Persona TKA With iASSIST Knee System and iASSIST Knee System: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Persona TKA With iASSIST Knee System and iASSIST Knee System (NCT03227692), a randomized na study. The primary outcome is Number of Participants With Alignment Accuracy of the Knee Femoral Components in Coronal Plain.

2. Clinical Question

3. Trial Design

This was a randomized, parallel-group controlled study comparing iASSIST Knee with conventional instrumentation during total knee arthroplasty. The registry lists quadruple masking. That label indicates a masking designation in the record, but the specific roles of the people masked and the practical masking procedures are not reported in the registry record. The study was sponsored by Zimmer Biomet and is recorded as completed.

The registry lists an enrollment of 93. It gives a start date of 2017-08-18 and a primary completion date of 2019-11-14. The study's stated purpose was to compare the accuracy of knee component alignment between patients operated with iASSIST Knee and patients operated without it, using the same implant system. The two arm descriptions distinguish navigation-assisted surgery from surgery performed with conventional instruments and without the navigation system.

The primary outcome focused on femoral component alignment in the coronal plane. It was based on postoperative CT data, with the stated assessment at 6 month after surgery. The registry also identifies secondary outcomes concerning surgery time, instrument trays, knee scores, patient satisfaction and expectations, and EQ-5D-3L. The registry lists 12 outcome measures, but it does not report results for those outcomes in the information available for this analysis.

Randomization supports a comparison between assigned surgical approaches, but it does not by itself show that the groups were comparable in every characteristic or that all randomized participants contributed to every outcome. The registry record does not report the randomization procedure, the allocation-concealment process, or a participant flow description for the primary outcome. Those details matter when assessing how closely the analysis followed the randomized comparison.

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: Patients who have CT data at 6 month after surgery were included in the analysis.

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 Number of Participants With Alignment Accuracy of the Knee Femoral Components in Coronal Plain, measured over Postoperative 6 months.

The primary endpoint counts participants whose knee femoral component met the registry's alignment criterion. A participant qualified if the implant was positioned within 3 degrees from perpendicular to the mechanical axis of the lower extremity. The registry describes this as an assessment of alignment accuracy in the coronal plane, using CT data collected at 6 month after surgery.

This type of endpoint reduces an imaging measurement to a count: each assessed participant either meets the defined alignment threshold or does not. That can make a comparison easier to interpret as the proportion of assessed participants reaching a prespecified target. It also means the count does not retain all the detail in the underlying angle measurement. Two measurements on opposite sides of the threshold could be classified differently even if they were close, while different measurements within the accepted range share the same endpoint classification.

The endpoint is relevant to the stated study purpose because it assesses component positioning after surgery, rather than relying only on symptoms or patient-reported scores. It is a surrogate technical measure, however, and the registry record does not establish how it relates to later function or other patient outcomes. CT-based assessment also means that inclusion in the described primary analysis depended on having CT data at 6 month after surgery. The number of participants meeting the criterion, the group-specific outcome counts, and a single between-group estimate are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the study as randomized, quadruple masked, and parallel group. In general, randomization is intended to make treatment assignment independent of participants' measured and unmeasured characteristics on average. It therefore provides a basis for comparing outcomes by assigned group. Randomization does not guarantee exact balance, especially in a study of limited size, and the registry record does not report the allocation sequence method or concealment procedures. The masking designation is recorded, but who was masked and how masking was maintained are not reported in the registry record.

What does the endpoint count?

The primary outcome is a binary classification at the participant level: whether CT assessment showed a femoral component within the stated alignment threshold. For a binary outcome, the basic descriptive information is the count meeting the criterion and the number assessed in each group. A comparative analysis can then express how the groups differ using an appropriate measure of effect and its uncertainty. The registry record does not provide a single primary comparison or the group-specific endpoint counts, so a numerical comparison cannot be interpreted from this record.

The threshold makes the endpoint straightforward to classify, but dichotomizing a measurement discards detail. General statistical reasoning: an outcome based on a cutoff can be sensitive to measurement variability for observations near that cutoff. It also does not distinguish degrees of alignment among participants who all meet the criterion. The registry describes CT data at 6 month after surgery but does not report the measurement protocol, assessor agreement, or handling of borderline or uninterpretable scans.

How should uncertainty be understood?

General statistical explanation: a confidence interval describes the range of effect values that are reasonably compatible with the observed data under the assumptions of the analysis. A narrower interval indicates greater precision, while a wider interval indicates more uncertainty. A point estimate without its interval can obscure that uncertainty. Here, no single primary estimate or confidence interval is reported in the registry record, so the precision of the primary comparison cannot be evaluated.

A hypothesis test, when reported, addresses compatibility of the data with a specified null hypothesis under a particular model. A p-value does not measure the probability that the null hypothesis is true, nor does it by itself describe the size or practical importance of an effect. The registry record does not report a single primary test result. It also does not report a statistical analysis plan or identify the test or model used for the primary endpoint. Those methods should not be inferred from the endpoint type alone.

