Lumbar Plexus Block for Postoperative Pain Control After Hip Arthroscopy. A Randomized Controlled Trial: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Lumbar Plexus Block for Postoperative Pain Control After Hip Arthroscopy. A Randomized Controlled Trial (NCT01286805), a randomized phase 4 study. The primary outcome is Numeric Rating Scale (NRS) Pain at Rest (0-10) on Day of Surgery Prior to Discharge.

2. Clinical Question

The clinical question is about pain reported at a specific postoperative time, not pain across the entire recovery period. The primary endpoint was a 0-to-10 Numeric Rating Scale (NRS), with 0 meaning no pain and 10 meaning the worst pain imaginable. The posted results also address readiness for discharge from the post-anesthesia care unit, narcotic medication needed, nausea, vomiting, rescue antiemetic use, satisfaction, and a physical-comfort dimension of quality of recovery. Detailed results are posted for only some of these secondary outcomes. The registry record does not report the criteria used to select participants or additional details about the surgical population.

3. Trial Design

The registry describes a completed, phase 4, randomized, double-masked, parallel-group trial sponsored by Hospital for Special Surgery, New York. The study started in 2010-05, and primary completion was recorded in 2010-10. The registry lists an enrollment of 83. The outcome summaries list 41 participants in each primary-outcome arm; the record does not explain the relationship between the enrollment figure and the outcome denominators.

The randomized groups were Lumbar Plexus Blockade + CSE and Control Group. Both received a combined spinal-epidural; the intervention group also received a lumbar plexus blockade. The registry describes the block’s local anesthetic mixture and volume, but further procedural details are not reported in the registry record. The term double-masked is recorded, but the identities of the masked people and how masking was maintained are not reported in the registry record.

The primary endpoint was mean pain at rest before discharge on the day of surgery. Secondary outcomes covered recovery and discharge, narcotic medication, nausea and vomiting, rescue antiemetic use, satisfaction, and physical comfort. The record lists 8 outcome measures and 7 posted secondary outcomes. Results are available for the primary endpoint and for several secondary outcomes, but no reported analyses are listed for the secondary outcomes. The protocol’s planned analysis methods, original sample-size justification, and any interim analyses are not reported in the registry record. Randomization supports a comparative interpretation, but the posted summaries alone do not establish what analysis population or adjustment strategy the trial used.

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 Numeric Rating Scale (NRS) Pain at Rest (0-10) on Day of Surgery Prior to Discharge, measured over Day of surgery prior to discharge.

The primary endpoint is the mean Numeric Rating Scale (NRS) pain-at-rest score on the day of surgery before discharge. Participants were asked to rate pain on a scale from 0 to 10, where 0 represents no pain and 10 represents the worst pain imaginable. The registry reports a mean and standard deviation for each group, making this a continuous outcome in the posted summary.

A numeric pain scale gives participants a common way to report a subjective experience. A group mean describes the average reported score, while the standard deviation describes how spread out the individual scores are around that average. The mean is useful for comparing groups, but it does not show the full distribution: people in the same group may report quite different levels of pain. Nor does a group mean establish what any one participant experienced.

The measurement was taken at a defined point—before discharge on the day of surgery—so the result speaks to pain at that time, not to pain at other times or across recovery as a whole. The record does not report additional measurement details, such as how the timing was standardized across participants or how incomplete NRS responses were handled. The endpoint was selected to address the trial’s question about postoperative pain; the record does not report a threshold for interpreting a difference as clinically important.

7. Results Posted in the Registry

• Lumbar Plexus Blockade + CSE: mean 3.30 versus 4.20 on control; difference -0.90 (95% CI -1.77 to -0.03), standardized effect d = -0.45; z-test p = 0.043.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Readiness to Discharge From Post-Anesthesia Care Unit (PACU)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Lumbar Plexus Blockade + CSE: mean 216.00 versus 187.00 on control; difference 29.00 (95% CI -2.92 to 60.92), standardized effect d = 0.39; z-test p = 0.075.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Lumbar Plexus Blockade + CSE and the control. The interval gives the range of effects that remain compatible with the data.

Narcotic Pain Medication Needed

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Lumbar Plexus Blockade + CSE: mean 21.00 versus 29.00 on control; difference -8.00 (95% CI -16.27 to 0.27), standardized effect d = -0.42; z-test p = 0.058.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Lumbar Plexus Blockade + CSE and the control. The interval gives the range of effects that remain compatible with the data.

Incidence of Nausea

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Lumbar Plexus Blockade + CSE: 34.1% (14/41) versus 19.5% (8/41) on control; risk difference 14.6 percentage points (95% CI -4.3 to 33.6), risk ratio 1.75 (0.82–3.72); unadjusted two-proportion z-test p = 0.135.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Lumbar Plexus Blockade + CSE and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes span recovery timing, medication use, postoperative symptoms, patient experience, and quality of recovery. Results are posted for readiness to discharge from the post-anesthesia care unit, narcotic medication needed, and nausea. The registry names additional secondary outcomes—vomiting, rescue antiemetic use, patient satisfaction, and the physical-comfort dimension of QoR-40—but detailed results for those measures are not reported in the posted secondary summaries.

