This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Ultrasound-Monitored Changes in Achilles Tendinopathy After Extracorporeal Shock Wave Therapy (NCT04780919), a randomized na study. The primary outcome is Change in Cross-sectional Area at the Place of Maximum Tendon Width.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04780919 |
| Phase | NA |
| Condition | Achilles Tendinopathy |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Single |
| Enrollment | 18 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University Hospital, Motol |
| Results posted | Yes |
2. Clinical Question
Population
People with Achilles tendinopathy were eligible for this trial. The registry record reports enrollment of 18 participants and describes two groups of 9 in its safety figures. Further eligibility criteria, such as symptom duration or diagnostic thresholds, are not reported in the registry record.
Intervention
The intervention was focused extracorporeal shock wave therapy (ESWT), delivered with a BTL-6000 FSWT device. The treatment-group description specifies weekly applications for 5 weeks, using 0,12 mJ/mm2, 10 Hz, and 1300 shocks per application.
Comparator
The comparison was sham ESWT using a BTL-6000 FSWT with sham applicator. The registry describes weekly sham applications for 5 weeks and lists the same stated parameters as the active group, with a modified applicator. The description of what the modified applicator does is incomplete in the registry record.
Primary question
The primary endpoint was change in the cross-sectional area at the place of maximum tendon width, measured by ultrasound. The planned follow-up was 3 weeks after the last application, described as the 8th week. The registry record does not report the group results for this endpoint, so it does not establish the size or direction of the observed difference between active and sham treatment.
The central statistical question is whether the mean change in the ultrasound-measured area differed between the randomized groups at the stated follow-up. A randomized comparison can help assess whether a group-level difference is compatible with an intervention effect, but interpretation depends on the actual estimates, their uncertainty, and the analysis procedures. Those primary numerical results and procedures are not reported in the registry record. The posted information therefore describes the question and design, but does not allow the primary comparison to be evaluated quantitatively.
3. Trial Design
This was a randomized, parallel-group, sham-controlled trial. The registry lists single masking, but does not report which people were masked or how masking was maintained. Enrollment was 18. The trial status is completed; the listed start date is 2021-02-01 and the listed primary completion date is 2021-04-02. The sponsor was University Hospital, Motol. The phase is listed as NA.
The brief summary describes a common assessment program for both groups. At the initial examination, participants had a clinical examination by a physiotherapist, an ultrasound examination, and completed a VISA-A questionnaire. Random assignment took place at the end of that examination, followed by the first application. The summary describes additional weekly applications during the next 4 weeks, for a total of 5 active or sham applications. The interval between applications was intended to be at least 7 days. A final examination was scheduled 3 weeks after the last application and was to repeat the initial procedures. The summary characterizes the total research period for a participant as 8 weeks.
The active group received focused ESWT. The sham group received treatment with a sham applicator; the registry states that its listed parameters matched those of the active group but the applicator was modified. The description ends before fully explaining the modification, so the exact physical distinction between active and sham delivery is not reported in the registry record.
Random allocation supports a comparison between groups, while a sham procedure can help separate effects associated with receiving the treatment procedure from those associated with active ESWT. These are general design considerations, not evidence that masking succeeded or that the groups were balanced. The allocation method, sequence generation, concealment procedures, and masking assessment are not reported in the registry record. The record also does not report participant flow, withdrawals, adherence, or the number assessed at each follow-up.
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
| Stage | Treatment Group (A) | Sham Group (B) |
|---|---|---|
| STARTED | 9 | 9 |
| COMPLETED | 9 | 9 |
| NOT COMPLETED | 0 | 0 |
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.
