ROSA Total Knee Post Market Study EMEA: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for ROSA Total Knee Post Market Study EMEA (NCT04338893), a non-randomized na study. The primary outcome is Alignment Accuracy.

2. Clinical Question

The broader study was designed to collect information on surgical workflow efficiency, pain and function outcomes, and adverse events. Listed secondary outcomes include operative workflow efficiency, Oxford Knee Score, EuroQol 5D scores, pain ratings, Forgotten Joint Score and patient satisfaction questions. The registry record does not report comparative results for these outcomes. The central alignment question therefore remains unanswered by the posted results, while the non-randomized design also means that any observed group differences would need to be interpreted with care.

3. Trial Design

This was a prospective, multicenter post-market clinical follow-up study in the EMEA region. The registry lists the study status as completed and enrollment as 252. The study began on 2020-12-15, and its primary completion date is listed as 2025-08-22. The sponsor is Zimmer Biomet. The phase is listed as not applicable.

The registry describes a parallel, non-randomized design with no masking. Participants underwent total knee arthroplasty using either ROSA Total Knee robotic instrumentation or conventional instrumentation. These are the two listed arms; the registry does not report how participants entered each arm or provide details of allocation procedures beyond identifying the study as non-randomized. The intervention list includes Persona Total Knee, NexGen Total Knee and Vanguard Total Knee devices, and the study summary says it might include these product families.

The primary objective was to assess implant alignment accuracy. The planned measure was femoral rotation in the axial plane, assessed using pre-operative and post-operative CT scans, with the primary timeframe listed as pre-operative and 3 months. However, the registry says that the CT scan analysis was not performed. It cites the longer study duration, fewer enrolled patients than originally planned, reduced interpretability with the smaller sample, and reallocation of resources.

The record lists 11 outcome measures and zero analyses. It names several secondary outcomes, including workflow efficiency, knee and general health scores, pain, joint awareness and satisfaction. The registry record does not report a statistical analysis plan, a sample-size justification for the trial, or comparative estimates for those outcomes. The study's completed status should therefore not be read as meaning that the planned primary comparison was analyzed or that results for every listed outcome were posted.

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: 31 patients not assigned to any group: 27 screen failures, 1 cancelled operation, 3 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: CT scans were taken from participants enrolled in this patients sub-cohort; however, following longer study duration and fewer enrolled patients than originally planned, the scans analysis was not performed, as the reduced sample size limited interpretability, resources were reallocated, and the research question was no longer considered novel. The study documents did not specify what to do in the case of incomplete enrollment and there are no plans to process the images in the future.

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 Alignment Accuracy, measured over Pre-operative, 3 months.

The primary endpoint was alignment accuracy: the accuracy of implant component alignment for robotic instrumentation compared with conventional instrumentation. The specified measurement focused on femoral rotation in the axial plane, assessed from pre-operative and post-operative CT scans, with the timeframe listed as pre-operative and 3 months.

In general, an alignment measure is intended to describe how the implanted component is positioned relative to the planned or assessed orientation. CT imaging can be used to assess component orientation in a defined plane. The registry does not report the exact alignment target, the rule used to classify accuracy, or a threshold for a clinically important difference. Those details are not reported in the registry record.

The endpoint could have supported a direct comparison of the two instrumentation approaches if the planned scans had been analyzed and an estimate with suitable uncertainty had been reported. The registry states that the CT scan analysis was not performed, citing fewer enrolled patients than originally planned, limitations to interpretation, the longer study duration and reallocated resources. As a result, no primary endpoint estimate or comparative conclusion about alignment accuracy is reported. This absence of an analysis is different from an analysis that finds no difference: the posted record does not give a result that can establish the size or direction of any alignment difference.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes a parallel, non-randomized study with no masking. A parallel design means the study compares groups receiving different instrumentation approaches rather than comparing the same participant under both approaches. In general, random allocation helps balance measured and unmeasured participant characteristics across groups on average. Because allocation was non-randomized, the registry's group comparison would need to be interpreted with attention to possible baseline differences and treatment-selection factors. The record does not report an adjustment strategy or the participant characteristics used for such an assessment.

The primary outcome was a CT-based assessment of femoral rotation in the axial plane. In general, a continuous measurement can be summarized by a group estimate and a contrast between groups. A confidence interval describes the range of values compatible with the data and analysis under its assumptions; it conveys precision as well as direction and magnitude. No primary endpoint estimate or confidence interval is reported because the registry says the CT scan analysis was not performed.

