Prosthetic Components and Stability in Amputee Gait: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prosthetic Components and Stability in Amputee Gait (NCT00167778), a randomized na study. The primary outcome is Local Dynamic Stability (Hip During Straight Walking).

2. Clinical Question

The broader study addressed turning as well as straight walking. Its stated aims included comparing intact participants and amputees, examining dynamic stability and prosthetic interventions, and investigating whether pylon rotation could affect comfort and mobility in daily activities. However, the primary endpoint posted in the registry is specifically about hip stability during straight walking, not turning or daily activity.

3. Trial Design

The registry identifies this study as randomized, single-masked, and crossover, with the study marked completed. The listed devices were a transverse-plane rotation-adapter pylon and a rigid pylon. The arm descriptions identify the novel prosthetic pylon and rigid pylon, while the results label the conditions torsion-adapter pylon and rigid pylon. The registry states that each participant wore both study prostheses, so the comparison is between conditions experienced within the study rather than a simple comparison of separate parallel groups.

The listed enrollment is 12. For the primary endpoint, each pylon condition has 10 observations. The registry does not explain why the analysis counts differ from enrollment, whether any observations were excluded, or how the crossover sequence and period effects were handled. The order of the two conditions and the masking details beyond the designation “single” are not reported in the registry record.

Measurements for the primary and listed secondary outcomes were taken after wearing the study prostheses for three weeks. The registry gives a study start of 2005-01 and primary completion of 2008-09. The sponsor is the US Department of Veterans Affairs. Listed conditions include diabetes mellitus, leg injuries, and traumatic amputation; these are registry condition labels and do not by themselves specify the eligibility criteria or the clinical characteristics of participants.

The study description sets out aims involving turning biomechanics, stability, and the effects of prosthetic rotation. Its listed outcomes include the primary hip-stability measure and secondary measures of external rotation moments while turning, activity level, and six-minute walk distance. The record does not report the rationale for the enrollment target, a sample-size justification, or enough detail to reconstruct the full 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.

Before assignment: The prostheses used in this study were built and aligned by a certified and licensed prosthetist prior to beginning starting the protocol. 12 individuals provided informed consent. 1 withdrew prior to starting for personal reasons. 1 withdrew due to unrelated back pain after being fit with both study prostheses and starting with the rigid pylon.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Each participant wore both study prostheses.

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 Local Dynamic Stability (Hip During Straight Walking), measured over Measurements were taken after wearing the study prostheses for three weeks..

The primary endpoint is local dynamic stability of the hip during straight walking, reported as a dimensionless mean. The registry says maximum finite-time Lyapunov exponents were used to estimate local dynamic stability for sagittal-plane hip, knee, and ankle angles of the prosthetic limb. The specific primary endpoint is the hip measure during straight walking, rather than the measures during turning that are also described in the outcome definition.

In general, a Lyapunov exponent describes how quickly nearby movement trajectories separate over time. The registry explains that the estimate reflects the rate of kinematic separation of a gait-cycle trajectory perturbed by naturally occurring disturbances and neuromuscular control errors. A positive exponent indicates divergence, and the registry states that increasing values indicate a less stable system. This interpretation concerns the movement measure, not a clinical outcome by itself.

Local dynamic stability is used as a biomechanical measure because the study’s stated purpose was to examine gait stability and prosthetic components. It offers a way to quantify movement response to small disturbances during walking. It does not directly measure falls, injury, comfort, or everyday function. The study also describes turning-related stability measures, but the reported primary title specifies the hip during straight walking. Measurements were taken after wearing the study prostheses for three weeks.

7. Results Posted in the Registry

• Torsion Adapter Pylon: mean 0.74 versus 0.74 on control; difference 0.00 (95% CI -0.11 to 0.11), standardized effect d = 0.00; z-test p = 1.000.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Peak External Rotation Moment of the Outside Hip While Turning

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Torsion Adapter Pylon: mean -88.00 versus -70.00 on control; difference -18.00 (95% CI -61.57 to 25.57), standardized effect d = -0.36; z-test p = 0.418.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Torsion Adapter Pylon and the control. The interval gives the range of effects that remain compatible with the data.

