NMES for Achilles Tendon Rupture: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for NMES for Achilles Tendon Rupture (NCT04727047), a randomized na study. The primary outcome is Ability to Perform a Single Heel Rise.

2. Clinical Question

The study is titled “NMES for Achilles Tendon Rupture,” and its stated goal is to evaluate a rehabilitation protocol using neuromuscular electrical stimulation in relation to muscle atrophy and tendon properties. Its primary endpoint narrows that broader aim to a functional task: ability to perform a single heel rise. The posted primary result is a count of participants, not a continuous measure of strength or a scale score.

The clinical question is therefore about the observed number of participants able to complete that task in each randomized group at the specified assessment time. The record does not establish how the heel-rise result was used in a formal statistical test, because an analysis comparing the groups is not reported. Nor does it describe participant-level characteristics or the reasons for the study’s termination. Those omissions limit how fully the clinical context and the observed counts can be interpreted.

3. Trial Design

The registry record describes a randomized, parallel-group study sponsored by Penn State University. It lists an enrollment of 8 and identifies the study status as terminated. The record gives a start date of 2023-02-15 and a primary completion date of 2024-12-31. It does not report why the study was terminated, so no reason should be inferred from the status alone.

One group received neuromuscular electrical stimulation applied to the calf muscles, in addition to standard therapy for Achilles tendon repair. The described stimulation level was increased weekly from 10 to 30 mA during the first 6 weeks after surgery. The control group followed standard therapy for Achilles tendon repair. These descriptions identify the intended difference between groups; they do not establish how consistently each participant received the assigned regimen.

The study is listed as randomized, with no masking and a parallel model. In a parallel design, participants are assigned to a group and outcomes are assessed by group rather than by having each participant receive both regimens in sequence. With no masking recorded, the registry does not indicate that participants or study personnel were blinded to assignment. Further details about allocation procedures, concealment, adherence, or any deviations from assigned treatment are not reported in the registry record.

The arm-level primary counts are reported for 7 participants in the neuromuscular electrical stimulation group and 1 participant in the control group. This is a highly uneven distribution of the posted outcome observations. The record does not explain why the group counts differ or whether they represent all randomized participants, all enrolled participants, or a particular analysis population. The planned sample-size justification, if any, is not reported in the registry record. A planning illustration based on an observed effect is not a substitute for information about the trial’s original design rationale.

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.

Population: No difference between baseline participants and patients completing the data collection.

6. Primary Endpoint

The registry lists the primary outcome as Ability to Perform a Single Heel Rise, measured over Week 12.

The primary endpoint is titled “Ability to Perform a Single Heel Rise.” It is recorded as a count of participants and assessed at Week 12. The description says the ability to perform a single heel rise using the injured side will be tested. The reported result is therefore a binary outcome for each participant—able or not able to perform the task—summarized as the number able in each group.

A single-task functional endpoint can offer a direct, interpretable description of whether participants can complete a specified movement. Unlike a continuous measurement, such as a length or area, this endpoint records whether a criterion is met rather than the degree of performance. That distinction affects the information available for analysis: the registry posts participant counts, but the small and unequal group sizes leave little basis for a stable two-group comparison from these counts alone.

The endpoint should be interpreted at its stated assessment time, Week 12. It is not a measure of every aspect of recovery, tendon structure, muscle size, pain, or confidence. The registry separately lists secondary outcomes involving tendon measurements, muscle measurements, and questionnaire scores, but their presence does not change what the primary task itself measures. Detailed operational rules for how a heel rise was judged, whether repeat attempts were allowed, or how an inability to complete the task was distinguished from missing assessment are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Outcome type and summary. The primary outcome is binary at the participant level: a participant either performed a single heel rise or did not. The registry summarizes it as the number of participants with the event, where the event is the ability to perform the task. This count is an understandable descriptive summary, but a count alone is not a complete comparison between randomized groups. A comparison generally needs to account for how many participants were assessed in each group and how uncertain the observed group results are. Here the posted arm counts are 7 and 1, and the record does not report a two-arm analysis that can be interpreted as a comparative estimate.

Why uncertainty matters. A confidence interval is a range of values generated by a statistical method to convey uncertainty about an estimate. It is not a guarantee that the true effect lies within that range, and it does not replace attention to the design or data quality. For a binary outcome, uncertainty depends on both the number of participants and the distribution of outcomes. When a group has very few observations, its result can change substantially with the outcome of a single participant. The registry record does not report a confidence interval for the primary comparison, so precision cannot be assessed from an interval estimate.

Comparative tests and estimates. Statistical procedures for binary outcomes can be used to test whether group results are compatible with a specified null hypothesis, or to estimate a contrast between groups. The choice of method depends on the design, sample size, event pattern, and analysis plan. A p-value, if reported, would address compatibility with a null model under the assumptions of the test; it would not state the probability that a treatment is effective or measure clinical importance. No such inferential result is reported for the primary comparison in the registry record. It would be inappropriate to reconstruct one from the counts and present it as the study’s analysis.