What can the planning calculations tell readers?

The registry's sample-size assumptions describe planning illustrations based on the observed effect, a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The stated effect to detect is a fraction of the observed effect. The record distinguishes participants per arm for non-time-to-event outcomes from total events for time-to-event outcomes. These are planning calculations, not observed power and not the trial's own design justification. The sample-size justification for this trial is not reported in the registry record.

General statistical explanation: planning calculations show what sample size might be required under chosen assumptions about an effect, variability, significance level, power, and allocation. They depend on those assumptions and do not establish that a completed trial had adequate power. Calculations based on an observed effect can also be optimistic if that observed effect is imprecise. In this case, the primary outcome was not reduced to one comparison in the registry record, and no single primary effect estimate is reported there. The record therefore does not support a reader's independent interpretation of a primary-outcome planning estimate as evidence about the achieved precision of the trial.

Why do missing outcome data matter?

The primary population is described as participants who had CT data at 6 month after surgery. General statistical explanation: when an outcome is available only for a subset of randomized participants, the comparison among those assessed may differ from the comparison that would have been seen if outcomes were available for everyone. The direction and size of any resulting bias depend on why data are missing and how missingness relates to group assignment and outcome. The registry record does not report the number lacking CT data, reasons for missing data, or an imputation or sensitivity-analysis approach.

For this reason, the randomized enrollment and the primary analysis population must be kept distinct. The enrollment is 93, but the record does not state how many contributed CT data to the primary outcome. It is not appropriate to assume that all enrolled participants were included in that outcome analysis. Nor does the available record establish whether the analysis followed assigned group, excluded participants without scans, or used another approach.

What is not specified?

The registry record does not report a single primary statistical analysis, the handling of multiple outcomes or time points, adjustment for baseline characteristics, or a prespecified missing-data strategy. General methods such as logistic regression, risk comparisons, or exact tests might be considered for binary outcomes in other settings, but none should be attributed to this trial without documentation. The listed randomization and endpoint definition are not enough to reconstruct the sponsor's analysis. Any recalculation from group summaries is also unavailable for the primary endpoint because the required single-comparison summaries are not reported. The record should therefore be read as describing the intended endpoint and design, not as providing enough information to reproduce or evaluate a primary statistical result.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 12 outcome measures, including the primary alignment outcome and secondary outcomes concerning surgery time, instrument trays, knee scores, satisfaction, expectations, and EQ-5D-3L. It also records 0 analyses. The primary outcome description refers to several categories or time points and states that it was not reduced to one comparison. No single primary result is reported in the registry record.

When a study evaluates multiple outcomes, time points, or subgroup comparisons, the chance of finding at least one apparently notable result can increase if each is tested separately without an appropriate plan. General statistical explanation: multiplicity methods may control that risk, while a clearly specified hierarchy can distinguish confirmatory from exploratory questions. The registry record does not report whether multiplicity was addressed, how the primary comparison was selected from the categories or time points, or whether secondary results were adjusted. No such procedure should be assumed.

The primary outcome population is described as patients with CT data at 6 month after surgery. The registry record does not report how many participants lacked CT data, why data were missing, or how missingness was handled. It also does not report a complete analysis population definition or a participant flow for the endpoint. These gaps limit assessment of whether the analysed participants represent the randomized groups and whether missing outcomes could affect the comparison.

Without the analysis plan, a single primary estimate, and information about missing outcomes, readers cannot distinguish a prespecified confirmatory analysis from analyses selected after outcome data were examined. This uncertainty concerns reporting and interpretation; it does not establish that the trial used an inappropriate method.

11. 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 serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: malignant lymphoma (2.4%).

The registry reports adverse-event counts by group. In the Persona With iASSIST Knee group, 0 of 42 were reported with a serious adverse event, and 0 of 42 with another adverse event. In the Persona Without iASSIST Knee group, 1 of 41 was reported with a serious adverse event, and 1 of 41 with another adverse event. Deaths are recorded as 0 in both groups. These are descriptive counts in the registry record, not a complete comparative safety analysis.

The record lists Malignant Lymphoma at 2.4% among the top serious adverse event terms. It does not provide enough context in the information available to assign that term to a particular participant-level timeline or to interpret its relationship to the procedure or device. The listed event counts do not establish causation.

Small event counts provide limited information about uncommon harms. General statistical explanation: an observed zero count does not prove that an event cannot occur; uncertainty remains when the number of people observed is limited. The record does not report event severity details beyond the serious/other categories, timing, duration, adjudication, or a formal comparison with uncertainty. These figures should therefore be read as registry-reported counts, not as proof of equal safety or as evidence of a causal safety difference.

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

The trial's central statistical question is whether use of iASSIST navigation changed the number of participants meeting a defined CT-based femoral alignment criterion after total knee arthroplasty. The registry record describes randomized allocation, the two surgical approaches, and the outcome threshold. These details clarify what the study set out to compare.