Peak External Rotation Moment of the Outside Knee While Turning

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Torsion Adapter Pylon: mean -15.00 versus -7.00 on control; difference -8.00 (95% CI -24.00 to 8.00), standardized effect d = -0.44; z-test p = 0.327.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Torsion Adapter Pylon and the control. The interval gives the range of effects that remain compatible with the data.

Peak External Rotation Moment of the Outside Ankle While Turning

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Torsion Adapter Pylon: mean -42.00 versus -28.00 on control; difference -14.00 (95% CI -42.06 to 14.06), standardized effect d = -0.44; z-test p = 0.328.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Torsion Adapter Pylon and the control. The interval gives the range of effects that remain compatible with the data.

The posted secondary outcomes include external rotation moments at the outside hip, knee, and ankle while turning, along with other listed outcomes such as activity level and six-minute walk distance. Across the three turning-moment results with numerical summaries, the condition means differ in the direction of more negative values for the torsion-adapter pylon, but the recalculated confidence intervals include zero and the unadjusted p-values do not indicate clear between-condition differences. These outcomes are related to turning biomechanics, whereas the primary endpoint concerns hip stability during straight walking. They therefore provide a broader but not identical view of the study’s questions.

The overall pattern does not establish a consistent, statistically clear distinction between pylon conditions in the outcomes with numerical results described in the record. The primary mean values are equal at the reported precision, and the listed turning-moment comparisons are uncertain. This is a description of the posted data, not evidence that the devices are equivalent or that all study aims have been answered. The record lists 23 outcome measures, 22 analyses, and 14 secondary outcomes posted; the listed secondary outcomes also include activity level and six-minute walk distance.

Unadjusted secondary results carry less weight when multiple outcomes are tested. In general, examining many outcomes increases the opportunity for chance findings if no multiplicity strategy is applied. The registry does not report whether adjustments were made, which outcomes were designated confirmatory, or whether a hierarchy governed interpretation. Secondary p-values and planning illustrations should therefore be viewed as exploratory context rather than independent confirmation of a treatment effect. The sample-size illustrations are based on observed effects and are not observed power estimates or evidence that the study was designed to detect those effects.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Peak External Rotation Moment of the Outside Hip While Turning
• Peak External Rotation Moment of the Outside Knee While Turning
• Peak External Rotation Moment of the Outside Ankle While Turning
• Peak External Rotation Moment of the Inside Hip While Turning
• Peak External Rotation Moment of the Inside Knee While Turning
• Peak External Rotation Moment of the Inside Ankle While Turning
• Activity Level
• Six-minute Walk Distance

9. Statistical Interpretation

10. Statistical Methods Explained

The registry reports a mixed models analysis for the primary comparison and a p-value of >0.99. A mixed model is a general statistical approach that can represent both systematic effects and the dependence among observations from the same participant. That feature can be relevant in crossover studies, where a person contributes measurements under more than one condition. The registry does not report the model specification, the terms included, or how it addressed order, period, or carryover effects, so the reported model cannot be reconstructed from the record.

What does the recalculation represent?

The recalculated estimate is a simple unadjusted comparison from the posted group summaries. It contrasts the condition means, using the reported standard deviations and observation counts to describe uncertainty. For the primary endpoint, the posted means are the same, yielding a recalculated mean difference of 0.0. The recalculated confidence interval spans zero, and the recalculated unadjusted p-value is 1.0. These calculations do not incorporate individual paired measurements or any covariates that may have been included in the sponsor’s mixed model.

In general, a standard deviation describes the spread of individual observations around a mean. It is not the same as a standard error, which describes the uncertainty of an estimated mean. For a crossover comparison, the precision of the within-person contrast also depends on how measurements from the two conditions relate to one another. That relationship is not reported in the registry record. Therefore, a comparison reconstructed from separate condition summaries may not reproduce the precision of a model using participant-level paired data.

Why does the crossover structure matter?

