Clinical Outcomes With Passive MPKs vs. Powered Prosthetic Knees: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Clinical Outcomes With Passive MPKs vs. Powered Prosthetic Knees (NCT05267639), a randomized na study. The primary outcome is Daily Step Count.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, unmasked crossover study of a passive microprocessor knee and a powered prosthetic knee. The study was marked completed. The listed start date is 2022-05-01, and the primary completion date is 2024-08-28. The sponsor was Liberating Technologies, Inc. The phase is listed as NA.

In the Control (MPK) condition, participants were to wear their usual microprocessor knee for 3 months. In the Power Knee condition, they were to wear the Ossur PK in place of their usual device for 3 months. Laboratory outcome measures were planned in both conditions. For daily step count, activity monitoring was planned during the final month of each condition. The registry record describes the study as community-based in its project aims, but details of the actual setting and monitoring procedures are not reported in the registry record.

Random allocation and crossover describe different features of the design: randomization concerns how participants are assigned, while crossover means that participants experience more than one condition. General: crossover designs can allow comparisons within the same participant, which can account for stable differences between people. That advantage depends on having usable outcome data from both conditions and an analysis that respects the paired structure. The sequence assigned to participants, any washout or transition procedures, and the statistical handling of repeated measurements are not reported in the registry record.

The reported enrollment was 13. The registry record says one participant withdrew without data in either condition. The posted primary-endpoint summaries list 12 participants for the Control (MPK) condition and 2 for the Power Knee condition. The record also says that 8 participants transitioned early and did not reach the final month for collection. These details indicate that the planned crossover did not yield similarly complete endpoint data for both conditions. The reason for each missing observation and the relationship between the participants contributing data in each condition are not fully described.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 13 total participants. 1 participant withdrew (no data in either condition). Comparator Baseline: no data from withdrawn participant. Power Knee: step count successfully collected from 2 participants. 8 participants transitioned early and did not make it to the final month for collection. 1 activity monitor was lost in the mail. 1 file was unable to be processed/corrupt.

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 Daily Step Count, measured over 1 Month.

The primary endpoint was Daily Step Count, measured in steps per day. It represents the average number of steps per day recorded during the final month of each condition. The registry record describes use of an activity monitor, such as GeneActiv™, during the final month and says that a higher value indicates a better outcome. The endpoint therefore captures day-to-day activity outside the laboratory rather than only performance during a supervised test.

Daily step count is a continuous measure: it can take many numerical values, and the registry record summarizes it with a mean and standard deviation. General: continuous activity measures can help describe how much participants move in everyday settings, while a mean provides a measure of the group’s average and a standard deviation describes variability among observations. Neither summary alone shows the full distribution of individual values or establishes that a difference between conditions is attributable to the device.

The posted mean was 5747 steps/day for the Control (MPK) condition and 3162 steps/day for the Power Knee condition. The corresponding standard deviations were 3212 and 1031. The registry record lists the endpoint timeframe as 1 Month, consistent with collection during the final month of each condition. It does not report the activity-monitor wear-time rules, how incomplete days were handled, or the minimum amount of monitoring required for a participant’s mean to be included.

The intended comparison concerns activity in the two device conditions. Because the endpoint summaries are based on markedly different numbers of participants, and the record does not report a paired analysis, these descriptive means should not be treated as a complete estimate of the within-participant effect.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean describe?

The primary endpoint is continuous, and the registry record reports a mean for each condition. A mean describes the average of the observations included in a summary. The reported means are 5747 steps/day for Control (MPK) and 3162 steps/day for Power Knee. These values describe the participants whose data contributed to each condition’s summary; they do not necessarily describe all enrolled participants or the full population of K4-level transfemoral amputees.

The standard deviations are 3212 for Control (MPK) and 1031 for Power Knee. General: a standard deviation describes how dispersed observed values are around their mean. It is not a confidence interval, and it does not show how precisely a difference between conditions has been estimated. A standard deviation can also be difficult to interpret when the sample is very small, because a few observations can strongly influence both the mean and the apparent spread.

