Knee Kinematics for Subjects With Zimmer-Biomet Posterior Cruciate Retaining or Posterior Stabilizing Total Knee Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Knee Kinematics for Subjects With Zimmer-Biomet Posterior Cruciate Retaining or Posterior Stabilizing Total Knee Arthroplasty (NCT04103515), a registered phase not stated study. The primary outcome is Lateral Condyle Kinematic Translations - Step up.

2. Clinical Question

3. Trial Design

NCT04103515 is a completed study sponsored by The University of Tennessee, Knoxville. The registry lists a start date of 2019-01-03 and a primary completion date of 2020-11-06. Its enrollment is 50. The study summary describes 25 subjects implanted with a Zimmer-Biomet Posterior Cruciate Retaining total knee arthroplasty and 25 subjects implanted with a Zimmer-Biomet Posterior Stabilizing total knee arthroplasty.

Participants were asked to perform stepping-up and deep-knee-bend activities while under fluoroscopic surveillance. The stated purpose was to compare movements between the two implant groups. The primary outcome described in the record is lateral condyle kinematic translation during a step-up activity. The record lists four outcome measures, but it does not give group-level outcome results in the information. The primary outcome is identified as a mean with standard deviation, measured at baseline.

The study is not a randomized comparison, and the registry does not state how implant assignment or selection occurred. Consequently, the groups should not be treated as if they were created by random allocation. Differences between them could reflect characteristics other than implant type; the record does not provide enough information to assess those possibilities or determine whether any adjustment was made. There are no analysis records listed. The protocol’s statistical plan, any sample-size justification, and any interim analyses are not reported in the registry record. Completion status indicates the study is marked completed, but it does not establish that all planned analyses or results are present in the registry.

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 Lateral Condyle Kinematic Translations - Step up, measured over Baseline.

The primary endpoint is titled “Lateral Condyle Kinematic Translations - Step up.” It measures the motion of the lateral femoral condyle, a specified part of the femur, from the beginning to the end of a step-up activity. The measure is expressed in millimeters. Positive values represent anterior motion of the femur, while negative values represent posterior rollback. The registry describes the endpoint as a mean with standard deviation, and identifies its timeframe as baseline.

In general, a kinematic measure can describe how a joint or part of a bone moves during a defined activity. Recording motion during a task makes the measurement specific to that task; it does not, by itself, describe motion in other activities or everyday circumstances. The registry states that data are collected at a single time point, so this endpoint is not a measure of change over time. Nor is it a clinical symptom or a direct measure of function. It is a motion outcome intended to support comparison of the two implant groups during the specified activity.

The record does not report the group means, standard deviations, or a between-group estimate for this endpoint. It is therefore not possible to describe the observed movement in either group or the precision of a group comparison from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean represent?

The primary outcome is specified as a mean of a continuous measurement. In general, a mean is the arithmetic average of the measurements included in an analysis. For a motion outcome, the mean can provide a concise description of the group’s typical measured translation during the specified activity. It does not show whether all participants moved similarly: very different participant-level patterns can produce similar means. The registry does not report the actual means for the PCR or PS group.

What does the standard deviation describe?

The record identifies standard deviation as the measure of dispersion. In general, a standard deviation describes how spread out individual observations are around their group mean. A larger spread indicates greater variability among measured values; a smaller spread indicates measurements closer to the mean. It is not the same as the uncertainty in the estimated mean, and it is not a confidence interval. The record does not report the group standard deviations, so the observed variability cannot be assessed.

How should a group comparison be interpreted?

In general, a comparison of two means estimates how far apart the group averages are on the measurement scale. An estimate in millimeters would retain the clinical and biomechanical units of the endpoint. Its precision depends on the amount of information in the data and the variability of the measurements, among other factors. A confidence interval would communicate uncertainty around that estimate. No between-group estimate or confidence interval is reported in the registry record, so neither the magnitude nor precision of a difference can be described.

A p-value, when used, is interpreted in relation to a statistical model and a null hypothesis. It does not measure the size or importance of an effect, and it does not establish that a finding is true or false. The registry lists no analysis records and does not report a p-value for the primary comparison. The statistical test, model, and handling of potential covariates are not reported in the registry record. It would be inappropriate to infer these choices from the endpoint description alone.

Why does study design matter to the analysis?

