Achilles Pain Block: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Achilles Pain Block (NCT03316378), a non-randomized phase 2, phase 3 study. The primary outcome is Central Sensitization.

2. Clinical Question

The study’s stated purpose was to examine how reducing peripheral pain might relate to pain perception and task performance in people with Achilles tendinopathy. Its rationale concerns the interaction between peripheral and central nervous system processes and movement strategies. The registry describes a hypothesis that central nervous system factors contribute to persistent pain and disability, but a hypothesis is not a finding.

The primary endpoint is titled “Central Sensitization” and is a continuous measurement: pressure pain threshold, recorded in kilopascals. The registry record does not report the outcome values or an estimated change between baseline and the post-injection assessment. It therefore does not establish whether the measured threshold changed, how large any change was, or how precisely it was estimated.

3. Trial Design

The registry lists the study as completed, with phases II and III, non-randomized allocation, no masking, and a single-group model. It records enrollment of 46. The description of the groups, however, also includes a group with Achilles tendinopathy and a group without Achilles tendinopathy. The registry record does not explain how its single-group model label relates to those two group descriptions.

Participants with Achilles tendinopathy received ropivacaine around the painful area of the tendon. The description says an orthopaedic physician used ultrasound while administering the injection; the needle could be directed just under the skin and above the tendon, and/or deep to the tendon. The group without Achilles tendinopathy did not receive an injection between test repetitions. Allocation was non-randomized, and the registry’s own description cautions that the groups are not a like-for-like control comparison.

The primary measure was recorded within a session at baseline and 30 minutes after anesthetic injection. This timing describes the assessment schedule, not the duration of any effect. The record does not report longer-term follow-up for this endpoint. It also does not report whether the comparison used paired measurements, an adjusted model, or another analysis approach.

The registry lists 46 enrolled participants and identifies 23 participants at risk in each group for the adverse-event reporting. Those figures should not be treated as evidence about the analysis population for the primary endpoint: the number with usable outcome measurements and the handling of missing observations are not reported in the registry record. The record also does not give the allocation procedure, recruitment setting, eligibility criteria beyond the group descriptions, or a rationale for the sample size. The listed study dates are 2016-01-28 for the start and 2018-05-10 for primary completion.

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 Central Sensitization, measured over Within session, baseline and 30 minutes after an anesthetic injection.

The primary endpoint is pressure pain threshold at the heel on the side opposite the painful Achilles tendon, reported in kilopascals. A pressure algometer was applied perpendicular to the skin, and pressure was increased at a rate of 50 kilopascal/s using a 1cm2 tip. Participants pressed a button when pressure first became painful, defined in the registry description as 1/10 on the NPRS. The mean of 3 trials per area represented the pressure pain threshold.

This measure is used to quantify the pressure level at which a participant reports pain. The registry labels the endpoint “Central Sensitization,” and the contralateral heel location is part of its specified assessment. In general, a pressure pain threshold is a sensory measurement: its value reflects a reported transition from pressure to pain under the stated testing procedure. It does not, by itself, identify the biological mechanism responsible for that response.

The scheduled comparison is baseline versus 30 minutes after injection within the session. The registry reports the endpoint as a mean with a 95% confidence interval. It does not report the mean values, the estimated change, or the confidence interval limits. Consequently, the magnitude and precision of the primary result cannot be described from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a continuous primary outcome: pressure pain threshold in kilopascals, summarized as a mean with a 95% confidence interval. It also lists 3 outcome measures and 6 analyses. The record details do not identify the methods used for each analysis, or provide the numerical results for the primary endpoint. The explanations below describe general statistical concepts relevant to the stated design; they are not claims about unreported methods used in this study.

What does a mean represent?

For a continuous measurement, the mean is an average of the observed values in the analysis set. In this study, each participant’s pressure pain threshold was based on the mean of 3 trials per area, as described in the endpoint procedure. A group mean then summarizes participant-level measurements. A mean can be useful for describing the center of a distribution, but it does not show the spread of individual values or whether observations are clustered, skewed, or affected by unusual measurements. The registry record does not report those distributional details.

What does a 95% confidence interval communicate?

In general, a confidence interval gives a range of estimates compatible with the data under the statistical method used. It communicates precision as well as the estimated value: intervals with less width indicate greater precision, while wider intervals indicate greater uncertainty. A 95% confidence interval is not a guarantee that a particular interval contains the true value, and it does not by itself establish clinical importance. Its interpretation depends on what quantity it surrounds, how it was calculated, and the assumptions of the analysis. The registry identifies the reported dispersion as a 95% confidence interval, but does not give its limits or describe the calculation method.