| Characteristic | Unit | Treatment Group (A) | Sham Group (B) | Total |
|---|---|---|---|---|
| Participants analysed | 9 | 9 | 18 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 9 | 9 | 18 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 |
| Age, Continuous | years | 35.3 (SD 9.6) | 43.2 (SD 12.3) | 39.3 (SD 11.5) |
| Sex: Female, Male: Female | Participants | 4 | 5 | 9 |
| Sex: Female, Male: Male | Participants | 5 | 4 | 9 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Body Mass Index | kg/m^2 | 26.5 (SD 4.4) | 32.7 (SD 7.5) | 29.6 (SD 6.8) |
| Duration of difficulties | months | 6 (SD 3.8) | 7.6 (SD 4.4) | 6.8 (SD 4.1) |
| Baseline maximal pain | units on a scale | 6.6 (SD 1.7) | 6.1 (SD 2.3) | 6.3 (SD 2) |
| Baseline VISA-A score | score on a scale | 64.3 (SD 12.1) | 65.3 (SD 15.9) | 64.8 (SD 13.7) |
6. Primary Endpoint
The registry lists the primary outcome as Change in Cross-sectional Area at the Place of Maximum Tendon Width, measured over Change of initial values at 3 weeks follow up after last application (8th week)..
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | cm^2 |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is change in cross-sectional area at the place of maximum tendon width. It is a continuous ultrasound measurement, recorded in cm^2, and the registry says the outcome is summarized using a mean and standard deviation. The stated assessment is change from initial values at the follow-up 3 weeks after the last application, designated as the 8th week.
According to the measurement description, the ultrasound operator identifies the position with maximum tendon width in a linear view, rotates the ultrasound head to a horizontal view, and measures cross-sectional area in that view. This yields a numerical measure of tendon size at a defined location, rather than a categorical assessment such as whether an abnormality is present. Repeated measurement at the initial and follow-up examinations allows change to be considered, although the registry record does not report the actual values or how individual changes were calculated for analysis.
In general, an ultrasound endpoint can provide a structural measure that complements clinical assessments and questionnaires. It is important to distinguish a measured structural change from a change in symptoms or function: they are different types of outcomes and need not provide identical information. The registry lists several secondary outcomes, including VISA-A questionnaire score and functional tests, but does not report their results in the information available for this analysis. The primary endpoint’s clinical interpretation also depends on measurement reliability, which is not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies a randomized comparison of focused ESWT with sham ESWT, but it does not report numerical results for the primary endpoint. There is no posted group mean change, between-group estimate, standard error, confidence interval, or test result for the cross-sectional-area outcome. As a result, the direction and magnitude of the primary comparison, and the precision with which it was estimated, cannot be described from the posted results. The absence of those values is not evidence that the groups had the same outcome.
The record states that the primary endpoint is a mean change in ultrasound-measured cross-sectional area at follow-up. To interpret such a comparison, readers would generally look for the estimated difference between groups and an interval expressing its uncertainty. A confidence interval describes a range of values compatible with the data under the analysis assumptions; a narrow interval indicates greater precision than a wide interval. Neither an estimate nor a confidence interval for the primary comparison is reported in the registry record. A p-value and the statistical test used for the primary comparison are also not reported in the registry record.
Enrollment was 18, and the safety figures identify 9 participants at risk in each group. These figures do not establish how many participants contributed primary-outcome measurements. Participant flow, missing endpoint observations, and analysis populations are not reported in the registry record. The randomized sample is small in absolute terms, but without outcome variability and the primary estimate, the degree of uncertainty cannot be quantified. It would be inappropriate to infer the observed effect or its statistical significance from enrollment alone.
The primary outcome is described as change from initial values at a follow-up 3 weeks after the final application, designated as the 8th week. The registry gives a mean and standard deviation as the summary format, but does not specify whether the between-group analysis compared changes, adjusted follow-up values for baseline, or used another approach. These choices can affect estimation and precision, so they matter when interpreting a trial result. The analysis method is not reported in the registry record.
Other outcomes include the number of participants with hypoechogenic areas, the number with increased tendon thickness, change in VISA-A questionnaire score, change in the single leg heel rise test, and change in the single leg hop test. The registry lists 9 outcome measures and 5 analyses, but the corresponding estimates and analysis details are not reported in the registry record. No conclusion about these outcomes can be drawn from their names alone.
The trial’s completed status describes its administrative status, not the direction or credibility of its results. Likewise, the planned sham-controlled randomization is a design feature, not a result. The appropriate statistical reading is therefore limited: the registry describes the intended comparison and measurement schedule, while the numerical evidence needed to estimate an effect and judge its precision is not reported in the registry record.
