Measures of Gait Efficiency of Three Multi-Axial, Vertical Shock and Energy Storing-Return Prosthetic Feet During Simple & Complex Mobility Activities: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Measures of Gait Efficiency of Three Multi-Axial, Vertical Shock and Energy Storing-Return Prosthetic Feet During Simple & Complex Mobility Activities (NCT01404559), a randomized na study. The primary outcome is Obstacle Course Completion Time.

2. Clinical Question

3. Trial Design

The registry classifies this completed study as randomized, triple masked, and crossover, with no applicable phase. It lists 28 participants enrolled. The intervention conditions were three prosthetic feet: Ossur Variflex, Ossur Ceterus, and Endolite Elite Blade. A separate non-amputee control group was observational, with no intervention. The primary outcome summaries list 14.0 participants for each prosthetic-foot condition and 14.0 non-amputee controls. Because the study is identified as a crossover, the condition summaries should not automatically be read as four wholly separate groups of people; the participant flow and exact relationship among those counts are not reported in the registry record.

The primary endpoint timeframe was 21 days total, with 7 days per prosthetic-foot condition. The registry record does not report the order in which participants used the feet, whether any washout period was used, or how the crossover structure was incorporated into the statistical analysis. It also does not describe the masking procedures, so the meaning and implementation of triple masking cannot be assessed from the record alone.

The study began in 2012-07 and reached primary completion in 2013-06; its status is completed. The University of South Florida is listed as sponsor. The registry summary frames the study around possible biomechanical or bioenergetic differences among multi-function prosthetic feet, but the posted primary result concerns obstacle-course completion time. The registry record does not report the trial’s original sample-size assumptions, detailed protocol, or a statistical analysis plan.

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 Obstacle Course Completion Time, measured over 21 days total (7days per prosthetic foot condition).

The primary endpoint is obstacle-course completion time, measured in seconds. Laser timing lights were positioned in pairs at the beginning and end of a 17 task obstacle course. Participants triggered the lights as they passed, and the times were recorded on a laptop computer. The registry specifies the mean as the summary measure and the standard deviation as the measure of spread.

Time is a direct, quantitative measure of how long a participant took to complete this particular course. In general, a timed task can capture performance across a sequence of mobility demands in a way that is readily summarized and compared. The course is described as a complex mobility activity, making its completion time relevant to the study’s stated interest in gait efficiency during simple and complex activities. That relevance is specific: the endpoint reflects performance on the defined course under the recorded conditions, not all facets of gait, daily activity, energy use, or military duty.

The registry describes how the timing was collected, but does not report details such as the course layout beyond its 17 tasks, whether repeated attempts were made, or how a participant’s times were selected if multiple measurements were taken. Those details are not reported in the registry record.

7. Results Posted in the Registry

• Prosthetic Foot 1 (Ossur Variflex): mean 425.00 versus 287.00 on control; difference 138.00 (95% CI 56.68 to 219.32), standardized effect d = 1.26; z-test p = <0.001.
• Prosthetic Foot 2 (Ossur Ceterus): mean 444.00 versus 287.00 on control; difference 157.00 (95% CI 37.82 to 276.18), standardized effect d = 0.98; z-test p = 0.010.
• Prosthetic Foot 3 (Endolite Elite Blade): mean 419.00 versus 287.00 on control; difference 132.00 (95% CI 57.43 to 206.57), standardized effect d = 1.31; z-test p = <0.001.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is continuous: completion time can take a range of numerical values, and the registry summarizes it with a mean and standard deviation. In general, a mean describes the central average of a set of measurements, while a standard deviation describes how dispersed the measurements are around that average. The group summaries are 425.0 seconds with a standard deviation of 144.0 for Variflex, 444.0 seconds with a standard deviation of 220.0 for Ceterus, 419.0 seconds with a standard deviation of 130.0 for the Endolite Elite Blade, and 287.0 seconds with a standard deviation of 58.0 for controls. These summaries convey both typical recorded time and the extent of variation, but they do not reveal the full distribution of individual times.

What does a mean difference describe?

A mean difference expresses the gap between two group means in the original measurement units. The recalculated contrasts are the prosthetic-foot mean minus the control mean, so they are expressed in seconds. The Variflex contrast is 138.0 seconds, the Ceterus contrast is 157.0 seconds, and the Endolite Elite Blade contrast is 132.0 seconds. In general, a positive value under this subtraction order means the first mean is larger than the comparison mean. These estimates are not direct comparisons among the prosthetic feet.

