Pain Control With Total Knee Replacement: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Pain Control With Total Knee Replacement (NCT01680549), a randomized phase 4 study. The primary outcome is Patient Pain Scores.

2. Clinical Question

The trial’s stated purpose is to study gabapentin’s effects on pain control in the perioperative and postoperative period of total knee arthroplasty. The primary question is therefore about pain scores over the recorded postoperative assessment period, not simply whether a participant did or did not experience pain. Narcotics consumption, knee range of motion, and patient restfulness are listed as secondary outcomes, but the registry record does not report their results either.

The clinical interpretation is constrained by the absence of outcome data. The registry record lists the trial as completed, but completion status is not itself evidence that an intervention changed pain or any secondary outcome. Without reported group results and an analysis, the effect of gabapentin relative to placebo cannot be determined from this record.

3. Trial Design

The registry describes a phase 4, randomized, double-masked, parallel trial sponsored by Texas Tech University Health Sciences Center. Enrollment is listed as 50. The study start is recorded as 2012-09, and primary completion as 2016-02; the overall status is completed. The record does not report how participants were assigned, who was masked, or whether masking was assessed.

The study compares a gabapentin regimen with a placebo regimen around total knee arthroplasty. The gabapentin arm is described as 600mg PO pre-operatively and continued postoperatively at 300 mg PO q8 hours x 3 days. The placebo arm is described as placebo 600 mg po preoperatively and continued postoperatively at 300 mg po q8hours X 3 days. The registry record does not provide further details about medication adherence, changes to the regimens, or concomitant care.

The primary outcome is patient pain measured with the VAS over 3 days, with assessments on postoperative days 0, 1 and 2. The scale is described as ranging from 0-100, with higher values indicating more pain. Narcotics consumption, knee range of motion, and patient restfulness are listed as secondary outcomes. Four outcome measures are listed, but the record does not provide results for them.

Randomization and masking are design features intended, in general, to reduce the influence of allocation choices and expectations on comparisons. Their practical implementation and success cannot be evaluated from the information in the registry record. The record does not report the allocation ratio or analysis population. Nor does it report a participant flow, withdrawals, or completion of follow-up. These details matter when interpreting which participants contributed data and whether the reported groups remained comparable during analysis.

Although the trial is marked completed, the registry record lists no analyses and does not give a primary-outcome result. The primary completion date indicates the recorded timing of that milestone; it does not supply an estimate of the treatment contrast or its precision.

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 Patient Pain Scores, measured over 3 days.

The primary endpoint is patient pain assessed using the Visual Analog Scale (VAS). The registry describes the outcome as a mean, with standard deviation as the measure of dispersion, and gives the unit as units on a scale- VAS. Assessments are specified for postoperative days 0, 1 and 2, within a timeframe of 3 days. The scale range is 0-100, and higher values mean more pain.

A continuous pain score can retain information about the degree of reported pain rather than reducing each assessment to a binary category. In general, a mean describes the average score in a group, while a standard deviation describes how spread out individual scores are around that average. Those summaries can help readers understand both the group’s typical score and variation among participants. They do not, by themselves, establish whether a difference between groups is precise or clinically important.

The repeated postoperative assessments describe pain at several points in the specified period. The registry record does not report the group means, standard deviations, or a statistical comparison for any assessment. It also does not state a single combined pain score or identify one time point as the sole primary comparison. The endpoint’s planned measurement is therefore clear, but its observed values and treatment contrast are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The trial is described as randomized, double-masked, and parallel. In general, random assignment is intended to make treatment groups comparable with respect to both measured and unmeasured characteristics, on average. Masking is intended to limit the influence of expectations on care, reporting, and assessment. A parallel design means the compared groups receive their respective assigned regimens rather than being described as crossing from one regimen to the other. These are general explanations of the design labels; the registry record does not give operational details about assignment or masking.

What does a mean and standard deviation tell readers?

The primary outcome is identified as a mean of a continuous measure, with standard deviation as dispersion. In general, the mean is the arithmetic average of recorded scores, while the standard deviation describes how much scores vary around that average. A group mean alone does not show whether participants’ scores were tightly clustered or widely dispersed. The standard deviation provides information about that spread, but does not directly quantify uncertainty in the group mean or in a difference between groups.

To interpret a comparison, readers would need the observed group summaries and an estimate of the difference, ideally with an uncertainty measure such as a confidence interval. Those results are not reported in the registry record. The stated scale direction is useful for interpreting any future reported estimate: higher VAS values represent more pain. It does not provide the result itself.

Why do the several time points matter?