9. Statistical Methods Explained
For a continuous endpoint summarized by a mean and standard deviation, a basic group comparison concerns the average outcome in each randomized arm. The primary endpoint in this trial is a change in cross-sectional area, rather than a binary event. In general, the main contrast could be expressed as the difference between average changes in the active and sham groups. The registry record does not report the numerical group summaries or specify the exact contrast used, so no estimate can be reconstructed.
What does a confidence interval communicate?
In general, a confidence interval communicates uncertainty around an estimated effect. It is not a guarantee that the true effect lies within the interval, nor is it a measure of clinical importance by itself. Its interpretation depends on the design, the analysis, and the assumptions used to calculate it. For this trial, no confidence interval for the primary comparison is reported in the registry record. Consequently, the precision of the estimated treatment difference cannot be assessed.
Why does the choice of analysis matter?
For an endpoint measured at baseline and follow-up, common general approaches include comparing participant-level changes between groups or comparing follow-up values while accounting for baseline values. These approaches are not identical in every setting. Baseline adjustment can account for chance differences in initial measurements and may improve precision when the assumptions are appropriate. A direct change comparison uses each participant’s baseline-to-follow-up difference. The registry record does not state which approach was used, whether any covariates were included, or whether the analysis followed a prespecified plan.
The measurement description gives a clear anatomical target: the maximum tendon-width location, measured in a horizontal ultrasound view. However, the record does not report who performed measurements, whether the same operator assessed each participant, whether assessors were masked to group, or how measurement reproducibility was evaluated. In general, measurement error can add variability and make estimates less precise. If measurement procedures differ systematically between groups, interpretation can be more complicated. These are general measurement considerations; whether they occurred in this trial is not reported in the registry record.
What can randomization support?
In general, random assignment helps make treatment groups comparable with respect to both measured and unmeasured factors in expectation. With a small enrolled sample, chance imbalances can still occur. Randomization does not itself guarantee that all participants complete follow-up, that outcome assessment is unbiased, or that the analysis preserves the randomized comparison. The registry record identifies the trial as randomized but does not describe the sequence-generation or allocation-concealment procedures, baseline characteristics by group, participant flow, or analysis population. The extent to which those safeguards were achieved cannot therefore be judged from the record.
Single masking is listed, but the identity of the masked party is not reported in the registry record. A sham comparator can be used to reduce the influence of expectations and treatment-context effects, as a general design principle. The sham description says a modified applicator was used and lists the same stated parameters as the active group, but the text does not complete its account of what the applicator modification allows or prevents. The success of masking and the degree of similarity between experiences cannot be inferred from the registry description.
How should significance and precision be separated?
In general, a p-value summarizes how compatible observed data are with a specified null hypothesis under a statistical model. It does not measure the probability that the null hypothesis is true, and it does not quantify the size or practical importance of an effect. A confidence interval, the point estimate, and the context of the endpoint are needed for a fuller interpretation. The registry record does not report a primary p-value, an effect estimate, or an interval, and does not name the statistical test. Statistical significance therefore cannot be assessed.
Standard deviations describe the spread of observations around a mean in the relevant group. They are not the same as standard errors, which describe uncertainty in an estimated mean. For a small study, estimates can be imprecise, but the actual uncertainty depends on observed variability, the analysis, and the available outcome data. None of the primary outcome summaries needed to assess that uncertainty are reported in the registry record.
What is over-dispersion, and is it relevant?
In general, over-dispersion means that observed variability is greater than a statistical model expects. It is a concern for some count outcomes and can make standard model-based uncertainty estimates too small if it is ignored. The primary endpoint in this trial is continuous, and the registry does not report a count-model analysis for it. The record provides no information indicating whether over-dispersion was assessed for any secondary count outcome, so no trial-specific claim about it is warranted.
The registry’s sample-size assumption describes a planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation; it also describes considering a stated fraction of the observed effect. Such planning calculations are general illustrations and are not observed power. The registry record does not report the trial’s own sample-size justification, target difference, or prospective power calculation. In addition, the primary outcome is not reduced to one comparison in the listed outcome information. No planning sample-size result should therefore be treated as evidence about the trial’s achieved precision or as a design justification.
