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 Local Injection of Local Anesthetic 24 Hours After Knee Replacement Surgery May Decrease Pain for Several More Hours (NCT02420951), a randomized na study. The primary outcome is Pain Assessed Using the VAS 0-10 Pain Scale.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02420951 |
| Phase | NA |
| Condition | Arthroplasty, Knee, Pain |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 50 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Brigham and Women's Hospital |
| Results posted | Yes |
2. Clinical Question
The trial asked whether an additional local anesthetic injection immediately before removal of a local anesthetic infiltration catheter on postoperative day one would affect pain and other outcomes after unilateral total knee replacement. Its stated hypothesis was that an injection of 30ml of .5% bupivacaine would provide pain reduction, patient satisfaction and outcome measures equal or superior to catheter removal without an additional injection. The posted primary outcome was pain assessed using the VAS 0-10 pain scale, with a 7 days timeframe.
Population
People undergoing unilateral total knee replacement who chose to participate. The registry reports enrollment of 50 participants, with 25 in each posted arm.
Intervention
An injection of 30ml of .5% bupivacaine into the local anesthetic infiltration catheter immediately before its removal on postoperative day one.
Comparator
No additional bupivacaine injection before catheter removal. The brief summary describes no additional medication during catheter removal in this group.
Primary question
What pain scores were recorded on the VAS 0-10 pain scale over the 7 days timeframe, and did the posted results include a statistical comparison between the randomized groups?
The registry describes additional outcomes concerning pain medication consumption, swelling, proprioception and quadriceps strength. Although the trial summary also mentions patient satisfaction, a satisfaction measure is not included in the listed secondary outcomes. The registry record does not report a formal comparison of the groups for the primary endpoint, so the clinical question cannot be answered from a posted comparative estimate or test.
3. Trial Design
The record identifies this as a randomized, parallel-group trial with no masking. It reports an enrollment of 50 and a completed status. The start date is 2015-10-05, and the primary completion date is 2016-03-22. The two posted arms are Injection and No Injection, each with 25 participants. The condition terms are knee arthroplasty and pain.
Participants undergoing unilateral total knee replacement who chose to participate were to be assigned to one of the two groups. In the Injection arm, 30ml of .5% bupivacaine was to be injected through the local anesthetic infiltration catheter immediately before removal on postoperative day one. In the No Injection arm, no additional bupivacaine injection was described. The record labels masking as none, so the study was not masked according to the registry entry. Whether outcome assessors or analysts were masked is not separately reported in the registry record.
Randomized allocation helps establish a design for comparing groups, but the registry record does not describe how the random sequence was generated, whether allocation was concealed, or the details of participant recruitment and follow-up. It also does not describe withdrawals, exclusions, or participant flow from enrollment through outcome assessment. The number enrolled and the arm sizes in the posted results do not, by themselves, establish that every enrolled participant contributed data to every outcome.
The primary endpoint is listed as mean pain on the VAS 0-10 pain scale, with a timeframe of 7 days. The record lists five secondary outcomes, including pain medication consumption, swelling, proprioception and quadriceps strength measures. The exact assessment schedule for these outcomes and the full set of analytic procedures are not reported in the registry record.
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 | Injection | No Injection |
|---|---|---|
| STARTED | 25 | 25 |
| COMPLETED | 25 | 25 |
| NOT COMPLETED | 0 | 0 |
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 | Injection | No Injection | Total |
|---|---|---|---|---|
| Participants analysed | 25 | 25 | 50 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 7 | 9 | 16 |
| Age, Categorical: >=65 years | Participants | 18 | 16 | 34 |
| Age, Continuous | years | 68.96 (57 to 81) | 66.44 (50 to 79) | 67.7 (50 to 81) |
| Sex: Female, Male: Female | Participants | 15 | 14 | 29 |
| Sex: Female, Male: Male | Participants | 10 | 11 | 21 |
6. Primary Endpoint
The registry lists the primary outcome as Pain Assessed Using the VAS 0-10 Pain Scale, measured over 7 days.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Full Range |
| Unit | units on a scale |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is pain assessed using the VAS 0-10 pain scale. The registry description defines 0 as no pain and 10 as the worst imaginable pain. A visual analogue scale records a participant’s position along a range of pain intensity; using a consistent scale allows pain reports to be summarized numerically and compared between groups. The endpoint is listed as a mean, so its reported group value represents an average rather than the experience of every individual participant.
The listed timeframe is 7 days. The record does not specify the exact assessment times within that timeframe, whether measurements were taken repeatedly, or how multiple measurements were combined into the posted mean. The time point or summary rule used for the endpoint is therefore not reported in the registry record.
