A Study of Ropivacaine Complex Methylene Blue Fascia Iliaca Compartment Block on Analgesia in Patients Undergoing Hip Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study of Ropivacaine Complex Methylene Blue Fascia Iliaca Compartment Block on Analgesia in Patients Undergoing Hip Arthroplasty (NCT06284941), a randomized na study. The primary outcome is Visual Analogue Scale（VAS）.

2. Clinical Question

The registry’s rationale is that postoperative pain can hinder recovery after total hip arthroplasty, while a single fascia iliaca block may provide limited-duration analgesia. It describes combining ropivacaine with methylene blue as an approach intended to prolong pain relief. That rationale explains the research question; it is not itself evidence that the added drug changes pain scores or recovery.

The trial’s registered secondary outcomes include inflammatory markers, physiological measurements, rescue analgesia, and walking distance at first mobilization. Those outcomes broaden the questions beyond pain scores, but their names alone do not establish what the trial found. Results for those outcomes are not reported in the registry record.

3. Trial Design

The registry describes a completed, randomized, double-masked, parallel-group study. The listed enrollment is 90, and the outcome summaries identify 45 participants in each arm. In a parallel design, participants are assigned to one of the treatment groups and remain in that group for the comparison. Random allocation is intended to make baseline differences less systematic on average, although the registry record does not report the sequence-generation method, allocation concealment, or baseline characteristics.

The two groups received fascia iliaca blocks with the same listed volume and concentration of ropivacaine; methylene blue was included in one group. The treatment descriptions identify 30ml of 0.25% ropivacaine in the control group and 30ml of 0.25% ropivacaine plus 0.05% methylene blue in the other group. Further procedural details, including the timing of the block relative to surgery and whether other analgesic care was standardized, are not reported in the registry record.

Masking is recorded as double, but the record does not specify which participants, clinicians, outcome assessors, or other personnel were masked, or how masking was maintained. The study is listed as phase NA. It is marked completed; its recorded start date is 2023-06-20 and its primary completion date is 2024-02-28. The sponsor is listed as Wang wanxia.

The primary outcome is VAS pain score, described as a median with an inter-quartile range. The registry states that scores were recorded before the block and at 2, 6, 12, 24, and 48 hours after surgery, both at rest and during activity defined as passive straight leg raise at 45°. Although the record includes one arm-level summary for each group, it does not connect those summaries to a particular time point or rest/activity condition. A specific sample-size justification, analysis plan, and approach to repeated measurements are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

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 Visual Analogue Scale（VAS）, measured over From enrollment to 48 hours after surgery， the VAS scores at both rest and with activity (passive straight leg raise at 45°) were recorded at the following time points: before block and at 2, 6, 12, 24, and 48 h postoperatively.

The primary endpoint is pain intensity measured with a visual analogue scale. The registry describes a ruler about 10 cm long, with 10 ticks on one side and endpoints labelled 0 and 10. A score of 0 means no pain, while 10 means the most severe, unbearable pain; higher scores indicate greater pain. This type of scale gives participants a way to express pain intensity along an ordered continuum.

Pain was to be assessed at rest and during activity, defined as passive straight leg raise at 45°. The registered schedule includes a measurement before the block and postoperative measurements at 2, 6, 12, 24, and 48 hours. Repeated assessments can describe how pain changes during the early postoperative period, while measurements during activity can capture pain associated with movement as well as pain at rest. These are general reasons to assess pain under more than one condition and at more than one time.

The registry reports the primary outcome using medians and inter-quartile ranges. A median describes the middle of the observed scores when ordered; the inter-quartile range describes the central half of those scores. These summaries can be useful when a distribution is skewed or when a small number of unusually high or low scores could make a mean less representative. The record does not state why this summary approach was selected.

For the ropivacaine-only arm, the posted median is 3, with an inter-quartile range from 2 to 3.5. For the combination arm, the posted median is 4, with an inter-quartile range from 4 to 5. Because the record does not attach these arm summaries to a particular time point or assessment condition, they should not be treated as a complete account of the registered repeated VAS assessments.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a randomized, double-masked, parallel-group design and reports median VAS scores with inter-quartile ranges. Those labels describe broad design and reporting choices, but they do not provide a complete statistical analysis plan. The specific methods used to compare the groups, account for repeated assessments, or handle incomplete observations are not reported in the registry record.