Across the reported comparisons, the numerical directions differ by outcome. The continuous estimates do not have confidence intervals that clearly exclude no difference, and the nausea risk-difference interval also includes zero. This leaves uncertainty about the size and direction of the secondary contrasts. The secondary measures can add context to the pain result, but they do not directly answer the primary question about mean pain at rest before discharge.

These comparisons carry less weight than a prespecified primary analysis because multiple outcomes create more opportunities for chance findings, and the registry does not report a multiplicity strategy. No reported analyses are listed for the secondary outcomes. Their posted summary statistics are therefore best read as descriptive or exploratory evidence, not as a set of independent confirmatory tests. The record also does not report whether the secondary outcomes were prespecified in the protocol, how missing observations were handled, or whether any covariate adjustment was used. The overall secondary pattern does not resolve the uncertainty around the primary estimate or establish effects on outcomes whose detailed results are absent.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Readiness to Discharge From Post-Anesthesia Care Unit (PACU)
• Narcotic Pain Medication Needed
• Incidence of Nausea
• Incidence of Vomiting
• Requirement of Antiemetic Rescue
• Patient Satisfaction
• Quality of Recovery (QoR-40) Physical Comfort Dimension

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is continuous: each participant’s pain rating is represented by a number on the NRS, and the registry reports group means and standard deviations. A mean difference is a natural summary for this type of outcome because it expresses the contrast in the original scale’s units. Here the contrast is calculated as the intervention-group mean minus the control-group mean, so a negative value indicates a lower mean score in the intervention group.

What does the confidence interval add?

A confidence interval expresses the uncertainty around an estimated difference under the assumptions of the method used to calculate it. It gives a range of values that are reasonably compatible with the observed data and method; it is not a range containing every individual participant’s score, nor does it state the probability that the true effect lies within that particular interval. The posted interval for the primary mean difference runs from -1.77 to a value just below zero. Because it approaches zero, the estimate leaves room for a small difference as well as a larger reduction in the intervention group. The registry does not report the exact inferential procedure used by the trial sponsor, so the posted recalculation should be understood as a simple unadjusted calculation from summary statistics.

How should the p-value be read?

The primary unadjusted p-value is 0.043. A p-value measures how unusual data at least as discrepant as those observed would be under a specified null hypothesis and statistical model. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of a difference. The registry record does not report a multiplicity adjustment or the sponsor’s own analysis. The p-value should therefore be read alongside the estimated difference and its confidence interval, rather than as a stand-alone verdict.

Why does variability matter?

The standard deviation describes the spread of participant scores around a group mean. The primary standard deviations are 2.2 for the blockade group and 1.8 for the control group. Larger within-group variability generally makes a group contrast less precise when other features are held constant, because participant responses are less tightly clustered around the mean. The values are summaries of spread, not uncertainty intervals for the means. The posted comparison also uses the group sizes, so its precision reflects both spread and the amount of outcome information available.

What do the secondary measures represent?

The registry posts mean summaries for readiness to discharge and narcotic medication needed, and participant counts for nausea. A mean difference expresses contrasts for the continuous measures in their original units. A risk difference expresses the difference in the proportions experiencing a binary outcome. The registry also gives relative measures for nausea, but interpreting such measures requires attention to their uncertainty and the number of events. The secondary comparisons are unadjusted, and the registry does not list reported analyses for them. They should not be treated as independent confirmation of the primary result.

What is not established by these summaries?

Summary statistics do not reveal the full distribution of scores, whether observations were missing, or how any missing data were handled. They also do not disclose whether the trial used an adjusted analysis, which covariates might have been included, or which population was used for analysis. Those details are not reported in the registry record. Consequently, the recalculated comparisons are useful for describing the posted means and their approximate uncertainty, but they cannot substitute for a complete trial analysis or protocol. The registry identifies the design as randomized and double-masked; it does not report enough detail to assess the randomization process or masking implementation.

11. Confidence Intervals and Precision

The primary mean difference is -0.9 NRS units, with a confidence interval from -1.77 to a value just below zero. This interval conveys uncertainty around the difference in group means, not the range of pain scores among participants. Its endpoints indicate that the data are compatible with a more substantial lower mean in the blockade group, but also with a difference very close to zero. The point estimate is therefore more precise in direction than in magnitude: the estimated mean is lower in the intervention group, while the exact size of the contrast remains uncertain.