In general, a crossover design can make each participant their own comparator, reducing the influence of stable differences between people. It also requires attention to the order in which conditions are experienced, changes over time, and possible persistence of an earlier condition’s effects. The registry identifies the design as crossover and states that participants wore both prostheses, but it does not report the randomized sequences, the interval between conditions, or how potential period and carryover effects were assessed. No conclusion about those design features can be drawn from the summary results alone.

How should the p-values be read?

In general, a p-value describes how compatible data are with a specified statistical model and a null hypothesis, under that model’s assumptions. It is not the probability that the null hypothesis is true, and it does not show whether an effect is clinically important. The registry’s primary mixed-model result is p >0.99; the recalculated unadjusted value is 1.0. These are different analyses and should not be treated as interchangeable estimates of a single exact quantity. Their broad message is similar: neither indicates evidence of a difference in the posted primary comparison.

The registry also reports 23 outcome measures and 22 analyses. It lists 14 secondary outcomes as posted. When many outcomes are examined, the chance of finding a nominally unusual result can increase if each is assessed independently without adjustment. Whether the analyses were adjusted for multiplicity, or whether outcomes followed a prespecified hierarchy, is not reported in the registry record. Consequently, unadjusted secondary p-values should be treated as exploratory rather than as stand-alone confirmatory evidence.

What do the planning illustrations mean?

General sample-size illustrations use an assumed effect, variability, significance level, allocation, and target power to describe how many participants per arm might be needed under those assumptions. The registry’s planning assumptions state a two-sided significance level of 0.05, equal allocation between arms, a normal approximation, and an effect to detect set as a stated fraction of the observed effect. The secondary-outcome planning entries are labeled by the fraction of the observed effect and give participants per arm for 80% power and 90% power. They are planning illustrations based on observed effects, not the trial’s original design justification and not observed power. The record does not report the trial’s own sample-size justification.

11. Confidence Intervals and Precision

The primary condition means are both 0.74. The recalculated mean difference is 0.0, and the recalculated confidence interval crosses zero. A confidence interval is a range of estimates compatible with the data and the assumptions used to construct it. In general, a wider interval indicates less precision, while an interval that includes zero does not establish a direction of difference at the corresponding confidence level. The registry reports the sponsor analysis as a mixed models analysis with a 95% confidence-interval level, but it does not provide the sponsor’s interval bounds or an estimated model contrast.

The recalculated interval is based on posted summary statistics, not on participant-level paired observations. In a crossover study, within-person correlation can affect the precision of the condition contrast. Because that correlation and the model details are not reported, the recalculated interval should be understood as a simple unadjusted illustration rather than a substitute for the sponsor’s analysis. It does not account for any adjustment or structure that may have been part of the mixed model.

The primary analysis has 10 observations reported for each condition, whereas enrollment is 12. These condition-specific counts indicate that the posted summary does not include the full enrolled count for each condition, but the reasons are not reported in the registry record. The record does not describe missing-data handling, exclusions, or an analysis population. As a result, the precision of the posted estimate cannot be assessed in relation to the unreported observations or the analysis decisions.

The interval includes both a possible difference in one direction and a possible difference in the other. Thus, the result is not evidence of exact equality. No clinically meaningful margin is reported, so the interval cannot be judged against a threshold for equivalence or practical importance. The appropriate reading is that the observed means match at the reported precision, while the data and reporting do not rule out all potentially relevant differences.

12. Analyses Reported by the Sponsor

The sponsor’s reported primary analysis is a mixed models analysis with p >0.99. The simple recalculation from the posted summaries gives a mean difference of 0.0, a confidence interval spanning zero, and an unadjusted p-value of 1.0. These results are broadly aligned in their lack of evidence for a primary-condition difference, but they are not identical analyses. The recalculation uses the posted means, standard deviations, and condition counts; the registry does not provide enough information to reproduce the sponsor’s model.

Because the registry includes a sponsor analysis and the discrepancy flag is false, the sponsor’s own analysis takes precedence over the unadjusted recalculation as the trial-reported analysis. The model result is the appropriate record of the sponsor’s stated inferential analysis, while the recalculation is a transparent descriptive check based on summary statistics. The registry does not report the model’s estimated contrast, confidence-interval bounds, covariates, or handling of crossover-specific effects. It is therefore not possible to determine precisely how its estimate or uncertainty compares with the summary-based calculation.