The posted contrasts are labeled recalculated and are unadjusted calculations from summary statistics. In general, a recalculation from means, standard deviations, and sample sizes does not use participant-level records. It therefore cannot account for features that require the individual observations, such as the correlation between measurements made on the same person in a crossover study. The registry identifies the design as crossover, but the analysis approach and any adjustment for within-person measurements are not reported in the registry record. This limits how closely the recalculations can represent a design-aware analysis.

What do the p-values and confidence intervals convey?

A p-value describes how incompatible the observed data are with a specified null hypothesis under the assumptions of a statistical test. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. The unadjusted recalculated p-values are p < 0.001 for Variflex versus controls, p = 0.01 for Ceterus versus controls, and p < 0.001 for the Endolite Elite Blade versus controls. The registry record does not report the sponsor’s own analysis procedure or whether these comparisons were part of a prespecified testing strategy.

A confidence interval gives a range of values compatible with the data and the method used to calculate it. In general, narrower intervals indicate more precise estimates than wider intervals, while an interval’s width reflects sampling uncertainty under the method’s assumptions. For the three recalculated contrasts, the intervals are 56.68 to 219.3 seconds, 37.82 to 276.2 seconds, and 57.43 to 206.6 seconds, respectively. They describe uncertainty around the mean differences, not a range expected to contain individual participants’ times.

Why does the crossover design matter?

In general, a crossover design can compare conditions within the same participants, which makes the relationship between repeated measurements relevant to estimation and uncertainty. It also makes condition order and possible period or carryover effects relevant considerations. The registry labels this study a crossover and reports 7 days per prosthetic-foot condition, but does not describe condition sequence, washout, period effects, or the statistical method used for repeated measurements. Those omissions mean the assumptions needed for a crossover analysis cannot be evaluated from the record.

The standardized effect estimates in the recalculations express mean differences relative to a pooled measure of spread. Such standardization can help describe the size of a contrast on a common scale, but does not change the original outcome or resolve the design limitations. No standardized-effect interpretation should be taken as a clinical threshold: the registry does not report a threshold for meaningful change in course time.

What do the sample-size illustrations assume?

The planning illustrations are based on the observed effect and use a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They consider detecting the stated fractions of the observed effect. In general, sample-size calculations depend on the assumed effect, variability, significance threshold, power target, and analysis design. The posted illustrations use a two-arm planning setup; they are not a report of the original crossover trial’s design assumptions. The registry record does not report the original sample-size justification or the statistical analysis plan.

10. Confidence Intervals and Precision

The recalculated 95% confidence intervals quantify uncertainty in the mean differences between each prosthetic-foot condition and non-amputee controls. For Variflex, the estimated difference is 138.0 seconds, with an interval from 56.68 to 219.3 seconds. For Ceterus, the estimate is 157.0 seconds, with an interval from 37.82 to 276.2 seconds. For the Endolite Elite Blade, the estimate is 132.0 seconds, with an interval from 57.43 to 206.6 seconds. Each interval is on the original seconds scale and uses the subtraction order of prosthetic-foot mean minus control mean.

In general, a confidence interval reflects both the estimated contrast and its sampling uncertainty under the method used. Its width is not a measure of how much individual completion times vary; that variation is described separately by the group standard deviations. The Ceterus estimate has the widest reported interval among these contrasts, while the other two are also bounded by intervals of substantial width. The posted intervals show uncertainty around each control comparison, not uncertainty around a direct comparison between prosthetic feet.

All three intervals have positive lower limits, but this should be interpreted within the unadjusted recalculation method and the limitations of summary-statistic calculations for a crossover design. The registry record does not report an analysis that accounts for the within-person structure, nor does it report an adjusted confidence interval. Thus these intervals do not establish the precision of a design-aware crossover estimate. They also do not indicate whether a difference is important for mobility or duty, because the registry record does not report a threshold for a meaningful change in completion time.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The sample-size illustrations give participants per arm for 80% power and participants per arm for 90% power. They are not total event counts: the outcome is a continuous completion time, and the planning values refer to participants in each of two planned arms. The assumptions listed for these illustrations are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as the stated fraction of the observed effect, with illustrations for 100%, 75%, and 50% of that effect.

