Evaluation of Preoperative N1539 in Total Knee Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of Preoperative N1539 in Total Knee Arthroplasty (NCT03434275), a randomized phase 3 study. The primary outcome is Opioid Use Hour 0-24.

2. Clinical Question

The registry record identifies postoperative pain as the condition and describes opioid consumption as the primary objective. This makes the comparison about opioid use during a specified postoperative interval, rather than a direct measure of pain intensity or longer-term recovery. No additional primary clinical questions are reported in the registry record.

3. Trial Design

This was a phase 3b, randomized, parallel-group trial, with 194 participants listed as enrolled. Its official title describes a multicenter, double-blind evaluation; the registry’s masking classification is quadruple. The record does not identify which people or roles were masked, or explain how masking was maintained. It lists the trial as completed.

Participants were assigned to N1539 30 mg or IV placebo. The arm descriptions state that each was administered every 24 hours. The trial focused on preoperative administration of N1539 for people undergoing open unilateral total knee arthroplasty. The registry record lists the study start as 2018-02-19 and primary completion as 2019-05-21.

The primary outcome results list 93 participants for N1539 and 88 for placebo. These outcome counts are not the same as the overall enrollment figure. Reasons for the difference, including exclusions from the endpoint analysis, are not reported in the registry record. The record describes the outcome as continuous and reports least-squares means with standard errors. It does not report the analysis population, model specification, or the reasons for using those group counts in the primary analysis.

The registry record lists one outcome measure and no secondary outcome results. It does not report a detailed protocol, allocation procedure, or original sample-size justification. Consequently, the randomized design and listed group results establish the basic comparison, while important operational details needed to reconstruct the analysis are unavailable.

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.

Population: Safety Population - Subjects who received at least 1 study dose

6. Primary Endpoint

The registry lists the primary outcome as Opioid Use Hour 0-24, measured over Up to 24 Hours.

The primary endpoint is titled “Opioid Use Hour 0-24.” It measures total opioid analgesia from Hour 0 through 24, expressed as IV morphine equivalent dose in mg. The registry record gives the timeframe as up to 24 hours. The outcome is continuous, and the group summaries are least-squares means with standard errors.

Expressing opioid use as morphine equivalent places opioid analgesia on a common dose scale, which is useful when total use is the outcome of interest. This is a general statistical and measurement explanation; the registry record does not describe the conversion method used for individual opioid medications. Nor does it clarify the precise event defining Hour 0.

The endpoint closely matches the stated objective: assessing the effect of preoperative N1539 on opioid consumption compared with placebo. It addresses use of opioid analgesia over a short, defined interval. It is not itself a measure of pain severity, satisfaction, function, or later opioid use. Those outcomes are not reported as secondary results in the registry record.

Least-squares means are model-based group summaries in general statistical usage. Their interpretation depends on the model and any adjustments included. The registry record does not report the model specification or covariates, so the basis of these least-squares means cannot be examined in detail. The standard errors describe estimated uncertainty around the group summaries, but do not by themselves give the full uncertainty for the difference between groups.

7. Results Posted in the Registry

• N1539 30 mg: mean 18.94 versus 27.73 on control; difference -8.79 (95% CI -12.52 to -5.06), standardized effect d = -0.69; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The reported outcome is continuous: each participant’s total opioid use over the specified interval is represented on an IV morphine equivalent scale. For a continuous endpoint, a common comparison summarizes the average value in each group and the difference between those averages. Here, the registry reports least-squares means rather than identifying the summaries simply as raw arithmetic means. In general, least-squares means are model-based estimates; their meaning can depend on model terms and adjustments. The model and adjustment variables are not reported in the registry record.

What does the mean difference represent?

The posted contrast is -8.79 mg morphine equivalent, with N1539 compared against placebo. Its negative sign indicates a lower estimated value for N1539 on the stated opioid-use scale. The group summaries are 18.94 for N1539 and 27.73 for placebo. These values and the contrast are reported results; the underlying participant-level data and the detailed calculation are not reported in the registry record. Interpreting a mean also depends on whether the distribution is adequately represented by a mean-based summary. The record does not provide outcome distributions or diagnostics.