Neither result establishes equivalence or proves that the conditions have identical effects. The similarity of the means and the reported p-value should be interpreted for this endpoint and the reported analysis, not as a conclusion about every biomechanical or functional outcome included in the broader study aims.

13. Multiplicity, Missing Data and Analysis Populations

The registry reports 23 outcome measures, 22 analyses, and 14 secondary outcomes posted. This indicates that the study addressed a broad set of measures, but the record does not describe how the primary and secondary analyses were prioritized. A prespecified hierarchy, if any, is not reported in the registry record. It is also not reported whether p-values or confidence intervals were adjusted for multiple comparisons. Without that information, secondary findings should not be treated as confirmatory merely because an individual result appears notable.

The registry identifies the analysis method for the primary comparison as mixed models analysis. It does not report the statistical model specification, the covariates, the handling of the crossover sequence, or whether period or carryover effects were evaluated. The registry also does not report a statistical analysis plan, interim analyses, or a sample-size justification. Those omissions limit the ability to assess whether the posted analysis matches a prespecified plan or to reproduce the sponsor’s analysis.

Enrollment was 12, while each primary condition summary has 10 observations. The record does not explain the difference, report reasons for missing observations, or describe any imputation or other missing-data method. It does not identify an intention-to-treat, per-protocol, or other analysis population. The registry states that each participant wore both study prostheses, but does not give the participant-level paired data needed to verify the condition comparison or assess incomplete crossover participation.

These reporting gaps do not establish that the analyses were inappropriate; they mean that key methods cannot be evaluated from the registry record. They also constrain interpretation of uncertainty and generalizability. The posted results can be described as reported, while conclusions about missing-data assumptions, multiplicity control, or analysis-population choices remain unavailable.

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 adverse-event record lists 12 amputees at risk for serious adverse events and 0 affected. It also lists 12 at risk for other adverse events and 0 affected. These figures mean that no serious or other adverse events are recorded as affecting the listed group in this registry entry. The deaths field is null, so death information is not reported in the registry record.

Zero recorded events should not be read as proof that no adverse events occurred beyond the information captured in this entry, or as evidence that either pylon is risk-free. The registry does not provide event descriptions, exposure time by condition, a condition-specific safety comparison, or a detailed safety-collection method. The adverse-event group is labeled “Amputee,” rather than separately by pylon condition, so these figures do not show comparative safety between the torsion-adapter and rigid pylon. The data support only a limited description of what is recorded.

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

The primary result describes local dynamic stability of the prosthetic-limb hip during straight walking after three weeks of wearing the study prostheses. The posted means are 0.74 for both the rigid and torsion-adapter pylon conditions. The simple unadjusted recalculation gives a mean difference of 0.0, with an interval that crosses zero. The sponsor’s mixed-model analysis reports p >0.99. Taken together, these results do not indicate a clear difference in this posted primary measure.

That conclusion is limited to the endpoint, conditions, and analysis reported. It does not show that the conditions are equivalent, since no equivalence margin is reported. It does not establish that small or potentially important differences are absent, and it does not demonstrate a change in falls, injury, comfort, safety, or everyday mobility. Local dynamic stability is a biomechanical measure; it is not a direct measure of all those outcomes.

The study’s broader stated aims included turning biomechanics, stability, prosthetic interventions, comfort, and mobility. A result for hip stability during straight walking cannot answer all of those questions. The registry also lists turning-related moment measures and activity and walking-distance outcomes, but the posted summaries and analyses are incomplete relative to the full set of stated aims. Results should therefore be interpreted outcome by outcome rather than generalized across all functions or contexts.

The crossover design means participants wore both study prostheses, as reported in the registry. However, participant-level data and details of the crossover analysis are not reported, and the condition-specific primary counts are 10 against an enrollment of 12. Those limitations affect how fully the comparison and its precision can be assessed. The defensible reading is descriptive: the condition means match at the reported precision, and the reported analysis does not show a clear difference for this primary endpoint. It is not a general claim about which pylon is preferable or about clinical benefit.