Pain is relevant to the trial question because the intervention was intended to affect pain after catheter removal. However, the scale records subjective pain ratings, and a group average does not show how individual responses varied. The record lists means of 2.763 for Injection and 2.483 for No Injection. It also lists accompanying bounds of 1.99 to 3.33 and 1.89 to 2.89, respectively; the statistical meaning of these bounds is not reported in the registry record. They should not be assumed to be confidence intervals or another specific measure of uncertainty.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary outcome values are means of 2.763 in the Injection arm and 2.483 in the No Injection arm. Descriptively, the listed mean is higher in the Injection arm. These values are group summaries, not a reported estimate of the randomized treatment effect. The registry record reports zero analyses and indicates that values were missing or not estimable for a two-arm comparison for this endpoint type. It therefore does not post a formal between-group estimate, confidence interval, or p-value for the primary outcome.
The registry also lists bounds of 1.99 to 3.33 for Injection and 1.89 to 2.89 for No Injection. Their interpretation is not specified in the registry record. Without knowing whether they represent confidence intervals, another uncertainty interval, or a different summary, they cannot support a particular inferential conclusion. They should not be treated as evidence of statistical significance or non-significance.
Randomization is intended to make treatment groups comparable on average, but it does not replace a reported analysis. To assess the primary question, readers would need a clearly defined comparison of the groups, an effect estimate, and a description of its uncertainty. Those are not reported in the registry record. In particular, the two arm means alone do not establish whether any observed difference is compatible with random variation, nor do they quantify the size or precision of a treatment effect.
The arm sizes are 25 participants each, and the total enrollment is 50. These figures describe the posted group sizes and enrollment; they do not indicate how many participants contributed to the primary endpoint or whether there were missing outcome data. The registry does not report analysis populations, missing-data methods, or reasons for any unavailable measurements.
Accordingly, the most defensible reading is descriptive: the registry lists the two arm means and accompanying bounds, but does not report a formal comparison that answers whether the randomized groups differed. This is not evidence that the groups were equivalent. Demonstrating equivalence or non-inferiority would require an appropriate design and analysis, including a prespecified margin; such details are not reported in the registry record. Nor does the absence of a posted comparative result establish that no analysis was performed outside the registry.
9. Statistical Methods Explained
Several statistical ideas help distinguish the posted descriptions from evidence about a treatment effect. The explanations below are general statistical guidance; they do not assert that a particular procedure was used in this trial.
What does randomization contribute?
In general, random assignment aims to balance both measured and unmeasured participant characteristics between groups in expectation. This supports a fair comparison of outcomes, provided the assignment process is implemented appropriately and participants are analyzed in a way that preserves the randomized groups. Randomization does not guarantee that the groups will be identical in a particular trial, especially with modest group sizes. The registry identifies the allocation as randomized, but the sequence-generation and concealment procedures are not reported in the registry record.
A parallel-group design assigns participants to one group and compares outcomes across groups. Here, the registry lists Injection and No Injection as the two arms. The record does not describe any crossover or repeated assignment. It labels masking as none. In general, lack of masking can affect how participants report subjective outcomes or how outcomes are assessed, though the direction and extent of any influence cannot be inferred from the design label alone. Details about masked assessors are not reported in the registry record.
What does a mean describe?
A mean is the arithmetic average of observed values. It provides a compact summary of the center of a group’s results, but it does not show their full distribution. Two groups can have similar means while differing in variability or in the pattern of individual responses. Conversely, a difference between means does not by itself indicate whether the groups differ beyond what might occur by chance. Interpretation depends on the variability, sample size, analysis method and uncertainty around the contrast.
The VAS is bounded by the stated scale endpoints: 0 means no pain, and 10 means the worst imaginable pain. A scale score remains a participant-reported measurement; converting it to a mean does not make the individual ratings objective measurements or reveal whether changes are important to participants. The registry lists the endpoint as a mean and identifies a 7 days timeframe, but the precise schedule and summary approach are not reported in the registry record.
Why is a between-group estimate important?
For a randomized trial, the main inferential question is usually about the contrast between groups, not whether either group’s value is considered on its own. An analysis would ordinarily define the target contrast and report its estimate with an uncertainty measure. A confidence interval, in general, describes a range of values compatible with the data and the method’s assumptions; it is not a guarantee that the true effect lies within that particular interval. A p-value, when used, measures how incompatible the observed data are with a specified null model under the analysis assumptions. Neither can be interpreted without knowing the comparison and method.