Pain was assessed on postoperative days 0, 1 and 2. Repeated measurements can describe how an outcome changes over time, but they also create choices about the target comparison. An analysis might focus on a specified assessment, compare patterns across time, or define a combined summary. These approaches answer related but not identical questions. The registry record does not report a single reduced comparison, and the posted information does not identify a model or a rule for combining the assessments.

General statistical analyses of repeated measurements need to account for the fact that observations from the same participant may be related. Treating related observations as if they were independent can misstate uncertainty. A suitable approach depends on the data structure and the question of interest. The registry record does not report the method used for the repeated pain assessments, so no specific approach can be attributed to this trial.

What can an inferential result add?

In general, an estimated treatment contrast describes the size and direction of a difference between groups, while a confidence interval describes the precision of that estimate under the analysis. A p-value, when reported, addresses compatibility between the data and a specified null hypothesis under model assumptions; it is not a measure of the size or clinical importance of an effect. None of these inferential results is reported for the primary pain outcome in the registry record. Statistical significance, precision, and the magnitude of an observed effect therefore cannot be assessed.

Interpretation also depends on the analysis population and handling of missing observations. An analysis using all randomized participants can address a different estimand from one restricted to participants with observed outcomes or adherence to treatment. General methods for missing data rely on assumptions, and conclusions can depend on whether those assumptions are credible. The registry record does not state the analysis population, how missing pain assessments were handled, or whether sensitivity analyses were conducted.

How should planning calculations be understood?

General sample-size planning asks how much information may be needed to detect a prespecified effect under chosen assumptions. The registry record describes a planning illustration based on the observed effect, a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation; the effect to detect is expressed as a stated fraction of the observed effect. Such planning figures are illustrations, not evidence about what the completed trial found. They are not observed power, and they do not replace an estimate and uncertainty interval from the trial’s results.

The record does not report the trial’s own sample-size justification. It also does not report a statistical analysis plan, assumptions underlying any trial-specific planning, or whether planning was revised. Because primary-outcome results and analyses are absent, the registry record does not support a recalculation of the treatment effect or its precision.

More generally, continuous outcome analyses can be sensitive to distributional features, outliers, unequal variability, and model assumptions. These concerns are reasons to examine the data and analysis details, not evidence that any particular problem occurred in this trial. The registry record does not provide outcome distributions or diagnostics with which to assess them.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome includes VAS assessments on postoperative days 0, 1 and 2. Multiple assessments raise a general multiplicity question: if several comparisons are tested, the chance of at least one apparently unusual result can increase unless the analysis and interpretation account for the number and structure of tests. A prespecified primary time point, an overall repeated-measures test, or another defined approach can address a different question. The registry record does not identify a single reduced comparison or report a multiplicity strategy.

The record lists secondary outcomes of narcotics consumption, knee range of motion, and patient restfulness, in addition to four outcome measures overall. Considering several outcomes can also raise multiplicity concerns. The registry record does not report which secondary analyses were performed, whether any were prespecified in an analysis plan, or how multiple comparisons were handled. No results are reported for these secondary outcomes.

Missing-data handling is also not reported. The registry record does not state whether any assessments were missing, how missing values were treated, or whether sensitivity analyses examined alternative assumptions. In general, missing-data methods can affect both the estimate and its uncertainty, especially when the reasons for missingness relate to outcomes or treatment. The record does not permit assessment of those issues.

The analysis population is not reported, and participant flow is not described. It is therefore unclear from the registry record which randomized participants, if any, contributed to each outcome analysis. Although the enrollment is listed as 50, the number analyzed for the primary endpoint is not reported. The registry record also lists no analyses, so it does not establish how the planned outcome measurements were evaluated.

11. Safety Results

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

Other (non-serious) adverse events

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

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: postoperative illeus (5.9%), bradycardia and vasovagal syncope (5.9%), traumatic foley insertion (5.0%).

The registry record lists serious adverse event figures separately by group. For Placebo, serious events are reported for 2 of 17 at risk; for Gabapentin, they are reported for 1 of 20 at risk. No other events are reported for either group in the listed serious-event fields. Deaths are recorded as null for both groups, which is not the same as a stated count of zero.

The record also lists serious-event terms with percentages: Postoperative illeus, 5.9%; Bradycardia and vasovagal syncope, 5.9%; and Traumatic foley insertion, 5.0%. The record does not identify these terms as arm-specific in the listed top-term summary, so the percentages should not be assigned to either treatment group. The registry record does not provide further details about event timing, severity criteria, relatedness to treatment, or how the listed terms correspond to the group-level figures.

These safety summaries describe reported events, not proof that a regimen caused them. The group figures should not be treated as a complete safety comparison without information about ascertainment, follow-up, and analysis. The registry record does not report those details or a statistical comparison of adverse events.

