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 Analgesia After Total Knee Arthroplasty: Peri-Articular Injection Versus Epidural + Femoral Nerve Blockade (NCT01335542), a randomized phase 4 study. The primary outcome is The Primary Outcome is Time Until a Patient is "Ready for Discharge.".
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT01335542 |
| Phase | Phase 4 |
| Condition | Readiness to Discharge |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 91 |
| Arms in the primary outcome | 2 |
| Lead sponsor | Hospital for Special Surgery, New York |
| Results posted | Yes |
2. Clinical Question
Population
Patients undergoing total knee arthroplasty at the participating institution were the focus of the study. The registry describes readiness for discharge as the condition of interest and reports enrollment of 91 participants. It does not provide further eligibility criteria or a fuller description of the enrolled population.
Intervention
The intervention was peri-articular injection: pain medication injected around the knee. The registry summary describes this pathway as also involving pain pills and a pain patch on the skin. The arm is labeled “Local Infiltration” in the posted outcome results.
Comparator
The comparator was the epidural pathway, identified in the registry as PCEA+FNB. The summary describes epidural analgesia, a femoral nerve block, and pain pills. Additional operational details for either pathway are not reported in the registry record.
Primary question
The main question was how long it took participants to meet the stated criteria for being ready for hospital discharge. The primary outcome is expressed in days and was followed over the hospital stay. The registry reports an outcome value of 3.2 days for each arm, but does not report a formal between-group estimate, confidence interval, or test of the difference.
The registry describes this as a comparison of two approaches to managing pain after knee replacement, with readiness for discharge as its principal outcome. This outcome is broader than a pain score: the criteria include pain, nausea, diet, urination, wound status, medical stability, and physical therapy milestones. The posted results therefore address the time to a combined discharge-readiness state, rather than pain relief alone. The clinical question is whether the recorded time to that state differed between the peri-articular injection pathway and the epidural pathway. The available results provide group-level summaries but do not establish whether any observed difference is statistically distinguishable from chance or clinically important.
3. Trial Design
The registry identifies this as a Phase 4, randomized, double-masked, parallel-group trial. Participants were assigned to peri-articular injection or the epidural pathway. The listed enrollment is 91. The outcome results list 45 participants in each arm; those arm counts do not account for all the listed enrollment. The reasons for this difference are not reported in the registry record.
The study was sponsored by Hospital for Special Surgery, New York. The registry gives a start date of 2010-03 and a primary completion date of 2011-03, and lists the study status as completed. These entries describe the study’s registration record; they do not specify when individual participants were enrolled or when each outcome was assessed.
The parallel design indicates that the recorded groups were compared as separate treatment pathways rather than as repeated treatment periods within the same participants. Random allocation is intended, in general, to reduce systematic differences between groups at the start of a trial. The registry does not report how the allocation sequence was generated, how assignments were concealed, or whether randomization was stratified. Those details are not reported in the registry record.
Masking is recorded as double, but the registry does not identify which people were masked or describe how masking was implemented. Since the interventions involve different procedures and care pathways, the record alone does not allow the reader to assess what masking could practically cover. The protocol details needed to clarify this are not reported in the registry record.
The record lists one outcome measure, the primary time-to-readiness outcome, and reports no posted secondary outcomes. It does not provide a detailed statistical analysis plan, sample-size justification, interim-analysis plan, or analysis-population definitions. The design labels help describe the trial’s broad structure, but they do not fill in these unreported methods.
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.
Before assignment: One patient in the local infiltration group was deemed ineligible due to a rheumatoid arthritis. Only 90 patients were randomized to the study.
Overall Study
| Stage | Epidural Pathway | Local Infiltration |
|---|---|---|
| STARTED | 45 | 45 |
| COMPLETED | 45 | 45 |
| 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.
