Trigger Point Injection in Reducing Pain Following Total Knee Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trigger Point Injection in Reducing Pain Following Total Knee Arthroplasty (NCT06955923), a non-randomized phase 2 study. The primary outcome is Pain Scores on the Visual Analog Scale.

2. Clinical Question

The trial’s stated rationale connects tissue manipulation during knee replacement with postoperative pain and myofascial pain. Its stated aim is to evaluate whether trigger point injections affect pain scores and opioid use compared with a sham procedure. That aim defines the research question; it does not establish that one procedure improved either outcome.

The registry identifies the study as a phase 2, parallel, non-randomized trial with single masking. It explicitly cautions that the arms are not a like-for-like control comparison. Without random allocation, group differences may reflect factors other than the assigned procedure. The record does not report which participant characteristics or clinical factors were measured or accounted for in an analysis.

3. Trial Design

The registry describes a completed phase 2 pilot study with a parallel-group design. Participants were assigned to an experimental group receiving trigger point injections or a sham comparator group. Allocation was non-randomized, and the record itself cautions that the arms are not a like-for-like control comparison. This limitation matters when interpreting any apparent difference: without random allocation, differences between groups may have existed before the procedure or may reflect how participants came to be assigned.

The experimental procedure was trigger point injection with 1% lidocaine without epinephrine immediately after total knee arthroplasty. The described sites were two muscles in the thigh and two in the calf. The sham procedure was intended to mimic the injection setup without injecting fluid. The summary states that the needle would be pressed against the skin without fluid being injected. The registry labels masking as single and describes an effort to keep the patient unaware of whether an injection was given.

Enrollment was 11. The registry summary characterizes the study as a pilot, states a maximum of 100 total patients, and says the planned size was much smaller, with 10-15 patients per group. These are planning statements, not the number enrolled or a report of a completed sample-size justification. The protocol’s rationale for the planned size is not reported in the registry record.

The registry lists pain measured by a visual analogue scale as the primary outcome, from enrollment to the end of treatment at 6 weeks. Follow-up is described for POD1 and weeks 2 and 6. Opioid use is listed as a secondary outcome. The record does not report the observed pain scores, opioid-use results, or an analysis comparing the groups.

The study is marked completed. Its start date is 2025-05-30 and its primary completion date is 2025-08-25. Completion status indicates the registry’s recorded study status; it does not establish that all planned measurements were obtained or that the outcome analysis was reported.

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

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Limited timeline for follow-up restricted total number of participants for the last follow-up interval (6 week)

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 Pain Scores on the Visual Analog Scale, measured over From enrollment to the end of treatment at 6 weeks.

The primary endpoint is change in pain scores measured using the visual analogue scale. Participants were asked to mark a numbered scale from 0-100, where zero indicates no pain and 100 indicates severe intolerable pain. The description specifies that the score represents the average level of pain since discharge. The stated timeframe runs from enrollment to the end of treatment at 6 weeks.

A visual analogue scale represents a continuous measure: it can express differing degrees of symptom intensity rather than sorting participants into only a few categories. A change score is intended to describe how a participant’s reported pain differs over the defined follow-up period. For interpretation, the timing and completeness of the measurements matter, as does whether the analysis compares changes within each group or contrasts changes between groups. The registry does not report those analysis details.

Repeated pain assessments are described at POD1 and weeks 2 and 6. These observations can describe pain at different stages after surgery, but they are not interchangeable with a single result at the final visit. The primary outcome timeframe is stated as enrollment through the end of treatment at 6 weeks; the registry does not specify how measurements across visits were combined into the primary analysis.

Pain is the primary outcome because the study’s stated question concerns postoperative pain following knee replacement. Opioid use is listed separately as a secondary outcome. The actual pain scores, change estimates, variability, and comparison results are not reported in the registry record, so the endpoint definition alone does not indicate the direction or size of any observed change.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry classifies the primary outcome as a mean of a continuous measure, with standard deviation as its dispersion measure. In general, a mean describes the center of a set of measurements, while a standard deviation describes how spread out individual measurements are around that center. Neither statistic alone expresses how precisely a group mean or a between-group contrast has been estimated. A confidence interval is commonly used for that purpose: it gives a range of values compatible with the data and the stated statistical procedure. The registry record does not report group means, standard deviations, confidence intervals, or a primary analysis result.

What does a change score represent?

In general, a change score is a participant’s follow-up measurement compared with an earlier measurement. A group mean change can describe the average direction and magnitude of change in that group. A between-group analysis might compare the groups’ mean changes, or use another model that accounts for repeated measurements. Those approaches answer related but not identical questions. The registry identifies the outcome as change in visual analogue scale pain scores and gives a timeframe from enrollment to 6 weeks, but the specific calculation and model are not reported in the registry record.

The record describes assessments at POD1 and weeks 2 and 6. Repeated measurements within a participant are statistically related: a person’s measurements over time are not generally independent observations. As a general methods point, analyses of repeated outcomes should account for that dependence if they combine multiple visits. A single endpoint analysis at a specified visit raises different considerations from a model using all visits. The registry does not state which strategy was used, whether all visits were included in a model, or how incomplete follow-up was handled.