The interval is relatively close to zero at one end, and the unadjusted p-value is 0.043. These summaries are related ways of expressing evidence about the group contrast, but neither establishes clinical importance. The registry record does not report a threshold for a clinically important NRS difference, so the size of the estimate cannot be judged against such a threshold from this record alone.

Standard deviations of 2.2 and 1.8 indicate that individual scores varied within both groups. The group means thus conceal differences among participants. A confidence interval around a mean difference addresses uncertainty in the group contrast; it does not imply that all participants would have scores near the group mean or that the same contrast applies to every participant.

Precision also depends on how outcomes and analyses were handled. The registry does not report missing-data methods, analysis-population definitions, or a sponsor-reported inferential analysis. The posted recalculated interval should be interpreted as an unadjusted summary-based estimate, not as a substitute for those unreported details.

12. 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 participants or total events. They are planning illustrations based on the observed primary effect, not the trial’s own original design assumptions. The registry’s listed planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. Each planning row considers detecting the stated fraction of the observed effect. The trial’s original sample-size justification is not reported in the registry record.

The 80% power column gives the planned participants per arm for a hypothetical study designed to have an 80% chance of detecting the stated effect under the listed assumptions, if that effect and the model assumptions are correct. The 90% power column gives the corresponding per-arm planning figure for a 90% chance. These are design probabilities for hypothetical repeated studies, not guarantees about a particular study’s outcome. The calculations are based on the observed effect, which is itself uncertain.

The rows for 100%, 75%, and 50% of the observed effect illustrate how the planning requirement changes when the target difference is made smaller. Smaller effects need more participants because they are harder to distinguish from ordinary sampling variation. For example, planning for 75% of the observed effect requires more participants per arm than planning for the full observed effect, and planning for 50% requires more still. These figures are not observed power; they are planning illustrations and should not be used as evidence that the completed trial did or did not have adequate power.

13. 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 = -0.900; pooled standard deviation σ = 2.010.
2. n = 2 × (1.96 + 0.842)² × 2.010² / -0.900² = 78.3, rounded up to 79 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 <- -0.9                      # observed difference in means
sigma <- 2.00997512422418                     # 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(1286805)
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 = 79 (80% power), 105 (90% power)
 75% of observed effect: n per arm = 140 (80% power), 187 (90% power)
 50% of observed effect: n per arm = 314 (80% power), 420 (90% power)
power.t.test: 79.3 
Simulated power at n = 79 per arm: 0.797 (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.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists a primary outcome and several secondary outcomes. Considering multiple outcomes raises a multiplicity issue: when many comparisons are examined, the chance of at least one apparently notable result arising by chance can increase. The record does not report whether the trial adjusted for multiple comparisons, designated a hierarchy among secondary outcomes, or used another strategy to control this issue. The primary result is therefore presented with its unadjusted p-value, and the secondary results should be interpreted cautiously rather than as a collection of confirmatory findings.

Missing-data handling is not reported in the registry record. The posted primary summaries list 41 participants per arm, while the registry lists enrollment of 83; the record does not explain the difference. This alone does not show that outcome data were missing or identify why the denominators differ. The record does not provide participant-flow details, numbers with missing measurements, imputation methods, or sensitivity analyses. It is not possible to assess from these summaries whether missingness could have affected the estimates.

The analysis population is also not reported in the registry record. The record does not state whether the trial used an intention-to-treat, per-protocol, or other population for its own analysis. The number of reported analyses is listed as zero, and no reported analyses are listed for the secondary outcomes. The presented comparisons are unadjusted recalculations from posted summary statistics, not documented sponsor analyses. The statistical plan, covariate adjustments, interim analyses, and original sample-size justification are not reported in the registry record. These omissions limit assessment of how closely the posted calculations follow the trial’s planned analysis.

15. 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 5% reporting threshold.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: fall (4.8%), admission for nausea (2.4%), admission for oxygen desaturation (2.4%), admission for epidural spread (2.4%).

The serious adverse event summaries list 42 at risk in the Lumbar Plexus Blockade + CSE group and 41 at risk in the Control Group. The registry lists 3 serious adverse events for the blockade group and 2 for the control group. The counts should be read in the context of the listed at-risk denominators; the record does not provide event-level narratives or enough detail to assess timing, severity, or causal attribution for each event.

The registry lists Fall at 4.8%, Admission for nausea at 2.4%, Admission for oxygen desaturation at 2.4%, and Admission for epidural spread at 2.4% among the top serious adverse event terms. The posted terms do not establish whether events were judged related to the intervention. The registry also lists 0 other adverse events in each group. Death counts are not reported in the registry record.

These summaries are descriptive. They do not establish that an event was caused by a procedure or that risks are equivalent between groups. The counts are limited, and no inferential safety comparison or fuller event description is reported in the registry record. They should be interpreted as the adverse-event information recorded, not as a comprehensive safety assessment.