What does random allocation contribute?

In general, random allocation assigns participants to study groups using a chance-based process. Its statistical purpose is to reduce systematic differences between groups at assignment, including differences in measured and unmeasured characteristics. It does not guarantee that two groups will be identical, especially in a finite sample. Baseline summaries and the method of allocation can help readers assess how the groups were assembled, but the allocation procedure and baseline characteristics are not reported in the registry record.

Randomization also does not resolve every potential source of bias. For example, treatment deviations, loss to follow-up, or differences in additional care can affect interpretation after allocation. These are general considerations for randomized trials. The registry record does not give enough information to assess them for this study.

What does double masking tell readers?

Masking is intended to reduce the influence of expectations on treatment delivery, participant reports, or outcome assessment. For a subjective measure such as pain, masking may be particularly relevant as a general methodological consideration because the score is reported by the participant. However, the label double-masked does not identify which two groups of people were masked, whether the outcome assessor was masked, or how the treatment groups were kept indistinguishable. Those details are not reported in the registry record, so the practical success of masking cannot be evaluated from the label alone.

Why report a median and inter-quartile range?

The median is the central observation in an ordered set of values. The inter-quartile range marks the interval from the lower to the upper quartile and describes the middle half of the observations. In general, these summaries are often used when data are not well represented by a symmetric distribution or when extreme observations could strongly influence a mean. They describe the location and spread of scores, but do not directly provide a between-group effect estimate or its uncertainty.

The registry reports a median of 3 and an inter-quartile range of 2 to 3.5 for the ropivacaine arm, and a median of 4 and an inter-quartile range of 4 to 5 for the combination arm. The record does not state which assessment or assessments these numbers summarize. Nor does it explain whether the analysis used a rank-based test, a model, or another method. Such methods should not be inferred from the choice to report medians.

How should repeated measurements be considered?

The registered schedule includes measurements before the block and at multiple postoperative times, with assessments both at rest and during passive straight leg raise at 45°. Observations from the same participant are generally related rather than independent; this is a general statistical feature of repeated-measures data. Analyses may account for that dependence using an appropriate repeated-measures model or by defining a particular time point as the primary comparison. The registry record does not report which strategy was used, whether a specific time point was designated for inference, or how the rest and activity assessments were handled.

Without that information, the single arm-level summary cannot reveal trajectories, changes from baseline, or whether the groups differed at particular times or conditions. It also cannot show whether any overall comparison was adjusted for multiple assessments. These limitations concern what can be interpreted from the registry record; they do not establish what analyses may have been conducted outside it.

What would uncertainty estimates add?

In general, a confidence interval accompanies an estimated effect to show the range of values reasonably compatible with the data and the analysis assumptions. It helps readers distinguish a precise estimate from one with substantial uncertainty. A test statistic or p-value may also be reported, but neither replaces the effect estimate and interval. The registry record reports no primary-outcome inferential analysis, so there is no posted interval or test result to interpret.

Over-dispersion is a general issue for count outcomes when variation is greater than expected under a simple model such as a Poisson model. Methods that do not account for extra variation can yield uncertainty estimates that are too small. This concept may be relevant to some count outcomes in other settings, but the registry does not report a count-outcome model for this trial; no such method should be attributed to it.

What can be said about planning?

In general, sample-size planning uses assumptions about the target effect, outcome variability, significance level, power, allocation, and analysis method. The registry lists 90 participants and gives 45 participants in each arm, but a trial-specific sample-size justification and the assumptions behind it are not reported in the registry record. The posted arm summaries cannot retrospectively establish the design’s planned power. Planning illustrations based on observed effects, where available, are not observed power and should not be mistaken for the trial’s original design rationale.