For a baseline-to-follow-up question, the interval could describe a mean at each assessment or an estimated change; those are different quantities. The endpoint details specify means and the assessment times but do not state which estimate the interval accompanies. The analysis specification is not reported in the registry record, so the interval’s target quantity cannot be confirmed from these registry entries.

Why does the study design matter?

Random allocation, when used, helps balance measured and unmeasured participant characteristics between intervention groups on average. This study is listed as non-randomized, and its own registry description says the groups are not a like-for-like control comparison. The group without Achilles tendinopathy did not receive an injection between test repetitions. That group may provide descriptive context, but it is not equivalent to a randomized control group of participants with Achilles tendinopathy receiving no injection. A difference between the groups cannot be attributed to the injection alone on the basis of this design description.

The primary endpoint has a within-session baseline and post-injection schedule. In general, measurements from the same participant are related, so an analysis of change may need to account for that pairing. However, the record does not state whether the reported analysis used paired data, a repeated-measures model, an adjustment for baseline, or another method. No specific test or model should be assumed.

How should planning illustrations be read?

The registry’s planning assumptions describe illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that the study was designed around those assumptions. The registry record does not report its own sample-size justification. The actual illustration values are not included in the registry record for this explanation, so no sample-size result can be stated.

In general, a planning calculation asks what sample size might be needed under specified assumptions about the effect, variability, significance level, and desired power. Changing those assumptions changes the result. An illustration based on an effect observed in the same study is especially dependent on that estimate and should not be treated as an independent confirmation of the finding.

What cannot be inferred from the listed analysis count?

The registry lists 6 analyses and 3 outcome measures. These counts do not reveal which outcomes were tested, whether analyses were planned in advance, which model was used, or whether any adjustment for multiple testing was applied. They do not establish that all analyses were confirmatory. Those details are not reported in the registry record.

For continuous outcomes, variance describes how dispersed observations are around a mean. In general, unusually different variances between groups or a distribution that departs substantially from model assumptions can affect standard errors and confidence intervals. The record details do not provide variance estimates or diagnostic information, so the adequacy of any model assumptions cannot be assessed. This is a general consideration, not a finding about this dataset.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 3 outcome measures and 6 analyses. It does not report how those analyses were assigned to outcomes, which were designated primary or secondary beyond the stated primary endpoint, or whether the analysis plan identified a hierarchy of comparisons. No adjustment for multiple testing is described in the registry record.

In general, testing several outcomes or comparisons can increase the chance of finding at least one apparently notable result by chance. Methods for addressing this include prespecifying a primary comparison, controlling an error rate across tests, or treating secondary analyses as exploratory. The record details do not establish whether any such method was used, so none should be assumed. The missing primary outcome values also prevent assessment of the estimate or its uncertainty.

The registry does not report the number of participants with primary endpoint measurements at each assessment, exclusions from the analysis, or how missing values were handled. It does not describe whether all enrolled participants were included in an analysis population, whether any participants withdrew, or whether any imputation was used. These details are not reported in the registry record. Enrollment and adverse-event counts do not establish the endpoint analysis denominator.

The primary outcome is scheduled at baseline and 30 minutes after injection. In general, missing observations at either assessment can affect a change estimate, particularly if the reasons for missingness relate to participant characteristics or outcome values. Without an account of missingness and the analysis population, readers cannot judge how well the analyzed observations represent the enrolled groups. The registry entries also do not report interim analyses, a statistical analysis plan, or a sample-size justification.

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.

Most frequent non-serious adverse event terms

The registry lists no serious adverse events among the 23 participants at risk in the group with Achilles tendinopathy, and none among the 23 participants at risk in the group without Achilles tendinopathy. It records 2 participants affected by other adverse events in the group with Achilles tendinopathy and none in the group without Achilles tendinopathy. Deaths are listed as zero in both groups.

These are descriptive registry counts. The record details do not identify the types, severity, timing, or relatedness of the other adverse events, and no serious adverse-event terms are listed. The counts therefore cannot be used to characterize what those other events were or whether they were judged related to the injection. The absence of listed serious events in these groups does not establish that no unreported or unrecorded events occurred, and these figures alone do not support a comparative safety conclusion.

The at-risk figures are specific to the adverse-event reporting shown in the registry. They should not be assumed to equal the number of participants included in the primary endpoint analysis, because endpoint-specific analysis counts are not reported in the registry record.

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

The record identifies a focused measurement question: pressure pain threshold at the contralateral heel before and 30 minutes after an anesthetic injection in the group with Achilles tendinopathy. It also describes a group without Achilles tendinopathy that did not receive an injection between test repetitions. This gives context for the study’s interest in pain perception, but the groups do not form a randomized, like-for-like comparison according to the registry description.