What do standard errors describe?

A standard error describes the estimated sampling uncertainty of a statistic, such as a group mean. It is not the same as the spread of individual participants’ outcomes. The reported standard errors are 1.32 for N1539 and 1.371 for placebo. In general, the standard error of a difference also depends on the relationship between the group estimates and on the analysis method. For that reason, the reported interval for the group contrast is the direct source for assessing its precision. The registry record does not state how the standard errors were modeled.

How should the p-value be understood?

The unadjusted p-value is < 0.001. In general, a p-value is calculated under a null hypothesis and analysis assumptions; it quantifies how unusual results at least as extreme as the observed result would be if that null model held. It is not the probability that the treatment has no effect, and it does not measure the probability that the result will replicate. “Unadjusted” indicates that this posted value is not adjusted for multiplicity. The registry record does not report a multiplicity plan or other analysis details that would clarify how this value relates to any broader set of planned tests.

Why do the analysis details matter?

Model choices, covariate adjustment, and the handling of missing outcomes can affect estimates and their uncertainty. In general, prespecified methods help readers understand which comparison was intended and how deviations or incomplete data were addressed. The registry record does not report the primary analysis model, analysis population, missing-data methods, or interim analyses. These omissions limit the ability to independently evaluate the reported least-squares means and contrast. Randomization and masking describe important parts of the design, but do not replace those analysis details.

What does over-dispersion mean in general?

Over-dispersion is a concern when observed variability is greater than a statistical model expects. It is often discussed for count data, where failing to account for extra variability can make uncertainty appear too small. The primary outcome in this trial is a continuous dose measure, and the registry record does not report a count model or any assessment of over-dispersion. Therefore, over-dispersion is not identified as a reported issue for this endpoint. More generally, the appropriate uncertainty method depends on the outcome distribution and model assumptions, details that are not available in the registry record.

The record reports a randomized, parallel-group comparison, but does not give the randomization sequence method, concealment procedure, or further details of masking. These points matter because the design’s protections depend on how they were implemented. The registry’s masking classification is quadruple, while the official title uses the term double-blind; the record does not explain the terminology. The result can be interpreted as a posted randomized comparison, with the analytic and implementation details that remain unreported kept in view.

10. Confidence Intervals and Precision

The posted interval for the mean difference is -12.52 to -5.06 mg morphine equivalent, with N1539 compared against IV placebo. It gives a range of values associated with the estimate under the analysis used. In general, a confidence interval expresses uncertainty about an estimated quantity, rather than the range of individual participant outcomes. The registry record does not state the confidence level for this interval, so a level should not be assumed.

The interval lies entirely below zero, matching the negative direction of the reported estimate, -8.79. That makes the contrast’s direction clear within the reported interval. The interval’s width also matters: it indicates that the estimate is not a single exact value. Statistical precision is not the same as clinical importance, and the record does not report a threshold for interpreting a difference as clinically meaningful.

The group standard errors are 1.32 for N1539 and 1.371 for placebo. They describe uncertainty in the respective least-squares means, not the variation among individual opioid-use values. The group counts for the primary outcome are 93 and 88. The registry record does not explain why these outcome counts differ from the overall enrollment of 194, nor report how incomplete outcome data were handled.

Precision should therefore be understood in relation to the posted estimate and interval, not as a guarantee about future studies. Interpretation also depends on the model, outcome measurement, and analysis population. Those details, along with the interval’s confidence level, are not reported in the registry record.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm, not total events. The assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for planning is a stated fraction of the observed effect. The trial’s own original design assumptions and sample-size justification are not reported in the registry record.

For planning around 100% of the observed effect, the figures are 34 participants per arm for 80% power and 45 participants per arm for 90% power. For planning around 75% of the observed effect, they are 60 participants per arm for 80% power and 80 participants per arm for 90% power. For planning around 50% of the observed effect, they are 134 participants per arm for 80% power and 179 participants per arm for 90% power.