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

The posted primary comparison shows a lower mean pain-at-rest score before discharge in the group that received lumbar plexus blockade plus combined spinal-epidural than in the group that received combined spinal-epidural alone. The estimated mean difference is -0.9 NRS units, and the confidence interval reaches close to zero. This is evidence about the average score at the specified time in this trial, with uncertainty about the size of the group difference.

The result does not establish how participants’ pain changed over time, what their scores were after discharge, or whether any individual participant experienced a lower score. The registry record does not report a threshold for a clinically important difference, so it cannot determine from the posted information whether the estimated contrast is meaningful to patients. Nor does the result show that the intervention affects every secondary outcome. Several secondary comparisons are uncertain, and detailed results for some named outcomes are not posted.

The randomized design makes the group comparison relevant to the trial’s stated question, but important analysis and conduct details are not reported in the registry record. The posted summaries do not describe the allocation process, masking implementation, missing-data handling, analysis population, or sponsor’s inferential methods. The analysis shown is an unadjusted recalculation from group summaries. It should therefore be considered alongside, not in place of, a complete report of the trial methods and results.

The findings apply to the studied comparison and measurement time. The registry record does not provide enough information to establish whether the results generalize to other surgical settings or populations. The results describe statistical estimates; they are not medical advice and do not establish a treatment recommendation.

17. Why This Trial Matters Statistically

This trial illustrates the distinction between the direction of an estimated contrast and the precision of that estimate. The blockade group’s mean pain score is lower, but the confidence interval approaches zero. Reading the point estimate alone would miss the uncertainty; reading the p-value alone would miss the magnitude and scale of the contrast. Considering the mean difference, interval, group variability, and timing together gives a fuller statistical description.

It also shows why endpoint definition matters. The primary result concerns pain at rest before discharge on the day of surgery. It does not represent pain throughout recovery. Keeping the measurement time and outcome scale explicit prevents a narrow comparison from being interpreted as a broad statement about postoperative pain.

The trial’s several secondary outcomes demonstrate how one study can generate many comparisons. Without a reported multiplicity plan, secondary findings deserve less confirmatory weight than the primary endpoint. The registry’s absence of reported secondary analyses, missing-data methods, and analysis-population details further limits what can be concluded from the summaries.

Finally, planning calculations based on the observed effect can help illustrate how sample size relates to a target effect, but they do not recover the assumptions used to design the completed trial. The original justification is not reported in the registry record. Keeping that distinction clear helps prevent retrospective planning figures from being mistaken for evidence about the trial’s original design or observed power.

18. 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.

Important limitations for interpreting this particular record are the absence of detailed trial methods and a complete reported analysis. The registry identifies randomization, double masking, and a parallel design, but does not describe how the random sequence was generated, how allocation was concealed, or who was masked. Further participant eligibility and clinical-characteristic details are also not reported in the registry record.

The primary outcome denominator is 41 in each group, while overall enrollment is listed as 83. The record does not explain the discrepancy, give participant-flow information, or state whether outcome data were missing. Missing-data handling and the analysis population are not reported. These gaps make it difficult to assess how the posted outcome summaries relate to all enrolled participants.

The posted primary comparison is a simple unadjusted recalculation from summary statistics. The sponsor’s inferential analysis, statistical plan, covariate adjustments, and any interim analyses are not reported in the registry record. The registry also does not report a clinically important difference threshold for the NRS, limiting interpretation of the magnitude beyond its statistical scale.

Only some secondary outcomes have detailed posted results, and no reported analyses are listed for them. The record does not describe multiplicity control. Serious adverse event summaries lack event-level detail and do not establish causal attribution. These specific limitations mean the registry record supports a focused reading of the posted summaries, but not a complete assessment of trial conduct, analysis, or generalizability.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Lumbar Plexus Block for Postoperative Pain Control After Hip Arthroscopy. A Randomized Controlled Trial — NCT01286805.
• Registry record last updated 2013-06-05; status last verified 2013-05.
• Results first posted 2013-06-05.
• 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.

22. Record Summary

NCT01286805 is a completed phase 4 randomized, double-masked, parallel-group trial sponsored by Hospital for Special Surgery, New York. The registry records a start date of 2010-05, primary completion in 2010-10, and enrollment of 83.

The trial compared lumbar plexus blockade plus combined spinal-epidural with combined spinal-epidural alone for hip arthroscopy. The primary outcome was mean NRS pain at rest before discharge on the day of surgery. The posted summaries show means of 3.3 and 4.2, respectively, with a mean difference of -0.9 and an unadjusted p-value of 0.043. The confidence interval approaches zero, leaving uncertainty about the magnitude of the difference.

Some secondary outcome summaries and serious adverse event information are also recorded. The registry does not report the sponsor’s analysis methods, missing-data handling, analysis population, or multiplicity strategy, which limits interpretation beyond the posted summaries.