Population: One patient in the local infiltration group was deemed ineligible due to a rheumatoid arthritis. The remaining 90 patients were included in the baseline analysis population.
| Characteristic | Unit | Epidural Pathway | Local Infiltration | Total |
|---|---|---|---|---|
| Participants analysed | 45 | 45 | 90 | |
| Age, Continuous | years | 67 (50 to 84) | 65 (49 to 81) | 66 (49 to 82) |
| Sex: Female, Male: Female | Participants | 29 | 29 | 58 |
| Sex: Female, Male: Male | Participants | 16 | 16 | 32 |
| Region of Enrollment: United States | participants | 45 | 45 | 90 |
| BMI: Normal | participants | 3 | 2 | 5 |
| BMI: Overweight | participants | 19 | 20 | 39 |
| BMI: Obese | participants | 21 | 20 | 41 |
| BMI: Morbidly Obese | participants | 2 | 3 | 5 |
6. Primary Endpoint
The registry lists the primary outcome as The Primary Outcome is Time Until a Patient is "Ready for Discharge.", measured over Participants will be followed for the duration of their hospital stay, an expected average of 3 days.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Inter-Quartile Range |
| Unit | days |
| Endpoint classification | not reduced to a single comparison |
The primary outcome is the time until a participant was judged “ready for discharge,” measured in days. The record says participants were followed for the duration of their hospital stay, with an expected average of 3 days. This is a time-to-event type of outcome: the event is meeting the defined readiness criteria, not necessarily the actual date of leaving the hospital.
The criteria combine several aspects of recovery and discharge preparation. They include discontinuation of patient-controlled analgesia, absence of moderate or severe nausea within the last 4 hours, ability to eat solid food and urinate after Foley catheter removal, pain below the specified threshold, a dry surgical wound, and no acute medical problems. Physical therapy requirements include independent transfers, walking 40 ft. without assistance, and extension range of motion below 10 degrees.
Using a readiness milestone can capture the combined time to meet practical discharge conditions, rather than measuring only one symptom. It can also reflect multiple clinical and functional components at once. That breadth is useful for the question described in the registry, but it means the outcome does not isolate the effect of either pathway on pain, mobility, or any single criterion. The record does not report separate results for the components.
The primary outcome is labeled as a mean, with inter-quartile range listed as its dispersion. The posted arm values are 3.2 days for both groups. Lower and upper values are also recorded for each arm. The registry does not provide a separate explanation of how those values relate to the displayed summary, so they should not be treated as confidence limits or as a between-group interval.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The posted primary-outcome value is 3.2 days for the Epidural Pathway arm and 3.2 days for the Local Infiltration arm. Each arm lists 45 participants. This establishes what the registry reports as the group-level outcome values; it does not establish that the pathways have identical effects. Rounded summaries can conceal differences in the underlying participant-level data, and a formal comparison is needed to estimate uncertainty around a group contrast.
The registry lists lower and upper values of 1.8 and 7.0 for the Epidural Pathway and 1.0 and 14.0 for Local Infiltration. It labels dispersion as inter-quartile range, but does not report a separate comparison interval. These arm-level values describe spread as recorded in the registry; they are not confidence intervals for the treatment difference. Their interpretation is also limited because the record does not explain the bounds beyond the listed dispersion label.
No analysis results are posted for a two-arm comparison of this outcome. The registry record does not report an estimated difference between groups, a confidence interval for that difference, or a p-value. Thus, the equal displayed values cannot be used to conclude that the groups were equivalent, nor can they show whether a difference would be statistically or clinically meaningful. A finding of equivalence or non-inferiority would require an appropriate prespecified framework and supporting analysis, neither of which is reported in the registry record.
The broad endpoint is a composite readiness milestone. The summary cannot reveal which criteria most influenced the recorded time, or whether a pathway affected some components differently from others. No component-level results are posted. The record also does not describe how participants who did not meet readiness criteria before discharge, or whose outcome could not be determined, were handled.
The arm counts are 45 each, while total enrollment is listed as 91. The record does not explain the difference or indicate whether every enrolled participant contributed to the primary outcome. No analysis populations or exclusions are reported. These gaps matter when interpreting group summaries, because the relationship between enrollment, follow-up, and the reported outcome counts is not fully described.
