A Multicenter Prospective Randomized Control Study on Persona Total Knee System vs NexGen: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Multicenter Prospective Randomized Control Study on Persona Total Knee System vs NexGen (NCT03073941), a randomized na study. The primary outcome is Oxford Knee Score.

2. Clinical Question

3. Trial Design

This was a multicenter, prospective, randomized, parallel-group trial comparing the Persona total knee system with the NexGen total knee system in total knee arthroplasty. The registry classifies allocation as randomized and masking as single. Which people were masked, and how masking was maintained, are not reported in the registry record. The listed phase is NA.

The enrollment is 332. The primary outcome description reports that 157 patients were enrolled and randomized to each group, with 3 cases excluded intraoperatively: 2 in the NexGen group and 1 in the Persona group. The record does not explain the reasons for these exclusions beyond their timing. It also notes that some outcome data are missing because of missed follow-up visits or incomplete form completion.

The primary outcome was the Oxford Knee Score at 3 months, 1 year and 2 years postoperatively. The listed secondary outcomes include the Oxford Knee Score Activity & Participation Questionnaire, the Forgotten Joint Score, patient satisfaction and anchoring questions, the EuroQol 5D score, and radiolucency or osteolysis. The registry lists 10 outcome measures and 1 analysis, but a single reported analysis does not establish that only one statistical test or comparison was conducted.

The registry lists the study status as active, not recruiting. The start is recorded as 2016-12 and primary completion as 2021-11-23. Further details about the randomization procedure, allocation concealment, site locations, treatment adherence, and the prespecified analysis plan are not reported in the registry record.

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Before assignment: 18 patients not assigned to any group: 5 rescinded consent before surgery, 13 recorded as lost to follow-up for other reasons

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: 157 patients were enrolled and randomized to each group, but 3 cases were excluded intraoperatively: 2 in the NexGen group and 1 in the Persona group. Additionally, some data points are missing due to missed follow-up visits or incomplete form completion

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.

Population: 157 patients were enrolled and randomized to each group, but 3 cases were excluded intraoperatively: 2 in the NexGen group and 1 in the Persona group.

6. Primary Endpoint

The registry lists the primary outcome as Oxford Knee Score, measured over 3 months, 1 year and 2 years postoperatively.

The primary endpoint is the Oxford Knee Score (OKS), a patient-reported questionnaire developed to assess the patient’s perspective after total knee arthroplasty. Its 12 questions cover knee function and pain. Each question is scored from 0 (worst outcome) to 4 (best outcome), and the items are summed to produce a score with a maximum of 48, representing the best score possible.

The registry describes the endpoint as a mean score with standard deviation and specifies assessment at 3 months, 1 year and 2 years postoperatively. A mean summarizes the average score in a group; a standard deviation describes how dispersed individual scores are around that average. Together, these can help characterize both the typical reported outcome and the variability among participants. The registry record does not report the group means or standard deviations at the listed follow-up times.

The score categories in the endpoint description are Excellent for > 41, Good for 34 - 41, Fair for 27 - 33, and Poor for < 27. Such categories provide a descriptive way to interpret score ranges, but they do not replace the underlying continuous score or a between-group statistical comparison. The record does not state that the primary analysis used these categories.

Patient-reported measures are used because they capture symptoms and function from the participant’s perspective. Their interpretation depends on the completeness and timing of questionnaire responses as well as the scoring method. Missing follow-up visits and incomplete forms are specifically noted for this outcome.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies a continuous primary outcome summarized as a mean with standard deviation. This is a common descriptive approach when an outcome is recorded on a numerical scale. The mean gives the average score within a group, while the standard deviation indicates how much individual scores tend to vary around that average. Neither statistic alone describes the uncertainty in a between-group comparison; that requires an estimate of the difference and an accompanying measure of its precision, such as a confidence interval.

What does a confidence interval convey?