In general, an intention-to-treat analysis compares participants according to randomized assignment, while a per-protocol analysis may restrict attention to those who adhered to specified procedures. These approaches answer somewhat different questions and can be affected differently by nonadherence and missing data. The registry record does not report which analysis population was used or whether any participants were excluded from an analysis. The randomization label alone does not establish an intention-to-treat analysis.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary endpoint and secondary outcomes involving tendon imaging, VISA-A questionnaire score, and functional tests. It also reports 9 outcome measures and 5 analyses. Testing multiple outcomes or multiple comparisons can increase the chance of at least one apparently unusual result when all tests are interpreted together. In general, a prespecified testing hierarchy or multiplicity adjustment can help control that issue. The registry record does not report whether any multiplicity strategy was planned or used, how the listed outcomes map to the analyses, or which comparisons were considered confirmatory.
The primary outcome listing notes that it has several categories or time points and is not reduced to one comparison. This means a single primary contrast cannot be identified from the registry information for a recalculation. The outcome description does identify change at the stated follow-up, but numerical values and detailed analysis specifications are absent. It is not reported in the registry record how any categories or time points were handled in the final analysis.
Missing data can affect both the estimate and its uncertainty, especially when the chance of missing an assessment is related to outcome or treatment assignment. In general, interpretation depends on how many outcomes are missing, why they are missing, and what assumptions or methods are used to address them. The record does not report the number of participants with primary measurements, reasons for missing assessments, imputation methods, or sensitivity analyses. It also does not report a participant flow accounting for withdrawals or exclusions.
The registry record does not specify an intention-to-treat, per-protocol, or other analysis population. It does not report a statistical analysis plan, prespecified interim analyses, or rules for handling deviations. These omissions do not show that such procedures were absent from the conduct of the study; they mean the procedures are not reported in the registry record. Consequently, the effects of multiplicity and missing data cannot be evaluated from the posted results.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Treatment Group (A) | 0 | 9 | 0.0% |
| Sham Group (B) | 0 | 9 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Treatment Group (A) | 0 of 0 |
| Sham Group (B) | 0 of 0 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Treatment Group (A) | 0 of 9 |
| Sham Group (B) | 0 of 9 |
The registry safety figures list 9 participants at risk in the treatment group and 9 in the sham group. For each group, the record reports 0 participants affected by serious adverse events, 0 affected by other adverse events, and 0 deaths. No serious adverse-event terms are listed.
These are event counts as reported in the registry record. They do not provide a detailed account of event definitions, collection procedures, event severity beyond the serious-versus-other categories, relatedness assessments, or the observation window for safety reporting. Those details are not reported in the registry record. The figures also do not indicate whether every randomized participant completed every safety assessment, because participant flow and safety follow-up details are not reported.
In general, a zero count in a small trial does not establish that an event cannot occur or that two treatments have equivalent safety. It means only that no affected participants were recorded in the displayed categories for the reported groups. The registry safety information should be read separately from the primary ultrasound outcome: it does not provide evidence about changes in tendon cross-sectional area or other efficacy outcomes.
12. What the Result Does, and Does Not, Mean
The record establishes that a randomized, parallel-group comparison of focused ESWT and sham ESWT was conducted in people with Achilles tendinopathy, with ultrasound-measured change in cross-sectional area designated as the primary endpoint. It also describes the intended application schedule, follow-up, and several secondary outcomes. These features clarify what the study set out to compare.
The posted results do not include the numerical primary outcome comparison. Without group-level changes, a between-group estimate, and an uncertainty measure, the magnitude, direction, and precision of any difference cannot be stated. The record therefore does not support a conclusion that active ESWT produced more or less change than sham, nor does it establish that the groups were similar. Lack of a reported comparison must not be mistaken for a finding of no difference.
The record also does not provide results for the listed secondary outcomes, so no conclusion can be drawn about questionnaire scores, functional tests, hypoechogenic areas, or increased tendon thickness. The safety figures report no affected participants in the displayed serious and other adverse-event categories and no deaths, but those counts alone cannot characterize rare risks or establish comparative safety.
Even if numerical estimates were available, interpretation would depend on their uncertainty, analysis choices, completeness of follow-up, masking, and the reliability of ultrasound measurement. Those details are not fully reported in the registry record. The appropriate meaning of the posted information is therefore primarily descriptive: it documents a small randomized sham-controlled study and its intended endpoint, while leaving the treatment effect and its statistical precision unquantified.