The registry lists a primary timeframe of pre-operative and 3 months. A before-and-after assessment can describe change over time, while a comparison between treatment groups can assess whether those changes differ. In general, the interpretation depends on how the measurements are defined, which participants contribute data at each assessment, and how missing measurements are handled. The registry does not report the detailed measurement protocol, the number of available scans, or a statistical model for the intended comparison.

The record lists a set of secondary outcomes: operative workflow efficiency, Oxford Knee Score, EuroQol 5D score and VAS scale, Numeric Rating Scale pain, Forgotten Joint Score, and two patient satisfaction questions. In general, each outcome may have a different scale, distribution, time course and analysis method. A score might be analyzed as a numeric measure, while event outcomes may be analyzed as counts or proportions. The registry does not report outcome-specific estimates, methods, or comparative results for these listed measures.

The record lists zero analyses. It does not report the statistical analysis plan, whether adjusted analyses were intended, which analysis populations were defined, or how exclusions and missing outcome data were handled. In general, a prespecified analysis plan clarifies which outcomes and comparisons are primary, how estimates are calculated, and how uncertainty is quantified. Without those details or posted analysis results, readers cannot determine whether any unreported analytical choices were made.

Multiplicity concerns arise when many outcomes or comparisons are tested. In general, testing more hypotheses can increase the chance of finding a nominally notable result by chance, so an analysis plan may specify which outcomes are confirmatory and whether any adjustment is used. The registry lists multiple secondary outcomes but does not report a multiplicity strategy. Since no analyses are listed, there is no reported set of inferential results on which to assess multiplicity handling.

The registry also describes planning illustrations based on the observed effect, using a two-sided significance level of 0.05, equal allocation between arms and a normal approximation. The effect to detect is described as a stated fraction of the observed effect. In general, such illustrations show how a hypothetical future study's required sample size changes under chosen assumptions; they are not observed power and do not change the results of this study. The registry record does not report the trial's own sample-size justification. For time-to-event illustrations, the stated quantity is total events; other illustrations use participants per arm.

Over-dispersion is a general issue when count data vary more than a statistical model assumes. If present, a model that assumes less variability than the data contain can understate uncertainty. The registry does not report an over-dispersion assessment or a count-model analysis, so this general consideration should not be mistaken for a method used in this study.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists several secondary outcomes in addition to the primary alignment objective. In general, evaluating multiple outcomes raises a multiplicity question: whether the study prespecified a hierarchy or adjustment to control the chance of false-positive findings across comparisons. The registry record does not report a multiplicity plan, and it lists zero analyses. No conclusions about multiplicity adjustment can be drawn from the posted record.

The record does not report how missing data were handled, whether participants with incomplete follow-up were included in particular analyses, or how analysis populations were defined. It does say the CT scan analysis was not performed after longer study duration and fewer enrolled patients than originally planned, with reduced sample size limiting interpretability and resources reallocated. This is relevant to availability of the planned primary assessment, but it does not specify the extent or pattern of missing data for the CT scans or secondary outcomes.

In general, missing outcome information can affect both the precision and validity of an estimate, particularly when the reasons for missingness are related to participants' characteristics or outcomes. Different approaches to missing data rely on different assumptions. Because the registry does not describe an analysis population or missing-data method, the impact of missing information on any intended comparisons cannot be evaluated. The CT endpoint's omission should be read as an unperformed analysis, not as a finding of no difference.

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: stiffness/limited rom (3.0%), effusion/swelling/edema (2.0%), contralateral knee replacement (2.0%), vastus lateralis querruptur (1.0%), knee pain (1.0%).

The registry reports serious adverse events for the robotic group as 19 affected among 120 at risk, and for the conventional group as 13 affected among 101 at risk. It reports other adverse events as 21 affected among 120 at risk in the robotic group and 21 affected among 101 at risk in the conventional group. Deaths are listed as 0 in the robotic group and 1 in the conventional group.

The listed serious adverse event terms and percentages are stiffness/limited range of motion, 3.0%; effusion, swelling or edema, 2.0%; contralateral knee replacement, 2.0%; vastus lateralis querruptur, 1.0%; knee pain, 1.0%; and wound complication, 1.0%. These are descriptive entries in the registry record; it does not provide comparative estimates or uncertainty intervals for these terms.

In general, counts within groups describe what was recorded but do not establish that the instrumentation caused an event or that a difference between groups is meaningful. The groups were non-randomized, and the registry does not report an adjusted safety analysis. The serious and other adverse-event counts should therefore be read as separate descriptive summaries, not as proof of a causal safety difference.

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

The record documents a prospective, multicenter post-market study intended to evaluate workflow, patient outcomes and adverse events, with alignment accuracy as its primary objective. It also documents that the planned CT-based primary analysis was not performed. That distinction is central: a study objective is not itself a result, and a completed study status does not mean every planned outcome was analyzed.