The 80% power column means that, under the stated planning assumptions and effect size, the calculation targets an 80% chance of detecting an effect of that size using the specified test procedure if that effect is present. The 90% column uses a higher target chance of detection under the same general setup. These are planning probabilities, not probabilities that the trial result is correct. Smaller assumed effects need more participants to achieve the same power target, which is why the illustrations increase as the assumed effect is reduced.

The calculations are planning illustrations based on the observed effect, not the trial’s original design justification; that justification is not reported in the registry record. They use a two-arm planning framework and do not establish that the same assumptions suit a crossover study or account for repeated measurements. This is not observed power: the figures do not describe the probability that the completed study detected an effect after its results were known.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 138.000; pooled standard deviation σ = 109.772.
2. n = 2 × (1.96 + 0.842)² × 109.772² / 138.000² = 9.9, rounded up to 10 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 138                      # observed difference in means
sigma <- 109.772492000501                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(1404559)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 10 (80% power), 14 (90% power)
 75% of observed effect: n per arm = 18 (80% power), 24 (90% power)
 50% of observed effect: n per arm = 40 (80% power), 54 (90% power)
power.t.test: 11 
Simulated power at n = 10 per arm: 0.759 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures, but reports no posted secondary results. The primary outcome discussed in the record is obstacle-course completion time. The registry record lists no analysis records, so it does not identify which analyses were prespecified, how the outcomes were prioritized, or whether any multiplicity strategy was planned. The three recalculated comparisons each contrast a prosthetic-foot condition with controls, and their p-values are unadjusted. No correction for multiple comparisons is reported.

Multiplicity matters in general when several hypotheses are tested: considering many comparisons can increase the chance of at least one apparently unusual result under a collection of null hypotheses. The appropriate approach depends on the study questions and analysis plan. Since that plan is not reported in the registry record, it is not possible to determine whether the three control comparisons were intended as separate primary tests, whether a testing hierarchy existed, or whether any adjustment was used in the sponsor’s own analysis. The unadjusted p-values should therefore be read as individual, unadjusted comparisons rather than as results from a documented family-wise testing procedure.

The record does not report how missing outcome measurements were handled, whether all enrolled participants contributed to every condition, or whether any participants were excluded from particular analyses. It also does not describe an intention-to-treat or per-protocol population, participant flow, protocol deviations, or criteria for inclusion in the analysis. The listed sample size of 14.0 for each outcome group or condition is not enough to establish how many people contributed complete repeated measurements in the crossover study.

These gaps matter because missing observations and analysis-population choices can affect estimates, especially when repeated measurements are involved. In general, a crossover analysis may need to account for the pairing of measurements and condition sequence. The registry record does not report whether such considerations were included in the analysis.

14. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 5% reporting threshold.

The safety record lists unilateral transtibial amputees as the group at risk for serious adverse events, with 14 participants at risk and 0 affected. It also records 14 at risk and 0 affected for other adverse events. No serious adverse-event terms are listed. The deaths value is not reported in the registry record.

These are event counts in the registry record, not estimates that serious or other adverse events are impossible. In general, an observed count of zero means no events were recorded in the stated group during the recorded period; it does not establish the absence of risk. The relatively limited recorded group size also means the figures provide only a narrow basis for characterizing uncommon events. The registry record does not describe the adverse-event collection period, event definitions, monitoring procedures, or whether adverse-event data were collected for the non-amputee controls.

The safety counts should be interpreted separately from the obstacle-course results. They do not indicate whether any device caused or prevented an event, and the record does not provide comparative safety analyses among the three prosthetic-foot conditions.

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

The posted outcome summaries show higher mean obstacle-course completion times for each prosthetic-foot condition than for the non-amputee control group. The unadjusted recalculated estimates are 138.0 seconds for Variflex versus controls, 157.0 seconds for Ceterus versus controls, and 132.0 seconds for the Endolite Elite Blade versus controls. The confidence intervals and p-values describe statistical uncertainty under the recalculation method, not the cause of the group differences or their practical importance.

The comparisons do not show which prosthetic foot performed best relative to the other feet. No direct foot-to-foot contrasts are reported. The crossover label may be important for an appropriate analysis, but the registry record does not describe whether the posted comparisons account for repeated measurements on the same participants. The control group was observational and consisted of non-amputees, so these contrasts are not randomized comparisons between the prosthetic devices and a control intervention.

