Adductor Canal Block for Medial Compartment Knee Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Adductor Canal Block for Medial Compartment Knee Arthroplasty (NCT01818531), a randomized phase 4 study. The primary outcome is Verbal Pain Scores at 6 Hours Post Nerve Blockade..

2. Clinical Question

The clinical question is therefore a comparative one: whether pain scores following adductor canal blockade are similar to those following lumbar plexus blockade in this surgical setting. The outcome is patient-reported pain, rather than a direct measure of nerve-block activity. The record also lists opioid consumption, time to first analgesic, opioid-related side effects, and quadriceps motor strength as secondary outcomes. Their listing identifies additional topics of interest, but does not establish what those outcomes showed.

3. Trial Design

The registry describes a randomized, double-masked, parallel-group Phase 4 trial sponsored by Wake Forest University Health Sciences. The two groups were assigned to adductor canal block or lumbar plexus block before medial compartment knee arthroplasty. A parallel design means the groups receive their assigned approach rather than crossing over between approaches, as a general design concept. The record does not report the method used to generate the random sequence or conceal allocation.

The recorded enrollment is 150. This is the enrollment figure in the registry, not a reported count of participants included in each outcome analysis. The record lists the trial status as completed, with a start date of 2013-04 and primary completion of 2015-05. It does not report how many participants completed follow-up, were included in each analysis, or had missing outcome data.

Double masking indicates that the record classifies the study as masked, but it does not say which people were masked or how masking was maintained. Details such as the similarity of procedures, the identity of masked personnel, and whether masking was assessed are not reported in the registry record. The record describes the intervention as a single injection and identifies ultrasound guidance for the adductor canal block in the study summary; it does not give comparable procedural detail for the lumbar plexus block.

The study summary frames the primary comparison as pain scores at rest and with movement during the first 24 hours after nerve blockade. The registered primary outcome is specifically titled verbal pain scores at 6 hours post nerve blockade. That outcome is described as a mean score on a 0-10 scale, with higher scores denoting worse outcomes. The registry record does not provide a complete statistical analysis plan or explain how the multiple pain assessments were to be combined or compared.

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:

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 Verbal Pain Scores at 6 Hours Post Nerve Blockade., measured over 6 hours post block..

The registered primary endpoint is verbal pain score at 6 hours post nerve blockade. The score is on a 0-10 scale, and higher scores indicate worse pain. The description identifies two contexts for assessment: pain at rest and pain with movement. These contexts matter because a person's pain experience while still may differ from pain during activity; reporting both can make the outcome more informative than relying on only one situation.

The registry specifies a mean and standard deviation as the summary measures. In general, a mean describes the central level of scores, while a standard deviation describes how dispersed individual scores are around that mean. Neither summary alone reveals the full distribution of pain reports, and neither establishes whether a difference is important to patients.

Pain scores are used in this comparison because the trial's stated question concerns postoperative analgesia. The summary describes assessment across the first 24 hours, whereas the registered primary outcome specifies 6 hours. These descriptions do not establish how the other time points were analyzed. The record lists five outcome measures, but the primary result is not reported as a numerical comparison in the registry record. Arm-specific means, standard deviations, an effect estimate, a confidence interval, and a p-value are not reported in the registry record. Consequently, the endpoint definition can be described, but the size and precision of the primary comparison cannot be evaluated from this record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical information should be read in light of the endpoint and the analysis actually reported. The primary outcome is described as a continuous score summarized by a mean and standard deviation. In general, a mean expresses the average score in a group, and a standard deviation expresses how much individual scores vary around that average. These summaries can help describe the data, but a comparison between groups also needs an estimate of the difference and a measure of its uncertainty.

What does a confidence interval tell the reader?

In general, a confidence interval gives a range of values compatible with the observed data under the assumptions of the analysis. It communicates precision: a narrower interval indicates greater precision than a wider interval, while the interval's position indicates which effects remain compatible with the data. A confidence interval is not a guarantee that the true effect lies inside its endpoints. No confidence interval for the primary pain comparison is reported in the registry record, so its precision cannot be assessed.

Why does the equivalence claim need a margin?

The study summary states that the working hypothesis is equivalence of analgesia between the blocks. In general, an equivalence analysis asks whether the difference is confined to a prespecified range judged sufficiently small for the scientific question. The margin must be set before examining the results and must be interpreted alongside the estimated difference and its uncertainty. A nonsignificant test of a difference does not by itself demonstrate equivalence. The registry record does not report an equivalence margin or an equivalence analysis result, so the stated hypothesis cannot be evaluated from the posted outcome information.