The record lists bounds beside each mean but does not identify their statistical meaning. It does not report a two-arm estimate, confidence interval, or p-value for the primary endpoint. As a result, those bounds cannot be substituted for an uncertainty interval around the treatment contrast. The posted arm means are descriptive summaries and should be read separately from an inferential comparison.
How should planning illustrations be understood?
In general, a sample-size calculation is a planning exercise that depends on an assumed effect, variability, significance level, allocation, and desired power. The registry record does not report the trial’s own sample-size justification or the assumptions used to plan enrollment. Any separate planning illustration based on an observed effect is not the trial’s design rationale and is not observed power. Observed power is not a substitute for estimating an effect and its uncertainty after data collection.
The stated planning assumptions for the illustration use a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. No particular planning result is reported in the registry record. Such assumptions describe a calculation framework, not evidence about the trial outcome.
Why does outcome distribution matter?
Statistical methods should suit the form of the outcome and its distribution. General methods based on means and normal approximations can be sensitive to skewness, outliers, bounded scales, or unequal variability. Over-dispersion, in general, means that the observed variability is greater than a model assumes; if ignored, uncertainty can be understated. The registry record does not report distributional checks, model diagnostics, or any adjustment for over-dispersion. No claim can be made about whether these issues arose or how they were handled.
More broadly, a complete interpretation would need the analysis population, handling of missing outcomes, prespecified endpoint definition, and statistical model. These details are not reported in the registry record. The available descriptive means therefore do not support reconstructing an unreported analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary pain endpoint and five secondary outcomes. These include pain medication consumption assessed using questionnaire or hospital records, swelling measured using a perometer, proprioception measured using a SD Balancer, and quadriceps strength measured using a Biodex handheld dynamometer. Pain medication consumption appears twice in the list. The record does not explain whether the repeated entry represents separate assessments or a duplicate listing. Although the study summary mentions patient satisfaction, a corresponding outcome measure is not listed among the secondary outcomes.
When a study evaluates multiple outcomes or multiple time points, the chance of at least one apparently unusual result can increase if each is tested separately. General statistical approaches include prespecifying a primary outcome, adjusting for multiple comparisons, or interpreting secondary analyses as exploratory. The registry identifies the primary pain endpoint, but a multiplicity strategy or hierarchy for secondary outcomes is not reported in the registry record. No secondary analyses are posted, and the record reports zero analyses.
The record does not describe the amount or pattern of missing data for the primary or secondary outcomes. It also does not report imputation, complete-case analysis, sensitivity analyses, or an approach to withdrawals. The arm sizes in the results do not establish that every participant had complete measurements. The analysis population, including whether participants were analyzed according to randomized assignment, is not reported in the registry record.
These omissions limit assessment of how robust any outcome comparison might be. They do not show that missing data or multiplicity necessarily biased a result; rather, the information needed to assess those possibilities is not reported in the registry record.
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 |
|---|---|---|---|
| Injection | 0 | 25 | 0.0% |
| No Injection | 0 | 25 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Injection | 0 of 25 |
| No Injection | 0 of 25 |
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 |
|---|---|
| Injection | 0 of 25 |
| No Injection | 0 of 25 |
The registry lists serious adverse events for 0 of 25 participants in the Injection arm and 0 of 25 in the No Injection arm. It also lists other adverse events for 0 of 25 participants in each arm, and deaths for 0 participants in either arm. No serious adverse event terms are listed.
These figures describe events recorded in the registry, not proof that no participant experienced any adverse event. The definitions used, the ascertainment procedures, the observation period for safety, and whether all participants completed safety follow-up are not reported in the registry record. The figures also do not estimate or rule out rare risks. A zero count in a group of this size means that no events were posted for that category and group; it does not establish that the underlying risk is zero.
Counts should be interpreted separately from the pain outcome. The registry’s adverse-event entries do not provide a formal comparative safety analysis, and the absence of posted events does not establish that the two approaches have identical safety profiles.
12. What the Result Does, and Does Not, Mean
The registry describes a randomized comparison of an additional bupivacaine injection before catheter removal against no additional injection in people undergoing unilateral total knee replacement. It posts a mean VAS pain score of 2.763 for Injection and 2.483 for No Injection, with 25 participants listed in each arm. Those values describe the recorded group summaries. The registry does not report an inferential comparison for the primary endpoint, so the posted results do not establish the size or precision of a treatment effect.
The meaning of the accompanying bounds is also unspecified. Without a definition, they cannot be interpreted as confidence intervals or used to judge the uncertainty around a group contrast. The record does not report a p-value, an effect estimate, or a formal analysis for the primary endpoint. It is therefore not possible to determine from the registry entry whether the numerical difference between the means is distinguishable from random variation.