What the record does not provide is the single primary comparison needed to answer that question numerically. There are no reported group-specific counts for the alignment criterion, no effect estimate, no confidence interval, and no single primary test result. The registry explicitly notes that the primary outcome has several categories or time points and was not reduced to one comparison. The result must therefore be treated as unavailable for a direct statistical interpretation.

This absence does not mean the result was zero, that the approaches were equivalent, or that a clinically important difference was ruled out. Equivalence or non-inferiority requires a defined margin and an analysis designed to assess it; neither is reported in the registry record. Similarly, statistical significance cannot be inferred from trial completion or the randomized design alone. The available information does not establish either the direction or magnitude of an alignment difference.

Even if a difference in the alignment count were reported, it would address this particular imaging endpoint at the specified postoperative assessment. It would not by itself establish differences in pain, function, quality of life, later revision, or overall benefit. The registry names several postoperative outcomes, but their results are not reported in the record available for this analysis. The safety counts are separate descriptive information and cannot fill that gap.

The appropriate interpretation is therefore narrow: the registry record documents a randomized comparison of navigation-assisted and conventional instrumentation, with a specified CT-based alignment target, but does not provide a single primary result from which the comparative effect or its precision can be judged. Further conclusions require outcome and analysis information not reported in the registry record.

13. Why This Trial Matters Statistically

This study raises a useful statistical distinction between a precisely defined endpoint and a sufficiently reported result. The alignment threshold is explicit: a participant's femoral component is classified according to whether it falls within 3 degrees from perpendicular to the mechanical axis of the lower extremity. Yet a clear definition does not substitute for the observed counts, denominators, and comparative estimate needed to evaluate the endpoint.

The design also highlights why the analysis population matters. The registry describes the primary outcome as based on participants with CT data at 6 month after surgery. That definition makes imaging availability part of the endpoint analysis. Without a count of those assessed and a description of missing scans, readers cannot determine how much of the randomized comparison is represented in the reported outcome population.

Another statistical issue is the presence of multiple outcomes and time points. The registry lists a range of surgical, clinical, and patient-reported measures, while stating that the primary outcome has several categories or time points and was not reduced to one comparison. A prespecified hierarchy and multiplicity strategy can help readers understand which comparisons are confirmatory and how uncertainty should be interpreted. Those elements are not reported in the registry record.

Finally, the listed sample-size assumptions illustrate the difference between planning and inference. Planning calculations depend on assumptions and do not represent observed power or reveal the precision of the completed trial. The registry record does not report the trial's sample-size justification, and it does not give a single primary estimate to evaluate. This makes transparent outcome reporting, analysis-population details, and uncertainty intervals especially important for understanding what the study can establish.

14. 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 main limitation for statistical interpretation is that the registry record does not report the primary outcome as a single comparison. Although it defines the CT-based alignment criterion, it does not provide group-specific counts, denominators for that outcome, an effect estimate, a confidence interval, or a test result. The record itself says that the outcome has several categories or time points and was not reduced to one comparison.

The primary analysis population is limited to patients with CT data at 6 month after surgery, but the number assessed and the reasons for unavailable CT data are not reported in the registry record. Without participant flow or missing-data details, it is not possible to judge how complete the endpoint data were or how missingness may affect interpretation. The registry also does not report whether outcome assessors were masked, how CT alignment was measured, or how ambiguous scans were handled.

Although the study is described as randomized and quadruple masked, the registry record does not specify the randomization procedure, concealment, the roles covered by masking, or whether masking was maintained. A statistical analysis plan, primary model or test, adjustment variables, and handling of multiple outcomes and time points are also not reported.

The registry lists secondary outcomes but does not report their results in the information available for this analysis. It also does not provide enough detail to interpret the adverse-event term listing in relation to timing or causality. These limitations concern what can be concluded from the registry record; they should not be taken as evidence that the underlying trial did or did not collect additional information.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Persona TKA With iASSIST Knee System and iASSIST Knee System — NCT03227692.
• Registry record last updated 2020-07-02; status last verified 2020-01.
• Results first posted 2020-03-19.
• 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.

18. Record Summary

NCT03227692 is a completed randomized, parallel-group study sponsored by Zimmer Biomet. It compared total knee arthroplasty with the Persona Knee System and iASSIST Knee navigation against surgery using conventional instruments without iASSIST. The registry lists quadruple masking, enrollment of 93, a start date of 2017-08-18, and a primary completion date of 2019-11-14.

The primary outcome concerned the number of participants whose femoral component met the stated coronal alignment threshold on CT at 6 month after surgery. The primary population was described as patients with CT data at that assessment. The registry record does not report a single comparison for this outcome, and the group-specific counts, effect estimate, uncertainty interval, and primary statistical test are not reported. The record also lists secondary outcomes and descriptive adverse-event counts, but these do not replace the missing primary comparison.