In general, a confidence interval gives a range of values compatible with the observed data under a specified statistical method. A narrower interval indicates greater precision than a wider one, while the interval’s position relative to a value representing no difference can help readers assess which values remain plausible. No confidence interval for the Oxford Knee Score is reported in the registry record, so the precision of the group comparison cannot be evaluated from the posted outcome information.

Why does the timing of the outcome matter?

The OKS is listed at 3 months, 1 year and 2 years postoperatively. These are repeated follow-up assessments of the same trial population, rather than separate unrelated primary outcomes. Scores may change over follow-up, so a result at one time point would not automatically describe another. A complete analysis should make clear which time points were prespecified, how comparisons across time were handled, and whether the treatment effect was modeled as changing over time. Those details are not reported in the registry record.

When an outcome is measured repeatedly, statistical methods can account for the relationship among observations from the same participant. General approaches include analyzing each time point separately or using a model that includes repeated measurements. These approaches answer somewhat different questions and can differ in their assumptions. The record does not identify the method used for the OKS, nor does it report a model specification, covariates, or treatment of within-participant correlation.

What does randomization contribute?

In general, random allocation is intended to make treatment groups comparable with respect to both measured and unmeasured characteristics, on average. It supports a causal interpretation when the randomization process is preserved and the analysis appropriately accounts for participants’ assigned groups. Randomization does not guarantee identical groups in a particular trial, prevent missing outcome data, or correct analysis choices made after outcomes are known. The record identifies randomized allocation but does not report the sequence-generation method, concealment procedure, or primary analysis population.

The description says 157 patients were enrolled and randomized to each group, then notes 3 intraoperative exclusions. The registry does not explain whether the primary outcome analysis followed assignment regardless of what happened after randomization, included only participants who received an implant, or used another population. In general, an analysis based on randomized assignment preserves the original comparison more directly, while exclusions after allocation can affect how comparable groups remain. Which approach was used is not reported in the registry record.

How should missingness be considered?

The record notes missed follow-up visits and incomplete forms. These create missing outcome data, but their implications depend on how many scores are missing, when they are missing, and why. Missingness may be related to observed participant characteristics, the unobserved score itself, or other factors. General statistical methods may use complete cases, imputation, or models that use partial follow-up data, each relying on assumptions. The numbers missing at each time point, the method used, and any sensitivity analyses are not reported in the registry record.

Because the endpoint is a sum of 12 questionnaire items, incomplete form completion also raises a scoring question: whether a total can be calculated when some items are absent and, if so, how. The registry description does not report rules for handling incomplete questionnaires. Readers therefore cannot determine whether all reported scores, if any, would have been formed under a consistent item-completion rule.

What do planning calculations mean?

In general, sample-size calculations estimate how many participants may be needed to detect a chosen effect under stated assumptions. The planning illustration described for this trial uses a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation; it considers detecting a stated fraction of the observed effect. Such calculations are illustrations based on an observed effect, not evidence of observed power and not proof that the original trial was designed around that effect. The registry record does not report the trial’s own sample-size justification. No numerical planning estimates are reported in the registry record.

A significance level is a threshold used in a testing procedure; it does not measure the probability that a treatment effect is true. A p-value, if reported, would describe how incompatible the observed data are with a specified null model under the assumptions of the test. It would not by itself indicate the size or clinical importance of a difference. No primary-outcome p-value is reported in the registry record.

Finally, clinical trial interpretation commonly considers both the estimated effect and its uncertainty, along with the outcome’s measurement properties and the analysis population. The outcome description supplies the score scale and categories, but not a comparative estimate. Because the primary numerical results and analytic details are absent, the registry record supports an account of what was measured and how the study was organized, rather than a statistical conclusion about the primary comparison.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is assessed at 3 months, 1 year and 2 years postoperatively. The registry also lists several secondary outcomes, including activity and participation, joint awareness, patient satisfaction questions, EQ-5D, and radiolucency or osteolysis. Testing multiple outcomes or time points can increase the chance of at least one apparently notable result arising by chance. General approaches include prespecifying a primary comparison, adjusting for multiple testing, or interpreting secondary findings as exploratory. The multiplicity strategy is not reported in the registry record.