The most defensible reading is descriptive: the registry reports 3.2 days in both arms, along with arm-level spread information, but provides no inferential comparison. The reported data are not enough to assess precision of a treatment contrast or to draw a conclusion about comparative effects.
9. Statistical Methods Explained
What does random allocation contribute?
In general, random allocation is used to make treatment groups comparable on average with respect to both measured and unmeasured characteristics. This helps support a fair comparison, especially when outcomes are assessed consistently. Randomization does not guarantee that groups will be identical in a particular trial, and it does not remove the need to report baseline characteristics, participant flow, and an analysis that respects the assigned groups. The registry identifies the study as randomized, but the sequence-generation and allocation-concealment methods are not reported in the registry record.
What does masking mean?
Masking is intended to limit the influence of knowledge about treatment assignment on care, measurement, or reporting. The record labels the trial double-masked, but does not say which parties were masked or how masking was maintained. General interpretation therefore should not assume that participants, clinicians, outcome assessors, or analysts were all masked. The procedures and checks used to support masking are not reported in the registry record.
How should a group summary be distinguished from a treatment effect?
A group summary describes outcomes within an arm. A treatment effect is a contrast between arms, expressed using a chosen measure such as a difference in means or another suitable comparison. The posted value of 3.2 days in each arm is a group-level summary. It is not itself an estimated contrast with uncertainty. A treatment-effect estimate and its confidence interval would show both the direction and the precision of the comparison. Neither is reported for the primary outcome.
A confidence interval, in general, describes a range of values compatible with the data and the assumptions of the analysis. It is useful because a single point estimate does not show how uncertain the estimated effect is. The lower and upper figures listed for each arm are not a confidence interval for the difference: the registry labels the dispersion as inter-quartile range and does not post a comparison interval.
Why does the choice of summary matter?
The primary outcome is labeled as a mean, while dispersion is labeled as inter-quartile range. A mean describes an average, whereas an inter-quartile range describes the middle portion of a distribution. These summaries answer different descriptive questions. Time outcomes can have skewed distributions, for example when some participants take considerably longer than others to reach a milestone. In general, the choice between means and distribution-based summaries should be guided by the outcome distribution and the planned estimand. The registry does not report the distribution, the rationale for the summary choice, or a detailed analysis method.
Over-dispersion is a general concern when data vary more than a statistical model assumes. If a model understates variability, its standard errors can be too small and its intervals or tests can be misleading. Whether over-dispersion is relevant to the analysis of this endpoint cannot be assessed because no model or inferential analysis is reported. For this time outcome, the distribution and handling of participants who do not reach the readiness event would also matter; those methods are not reported in the registry record.
What is missing from the comparison?
A complete report of a two-arm primary analysis would ordinarily identify the target comparison, the analysis population, the estimate, its uncertainty, and any test used. The registry has no posted analyses and no reported p-value or confidence interval for the primary outcome. It also does not specify whether the analysis was based on assignment as randomized, on participants with observed outcomes, or on another population. These are not details that can be inferred from the arm summaries.
The registry says the endpoint is time until readiness, but the results are presented as an arm value with dispersion rather than as a time-to-event estimate. In general, time-to-event methods can account for differing follow-up and for participants whose event is not observed during follow-up, using a defined censoring approach. A simple comparison of summaries may not answer the same question as a time-to-event analysis. The registry does not report whether such methods were used, whether censoring occurred, or how discharge and readiness were distinguished analytically.
Sample-size planning also depends on a prespecified effect of interest, variability assumptions, significance level, desired power, and the planned analysis. The registry record does not report the trial’s sample-size justification or those design assumptions. Planning illustrations based on observed effects, when available, are not observed power and cannot reconstruct the original design rationale. No numerical planning illustration is reported in this record.