In general, power is the probability that a planned study will detect an effect of a specified size under its assumptions, if that effect is present. The 80% and 90% columns describe two alternative planning targets: the latter targets a greater chance of detecting the assumed effect and therefore requires more participants for each stated effect fraction. Smaller effects require more participants because they are harder to distinguish from random variation under the same assumptions. These figures are planning illustrations based on the observed effect, not observed power.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = -8.790; pooled standard deviation σ = 12.794.
2. n = 2 × (1.96 + 0.842)² × 12.794² / -8.790² = 33.3, rounded up to 34 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- -8.79                      # observed difference in means
sigma <- 12.7937017273449                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(3434275)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 34 (80% power), 45 (90% power)
 75% of observed effect: n per arm = 60 (80% power), 80 (90% power)
 50% of observed effect: n per arm = 134 (80% power), 179 (90% power)
power.t.test: 34.2 
Simulated power at n = 34 per arm: 0.794 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry record lists one outcome measure and no secondary outcome results. The primary endpoint is opioid use from Hour 0 through 24. It also reports an unadjusted p-value for the primary comparison. The record does not state whether additional outcomes, time points, or analyses were prespecified in the protocol, so the full family of planned statistical tests is not reported.

Multiplicity arises when several hypotheses are tested. In general, as the number of tests increases, the chance of at least one small p-value under null hypotheses can increase. Methods such as a prespecified hierarchy or adjustment can address that issue, but the multiplicity plan is not reported in the registry record. The reported p-value should therefore be described as unadjusted, without inferring how it would relate to any unreported analysis plan.

The record does not report an analysis population, such as whether the primary analysis followed all randomized participants or another defined group. The primary outcome lists 93 participants for N1539 and 88 for placebo, while overall enrollment is 194. Reasons for the outcome counts and the treatment of missing or unavailable measurements are not reported in the registry record. Missing-data methods can matter when the likelihood of an unavailable outcome is related to participant characteristics or outcomes; this is a general statistical concern, not a claim about what occurred in this trial.

The primary model, covariates, treatment of protocol deviations, and any interim analyses are also not reported in the registry record. Without those details, readers cannot determine whether the posted comparison follows a prespecified plan or assess sensitivity to alternative analysis choices. The absence of these details does not establish that a particular method was or was not used; it means the registry record does not document it.

14. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: pulmonary embolism (2.3%), atrial fibrillation (1.1%), cardiac failure congestive (1.1%), oesophageal stenosis (1.1%), cellulitis (1.1%).

The registry record lists serious adverse events for 3 participants in the N1539 30 mg group, with 93 at risk, and for 9 participants in the IV placebo group, with 88 at risk. It lists other adverse events for 65 participants in the N1539 group, with 93 at risk, and for 81 participants in the placebo group, with 88 at risk. Deaths are listed as 0 in each group.

These are counts reported for the two groups. The registry record does not define the precise event-counting rules, describe exposure-adjusted analyses, or provide further detail about the adverse-event collection period. The serious-event terms listed include Pulmonary embolism at 2.3%, Atrial fibrillation at 1.1%, Cardiac failure congestive at 1.1%, Oesophageal stenosis at 1.1%, Cellulitis at 1.1%, and Hyponatraemia at 1.1%. The listed percentages should be read as posted; the registry record does not give further context about their calculation in this summary.

These safety counts are descriptive and do not, by themselves, establish why an event occurred or whether it was caused by an intervention. They also do not describe every aspect of safety or allow conclusions about risks outside the trial’s reported groups and observation period.

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

The primary result describes a between-group comparison of opioid use over Hour 0 through 24 among participants represented in the posted outcome results. The estimated mean difference is -8.79 mg morphine equivalent for N1539 relative to IV placebo, with an interval from -12.52 to -5.06 and an unadjusted p-value of < 0.001. The negative estimate and interval indicate lower reported opioid use in the N1539 group on this endpoint’s scale. This is a statistical description of the posted result, not a recommendation or a general claim about treatment.