The posted record does not report a comparative estimate for femoral rotation or implant alignment. It therefore cannot quantify an alignment difference between ROSA Total Knee robotic instrumentation and conventional instrumentation, indicate the direction of any difference, or show how precisely such a difference could be estimated. The missing estimate should not be interpreted as evidence that the approaches are equivalent or that they differ.

The registry does report adverse-event counts for the two groups and lists several serious adverse-event terms. Those figures describe events recorded in the respective groups. Given the non-randomized design and lack of reported comparative safety analysis, they do not establish a causal relationship or a reliable between-group safety contrast. The registry also lists patient-reported and workflow outcomes, but does not report their comparative results.

In general, a result's interpretation depends on the design, the outcome definition, the analysis, and the uncertainty around an estimate. Here, the main alignment analysis is unavailable, and the record does not describe analytical methods for the listed secondary outcomes. The evidence in the registry is consequently limited to study design information, the stated reason for not conducting the primary CT analysis, and descriptive adverse-event figures. It does not answer the primary comparative question.

13. Why This Trial Matters Statistically

This study is statistically important as an example of the difference between registering an outcome and reporting an analysis of that outcome. The primary objective was explicit: compare implant alignment accuracy between robotic and conventional instrumentation using femoral rotation assessed by CT. Yet the registry reports that the scan analysis was not performed. Readers therefore have an objective and a reason for the missing result, but not an estimate answering the objective.

The record also illustrates why enrollment and outcome availability are not interchangeable. It lists enrollment as 252, while describing fewer enrolled patients than originally planned as one reason the CT analysis was not performed. The registry does not give the size of the CT sub-cohort or the number of scans available for analysis. Without those details and a reported estimate, the precision and interpretability of the planned comparison cannot be assessed.

The non-randomized design matters because group differences may reflect factors beyond instrumentation. In general, statistical adjustment can sometimes address measured differences, but it cannot guarantee removal of bias from unmeasured factors. The record does not report an adjustment method, so the potential role of confounding in any group comparison remains unclear.

Finally, the record lists numerous secondary outcomes but no analyses. This makes transparent reporting especially relevant: a reader needs to know which outcomes were analyzed, how missing information was handled, and whether multiple comparisons were considered. The registry's description of the unperformed primary analysis and its descriptive safety counts are useful context, but they cannot replace the missing comparative endpoint results.

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 is that the primary CT scan analysis was not performed. The registry attributes this to longer study duration and fewer enrolled patients than originally planned, with the reduced sample limiting interpretability and resources being reallocated. No estimate of the primary alignment endpoint is reported.

The design was non-randomized and unmasked. The record does not report how participants were allocated between the robotic and conventional approaches, whether baseline differences were assessed, or whether any adjustment was planned or used. Consequently, a causal interpretation of group differences would be difficult even if descriptive differences were available.

The registry lists enrollment as 252 but does not report the number of participants contributing to the CT sub-cohort or the number with usable scans. It also does not describe missing-data handling, analysis populations, outcome-specific follow-up completeness, or reasons for incomplete outcome information. These omissions prevent assessment of how available data might represent the enrolled participants.

The record lists several secondary outcomes but reports zero analyses. It does not provide comparative estimates, confidence intervals, statistical methods, or a multiplicity plan for those outcomes. The listed adverse-event counts are descriptive and are not accompanied by adjusted comparative analyses or uncertainty intervals. Finally, the registry does not report the trial's sample-size justification or a detailed statistical analysis plan. These limitations mean the posted record offers limited evidence for judging comparative effectiveness or safety.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: ROSA Total Knee Post Market Study EMEA — NCT04338893.
• Registry record last updated 2026-05-12; status last verified 2025-12.
• Results first posted 2026-01-21.
• 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

The registry record describes a completed, prospective, multicenter EMEA post-market follow-up study of ROSA Total Knee robotic versus conventional total knee arthroplasty instrumentation. It lists a non-randomized, unmasked, parallel design, enrollment of 252, and Zimmer Biomet as sponsor.

The primary objective was CT-based assessment of femoral rotation and implant alignment accuracy, with a timeframe of pre-operative and 3 months. The registry states that the CT scan analysis was not performed because of longer study duration, fewer enrolled patients than originally planned, reduced interpretability and reallocated resources. It lists several secondary outcomes and zero analyses.

Descriptive serious and other adverse-event counts are reported for both groups, along with a death count and selected serious adverse-event terms. No comparative primary endpoint estimate, secondary outcome analyses, or statistical analysis plan is reported. The posted record therefore does not answer the planned alignment comparison.