In general, random allocation can help balance measured and unmeasured participant characteristics between groups, though it does not guarantee perfect balance. This study is not a randomized comparison, and the registry does not state how the groups were formed. The implant groups may therefore differ in ways that are related to measured motion. The record does not describe adjustment methods or provide participant-level information to evaluate such differences. This limits how confidently a group contrast could be interpreted as attributable to implant type, even if an outcome contrast were available.

The endpoint is collected at a single time point and refers to motion during a defined activity. It does not estimate within-person change from an earlier assessment. In general, repeated measurements over time require methods that account for the relationship among measurements from the same participant. Such a longitudinal analysis is not described for this endpoint. The registry says the outcome is at baseline, but does not provide more detail about the timing of the assessment relative to implantation or other clinical events.

What can planning calculations establish?

The registry record does not report the trial’s sample-size justification or statistical plan. Any planning illustration based on an observed effect is not the trial’s original design justification and must not be read as observed power. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the intended effect is a stated fraction of the observed effect. Such calculations are conditional illustrations of sample size under assumptions, not evidence that the study had a particular probability of detecting an effect. The outcome estimates needed to understand those illustrations are not reported in the registry record.

In general, over-dispersion matters when data vary more than a proposed statistical model assumes. Underestimating variability can make uncertainty appear too small, while accounting for extra variation can widen uncertainty or alter model-based inference. This is a general concept, not a reported feature of this study. The registry does not identify an over-dispersion assessment or a statistical model for the primary outcome. The available record therefore supports a description of the endpoint and design, but not a reconstruction of the analysis.

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("Subjects Implanted With PCR TKA", "Subjects Implanted With PS TKA")
n   <- c(25, 25)
m   <- c(1.15, 2.28)
sp  <- c(3.03, 3.42)
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  Subjects Implanted With PCR TKA  25  1.150  3.030  -0.101  2.401
CARM  Subjects Implanted With PS TKA  25  2.280  3.420  0.868  3.692

11. Multiplicity, Missing Data and Analysis Populations

The registry lists four outcome measures, while identifying lateral condyle kinematic translation during a step-up activity as the primary endpoint. The information reported in the registry record does not provide the other outcome definitions or their results. It also does not describe a multiplicity plan, such as whether any adjustment was intended for testing several outcomes or comparisons. Without the analysis plan and results, it is not possible to determine how the study addressed the possibility of chance findings arising across multiple analyses.

The record lists no analysis records. It does not report which participants contributed measurements to each outcome, whether the analysis followed an intention-to-treat, per-protocol, or other analysis population, or how participants with incomplete measurements were handled. The study summary describes 25 subjects in each group, but these group descriptions do not establish the number included in any outcome analysis. Missing-data assumptions, exclusions, and sensitivity analyses are not reported in the registry record.

In general, missing measurements can affect both the analysis sample and the interpretation of a result. The consequences depend on why measurements are missing and on the method used to handle them. No missing-data method or explanation for missingness is described. Likewise, the registry does not report whether the primary endpoint was selected before examining the data or whether analyses were adjusted for other participant or activity characteristics. These omissions limit assessment of selective reporting and analytic flexibility; they do not establish that such practices occurred.

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.

The registry reports zero participants affected by serious adverse events in the PCR group, with 25 subjects at risk, and zero in the PS group, also with 25 subjects at risk. It reports zero participants affected by other adverse events in each group, with 25 subjects at risk in each. Deaths are reported as zero in both groups. No serious adverse event terms are listed.

These figures describe the adverse-event information entered in the registry. A count of zero affected participants means that the record reports no participants affected in the listed category; it does not establish that every possible event was assessed or that no event occurred outside the collection and reporting procedures. The registry record does not describe the safety surveillance period, event definitions, attribution procedures, or completeness of adverse-event ascertainment. It also does not provide event-level detail for the listed categories.

These counts should be read as descriptive safety reporting, not as proof that either implant is free of risk or as a comparison demonstrating a safety advantage. The study summary focuses on motion assessment during activities, and the record does not provide a statistical comparison of adverse events. The reported counts alone cannot establish equivalence between groups or quantify the uncertainty around rare events.

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

The registry record establishes that a completed study enrolled 50 participants and set out to compare knee motion in subjects implanted with PCR and PS total knee arthroplasties. It describes fluoroscopic assessment during stepping-up and deep-knee-bend activities and identifies mean lateral condyle translation during a step-up as the primary endpoint. The measure is defined in millimeters, with positive values indicating anterior motion and negative values indicating posterior rollback.