The record lists 10 outcome measures and 1 analysis, while noting that the primary outcome has several categories or time points and is not reduced to one comparison. Those entries do not specify which comparisons were made or whether any adjustment was applied. The number of analyses listed should not be treated as a complete description of all statistical tests unless the analysis details make that clear.

Missing outcome data are acknowledged: some data points are absent because of missed follow-up visits or incomplete form completion. The record does not report the amount of missingness at each follow-up, reasons by group, questionnaire scoring rules for incomplete forms, imputation methods, or sensitivity analyses. Without those details, the effect of missing data on the primary comparison cannot be assessed.

The primary outcome description reports 157 patients randomized to each group and 3 intraoperative exclusions, while the safety figures use at-risk group sizes of 156 and 155. The registry does not specify the population used for the OKS analysis or explain how participants were handled after exclusion. It is therefore not possible to determine from the record whether the primary analysis followed randomized assignment, included only treated participants, or used another analysis population.

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 1% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: contralateral knee replacement (3.2%), arythmia (2.6%), knee stiffness (1.9%), cancer (1.9%), infection (non-knee) (1.3%).

The registry lists serious adverse-event figures separately for the Persona CR and NexGen CR groups. The at-risk counts are 156 for Persona CR and 155 for NexGen CR. The serious adverse-event counts are 23 and 28, respectively. Other adverse-event counts are 16 and 20, and the recorded deaths are 1 and 0. These are counts as recorded; the registry information does not provide uncertainty intervals or an adjusted statistical comparison for them.

Counts alone do not describe the severity, timing, duration, recurrence, or clinical context of each event. Nor do they establish that an event was caused by an implant or treatment. The record does not report event-level detail or the method used to assess relatedness in the information. The at-risk counts also differ from the randomized counts because the primary outcome description records intraoperative exclusions; the registry does not give a full account reconciling all safety and outcome populations.

The listed leading serious-event terms include Contralateral Knee Replacement (3.2%), Arythmia (2.6%), Knee Stiffness (1.9%), Cancer (1.9%), Infection (non-knee) (1.3%), and Knee Pain (1.3%). These percentages are registry-listed values. The record does not give denominators or additional detail for these terms in the information available, so they should not be used to infer comparative risk between groups. Safety counts are descriptive registry entries, not a substitute for a prespecified safety analysis.

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

The trial record identifies a prospective randomized comparison of Persona and NexGen total knee systems and specifies the Oxford Knee Score as the primary outcome. It also describes the score’s content, scoring range, and postoperative assessment times. These details explain the question the study was set up to address, but they do not reveal the observed primary outcome.

The registry record does not report Oxford Knee Score means, standard deviations, confidence intervals, or p-values at 3 months, 1 year or 2 years. Consequently, the direction and magnitude of the comparison, and how precisely it was estimated, cannot be established from this record. The lack of a reported result is not evidence that the groups had the same scores, and it is not evidence that one group had better scores.

The safety entries give counts for serious and other adverse events and deaths, but do not provide an inferential comparison or enough detail to attribute events to either implant. The counts should be read as descriptive information recorded for the two groups. They do not independently establish differences in safety, causation, or the clinical importance of particular events.

Randomization is relevant because it is intended to support a fair comparison, but the registry does not report enough information about the analysis population, missing-data handling, or statistical methods to evaluate how the randomized comparison was carried through to the primary results. The stated missing follow-up and incomplete forms are particularly relevant because the primary measure depends on patient questionnaire responses.

Any sample-size figures based on the observed effect are planning illustrations rather than observed power or a record of the original design justification. Overall, the registry supports a description of the trial question, design, endpoint, and selected safety counts. It does not support a conclusion about comparative OKS outcomes or a definitive statistical judgment about differences between the systems.