Why is the crossover structure important?

The trial is described as a randomized crossover. General: when participants contribute measurements under both conditions, the two measurements from an individual are related. An analysis can use that pairing to compare each participant with themselves, rather than treating all observations as independent. This approach can account for stable person-to-person differences, but only when paired measurements are available and the analysis matches the design.

The posted condition summaries do not provide paired differences or participant-level data. The registry record does not report the sequence assigned to each participant, a period-specific analysis, or a model for repeated measurements. It is therefore not possible to assess from the registry record whether the reported summaries were analyzed using the crossover structure. The difference in the number of participants listed for each condition further limits direct interpretation of the means as a within-participant comparison.

What would an inferential comparison add?

General: an inferential comparison would estimate a contrast between conditions and quantify uncertainty around that estimate. A confidence interval describes a range of values compatible with the data and analysis assumptions; it communicates precision as well as the direction and plausible size of an effect. A p value, when used, summarizes how unusual the data would be under a specified null hypothesis and model. Neither quantity replaces scrutiny of the data quality or design.

No confidence interval, p value, or comparative effect estimate for daily step count is reported in the registry record. The record lists no analysis results and identifies the continuous two-arm comparison as not estimable. Without a reported contrast and its uncertainty, the descriptive means should not be converted into a claim of statistical evidence. No new numerical contrast should be inferred from the posted summaries.

Why do missing observations matter?

The registry record reports one withdrawal with no data in either condition, says that 8 participants transitioned early without reaching the final month, and reports successful Power Knee step-count collection from 2 participants. The posted condition summaries list 12 participants for Control (MPK) and 2 for Power Knee. The record does not explain all reasons for missingness, the amount of activity-monitor data required, or the rules used to determine whether a participant’s observation was usable.

General: missingness can affect both the amount of information and the representativeness of the observations. If participants with missing outcomes differ systematically from those with observed outcomes, a summary of observed values may not represent the experience of all enrolled participants. The direction and size of any such effect cannot be determined from the registry record. Whether imputation, sensitivity analyses, or other missing-data methods were used is not reported in the registry record.

How should variability and over-dispersion be considered?

General: step counts are nonnegative activity measurements, and their variability can be substantial. Over-dispersion means that variation is greater than a chosen statistical model expects. A model that understates variability can produce intervals that are too narrow and tests that appear more decisive than the data warrant. The registry record reports means and standard deviations but does not report a distributional model, a check for over-dispersion, or a robust variance method. The summaries alone are not enough to determine which model would be appropriate.

What is the role of planning calculations?

General: a sample-size calculation is a planning exercise based on assumptions about an effect, variability, significance level, allocation, and analysis. A calculation based on an observed effect is not evidence that the trial had a particular probability of detecting an effect, and it is not observed power. The stated planning assumptions describe a two-sided significance level of 0.05, equal allocation, a normal approximation, and effects expressed as fractions of the observed effect. The registry record does not report the trial’s own sample-size justification. Because no comparative effect estimate is reported for this endpoint, a planning illustration should not be mistaken for a trial result.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Control (MPK)", "Power Knee")
n   <- c(12, 2)
m   <- c(5747, 3162)
sp  <- c(3212, 1031)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Control (MPK)  12  5747.000  3212.000  3706.193  7787.807
CARM  Power Knee  2  3162.000  1031.000  -6101.167  12425.167

11. Multiplicity, Missing Data and Analysis Populations

The registry record lists 3 outcome measures, but reports no secondary outcome results. It does not provide a multiplicity adjustment or explain how the primary endpoint was selected for confirmatory testing. Whether multiplicity was considered in the trial’s statistical plan is not reported in the registry record. General: when several outcomes or comparisons are tested, the chance of a false-positive finding can increase unless the analysis plan accounts for that multiplicity. No claim about such a plan can be made from the available record.