Why does allocation matter?

Random allocation is a way to reduce systematic differences between treatment groups at the time of assignment. Here allocation is non-randomized, and the registry explicitly cautions that the arms are not a like-for-like control comparison. In general, group comparisons in non-randomized studies can be affected by confounding: a factor related both to group assignment and to the outcome can distort the apparent association between intervention and outcome. Statistical adjustment can sometimes address measured confounders, but it cannot guarantee removal of bias from unmeasured factors. The registry does not report a covariate adjustment plan or analysis model.

The parallel-group design means the study has separate intervention and sham groups followed over the stated period. The label single masking indicates masking in the registry classification, and the description states that the patient would not know whether fluid was injected. Masking may reduce some expectation-related influences on self-reported outcomes, but it does not remedy non-random allocation. The record does not give further details about who else was masked or how masking was assessed.

What do planning calculations mean?

In general, sample-size planning estimates how many participants may be needed to detect a chosen effect under specified assumptions. The registry describes planning illustrations based on a fraction of the observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. These calculations are not trial results and do not show the probability that this completed study detected an effect. That probability is often called power, but a planning illustration must not be described as observed power. The numerical illustrations and the observed effect are not reported in the registry record.

Planning assumptions also matter. A calculation based on an observed effect depends on that effect estimate, and an estimate from a pilot study can be uncertain. In general, planning for a smaller effect requires more information than planning for a larger effect, all else being equal. This is a conceptual relationship, not a conclusion about the size of the effect in this study. The registry’s planned enrollment statements do not establish that the study had adequate precision for its primary outcome.

What can be inferred from the analysis record?

The registry lists zero analyses. It therefore does not provide a reported statistical test or model for the pain outcome or opioid-use outcome. A p-value, if reported, would quantify how incompatible the observed data are with a specified null model under the assumptions of that test; it would not measure the size or clinical importance of an effect. A confidence interval would add information about uncertainty. Neither kind of inferential result is available in the registry record. The stated outcome definitions and design features are not substitutes for estimates and their uncertainty.

Because the outcome is continuous, a mean and standard deviation could be useful summaries, but interpretation would also depend on the number of observations at each visit, the distribution of the measurements, and the method used for incomplete records. If measurements are highly skewed or have outliers, a mean and standard deviation may not fully describe the data. These are general considerations; the registry does not report the observed outcome distribution or analytic diagnostics.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies visual analogue scale pain scores as the primary outcome and opioid use as a secondary outcome. It also lists two outcome measures. When a study examines more than one outcome, visit, or comparison, the chance of a false-positive finding can increase if many statistical tests are conducted and each is interpreted without regard to the others. General approaches include identifying a primary analysis in advance, controlling the family-wise error rate, or treating secondary analyses as exploratory. The registry does not report a multiplicity strategy or a detailed statistical analysis plan.

The pain outcome is described over a period extending to 6 weeks, with follow-up at POD1 and weeks 2 and 6. Several time points can lead to multiple possible comparisons. The record does not state whether one visit was designated as the sole primary time point for testing, whether measurements were combined, or whether any repeated-measures method was planned. It also does not report the statistical tests or models used.

Missingness is a particular concern because the record says limited follow-up time restricted the number of participants for the final, 6-week follow-up interval. It does not report how many participants contributed data at each visit, why individual measurements were missing, or whether missing values were imputed, excluded, or handled by a model. In general, complete-case analyses can be biased if the participants with observed results differ systematically from those without them. Assessing that risk requires information about missingness and the analysis population, which is not reported in the registry record.

The number analyzed for each outcome and the definition of the analysis population are also not reported in the registry record. It is therefore not possible to determine whether analyses followed an intention-to-treat principle, included only participants with available measurements, or used another population. The registry lists zero analyses, so no analysis-specific participant flow or missing-data procedure is available for interpretation.

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 0% reporting threshold.

The registry reports serious adverse events for the experimental group with 6 participants at risk and 0 affected, and for the sham comparator with 5 participants at risk and 0 affected. It reports other adverse events with 6 at risk and 0 affected in the experimental group, and 5 at risk and 0 affected in the sham group. Deaths are reported as 0 in each group. No serious adverse-event terms are listed.

These figures describe the adverse-event entries in the registry. They indicate that no affected participants or deaths are recorded in the stated at-risk groups. They should not be read as proof that adverse events cannot occur, or as a comparison demonstrating that the procedures have equivalent safety. With a small pilot study, event estimates would be imprecise even if events were recorded, and zero recorded events cannot rule out risk.

The registry record does not provide additional details about how adverse events were defined, collected, monitored, or attributed to the study procedures. It also does not report further follow-up information for safety. The figures therefore describe the recorded counts, not a complete characterization of safety or a basis for medical advice.