The registry record contains no analysis records for the posted comparison and does not provide a complete statistical plan. Details such as the primary contrast, adjustment for repeated testing, covariates, model diagnostics, and handling of missing data are not reported in the registry record. Consequently, the main statistical interpretation must remain descriptive rather than inferential.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is assessed across multiple postoperative time points and under both rest and activity conditions. Considering multiple assessments can create a multiplicity issue: the more comparisons examined, the greater the general possibility of finding an apparently unusual result by chance. Statistical plans may address this by prespecifying a primary time point, adjusting for multiple comparisons, or using an overall repeated-measures analysis. The registry record does not report which approach, if any, was used. It also does not identify a single time point or condition for the arm summaries that are posted.

The record lists nine secondary outcomes, including inflammatory measures, mean arterial pressure, heart rate, surgery duration, rescue analgesia, and first walking distance after getting out of bed. Together with the repeated primary assessments, this makes it important to distinguish prespecified confirmatory analyses from exploratory comparisons. A hierarchy of outcomes, multiplicity adjustment, or designation of exploratory analyses is not reported in the registry record. No results for the listed secondary outcomes are reported there.

Missing data can affect both the size and comparability of analyzed groups, particularly when measurements are repeated over time. In general, a complete account would describe how many participants contributed at each assessment, why observations were missing, and how missing outcomes were handled. The registry record does not report these details, nor does it specify an imputation method or a sensitivity analysis.

Analysis populations are also not described. The registry does not state whether the primary analysis included all randomized participants, only participants who received the assigned block, or another defined group. The distinction matters because excluding participants after randomization can weaken the balance created by random allocation. These points are not evidence that data were missing or that exclusions occurred; they identify information not reported in the registry record.

11. 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 4% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports serious adverse events in 0 of 45 participants in the ropivacaine-only group and 0 of 45 participants in the ropivacaine-plus-methylene-blue group. Deaths are also listed as 0 in each group. These are counts recorded for the groups, not estimates that serious events cannot occur. A zero count in a trial of this size does not establish the absence of risk.

For other, non-serious adverse events, the registry reports 7 affected participants in the ropivacaine group and 6 in the combination group, with 45 participants at risk in each. The record does not provide event descriptions in the posted summary, severity details, timing, or an analysis comparing the groups. These counts should therefore be read as descriptive counts rather than as evidence of a treatment-related difference.

In general, adverse-event interpretation depends on how events were defined, collected, and attributed, as well as on the duration and completeness of follow-up. Those details are not reported in the registry record. The registry lists no serious-event terms, so the types of serious events monitored or considered are not specified in the posted information.

Zero recorded serious events does not prove that a treatment is free of serious harms, and the difference between the non-serious counts should not be treated as a causal effect without an appropriate analysis and fuller event information. The registry record does not report such an analysis.

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

The registry records a randomized comparison of two fascia iliaca block regimens in patients undergoing hip arthroplasty. One group received 0.25% ropivacaine alone, and the other received 0.25% ropivacaine with 0.05% methylene blue. Both groups are listed with 45 participants. The primary endpoint is VAS pain score, with assessments planned at rest and during activity across the period from before the block through 48 hours after surgery.

The posted arm summaries are median 3 (inter-quartile range 2 to 3.5) for ropivacaine alone and median 4 (inter-quartile range 4 to 5) for the combination. Since higher VAS scores represent greater pain, these values describe the reported summaries in that direction. They do not provide a complete answer to the trial question because the registry does not say which time point or assessment condition they represent. They also do not quantify an adjusted or unadjusted treatment effect.

The registry record reports no inferential primary-outcome analysis, confidence interval, or p-value. It therefore does not show how precisely the groups differ or whether the descriptive contrast is compatible with chance variation under a specified statistical model. A clinical importance threshold is not reported either. No conclusion about whether one regimen works better or worse is warranted from the posted information.

The serious adverse-event counts are zero in each group; other adverse events are reported for 7 participants in the ropivacaine group and 6 in the combination group. These counts are descriptive and do not establish comparative safety. The registry does not report detailed event types or a statistical safety analysis.