What the record does not establish is the observed result of that primary comparison. Group means, standard deviations, a difference estimate, confidence intervals, and a statistical test are not reported. No conclusion about which group had more anterior motion, more posterior rollback, or greater variability can be drawn from the information reported. The absence of results in the registry record is not evidence that the groups were identical, nor is it evidence of a difference.

Even if group results were available, the design would remain important to interpretation. The comparison is not randomized, and allocation is not stated. Participant or clinical differences between groups could influence measured motion, and the record does not describe adjustment for such factors. The endpoint also concerns a specific movement at a single time point; it does not by itself establish long-term change, symptoms, function, or outcomes during other activities.

The safety entries report zero affected participants for the listed serious and other adverse-event categories and zero deaths in each group. Those registry counts are descriptive and do not prove an absence of risk. Overall, the record describes a biomechanical comparison and its intended measurement, but it does not supply the outcome results needed to assess the observed group contrast or its precision.

14. Why This Trial Matters Statistically

This study illustrates why a clearly defined outcome and a reported result are both necessary for statistical interpretation. The registry specifies a measurable endpoint, its unit, the activity during which it is recorded, and the meaning of positive and negative values. Those details make clear what the intended primary comparison concerns. Without group estimates and their uncertainty, however, readers cannot judge the size or precision of that comparison.

The design also highlights the distinction between comparing groups and estimating a causal effect. A nonrandomized comparison can describe differences between participants who received different implant types, but the registry’s information does not show that the groups were otherwise comparable. Allocation is not stated, and adjustment methods are not reported. Statistical interpretation must therefore account for the possibility that group differences reflect factors beyond the implant type.

The endpoint is biomechanical and activity-specific. This is useful for studying a defined aspect of knee motion, but it should not be conflated with broader clinical outcomes. A motion measurement does not itself measure symptoms, quality of life, or performance in activities not assessed by the study. The registry’s single-time-point description also distinguishes this measure from an estimate of change over time.

Finally, the record includes safety counts but no event terms or detailed surveillance information. Such counts have a limited descriptive role and should not be converted into a broad claim about comparative safety. Taken together, the study’s statistical importance lies in the defined question and the limits of what the available registry reporting allows readers to infer.

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 central limitation for interpretation is that the registry record does not report the primary outcome results. The group means and standard deviations are absent, as are an estimated contrast, a confidence interval, and a statistical test. Consequently, the observed direction, magnitude, variability, and precision of the primary comparison cannot be assessed.

The comparison is not randomized, and the registry does not state how participants came to receive either implant type. This leaves potential differences between groups unresolved. Participant characteristics, implant-selection factors, and any analytical adjustment for them are not reported in the registry record. The group contrast therefore cannot be interpreted as an unconfounded causal effect on the basis of this record.

The endpoint is motion during a step-up activity at a single time point. It does not describe change over time or motion in activities beyond those specified in the study summary. The record does not give details about measurement completeness, analysis populations, exclusions, missing data, or the timing of assessment relative to implantation. Although four outcome measures are listed, the remaining outcome definitions and results are not reported in the registry record. The statistical plan, sample-size justification, and interim analyses are also not reported.

Safety reporting is limited to the listed counts, without event terms or details of surveillance and ascertainment. These omissions limit interpretation of the zero counts and prevent a full assessment of comparative safety. These limitations concern the information reported in the registry record; they do not establish what may or may not have been assessed outside it.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Knee Kinematics for Subjects With Zimmer-Biomet Posterior Cruciate Retaining or Posterior Stabilizing Total Knee Arthroplasty — NCT04103515.
• Registry record last updated 2021-10-12; status last verified 2021-10.
• Results first posted 2021-10-12.
• 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

NCT04103515 is a completed study sponsored by The University of Tennessee, Knoxville, with enrollment of 50. The registry lists a start date of 2019-01-03 and a primary completion date of 2020-11-06. The study compares subjects implanted with Zimmer-Biomet Posterior Cruciate Retaining and Posterior Stabilizing total knee arthroplasties during stepping-up and deep-knee-bend activities under fluoroscopic surveillance.

The primary endpoint is mean lateral condyle kinematic translation during a step-up activity, measured in millimeters at baseline. The registry describes 25 subjects in each group, lists four outcome measures, and reports zero affected participants for the listed serious and other adverse-event categories in both groups, with zero deaths. The record does not report primary outcome results or analysis records. Allocation is not stated, and the comparison is not randomized.