16. Why This Trial Matters Statistically

This trial matters statistically because its comparison has a crossover structure: participants wore both study prostheses, and the central question concerns measurements under two device conditions. Such designs can be informative because the same person can contribute measurements to both conditions. At the same time, the validity and precision of the comparison depend on how the paired data and the order of conditions are handled. The registry names a mixed models analysis but does not report enough detail to evaluate those choices.

The primary summaries make the distinction between an observed estimate and an inference clear. Both condition means are 0.74, so the observed difference is 0.0. The recalculated interval spans zero, and the sponsor reports p >0.99. These registry entries do not imply exact equivalence. A useful statistical interpretation keeps the estimate, its uncertainty, and the limits of the endpoint separate rather than treating a large p-value as proof of no effect.

The record also illustrates why outcome multiplicity and reporting completeness matter. The study lists 23 outcomes and 22 analyses, but does not report a multiplicity strategy or a hierarchy of outcomes. The absence of these details makes it difficult to distinguish confirmatory from exploratory findings. Similarly, the discrepancy between enrollment and endpoint counts is not explained, limiting assessment of missingness and analysis populations.

Finally, the planning illustrations are based on observed secondary effects, not on the original design justification and not on observed power. This distinction is important when using small studies to plan future research: an observed estimate may be imprecise, and a planning calculation depends on its assumptions. The trial is therefore a useful case for reading effect estimates, uncertainty, crossover methods, and registry reporting together.

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.

The primary endpoint has 10 observations reported in each condition, while enrollment is 12. The registry does not explain the difference or say whether participants lacked measurements, were excluded, or were handled in another way. The primary comparison’s precision is also difficult to verify independently because participant-level paired values and the correlation between condition measurements are not reported.

The mixed models analysis is identified by name, but its specification is not reported. Details about randomized sequences, period effects, carryover, covariates, and model assumptions are unavailable. These gaps matter in a crossover comparison because the condition contrast can depend on the structure of the repeated measurements. The record also does not report the statistical analysis plan, a sample-size justification, interim analyses, an analysis population, or a missing-data method.

The primary endpoint is a biomechanical stability measure during straight walking. It does not directly establish effects on turning safety, falls, injury, comfort, or daily mobility. Although the broader study description includes those areas, the primary result should not be generalized to them. The registry lists secondary outcomes, but multiplicity handling and a confirmatory hierarchy are not reported. Unadjusted secondary analyses therefore warrant caution.

The enrollment is limited, and the posted summaries alone cannot establish whether the results apply beyond the studied participants and conditions. The registry’s condition labels and stated study aims do not provide a full description of participant characteristics or eligibility. In addition, the adverse-event record is not separated by pylon condition and does not provide death information. These limitations restrict both the clinical interpretation and assessment of comparative safety.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Prosthetic Components and Stability in Amputee Gait — NCT00167778.
• Registry record last updated 2014-08-15; status last verified 2014-07.
• Results first posted 2014-08-15.
• 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

NCT00167778, “Prosthetic Components and Stability in Amputee Gait,” is listed as a completed randomized, single-masked crossover study sponsored by the US Department of Veterans Affairs. Enrollment was 12. The registry describes comparison of a transverse-plane rotation-adapter pylon with a rigid pylon and states that each participant wore both study prostheses.

The primary endpoint was local dynamic stability of the hip during straight walking, measured after three weeks of prosthesis use. The posted means were 0.74 in each condition, with 10 observations reported per condition. The sponsor’s mixed models analysis reports p >0.99; the unadjusted recalculation gives a mean difference of 0.0 and p = 1.0.

The record lists 23 outcome measures and 22 analyses, with 14 secondary outcomes posted. It does not report key details about the analysis plan, missing data, multiplicity, or crossover-model specification. The adverse-event entry reports 0 serious and 0 other events among 12 at risk; death information is not reported in the registry record.