The result does not tell readers how VAS scores changed over time, whether rest and activity scores differed, or what happened for the listed secondary outcomes. It also does not establish the trial’s planned sample-size rationale, missing-data approach, or analysis population. Those details are not reported in the registry record. The appropriate reading is therefore limited: the record identifies the design, outcome schedule, arm summaries, and event counts, while leaving the central inferential comparison unresolved.

13. Why This Trial Matters Statistically

This trial is statistically interesting because it pairs a randomized design with a subjective, repeatedly measured primary outcome. Random allocation can support a fair comparison in principle, while masking can reduce some influences on treatment delivery and reported pain. At the same time, pain scores measured repeatedly in the same participant require careful definition of the primary comparison and suitable treatment of within-participant dependence. The registry record does not describe those analysis choices.

The outcome schedule includes assessments at rest and during movement. Those conditions need not represent the same aspect of pain, and measurements at different postoperative times address different points in recovery. A single median and inter-quartile range per arm cannot describe all these dimensions. Reporting time-specific results, group contrasts, and uncertainty would be needed to understand the observed pattern more fully.

The trial also illustrates why descriptive summaries should be separated from inferential results. Medians and inter-quartile ranges communicate the distribution’s center and spread, but they do not by themselves estimate uncertainty in the difference between randomized groups. Without a reported comparison and its precision, readers cannot determine how stable the observed arm summaries are as estimates of a broader treatment effect.

Finally, the registry lists multiple secondary outcomes alongside repeated primary assessments. This makes a prespecified analysis strategy important for distinguishing primary conclusions from exploratory findings. The record does not report a multiplicity plan, missing-data method, sample-size justification, or analysis population. These omissions limit statistical interpretation even though the trial design and outcome schedule are described.

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 principal limitation is that the registry’s single VAS summary for each arm is not linked to a specific time point or to the rest versus activity assessment. Because the registered endpoint involves repeated measurements under two conditions, the posted medians cannot reveal the full outcome pattern or support a clear time-specific interpretation.

The registry record does not report a primary between-group analysis, an effect estimate, confidence interval, or p-value. It also does not report the analysis method, handling of repeated observations, or a prespecified threshold for a meaningful score difference. The available summaries therefore cannot establish the precision or statistical significance of a comparison.

Further trial details are not reported in the registry record, including participant eligibility beyond the listed condition, baseline characteristics, allocation procedures, who was masked, and whether other postoperative care was standardized. Missing-data handling, analysis populations, and the sample-size justification are also not reported. These gaps prevent assessment of several aspects of risk of bias and statistical reliability.

The safety summary provides counts but not event descriptions, definitions, severity, timing, or a comparative analysis. Secondary outcomes are listed, but their results are not reported in the registry record. The record therefore supports only a restricted account of the study: its registered design, outcome framework, arm-level VAS summaries, and adverse-event counts.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Study of Ropivacaine Complex Methylene Blue Fascia Iliaca Compartment Block on Analgesia in Patients Undergoing Hip Arthroplasty — NCT06284941.
• Registry record last updated 2025-02-04; status last verified 2025-02.
• Results first posted 2025-02-04.
• 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

The completed study is listed as randomized, double-masked, and parallel-group, with enrollment of 90 participants. The recorded start date is 2023-06-20, and the primary completion date is 2024-02-28. The comparison is between 30ml of 0.25% ropivacaine for fascia iliaca block and 30ml of 0.25% ropivacaine plus 0.05% methylene blue. The registry lists 45 participants in each arm.

The primary outcome is VAS pain score, described as a median with an inter-quartile range, with measurements at rest and during passive straight leg raise at 45° from before the block through 48 hours after surgery. The posted medians are 3 (2 to 3.5) for ropivacaine and 4 (4 to 5) for the combination, but the specific time point and condition are not identified. No inferential primary analysis is reported in the registry record.

The registry reports zero serious adverse events and zero deaths in both arms; other adverse events are recorded for 7 and 6 participants, respectively. Detailed secondary-outcome results, a statistical analysis plan, missing-data methods, and a sample-size justification are not reported in the registry record.