strategy, or a detailed statistical analysis plan. These gaps constrain interpretation of the observed pattern and its precision.