Randomization and group balance. Random assignment is intended to make groups comparable on average, including with respect to measured and unmeasured characteristics. It does not guarantee balance in every realized study. In a very small study, chance differences can remain, and the very unequal reported arm counts make interpretation particularly limited. The record identifies the study as randomized but does not describe its allocation sequence, concealment procedures, or analysis population. Without those details, readers cannot fully assess how assignment was implemented or which participants were included in the reported outcome.

Planning illustrations. Any sample-size illustration based on an observed effect is a planning exercise, not an account of the trial’s original design rationale and not observed power. The stated illustration assumptions use a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. Such assumptions describe a calculation framework; they do not establish that the study was planned using that framework. They also do not resolve the uncertainty created by the sparse outcome counts. The registry record’s own sample-size justification is not reported.

Over-dispersion and this endpoint. Over-dispersion is a general concern when observed variation is greater than a statistical model expects. It is particularly relevant to outcomes modeled as counts across multiple units or repeated observations, where a basic model may understate variability. The primary endpoint is a participant-level binary outcome summarized by counts, not a repeated count process. The record does not report a model or an over-dispersion assessment, and there is no basis to claim that over-dispersion was examined or found.

Analysis specification. A complete statistical interpretation depends on knowing how the primary endpoint was coded, how missing assessments were handled, which participants were included, whether the analysis followed randomized assignment, and what comparison was planned. These details are not reported in the registry record. The absence of a reported analysis is not evidence that no analysis was ever conducted; it means the registry record does not contain enough information to describe one. The posted counts can be stated descriptively, while inferential claims should be limited to what the record actually reports.

Recalculation and sponsor analyses. Simple unadjusted recalculations from summary statistics, when available, are not equivalent to a sponsor’s prespecified analysis. Where the record flags a discrepancy, the sponsor’s own analysis takes precedence. No discrepancy is flagged in this record, but no primary comparative analysis is posted either. That distinction matters: there is no reported sponsor analysis to interpret, and the descriptive counts should not be relabeled as a formal recalculation or statistical test.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Neuromuscular Electrical Stimulation", "Control")
n      <- c(7, 1)
events <- c(2, 0)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Neuromuscular Electrical Stimulation  7  2  28.6  3.7  71.0  8.2  64.1  8.5  65.1
ARM  Control  1  0  0.0  0.0  97.5  0.0  79.3  1.3  84.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists 7 secondary outcomes: tendon length, tendon thickness, gastrocnemius muscle cross-sectional area, soleus muscle estimated volume, Foot and Ankle Outcome Score (FAOS), Achilles Total Rupture Score, and Tampa Scale for Kinesiophobia (TSK). The record lists 8 outcome measures overall. Assessing multiple outcomes can raise a multiplicity issue: when many hypotheses are tested, the chance of at least one apparently notable result may increase unless the analysis plan accounts for the number and relationships of the tests. Whether any multiplicity adjustment or outcome hierarchy was planned is not reported in the registry record.

Missing-data methods are also not reported. The record does not explain whether all randomized participants completed the Week 12 heel-rise assessment, how an unobserved assessment was classified, or whether any imputation or sensitivity analysis was used. The arm counts reported for the primary endpoint are 7 in the neuromuscular electrical stimulation group and 1 in the control group, but the record does not say why those counts differ or identify the analysis population used. It would be inappropriate to assume that every enrolled participant had an observed endpoint or that missing outcomes were handled in a particular way.

The registry does not report whether the primary analysis followed intention-to-treat, per-protocol, or another analysis population definition. Nor does it state how protocol deviations, withdrawal, or adherence were addressed. These are important distinctions because each defines which participants contribute to an analysis and what comparison the estimate represents. The absence of these details limits assessment of potential bias and reproducibility. No analysis plan, multiplicity strategy, missing-data approach, or analysis-population definition is reported in the registry record.

12. 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 adverse-event counts are reported separately for the two groups. No serious adverse events are recorded among 7 participants in the neuromuscular electrical stimulation group, and none are recorded among 1 participant in the control group. Deaths are recorded as 0 in each group. These figures describe the entries in the registry record; they do not establish that no events occurred outside the record or that the groups have equivalent safety profiles.

For other, non-serious adverse events, the record reports 3 affected participants among 7 in the stimulation group and 1 affected participant among 1 in the control group. With only one participant represented in the control group, that count is a description of that individual’s recorded status, not a stable estimate of the frequency expected in a broader population. The record does not provide event details for these other adverse events in the registry record. No serious adverse-event terms are listed.

Adverse-event counts require context about definitions, collection methods, observation periods, severity assessment, and completeness of reporting. Those details are not reported in the registry record. Zero recorded serious events in a small group should not be read as proof that serious events cannot occur; it means no serious events are recorded for the participants represented in these results. These figures are descriptive and do not support a comparative safety conclusion.

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

The posted result gives a limited description of the primary functional endpoint: 2 participants in the neuromuscular electrical stimulation group and 0 participants in the control group were recorded as able to perform a single heel rise at Week 12. The associated arm counts are 7 and 1. These are observed counts from a small, unevenly represented study, not a precise estimate of the difference that might be expected in a larger population.