Multiplicity refers, in general, to the increased chance of a false-positive finding when many outcomes, comparisons, or analyses are tested. The record lists one outcome measure and no posted secondary outcomes or analyses. It does not provide an analysis plan establishing whether additional outcomes or exploratory comparisons were considered. Consequently, the multiplicity strategy, if any, is not reported in the registry record.
These general methods explain why group summaries alone have limited inferential value. They do not imply that a particular unreported method was used. The available record supports description of the outcome values and trial labels, but not reconstruction of the statistical analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists one outcome measure and reports no posted secondary outcomes or analyses. It does not describe a hierarchy of outcomes, a family of planned tests, or an adjustment for multiple comparisons. Multiplicity is a general concern when several outcomes or analyses are tested, because the chance of a false-positive result can increase. Whether this concern applied to analyses conducted for the trial cannot be determined from the registry record.
Missing-data methods are not reported. The record does not state whether any primary outcomes were unavailable, how missing readiness times were handled, or whether participants were excluded from the reported summaries. The arm counts are 45 in each group, while listed enrollment is 91; the record does not explain this discrepancy or connect it to missing outcomes, exclusions, or follow-up.
Analysis populations are also not described. In general, an analysis based on assigned treatment can preserve the advantages of randomization, while a restricted analysis of participants with complete data may introduce bias if missingness is related to prognosis or treatment. The registry does not say which approach was used, so neither should be assumed.
The endpoint is described as time until readiness during the hospital stay. The record does not explain how participants who left hospital without meeting the criteria, had prolonged stays, or lacked an assessable readiness time were treated analytically. Censoring rules and sensitivity analyses are not reported in the registry record. These omissions limit assessment of potential bias and of how robust the group summaries are to incomplete follow-up.
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 |
|---|---|---|---|
| Epidural Pathway | 0 | 45 | 0.0% |
| Local Infiltration | 0 | 45 | 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 |
|---|---|
| Epidural Pathway | 0 of 45 |
| Local Infiltration | 0 of 45 |
The registry reports zero serious adverse events affecting participants in the Epidural Pathway group and zero in the Local Infiltration group. Each group lists 45 participants at risk for serious adverse events. It also reports zero other adverse events affecting participants in each group, with 45 at risk in each group for that category. Death counts are recorded as null rather than as a reported numeric result.
These figures describe what is posted in the registry record; they do not establish that no adverse events occurred outside the recorded categories or observation period. A zero count is not evidence of zero risk. The record does not give definitions for the adverse-event categories, event-collection procedures, follow-up duration for safety, or a detailed account of event severity and attribution. The top serious adverse-event terms are not listed.
With no reported events in the displayed categories, a comparative risk estimate cannot be obtained from these counts alone. The record also does not provide an uncertainty interval or a formal safety comparison. The safest interpretation is that the registry lists zero affected participants in both groups for these categories, while important details about ascertainment and the null death entries remain unreported.
12. What the Result Does, and Does Not, Mean
The posted outcome summaries describe time to readiness for discharge after total knee arthroplasty in two randomized groups. The registry reports 3.2 days for both the Epidural Pathway and Local Infiltration arms. It also lists arm-level lower and upper values and identifies the dispersion as inter-quartile range. These are descriptive results, not a formal estimate of the difference between pathways.
The result does not show that the pathways are equivalent. Equal displayed summaries can occur even when underlying distributions differ, and the record contains no confidence interval or test of the treatment contrast. A conclusion about equivalence or non-inferiority would require a specified margin and an analysis designed to assess that question; these are not reported in the registry record.
The result also does not isolate pain control. Readiness for discharge combines pain and nausea criteria with diet, urination, wound, medical, and physical therapy criteria. Since component-specific outcomes are not posted, it is not possible to determine which elements shaped the overall time or whether the groups differed on any individual element.
The available safety counts show zero reported affected participants in the serious and other adverse-event categories for both groups. They do not establish absence of harm, and the record lacks detail about event collection and the meaning of the null death values.