The primary outcome results are not reported in the registry record for this analysis. No conclusion can therefore be drawn about the observed direction or size of change, the precision of the estimate, or whether any difference was statistically distinguishable from no change. The outcome title and the study hypothesis describe the intended question and interpretation; neither substitutes for outcome data.

Even if a change in pressure threshold were reported, the measurement alone would not prove a particular nervous-system mechanism. In general, an observed sensory response can be consistent with a proposed explanation without uniquely identifying that explanation. The design features also limit causal interpretation: allocation was non-randomized, masking was absent, and the group without Achilles tendinopathy did not receive the intervention. The registry itself warns against treating the arms as a like-for-like control comparison.

The findings that can be described from the registry entries are therefore limited to the endpoint procedure, study design labels, assessment timing, enrollment information, and adverse-event counts. The record does not provide enough primary outcome information to judge the magnitude or clinical relevance of a result, or to determine whether the stated hypothesis was supported. These limits are about what the registry record reports, not evidence that an unreported result was positive or negative.

13. Why This Trial Matters Statistically

This study raises a statistical question about how a local intervention and a sensory measurement are connected. The endpoint is defined operationally: pressure is applied at the contralateral heel until the participant reports that it first becomes painful. Clear description of the measurement procedure matters because pressure pain threshold depends on a reported response under a specified testing approach.

The record also illustrates why design labels and comparison groups need careful interpretation. It lists a non-randomized allocation and warns that the groups are not a like-for-like control comparison. A control group without the condition and without an injection between test repetitions can offer descriptive context, but it does not isolate the injection’s effect in the way a randomized comparison among otherwise comparable participants might. Statistical adjustment, if any, cannot be assumed because it is not reported.

Another important point is the distinction between a measurement and the mechanism used to interpret it. The registry calls the endpoint “Central Sensitization,” while the recorded measurement is pressure pain threshold. Describing that measurement precisely helps readers separate an observed response from a broader biological explanation. Statistical estimates and their confidence intervals would be needed to assess the size and precision of an outcome, but those primary results are not reported in the registry record for this analysis.

Finally, the record lists multiple outcomes and analyses without describing their relationship or any multiplicity approach. That omission matters when interpreting a collection of tests: readers need to know which result was primary and whether secondary findings were exploratory or adjusted. The study is therefore informative about the question and measurement strategy, while the absence of reported primary results and analysis details limits what can be concluded statistically.

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.

Several limitations arise directly from the registry entries. The study is listed as non-randomized and unmasked, and the registry cautions that its arms are not a like-for-like control comparison. The group without Achilles tendinopathy did not receive an injection between test repetitions. As a result, any contrast between groups would combine differences in condition and intervention exposure rather than isolate a randomized treatment contrast.

The registry labels the model single-group but also describes a group with Achilles tendinopathy and a group without Achilles tendinopathy. It does not explain this discrepancy. The allocation procedure and the basis for placing participants into groups are not reported in the registry record. Eligibility details and participant characteristics are also not available in the registry record for this analysis.

The primary endpoint results, including means, estimated changes, and confidence interval limits, are not reported in the registry record. This prevents assessment of the finding’s direction, magnitude, and precision. The record also does not state whether the analysis accounted for within-participant measurements, what analysis population was used, how missing endpoint observations were handled, or what model assumptions were assessed.

Although 3 outcome measures and 6 analyses are listed, their relationship, prespecification, and handling of multiplicity are not reported. A sample-size justification and the study’s own statistical plan are also not reported in the registry record. Finally, the primary endpoint assessment is described within a session at baseline and 30 minutes after injection; longer-term endpoint follow-up is not described in the registry record.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Achilles Pain Block — NCT03316378.
• Registry record last updated 2019-07-05; status last verified 2019-07.
• Results first posted 2019-07-05.
• 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.

18. Record Summary

The registry identifies NCT03316378, “Achilles Pain Block,” as a completed study with phases II and III, non-randomized allocation, no masking, and a single-group model. It lists enrollment of 46. The intervention was ropivacaine injection around the painful Achilles tendon area in the group with Achilles tendinopathy; the group without Achilles tendinopathy did not receive an injection between test repetitions.

The primary endpoint, titled “Central Sensitization,” is pressure pain threshold at the contralateral heel, reported as a mean in kilopascals with a 95% confidence interval. It was assessed at baseline and 30 minutes after injection. Numerical primary outcome results and the statistical analysis details are not reported in the registry record.

The registry records no serious adverse events or deaths in either group, and lists 2 participants with other adverse events in the group with Achilles tendinopathy and none in the group without Achilles tendinopathy. Event details are not reported in the registry record for this analysis. The registry also lists 3 outcome measures and 6 analyses, without describing a multiplicity approach.