How should multiple assessments be understood?

The summary describes verbal numerical pain scores at rest and with movement over the first 24 hours, while the registered primary outcome names the 6-hour assessment. The record also indicates that the primary outcome has several categories or time points and was not reduced to one comparison. In general, testing or interpreting multiple outcomes, conditions, or times can make a simple single-comparison interpretation incomplete. An analysis plan should clarify which comparison is primary, how repeated measurements are handled, and whether any adjustment or hierarchy is used. Those details are not reported in the registry record.

What can the planning assumptions establish?

The registry text describes a planning illustration based on an observed effect, using a two-sided significance level of 0.05, equal allocation, and a normal approximation. It characterizes the effect to detect as a stated fraction of the observed effect. These assumptions describe an illustration, not the trial's own design justification. The registry record does not report the trial's sample-size justification or a numerical planning result. In general, a sample-size calculation depends on the assumed effect, variability, allocation, and chosen error rates. A planning illustration cannot be read as observed power or as evidence that the trial could detect a clinically important effect.

What do the adverse-event counts contribute?

The registry reports counts of participants affected by serious events, other events, and deaths, along with the corresponding at-risk counts. In general, safety summaries are descriptive and depend on how events were defined, collected, coded, and followed. Event counts do not by themselves reveal event type, severity beyond the reported category, timing, or causal attribution. The record does not give those details. Nor does it report a statistical comparison of safety outcomes. The listed counts should therefore be read as the registry's recorded summaries, not as a complete assessment of comparative safety.

Finally, a registered endpoint definition is not the same as a reported endpoint analysis. To assess the primary comparison, readers would need the outcome summaries for each group, the chosen contrast, its uncertainty, and the analysis population and method. Those items are not reported in the registry record. General statistical concepts can explain what such information would mean, but they cannot substitute for the missing results.

10. Multiplicity, Missing Data and Analysis Populations

The trial record describes more than one pain-score context and time point: rest and movement, with the summary referring to the first 24 hours and the registered primary outcome specifying 6 hours. It also lists secondary outcomes involving opioid consumption, time to first analgesic, opioid-related side effects, and quadriceps motor strength. When multiple outcomes or time points are considered, there can be more than one opportunity to observe a result that appears notable by chance. In general, a prespecified analysis hierarchy or multiplicity adjustment can clarify how such results should be interpreted. The registry record does not report a multiplicity strategy or explain how repeated pain measurements were analyzed.

Missing-data information is also important for interpreting patient-reported outcomes. The registry record does not report how many participants posted pain scores at each time point, whether any scores were missing, why data might be missing, or how missing values were handled. It does not report a comparison between the enrolled group and the participants included in any primary-outcome analysis.

The record lists the enrollment as 150, but does not report the analysis population for the pain outcome. It does not say whether analyses followed randomized assignment, included only participants with observed scores, or used another population definition. Those details are not reported in the registry record. Without them, it is not possible to assess whether the reported population, if any, reflects the randomized groups or how exclusions could affect interpretation.

The record also does not report a prespecified statistical analysis plan, an interim-analysis plan, or a sample-size justification. These omissions do not establish that such plans were absent; they mean the details are not available in the registry record.

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.

Most frequent non-serious adverse event terms

The registry lists serious adverse events for the adductor canal group as 0 affected among 74 at risk, and for the lumbar plexus group as 0 affected among 73 at risk. It records deaths as 0 in each group. For other adverse events, it lists 38 affected among 74 at risk in the adductor canal group and 43 affected among 73 at risk in the lumbar plexus group.

These are counts as entered in the registry, not a complete account of event types or their clinical importance. The record does not identify the other adverse events, describe their severity, give their timing, or state how events were collected and classified. It also does not report a statistical comparison of these safety counts. The counts alone therefore cannot establish whether there is a meaningful difference between groups or attribute events to either block.

The at-risk counts are the denominators recorded for these adverse-event summaries; they should not be assumed to represent the number analyzed for the pain endpoint. In general, absence of a recorded serious event in a registry summary is not proof that no event occurred outside the recorded follow-up or reporting process. The registry record does not provide further detail on safety follow-up or completeness.

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

The trial is relevant to a specific comparative question: postoperative analgesia after medial unicompartmental knee arthroplasty when patients receive an adductor canal block or a lumbar plexus block. Its randomized, double-masked, parallel-group description indicates a comparative trial design. The registered primary outcome focuses on verbal pain scores, with higher scores denoting worse outcomes, and the study summary describes assessment at rest and with movement.