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

The record establishes that a randomized, double-masked, parallel trial compared a perioperative gabapentin regimen with placebo in the setting of total knee arthroplasty. Its primary outcome was patient pain measured by VAS on postoperative days 0, 1 and 2. The scale is described as 0-100, with higher values indicating more pain. These details define the clinical and statistical question.

They do not answer that question. The registry record does not report pain scores by group, a treatment-effect estimate, an uncertainty interval, or an inferential test. It therefore cannot show whether the groups differed, the direction of a difference, or how precisely an effect was estimated. The same limitation applies to the listed secondary outcomes: narcotics consumption, knee range of motion, and patient restfulness.

The trial’s completed status and enrollment listing are not outcome findings. Nor does the design alone establish the quality of implementation or analysis. Randomization and masking can strengthen comparisons when properly carried out, but the registry record does not give enough detail to evaluate their implementation or the handling of outcome data.

The serious adverse event figures are descriptive registry entries. Their interpretation is limited by the absence of information about ascertainment, attribution, follow-up, and comparative analysis. They should not be read as demonstrating that an event was caused by a treatment or as a complete account of safety.

In general, a result is most informative when readers can see an effect estimate alongside its uncertainty, understand the analysis population and missing-data approach, and know how repeated time points and multiple outcomes were handled. Those elements are not reported in this record. The appropriate conclusion is therefore about the record’s limits: it describes a trial and its intended measurements, but does not provide the outcome evidence needed to assess the effect of gabapentin relative to placebo.

13. Why This Trial Matters Statistically

This trial illustrates an important distinction between a registered study design and a reported result. A randomized, double-masked comparison can be relevant to a clinical question, but the design labels do not provide an estimate of the treatment effect. For statistical interpretation, readers need the observed outcomes, the comparison method, and enough information to judge uncertainty and analysis choices.

The primary pain outcome was measured at several postoperative time points. This makes the target of inference important: a result for one assessment is not automatically equivalent to a result for the overall pattern across assessments. The record does not specify a single reduced comparison or report how the time points were analyzed. That absence limits interpretation independently of the study’s enrollment or design.

The record also names several secondary outcomes and serious adverse event summaries. Multiple outcomes can offer a broader picture, but they require transparent reporting of which comparisons were planned and how results were interpreted. The registry record does not report those analysis details or the outcome findings. Statistical transparency is therefore central to understanding what the completed trial can contribute.

More generally, the example reinforces that precision is not conveyed by a design description alone. Group summaries, an effect estimate, and an uncertainty interval are needed to understand the magnitude and reliability of a comparison. Without them, neither a positive nor a null conclusion is supported by the registry record. It remains possible to identify the question, measurement schedule, and broad design, while recognizing that the trial’s treatment-effect evidence is not reported there.

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 main limitation of the available record is the absence of primary-outcome results and analyses. Although the outcome is defined as mean VAS pain over the specified postoperative assessments, the record does not report group means, standard deviations, an effect estimate, a confidence interval, or a test result. The treatment comparison therefore cannot be quantified or interpreted for direction and precision.

The several assessment days are not reduced to one comparison in the registry record. The method for analyzing repeated measurements, the handling of multiplicity, and the designation of any primary time point are not reported. These omissions prevent assessment of how the outcome schedule informed the analysis.

Enrollment is listed as 50, but the number contributing to each outcome is not reported. The record does not describe participant flow, missing observations, withdrawals, adherence, or the analysis population. It also does not report baseline characteristics or details of allocation and masking implementation. These gaps limit assessment of comparability and the practical execution of the design.

The record gives serious adverse event summaries but does not report event ascertainment, timing, attribution, or a comparative safety analysis. The top serious-event terms are not identified as arm-specific in the summary. The registry record also does not report a statistical analysis plan, sample-size justification for the trial, or whether interim analyses occurred.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Pain Control With Total Knee Replacement — NCT01680549.
• Registry record last updated 2024-01-31; status last verified 2024-01.
• Results first posted 2017-03-17.
• 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

NCT01680549, titled Pain Control With Total Knee Replacement, is listed as a completed phase 4 randomized, double-masked, parallel trial sponsored by Texas Tech University Health Sciences Center. Enrollment is recorded as 50, with a study start of 2012-09 and primary completion of 2016-02.

The study compares perioperative gabapentin with placebo in total knee arthroplasty. Its primary outcome is patient pain assessed by VAS on postoperative days 0, 1 and 2; higher scores on the 0-100 scale indicate more pain. Narcotics consumption, knee range of motion, and patient restfulness are listed as secondary outcomes.

The registry record does not report primary or secondary outcome results, statistical analyses, participant flow, or an analysis population. Serious adverse event figures are listed by group, but further details needed to interpret them are not reported. The record therefore describes the study question and design without reporting the treatment-effect evidence.