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

The record establishes that a completed, non-randomized pilot study evaluated trigger point injections with 1% lidocaine after total knee arthroplasty against a sham procedure. It identifies visual analogue scale pain scores as the primary outcome and opioid use as a secondary outcome. It also records enrollment of 11 and states that limited follow-up time restricted the number available for the last, 6-week interval.

It does not establish what happened to pain scores or opioid use. Outcome values, group comparisons, uncertainty estimates, and statistical tests are not reported in the registry record. Therefore, the record does not support a conclusion that trigger point injections improved pain, reduced opioid use, had no effect, or differed from the sham procedure. A stated research aim is not a result.

Even if estimates were available, the non-randomized allocation would require caution. The registry explicitly warns that the groups are not a like-for-like control comparison. As a general principle, a difference between non-randomized groups may reflect pre-existing differences or other influences rather than the assigned procedure. Masking may help limit some expectation effects, but does not remove this source of potential bias.

The registry’s zero recorded adverse events and deaths are a description of its safety entries, not proof of no risk. The small pilot enrollment and restriction in final-visit follow-up also limit what can be learned about uncommon events or longer-term outcomes. The record does not report the protocol’s rationale for sample size, a detailed analysis plan, or how missing outcome data were handled.

The appropriate statistical reading is therefore limited: the registry describes the question, design, endpoint, and recorded safety counts, but does not provide the outcome analysis needed to judge the observed pain or opioid-use results. Planning calculations based on an observed effect are illustrations for study planning and do not constitute evidence of treatment effect or observed power.

13. Why This Trial Matters Statistically

This study raises several useful statistical issues for clinical research. Its primary outcome is a patient-reported continuous measure collected over follow-up, while opioid use is a secondary outcome. That combination illustrates why endpoint definitions need to specify not only what is measured, but also when it is measured and how repeated observations will be analyzed. The registry describes follow-up at POD1 and weeks 2 and 6 but does not report the analysis approach.

The non-randomized allocation is central to interpreting any comparison. The registry itself warns that the arms are not a like-for-like control comparison. This is a practical reminder that masking and a sham procedure do not replace randomization: masking concerns awareness of treatment assignment, while randomization concerns how participants enter comparison groups. They address different potential sources of bias.

The record also highlights the difference between a pilot study’s design statements and evidence from its results. A planned enrollment range or a sample-size illustration does not reveal the precision of the eventual outcome estimate. That requires observed results, visit-specific participant counts, and uncertainty measures. None of those primary outcome results are reported in the registry record.

Finally, limited follow-up at the final interval illustrates why missing outcome data are part of the statistical interpretation, not merely an administrative detail. Without counts and information about why data are missing, readers cannot judge whether the final assessment reflects the enrolled group. These issues make the record useful for understanding design and reporting considerations, while leaving the clinical outcome question unanswered.

14. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

The main limitation for interpreting this trial is that the registry record does not report results for either the primary pain outcome or secondary opioid-use outcome. There are no reported group means, standard deviations, changes, between-group estimates, confidence intervals, or tests. The record lists zero analyses. The direction, magnitude, and precision of any outcome difference therefore cannot be assessed.

Allocation was non-randomized, and the registry cautions that the two arms are not a like-for-like control comparison. The record does not report baseline characteristics or an adjustment strategy that would help assess or address group differences. Even a reported association would need cautious interpretation in light of this design.

Follow-up is described through 6 weeks, and the registry states that limited follow-up time restricted the number available for the final interval. It does not report visit-specific data counts or how missing observations were handled. The record also does not state the statistical model, the definition of the analysis population, or whether repeated measurements were analyzed jointly.

The study is described as a pilot with enrollment of 11. Its brief summary gives a planned 10-15 patients per group and a maximum of 100 total patients, but the registry does not report the rationale for the actual enrollment or a formal sample-size justification. No numerical outcome estimate is available to assess precision against those planning statements.

Safety reporting is limited to the recorded at-risk and affected counts, with no further details on event collection or monitoring. The record also does not report a detailed multiplicity plan, protocol-level statistical analysis plan, or additional information about masking. These limitations constrain both the interpretation of any potential comparison and the ability to reproduce an analysis from the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Trigger Point Injection in Reducing Pain Following Total Knee Arthroplasty — NCT06955923.
• Registry record last updated 2026-02-12; status last verified 2026-01.
• Results first posted 2026-02-12.
• 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 registry record describes NCT06955923, a completed phase 2, parallel, non-randomized study sponsored by David Grant U.S. Air Force Medical Center. The study evaluates trigger point injections with 1% lidocaine without epinephrine immediately after total knee arthroplasty, compared with a sham procedure. Enrollment was 11.

The primary outcome is change in visual analogue scale pain scores from enrollment through the end of treatment at 6 weeks. Opioid use is listed as a secondary outcome. Follow-up is described at POD1 and weeks 2 and 6. The record notes that limited follow-up time restricted the number available at the final interval.

Outcome results and statistical analyses are not reported in the registry record. The record cautions that non-randomized allocation means the arms are not a like-for-like control comparison. Its safety entries report no affected participants or deaths in the listed groups at risk, but provide no further event-collection detail.