13. Why This Trial Matters Statistically

This trial is statistically notable for its randomized, prospective, parallel-group comparison of two implant systems and for its use of a patient-reported primary outcome at multiple postoperative times. Randomization provides a basis for comparing groups, while repeated measurements make the analysis question more complex than a single endpoint measured once. The treatment contrast may be assessed separately at each time or through a model that incorporates the repeated scores; the registry record does not say which approach was used.

The outcome itself combines 12 questions about knee function and pain into a numerical score. That makes it important to distinguish the average score from the distribution of individual scores and to report uncertainty around the group comparison. The registry gives the scale definition and categories, but not the comparative estimates needed to assess either the magnitude or precision of the primary result.

Missing follow-up and incomplete forms are also statistically important. In general, missingness can change which participants contribute to an analysis and can bias estimates when the reasons for missing data relate to outcomes or group assignment. Reporting the extent, handling, and sensitivity of missing data helps readers judge robustness. Those details are not reported in the registry record.

Finally, several secondary outcomes and multiple OKS follow-up times create a multiplicity question: how should multiple comparisons be interpreted without overstating isolated findings? The analysis plan and multiplicity approach are not reported. The record thus illustrates why a trial’s design and outcome definitions are only part of statistical interpretation; the numerical results, uncertainty, analysis population, and missing-data strategy are also necessary to evaluate the evidence.

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 interpreting this trial from the registry record is that the primary numerical results are not reported. Although the OKS is defined and scheduled at 3 months, 1 year and 2 years postoperatively, the record does not provide group means, standard deviations, confidence intervals, or p-values. The comparative primary outcome therefore cannot be evaluated.

The outcome description reports missing data from missed follow-up visits or incomplete form completion, but does not state how many observations were missing at each time point or how incomplete forms were scored. It also does not report any imputation, sensitivity analysis, or other method for assessing the impact of missingness.

The record does not identify the primary analysis population or explain the handling of 3 intraoperative exclusions. It gives no detail on random-sequence generation, allocation concealment, who was masked, or whether the analysis followed randomized assignment. These omissions limit assessment of potential bias in the comparison.

The primary endpoint spans several follow-up times, and multiple secondary outcomes are listed. The registry does not report which comparisons were prespecified as primary, how multiplicity was handled, or the statistical models and covariates used. The sample-size justification for the original trial is also not reported in the registry record.

Safety information is presented as group counts and selected event terms, without a reported comparative analysis or full event-level context. The available record does not establish event relatedness, timing, or whether the counts represent unique participants or recurrent events. These limitations mean that the reported safety figures should be treated as descriptive rather than as a complete comparative safety assessment.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: A Multicenter Prospective Randomized Control Study on Persona Total Knee System vs NexGen — NCT03073941.
• Registry record last updated 2026-05-12; status last verified 2026-04.
• Results first posted 2025-01-17.
• 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

NCT03073941 is a multicenter, prospective, randomized, single-masked, parallel-group trial comparing Persona and NexGen total knee systems for total knee arthroplasty in people with knee osteoarthritis. Enrollment is 332, and the listed phase is NA. The primary endpoint is the Oxford Knee Score, assessed at 3 months, 1 year and 2 years postoperatively.

The endpoint description reports 157 patients randomized to each group and 3 intraoperative exclusions: 2 in the NexGen group and 1 in the Persona group. It also notes missing data from missed visits or incomplete forms. The registry lists 10 outcome measures and 1 analysis. Primary Oxford Knee Score numerical results and analysis details are not reported in the registry record.

Safety entries list serious adverse-event counts of 23 for Persona CR and 28 for NexGen CR, other adverse-event counts of 16 and 20, and deaths of 1 and 0. These entries are descriptive; the record does not report an adjusted safety comparison.