However, the registry record does not report the numerical primary-outcome results. Without arm-specific scores and a comparison with its uncertainty, readers cannot tell how large the observed difference was, how precisely it was estimated, or whether the data are compatible with a range of possible differences. No conclusion about equivalence can be drawn from the stated working hypothesis alone. An equivalence margin and an analysis supporting equivalence are not reported in the registry record.

The secondary outcomes and adverse-event counts provide context about the outcomes the study considered, but they do not fill this gap. The registry lists opioid consumption, time to first analgesic, opioid-related side effects, and quadriceps motor strength without reporting their results in the information available for this analysis. It gives some adverse-event counts but does not describe the events or report a comparative safety analysis.

Accordingly, the record can be used to understand the study question, design classification, endpoint definition, and selected safety summaries. It cannot establish which block produced lower pain scores, whether scores were equivalent, or what the listed secondary outcomes showed. This distinction is important: an unreported result is not a null result, and the absence of a reported comparison should not be interpreted as evidence of no difference.

13. Why This Trial Matters Statistically

This trial raises a useful statistical question about how to evaluate two approaches when the stated objective is equivalence rather than demonstrating that one is superior. In general, a superiority analysis asks whether the data support a difference in a specified direction or any difference, depending on the test. An equivalence analysis instead needs a clinically justified margin and enough precision to rule out differences outside that margin. The registry record states an equivalence hypothesis but does not report the margin or the analysis, making the distinction important when interpreting the study's stated aim.

The outcome also illustrates why time points and assessment conditions must be clearly defined. Pain at rest and pain with movement are related but distinct measurements, and the summary's first-24-hour description is broader than the registered primary outcome at 6 hours. A clear analysis plan would identify the primary contrast and explain how measurements across conditions and times contribute to inference. Such details are not reported in the registry record.

Finally, this record demonstrates the difference between a trial's design information and its outcome evidence. Randomization and masking describe intended protections against bias, but they do not supply a treatment-effect estimate or show how precisely it was measured. A completed status and an enrollment figure likewise do not indicate how many participants contributed to the endpoint analysis. For statistical interpretation, the endpoint results, analysis population, uncertainty, and handling of missing or repeated measurements are necessary. Their absence limits what can be concluded from this record, regardless of the clinical importance of the question.

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 trial-specific details needed to interpret the primary comparison are not reported in the registry record. These include the arm-specific pain-score means and standard deviations, the estimated between-group contrast, a confidence interval, and a p-value. The record also does not report an equivalence margin or an equivalence analysis, despite describing equivalence as the working hypothesis.

The endpoint descriptions differ in scope: the registered primary outcome is at 6 hours post block, while the summary describes pain at rest and with movement over the first 24 hours. The record does not explain how this set of assessments was represented in the primary analysis. It also does not report how multiple conditions or time points were handled, or whether multiplicity was addressed.

The recorded enrollment is 150, but the record does not report group-specific numbers included in the primary analysis, follow-up completeness, missing pain-score data, or the method used to handle missingness. It does not give participant characteristics or enough eligibility detail to assess how broadly the findings might apply. The randomization procedure and the people masked are not reported in the registry record.

For the secondary outcomes, the record lists outcome topics but does not report their numerical results in the information available for this analysis. Adverse-event categories are also limited: other-event types, event timing, collection procedures, and a comparative safety analysis are not reported. Finally, the trial's own sample-size justification and full statistical analysis plan are not reported. These gaps restrict assessment of both the result and the precision or applicability of any conclusions.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Adductor Canal Block for Medial Compartment Knee Arthroplasty — NCT01818531.
• Registry record last updated 2018-09-13; status last verified 2018-09.
• Results first posted 2018-09-13.
• 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

The registry record describes a completed, randomized, double-masked, parallel-group Phase 4 trial sponsored by Wake Forest University Health Sciences. It compares an adductor canal block with a lumbar plexus block before medial unicompartmental knee arthroplasty and records enrollment of 150. The registered primary outcome is verbal pain score at 6 hours post block, measured on a 0-10 scale, with higher scores denoting worse outcomes.

The summary states an equivalence hypothesis and describes pain assessments at rest and with movement over the first 24 hours. The registry record does not report a numerical primary-outcome comparison, equivalence margin, or analysis details needed to assess equivalence. It lists secondary outcomes and records adverse-event counts, but does not provide the primary result or further detail on event types. Consequently, the record describes the study question and selected design and safety information, while leaving the pain-score comparison and its precision unreported.