Overall, the registry supports a narrow descriptive statement about the reported group summaries. It does not provide enough statistical detail to determine the precision of a between-group effect, assess the role of missing data, or make a comparative efficacy or safety conclusion. The record should be read as an incomplete report of the trial’s statistical results, not as proof that the approaches have the same or different effects.
13. Why This Trial Matters Statistically
This trial illustrates why a posted group value and a statistical comparison are not interchangeable. The registry reports the same primary-outcome value, 3.2 days, for each arm. Without an estimated between-group contrast and its uncertainty, readers cannot judge how precise that apparent similarity is or what range of effects remains compatible with the data.
It also illustrates the importance of aligning an endpoint’s label, summary, and analysis. The outcome is described as time to a readiness event, but the record gives an arm-level mean and an inter-quartile range label. Those details do not reveal the participant-level distribution or explain whether the analysis accounted for incomplete event times. Clear reporting of the estimand and analysis method would help readers understand exactly what the reported value represents.
The endpoint is multidimensional. A discharge-readiness milestone may be operationally relevant because it combines clinical and functional criteria, but it cannot identify the effect on pain alone. Reporting component outcomes and their analysis would clarify which parts of readiness contribute to the overall result, while avoiding the assumption that a combined measure answers every related question.
Finally, the enrollment and arm-count entries do not fully reconcile, and the record does not report analysis populations or missing-data handling. Transparent participant flow and explicit analysis populations are essential for understanding who contributed to each estimate. The trial is statistically instructive because its registry entry contains a clear clinical question and arm-level outcome summaries, yet leaves the inferential details needed for a firm comparison unreported.
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 primary limitation is that no analysis of the two-arm comparison is posted. The record gives arm-level values but no treatment-effect estimate, confidence interval, or p-value. It therefore does not show the precision of the contrast or support a formal conclusion about a difference.
The registry describes the primary parameter as a mean and the dispersion as an inter-quartile range, but does not explain the listed lower and upper values or provide details of the statistical method. The outcome is a time-to-readiness measure, yet the record does not report how event times were analyzed, whether censoring was relevant, or how participants without an observed readiness time were handled.
Enrollment is listed as 91, while the outcome results list 45 participants in each arm. The record does not explain the mismatch, provide a participant-flow account, or specify analysis populations. Missing-data procedures, exclusions, and follow-up completeness are not reported.
The endpoint combines multiple discharge criteria, and no component-level results are posted. The registry also does not provide further eligibility details, baseline characteristics, intervention implementation details, sequence-generation methods, or information about which people were masked. These omissions limit assessment of comparability and generalizability.
The record does not report a sample-size justification, a detailed statistical plan, multiplicity handling, interim analyses, or a protocol-based analysis population. It lists zero affected participants in the posted adverse-event categories but does not explain event definitions or ascertainment. These limitations apply to interpretation of the registry entry and do not establish what may have been reported elsewhere.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Analgesia After Total Knee Arthroplasty: Peri-Articular Injection Versus Epidural + Femoral Nerve Blockade — NCT01335542.
- Registry record last updated 2022-04-14; status last verified 2022-04.
- Results first posted 2016-04-20.
- 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
NCT01335542 is a completed, Phase 4, randomized, double-masked, parallel-group trial sponsored by Hospital for Special Surgery, New York. The registry lists 91 participants enrolled, a start date of 2010-03, and a primary completion date of 2011-03.
The study compared peri-articular injection, labeled Local Infiltration in the outcome results, with an epidural pathway. Its primary outcome was time in days until participants met readiness-for-discharge criteria during the hospital stay. The registry reports a value of 3.2 days for each arm, with 45 participants listed in each arm and arm-level spread information.
No formal comparison, confidence interval, p-value, secondary outcome results, or statistical analysis plan is reported in the registry record. Serious and other adverse-event counts are listed as zero affected participants in both groups; death counts are null. The record does not explain the difference between listed enrollment and arm counts or report missing-data handling.