Missing endpoint data are a central concern. The record says one participant withdrew without data in either condition, 8 participants transitioned early and did not reach the final month for collection, and step count was successfully collected from 2 participants in the Power Knee condition. The condition summaries list 12 participants for Control (MPK) and 2 for Power Knee. The record does not give a complete accounting linking each missing observation to a specific reason or participant.

Whether the analysis included all randomized participants, only participants with available outcome data, or another analysis population is not reported in the registry record. The record also does not report an imputation method, a missing-data sensitivity analysis, or rules for incomplete activity-monitor wear. General: complete-case summaries describe observed outcomes, but can be biased if outcome availability is related to activity or to the assigned condition. The registry record does not provide enough information to assess that possibility.

The trial is a crossover, so handling incomplete pairs is also relevant. The record does not state how observations from participants with data in only one condition were used, or whether they were excluded from a paired comparison. No statistical analysis results are posted for the primary endpoint, and no secondary results are posted. The implications of missingness and multiplicity therefore remain unresolved rather than addressed by a reported analysis.

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 registry record reports serious adverse events for both conditions. For Control (MPK), 13 participants are listed as at risk, with 0 serious adverse events and 0 deaths. For Power Knee, 13 participants are listed as at risk, with 0 serious adverse events and 0 deaths. The record also lists 2 other adverse events in each condition, with 13 at risk in each.

These are counts as reported in the registry record. They should not be interpreted as a comparative safety estimate. The study is described as a crossover, so the same participant may contribute to more than one condition’s at-risk group; the record does not clarify participant overlap or provide event-level timing. The counts should therefore not be added across conditions or treated as independent groups.

Zero reported serious adverse events means that none were recorded in these condition summaries; it does not establish that serious events are impossible or that the conditions have equivalent safety. The meaning of the two other adverse events in each condition is not detailed in the record, and no serious-event terms are listed. The registry record does not report event severity beyond the serious/non-serious categorization, attribution, or the duration of adverse-event follow-up. These figures provide limited descriptive safety information for the recorded trial, not a precise estimate of comparative risk.

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

The primary-endpoint summaries document daily step counts among participants with available measurements in each condition. The reported average was 5747 steps/day with the usual microprocessor knee and 3162 steps/day with the Power Knee. The reported standard deviations were 3212 and 1031. These figures characterize the observations that were collected; they do not establish a causal effect of either device on daily activity.

The available evidence is particularly limited by the unequal numbers of participants contributing to the condition summaries. The registry record lists 12 participants for Control (MPK) and 2 for Power Knee, and states that 8 participants transitioned early without reaching the final month for collection. It also records one withdrawal with no data in either condition. The reasons for all unavailable data and the extent of overlap between condition samples are not fully reported.

The design is described as randomized and crossover, but the registry record does not report a paired comparative analysis, an effect estimate, a confidence interval, or a p value. Descriptive means cannot replace those results. In particular, they do not quantify uncertainty around a within-participant contrast, account for the crossover sequence, or show whether missing endpoint data could have changed the comparison.

The record also does not provide secondary outcome results, details of the statistical analysis plan, or the trial’s own sample-size justification. The safety counts are descriptive and do not establish equivalence between conditions. These limitations mean that the posted results are best read as incomplete descriptive evidence about activity monitoring in the two conditions, rather than as a definitive estimate of comparative clinical outcomes.

The trial’s stated aim was to gather community-based data to inform evidence-based prescription of powered prosthetic knees and to support future research. The reported endpoint summaries alone cannot determine which participants might benefit, whether a device should be selected for an individual, or how results would generalize beyond the people and conditions studied. Those questions require evidence and analyses beyond the descriptive data reported in the registry record.