The record does not include an inferential comparison for the endpoint. It therefore does not report an effect estimate with uncertainty or a statistical test that would support a formal claim about differences between the groups. The observed pattern should not be described as proof that the intervention improves or fails to improve function. A count in one arm being greater than a count in another is not, on its own, enough to determine the size, reliability, or clinical importance of a group difference.

The study’s broader stated aim includes muscle atrophy and tendon properties. The functional heel-rise result cannot stand in for those separate outcomes. The registry lists secondary measures of tendon dimensions, muscle size, and participant-reported scores, but the values and analyses for those measures are not reported in the record details available for this account. Conclusions about them would therefore go beyond the reported evidence.

The terminated status is a further point of context, but its cause is not reported. It cannot be used to infer the reason the study ended or the completeness of follow-up. The unequal arm counts also have no stated explanation. Without participant flow, missing-data details, or a defined analysis population, readers cannot determine how the reported observations relate to all participants assigned to the study groups.

In short, the result is a small descriptive snapshot, not a definitive comparative finding. It identifies what was recorded for the participants counted in each arm and highlights the substantial limitations in precision and interpretation. It does not establish a general treatment effect, a safety advantage, or a difference in tendon or muscle outcomes.

14. Why This Trial Matters Statistically

This study is statistically instructive because it illustrates the difference between randomization and a precise comparison. Random assignment is a valuable design feature, but it cannot by itself overcome very limited information in the observed outcomes. The registry reports 7 participants in one arm and 1 in the other for the primary endpoint. That imbalance and the small total enrollment mean the posted counts offer little information about the range of outcomes that might occur in either group.

It also demonstrates why descriptive results and inferential results should be distinguished. Counts tell readers how many participants were recorded as meeting the endpoint. A comparative analysis would add an estimate of the group contrast and an account of its uncertainty, using a stated method. The registry record does not report that analysis. A reader should not substitute an informal comparison of counts for an analysis that is absent from the record.

Another statistical lesson is that endpoint choice defines the scope of a result. Ability to perform a single heel rise is a functional outcome, while tendon dimensions, muscle measurements, and questionnaires address different features. The listed secondary measures broaden the study’s stated interests, but they cannot be interpreted without their reported values and methods. Keeping these outcomes distinct helps prevent a narrow result from being treated as evidence about every aspect of rehabilitation.

Finally, trial status and reporting completeness are part of statistical interpretation. Termination is recorded, but its reason is not. The registry also does not report the planned sample-size justification, missing-data approach, analysis populations, or multiplicity strategy. These omissions do not establish that no such plans or analyses existed; they limit what can be concluded from the registry record. The study matters statistically as a reminder that transparent reporting of design, analysis, and uncertainty is essential alongside the outcome counts.

15. 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 the very small enrollment and the uneven arm counts reported for the primary result. With 7 participants in the neuromuscular electrical stimulation group and 1 in the control group, the posted counts cannot provide a precise comparative picture. The control count is especially limited as a basis for describing outcomes in that group. The registry record does not explain the imbalance or report participant flow that could clarify it.

The primary comparison is not reported as an inferential analysis. There is no comparative estimate or uncertainty interval in the record details available for this account. Without such information, the magnitude and precision of any group difference cannot be assessed. The record also does not report the original sample-size justification, so it is not possible to assess what effect the study was designed to detect or how its enrollment target was determined.

Important study details are not reported in the registry record, including participant characteristics, allocation procedures, adherence, protocol deviations, the analysis population, and missing-data handling. The reason for termination is not reported. The record does not give detailed rules for assessing heel-rise ability, or explain how an incomplete or unavailable assessment would be treated. These limitations prevent a complete assessment of internal validity and the meaning of the arm-level counts.

Although 7 secondary outcomes are listed, their results and analysis details are not included in the registry record used for this account. The registry record also does not report a strategy for handling multiplicity. The safety counts are sparse and lack the event descriptions and collection context needed for detailed interpretation. Finally, results from this small terminated study should not be assumed to apply to people or settings beyond those represented in the reported observations.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: NMES for Achilles Tendon Rupture — NCT04727047.
• Registry record last updated 2026-09-22; status last verified 2026-08.
• Results first posted 2026-09-22.
• 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.

19. Record Summary

NCT04727047, “NMES for Achilles Tendon Rupture,” is a randomized, unmasked, parallel-group study sponsored by Penn State University. It is listed as terminated, with enrollment of 8. The record gives a start date of 2023-02-15 and a primary completion date of 2024-12-31; the reason for termination is not reported.

The intervention was calf-muscle neuromuscular electrical stimulation alongside standard therapy, compared with standard therapy alone. The primary outcome was ability to perform a single heel rise at Week 12. The posted counts are 2 of 7 in the stimulation group and 0 of 1 in the control group. A comparative analysis is not reported in the registry record. Seven secondary outcomes are listed, but their results are not included in the information summarized for this account.

The recorded serious adverse-event counts and deaths are 0 in each group. Other adverse events are recorded for 3 of 7 participants in the stimulation group and 1 of 1 in the control group. Given the small, uneven group counts and the absent comparative analysis, the primary results are descriptive and have substantial limitations for inference.