The study’s stated motivation includes possible return to active duty for service members with major limb amputation. However, return to duty is not the primary endpoint reported in these results. Completion time on a 17 task obstacle course does not by itself measure whether someone returns to duty, how they function in daily life, or whether a particular device is suitable for an individual. The registry record does not report a threshold defining a meaningful change in course time.

Accordingly, the results describe recorded group means and unadjusted estimates for this specific timed task. They do not establish the effectiveness of any device, a causal explanation for the differences, or a general conclusion about mobility beyond the measured course. Further interpretation depends on details of the trial’s analysis, missing data, and crossover procedures that are not reported in the registry record.

16. Why This Trial Matters Statistically

This trial illustrates why a numerical difference and its statistical interpretation are not the same thing. The outcome is measured in seconds, so the mean differences remain directly interpretable on the course-time scale. Confidence intervals convey uncertainty around those differences, while the standard deviations describe variation among recorded times. Keeping these quantities distinct prevents the variability of individual observations from being mistaken for uncertainty in the estimated mean.

The crossover classification also highlights the importance of matching analysis to design. In general, measurements from the same participant under different conditions are related, and the analysis may need to account for that relationship. A recalculation using group summaries cannot recover the participant-level pairing or establish whether condition order mattered. The registry record does not report how those features were handled, so the unadjusted estimates should be treated cautiously as descriptions of the posted summaries.

The study also demonstrates the difference between comparison groups and randomized treatment contrasts. The three prosthetic-foot conditions are compared with an observational non-amputee group, while the posted recalculations do not compare the feet with one another. The control contrast can describe how the reported group averages differ, but it cannot isolate a causal device effect or rank the feet.

Finally, planning illustrations based on the observed effect should not be confused with the original trial design justification or with power after the fact. The record’s missing analysis details and lack of posted secondary results limit assessment of multiplicity, missingness, and the intended analysis populations. These are central statistical qualifications, not merely reporting details, because they influence how confidently the recorded differences can be interpreted.

17. 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 are specific to the available record. Although the study is classified as crossover, it does not report the order of the prosthetic-foot conditions, whether condition periods were randomized individually, or whether washout was used. It also does not report an analysis accounting for the repeated observations or for possible period and carryover effects. Those design features can matter when estimating condition contrasts, so the unadjusted recalculations from summary statistics cannot resolve them.

The primary outcome summaries list 14.0 participants for each prosthetic-foot condition and 14.0 controls, while total enrollment is 28. The record does not explain participant flow or how those group counts relate to the crossover observations. It does not report the number of complete measurements, missing-data handling, or exclusions from analysis. As a result, the extent to which the displayed summaries represent all enrolled participants cannot be assessed.

The control group is observational and consists of non-amputees. It provides a descriptive reference, but is not a randomized comparator for the device conditions. The posted comparisons are against controls rather than directly between prosthetic feet. No threshold for a meaningful difference in obstacle-course time is reported, and the registry’s stated interest in return to duty is not itself measured by this endpoint.

The registry record also lacks a reported statistical analysis plan, the original sample-size justification, a multiplicity strategy, and posted secondary results. These absences limit evaluation of prespecification and the full set of outcomes and analyses. The results therefore support a description of the reported course-time summaries, but not a complete assessment of the intended statistical analysis.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Measures of Gait Efficiency of Three Multi-Axial, Vertical Shock and Energy Storing-Return Prosthetic Feet During Simple & Complex Mobility Activities — NCT01404559.
• Registry record last updated 2014-12-15; status last verified 2014-12.
• Results first posted 2014-12-15.
• 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.

21. Record Summary

The completed, randomized, triple-masked crossover study evaluated the Ossur Variflex, Ossur Ceterus, and Endolite Elite Blade prosthetic-foot conditions. It enrolled 28 participants and included an observational non-amputee control group. The primary endpoint was mean time in seconds to complete a 17 task obstacle course over a 21-day timeframe, with 7 days per prosthetic-foot condition.

Mean completion times were 425.0 seconds for Variflex, 444.0 seconds for Ceterus, 419.0 seconds for the Endolite Elite Blade, and 287.0 seconds for controls. Unadjusted recalculations estimate each prosthetic-foot mean minus the control mean; the corresponding confidence intervals and p-values are described in the statistical interpretation. The registry record does not report the trial’s detailed analysis plan, handling of missing data, crossover analysis procedures, or original sample-size assumptions. No secondary results or analysis records are listed.