13. Why This Trial Matters Statistically
This trial raises an important statistical distinction between a well-defined research question and an estimable result. The research question is identifiable: compare focused ESWT with sham ESWT on change in ultrasound-measured cross-sectional area at the stated follow-up. But a question cannot be answered quantitatively without the group outcomes and an analysis that links those outcomes to an effect estimate.
The trial is described as randomized and sham-controlled, features that can strengthen a treatment comparison when implemented and analyzed appropriately. At the same time, enrollment was 18, and the registry safety groups each list 9 participants at risk. In a study of this scale, estimates may be sensitive to individual observations and uncertainty may be substantial; the actual degree cannot be assessed without the outcome data. This is a general statistical consideration, not a calculation of the trial’s observed precision.
The primary endpoint is a structural ultrasound measurement, while the secondary outcomes include patient-reported and functional measures. Considering distinct outcome types can provide complementary information, but it also makes prespecification and multiplicity important. The record’s list of outcomes does not establish which analyses were primary beyond the named endpoint, how comparisons were prioritized, or whether multiplicity was addressed.
The trial also illustrates why registry design details and posted outcome results need to be read separately. Randomization, masking, and a sham procedure describe intended safeguards; they do not substitute for estimates, uncertainty intervals, participant flow, or analysis specifications. Since those primary numerical results and methodological details are not reported in the registry record, the strongest statistical contribution of the record is to identify the planned comparison and the information needed to judge it, rather than to quantify an effect.
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 trial-specific limitation for statistical interpretation is that numerical results for the primary endpoint are not reported in the registry record. No group means, standard deviations, between-group estimate, confidence interval, or p-value are available for the stated change in cross-sectional area. Accordingly, the effect’s direction, size, and precision cannot be assessed. Numerical results for the listed secondary outcomes are also not reported in the registry record.
The registry describes an 8-week research period, a baseline examination, 5 applications, and a final assessment 3 weeks after the last application. It does not report how many participants completed each stage or contributed measurements. Although enrollment is 18 and safety figures identify 9 participants at risk per group, those figures do not establish the primary endpoint analysis sample. Missing observations, withdrawals, and exclusions are not reported.
Several analysis details are absent: the method for comparing the groups, adjustment for baseline values, analysis population, handling of missing data, and any multiplicity procedure. The registry record does not report the sample-size justification or whether interim analyses were conducted. These gaps limit assessment of whether the analysis was prespecified and how robust any result would be.
The registry lists single masking but does not identify who was masked or report whether masking was successful. The sham applicator description is incomplete, and the record does not describe allocation concealment or the randomization sequence. Ultrasound measurement reliability, assessor masking, and operator procedures are also not reported. These details could affect confidence in outcome measurement and group comparability, but the registry record does not allow their influence to be judged.
Finally, the trial’s enrollment is limited, while the available record lacks the outcome variability needed to quantify precision. This is a limitation on interpretation, not proof that the trial was underpowered or that its findings were biased. The posted results are insufficient for those conclusions.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Ultrasound-Monitored Changes in Achilles Tendinopathy After Extracorporeal Shock Wave Therapy — NCT04780919.
- Registry record last updated 2021-06-28; status last verified 2021-06.
- Results first posted 2021-06-02.
- 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.
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18. Record Summary
NCT04780919 is a completed, randomized, single-masked, parallel-group trial sponsored by University Hospital, Motol. It enrolled 18 participants with Achilles tendinopathy and compared focused ESWT with sham ESWT. The listed start date is 2021-02-01, and the primary completion date is 2021-04-02.
The primary endpoint was change in ultrasound-measured cross-sectional area at the place of maximum tendon width, assessed 3 weeks after the last application and described as the 8th week. The registry describes 5 weekly active or sham applications. Secondary outcomes include ultrasound findings, VISA-A questionnaire score, and functional tests.
The safety figures list 9 participants at risk in each group and report 0 serious adverse events, 0 other adverse events, and 0 deaths in both groups. Numerical primary and secondary outcome results, detailed analysis methods, participant flow, and missing-data procedures are not reported in the registry record.