The result does not answer whether pain intensity differed, whether recovery was improved, or whether opioid use differed after the measured interval. The registry record lists no secondary outcome results. The endpoint is opioid consumption, not a direct measurement of pain or functional recovery. It also does not establish effects for other procedures, patient groups, dosing schedules, or care settings.

The trial’s randomized and masked design is relevant to the credibility of the comparison, but the registry record does not provide enough detail to assess the analysis fully. The model, analysis population, handling of missing data, confidence level for the interval, and multiplicity plan are not reported. The record also does not provide the protocol’s original sample-size assumptions or justification. These gaps limit how much can be concluded about robustness and generalizability.

Safety figures are also descriptive. The registry reports serious and other adverse-event counts and no deaths in either group, but these counts alone do not establish causality or fully characterize comparative safety. Overall, the posted evidence addresses one primary endpoint, over one stated time window, in this trial. Any broader interpretation would require information beyond what the registry record reports.

16. Why This Trial Matters Statistically

This trial illustrates how a clinical question can be expressed as a continuous endpoint and a direct contrast between randomized groups. Opioid use is measured as IV morphine equivalent dose, and the primary comparison is reported as a difference in least-squares means. That makes the scale and direction of the estimate interpretable: the negative value represents a lower estimated amount in the N1539 group than in the placebo group.

It also illustrates why effect estimates, intervals, and p-values answer related but different questions. The estimate gives the central contrast; the interval conveys uncertainty around it; and the unadjusted p-value summarizes compatibility with a null model under analysis assumptions. None of these measures, by itself, establishes clinical importance. The registry record does not state a threshold for a meaningful difference or identify the confidence level for the interval.

The planning illustrations show how assumptions about the effect to detect influence required sample size. Smaller assumed effects call for more participants per arm under the stated planning approach. These calculations are not a substitute for the trial’s original design rationale, which is not reported in the registry record. Nor do planning figures explain the outcome counts observed in the posted results.

Finally, the record demonstrates the value of reporting analysis details alongside results. Information about the model, analysis population, missing data, and multiplicity would help readers evaluate how the estimate was produced and how broadly it can be interpreted. The posted result is informative for the specified endpoint, while those unreported details define important limits on statistical appraisal.

17. 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 assess the primary result are not reported in the registry record. Although the outcome is described as a least-squares mean, the model, included covariates, and method for deriving the standard errors are not specified. The confidence level for the reported interval is also not stated. These omissions prevent a full reconstruction of the primary analysis from the registry record.

The registry lists 194 participants enrolled, while the endpoint results give group counts of 93 and 88. It does not explain the difference, report the analysis population, or describe how missing endpoint measurements were handled. The precise definition of Hour 0 and the method used to express different opioid medications as IV morphine equivalents are not reported in the registry record.

The official title describes the study as double-blind, while the registry masking classification is quadruple. The record does not explain which people or roles were masked or how masking was implemented. It identifies the study as multicenter but does not report the participating centers in the information summarized for this result.

The record lists no secondary outcome results and does not report the multiplicity plan, protocol-level sample-size justification, or interim analyses. It also does not provide individual outcome distributions or detailed safety follow-up information. These limitations do not determine whether the trial was conducted appropriately; they identify areas where the registry record does not provide information needed for deeper evaluation.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Evaluation of Preoperative N1539 in Total Knee Arthroplasty — NCT03434275.
• Registry record last updated 2023-05-25; status last verified 2023-04.
• Results first posted 2023-05-25.
• 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.

21. Record Summary

NCT03434275 is a completed phase 3b randomized, parallel-group trial evaluating preoperative N1539 against IV placebo in open unilateral total knee arthroplasty. The registry record lists 194 participants enrolled and identifies opioid use from Hour 0 through 24 as the primary endpoint, measured in mg morphine equivalent.

The posted least-squares means are 18.94 for N1539 and 27.73 for placebo. The mean difference is -8.79, with an interval from -12.52 to -5.06 and an unadjusted p-value of < 0.001. The registry also lists serious and other adverse-event counts and 0 deaths in each group.

The record does not report secondary outcome results, the primary analysis model, missing-data methods, the confidence level for the interval, or the trial’s original sample-size justification.