14. Why This Trial Matters Statistically

This trial is statistically notable because its randomized crossover design could, in principle, support within-participant comparisons of daily activity across device conditions. General: crossover studies can reduce the influence of stable differences between participants when each person contributes usable measurements in both conditions and the analysis models that pairing. That potential advantage is not automatically realized by a crossover label; it depends on data completeness and appropriate analysis.

The record reports markedly different numbers of participants in the primary-endpoint summaries: 12 for Control (MPK) and 2 for Power Knee. It also describes early transitions and a withdrawal without data in either condition. This makes the availability and structure of the data central to interpretation, rather than a technical detail. Without paired outcome data or a reported crossover analysis, the design’s potential efficiency cannot be assessed.

The endpoint is also relevant statistically because it reflects activity outside the laboratory. Day-to-day step counts can vary across people and over time. General: repeated measurements and adequate monitoring can help characterize that variability, while transparent rules for valid wear time and missing days are important for reproducibility. Those collection and analysis rules are not reported in the registry record.

The record illustrates why a numerical difference between two means is not itself a complete treatment-effect result. A reader also needs to know which participants contributed, how observations relate within participants, how missing outcomes were handled, and what uncertainty surrounds the contrast. In this case, the registry record provides condition-specific summaries but no inferential analysis for the primary endpoint.

The project aim is to inform future evidence on powered prosthetic knees and the people who may benefit from them. Statistically, the limited and unevenly available endpoint data underscore the importance of complete follow-up and a clearly reported analysis plan in future studies. The record does not show that the findings answer the broader prescription question, but it identifies the importance of collecting activity data in real-world conditions and reporting how those data support a comparison.

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 most direct limitation is the small and uneven set of observations contributing to the primary-endpoint summaries. The registry record reports 12 participants for Control (MPK) and 2 for Power Knee. It also reports one withdrawal with no data in either condition and 8 participants who transitioned early without reaching the final month for collection. The record does not fully explain the pattern of missingness or identify all reasons that participants did not contribute endpoint data.

The summaries do not provide paired measurements or participant-level information. Because the trial is described as a crossover, the relationship between the measurements from the two conditions is important. The sequence assigned to participants, any transition or washout arrangements, and a statistical analysis accounting for period or sequence are not reported in the registry record. No comparative effect estimate, confidence interval, or p value is reported for daily step count.

The endpoint collection details are also incomplete. The record says an activity monitor was to be worn during the final month, but does not report requirements for valid wear, handling of incomplete days, or whether monitor use differed across conditions. Whether missing values were imputed or examined in sensitivity analyses is not reported in the registry record. The interpretation of the observed summaries therefore depends on collection and missing-data details that are unavailable.

The record lists 3 outcome measures but reports no secondary results. It does not report the statistical analysis plan, multiplicity handling, or trial-specific sample-size justification. The adverse-event counts are descriptive, with no event-level details or reported comparative safety analysis. These limitations constrain interpretation of both activity and safety findings and limit the strength of conclusions that can be drawn from the registry record.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Clinical Outcomes With Passive MPKs vs. Powered Prosthetic Knees — NCT05267639.
• Registry record last updated 2026-09-17; status last verified 2026-08.
• Results first posted 2025-06-26.
• 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

The registry record describes a completed, randomized, unmasked crossover study of the usual microprocessor knee and the Ossur Power Knee in K4-level transfemoral amputees. Enrollment was 13. Each condition was planned for 3 months, with daily step count monitored during the final month. The primary endpoint is reported in steps per day.

The posted mean and standard deviation were 5747 and 3212 for Control (MPK), based on 12 participants, and 3162 and 1031 for Power Knee, based on 2 participants. The record reports one withdrawal with no data in either condition and 8 early transitions without final-month collection. No inferential primary-endpoint analysis or secondary outcome results are reported in the registry record.

The serious adverse-event summaries list 0 serious events and 0 deaths for each condition; each also lists 2 other adverse events. These counts are descriptive. The posted results do not establish a comparative effect on daily activity or a comparative safety estimate.