These results do not demonstrate equivalence, non-inferiority, superiority, or absence of an effect. Such conclusions depend on a prespecified question and an appropriate statistical analysis, and an equivalence or non-inferiority claim would require details such as a justified margin. Those details are not reported in the registry record. Similarly, the posted zero adverse-event counts should not be interpreted as proof that adverse events cannot occur.
The record does offer a clear description of the intervention, comparator, randomized parallel design, and intended pain measure. It also lists several secondary outcomes. However, the absence of reported analyses and methodological details prevents a fuller assessment of outcome uncertainty, missing data, and the secondary findings. The distinction is important: a registry entry can describe a trial and post descriptive values without providing enough information to support a comparative statistical conclusion.
13. Why This Trial Matters Statistically
This trial is statistically instructive because it illustrates the difference between reporting group summaries and reporting a randomized comparison. Means can help describe observed outcomes, but the principal question in a randomized trial concerns the contrast between assigned groups. That contrast should be paired with a measure of uncertainty and enough methodological detail to understand what was estimated. The registry lists arm means but does not report a formal primary comparison.
The distinction is especially important for a subjective, bounded endpoint such as a pain rating. A mean condenses responses across participants and does not show the distribution of those responses or how many participants had outcomes at different points on the scale. A reader also needs to know how the assessment timeframe was implemented and how the mean was formed. Those details are not reported in the registry record.
The entry also illustrates why registry design information and outcome analysis information answer different questions. Randomized allocation and parallel groups describe the intended comparison structure. They do not reveal whether every participant was analyzed as randomized, how missing observations were handled, or whether multiple outcome tests were adjusted. Those analytic details are not reported in the registry record.
Finally, safety counts require careful interpretation. Zero events posted in each arm is useful descriptive information, but it is not a guarantee of no risk and does not amount to a comparative safety analysis. Together, these points emphasize that statistical interpretation depends not only on the observed numbers, but also on the estimand, analysis plan, and uncertainty reporting.
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.
The registry record leaves several trial-specific uncertainties. Although allocation is labeled randomized, the process used to generate and conceal assignments is not reported. Masking is labeled none, and the record does not specify whether outcome assessors or analysts were masked. This matters particularly for a participant-reported pain scale, although the extent of any effect cannot be inferred from the registry entry.
The primary endpoint is described as mean VAS pain with a 7 days timeframe, but the timing of pain assessments and the method for producing the reported mean are not stated. The accompanying bounds are not defined. The record also does not post a formal two-arm analysis, effect estimate, confidence interval, or p-value, and indicates that a comparison was not estimable for this endpoint type.
Enrollment and arm sizes are reported, but participant flow, endpoint-specific denominators, withdrawals, and missingness are not. The analysis population and missing-data approach are not reported in the registry record. The record does not state the original sample-size justification, a prespecified statistical analysis plan, or a multiplicity strategy. It also does not explain the repeated listing of pain medication consumption or list patient satisfaction as a secondary outcome despite its mention in the study summary.
For safety, the registry posts zero serious and other adverse events in both arms, but definitions, monitoring procedures, and the safety follow-up period are not reported. These limitations do not establish that the trial was poorly conducted; they identify information absent from the registry record that is needed to assess precision, bias, and the completeness of the posted findings.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Local Injection of Local Anesthetic 24 Hours After Knee Replacement Surgery May Decrease Pain for Several More Hours — NCT02420951.
- Registry record last updated 2018-01-12; status last verified 2017-12.
- Results first posted 2017-03-31.
- 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.
Continue through the Clinical Biostats statistical pathway
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18. Record Summary
The registry describes a completed, randomized, unmasked, parallel-group study sponsored by Brigham and Women's Hospital. It reports enrollment of 50 and posted arm sizes of 25 for Injection and 25 for No Injection. The study start date is 2015-10-05, and primary completion is dated 2016-03-22.
The intervention was 30ml of .5% bupivacaine through the local anesthetic infiltration catheter immediately before removal on postoperative day one. The comparator involved no additional bupivacaine injection. The primary outcome was mean pain on the VAS 0-10 scale, with a 7 days timeframe. The posted means are 2.763 and 2.483, respectively, but no formal two-arm primary analysis is reported. Five secondary outcomes are listed, and zero serious adverse events, other adverse events, and deaths are posted in each arm.
The registry record does not report the meaning of the accompanying endpoint bounds, the original sample-size justification, analysis populations, missing-data methods, or a multiplicity strategy. These gaps limit interpretation of the descriptive results.