This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Stryker NTX Registry Scorpio NRG (Re-"Energize"), Triathlon Total Knee, Triathlon Partial Knee Resurfacing (PKR) With X3 Polyethylene Insert (NCT02525562), a non-randomized na study. The primary outcome is Survivorship of the Device.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02525562 |
| Phase | NA |
| Condition | Arthroplasty, Replacement, Knee |
| Allocation | Non-Randomized |
| Design model | Parallel |
| Masking | None (open label) |
| Enrollment | 237 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Stryker Orthopaedics |
| Results posted | Yes |
2. Clinical Question
Population
Patients eligible for total knee arthroplasty or partial knee resurfacing for knee arthroplasty are the intended population. The record describes patients eligible for each device arm, but further eligibility criteria and the characteristics of the participants are not reported in the registry record.
Intervention
The device options are the Scorpio NRG Total Knee System with X3 insert, the Triathlon Total Knee System with X3 insert, and the Triathlon PKR System with X3 insert. The procedures named are total knee replacement and partial knee resurfacing.
Comparator
The record organizes the study into parallel arms, but allocation was non-randomized. The arms therefore do not constitute a like-for-like control comparison: eligibility and the choice of procedure or device may differ between groups. No randomized comparator is described.
Primary question
The primary outcome concerns device survivorship, expressed as participants free from revision over the stated follow-up timepoints: preoperative to 1 year, 1 year, 3 years, and 5 years. The 10-year survivorship outcome was not analyzed because the study terminated. The record also lists patient outcomes assessed using the Knee Society Score, the Knee Injury and Osteoarthritis Outcome Score, and the EuroQuol-5 Dimension Health Questionnaire. Numerical primary outcome results and analyses are not reported in the registry record.
3. Trial Design
This is a non-randomized, parallel-model registry study of knee replacement and partial knee resurfacing systems with X3 inserts. The registry lists enrollment of 237 and identifies Stryker Orthopaedics as sponsor. The listed study start date is 2012-06-28, and the primary completion date is 2020-05-28. Its status is terminated. The phase is listed as NA.
The arms describe patients eligible for the Scorpio NRG Total Knee System with X3 insert, the Triathlon Total Knee System with X3 insert, or the Triathlon Partial Knee Resurfacing system with X3 insert. Named procedures include total knee replacement and partial knee resurfacing. Because allocation was non-randomized, the arms should not be read as randomized treatment groups or as a like-for-like control comparison. The registry record does not report how clinicians or participants selected among the options, or whether selection was influenced by measured or unmeasured characteristics.
Masking is listed as none. The record describes the study aim as collecting information on surgical and implant performance and patient clinical outcomes among people eligible for either total knee arthroplasty or partial knee resurfacing. Secondary outcomes include the Knee Society Score, the Knee Injury and Osteoarthritis Outcome Score patient questionnaire, and the EuroQuol-5 Dimension Health Questionnaire patient questionnaire. Further information about follow-up procedures, outcome assessment, and the analysis plan is 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: 237 participants enrolled - 14 participants censored = 223 participants followed. All participants received a Triathlon Total Knee Replacement. No participants received a Scorpio NRG Total Knee Replacement or a Triathlon Partial Knee Resurfacing Replacement.
Overall Study
| Stage | Triathlon Total Knee System | Scorpio NRG Total Knee System | Triathlon Partial Knee Resurfacing |
|---|---|---|---|
| STARTED | 223 | 0 | 0 |
| COMPLETED | 0 | 0 | 0 |
| NOT COMPLETED | 223 | 0 | 0 |
Reasons for not completing this period:
| Reason | Triathlon Total Knee System | Scorpio NRG Total Knee System | Triathlon Partial Knee Resurfacing |
|---|---|---|---|
| Death | 9 | 0 | 0 |
| Lost to Follow-up | 19 | 0 | 0 |
| Withdrawal by Subject | 37 | 0 | 0 |
| Revision/Removal of Study Device | 4 | 0 | 0 |
| Study Closed by Sponsor | 154 | 0 | 0 |
Analysis population for the primary outcome, as defined in the registry: This primary outcome measure (10 year) was not analyzed due to termination of the study. Results display number of participants at each timepoint (i.e., preoperative to 1 year, 1 year, 3 years, and 5 years) that remain free from revision; 10 year not reported due to study termination. Overall number of participants analyzed is based upon the preoperative to 1 year population, originally 223 participants with 4 early terms (no surgery), therefore n=219.
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: Includes participants who received the Triathlon Total Knee System and were not censored from analysis.
| Characteristic | Unit | Triathlon Total Knee System |
|---|---|---|
| Participants analysed | 223 | |
| Age, Continuous | Years | 68.61 (SD 8.08) |
| Sex: Female, Male: Female | Participants | 151 |
| Sex: Female, Male: Male | Participants | 72 |
| Race and Ethnicity Not Collected | Participants | — |
| Region of Enrollment: Luxembourg | participants | 30 |
| Region of Enrollment: United Kingdom | participants | 100 |
| Region of Enrollment: Germany | participants | 93 |
6. Primary Endpoint
The registry lists the primary outcome as Survivorship of the Device, measured over Preoperative to 1 year, 1 year, 3 years, and 5 years. Survivorship is unavailable at 10 years due to study termination..
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants free from revision |
| Endpoint classification | not reduced to a single comparison |
The primary outcome is device survivorship, described as the number of participants free from revision. Revision is used as an endpoint because it records a further procedure involving the device and can therefore provide a clinically interpretable measure of how long an implant remains without revision. The registry specifies follow-up from preoperative to 1 year, at 1 year, at 3 years, and at 5 years. It states that survivorship is displayed using Kaplan-Meier survival curves, a method for estimating survival over time from time-to-event data.
In general, a survival curve represents the estimated proportion remaining free of the event over follow-up while accounting for the timing of events and censoring. Censoring occurs when a participant's event status is not observed for the full follow-up period. The record does not report details of censoring or the underlying analysis population. It explicitly states that the primary 10-year outcome was not analyzed because the study terminated, so the endpoint cannot establish 10-year survivorship from this registry record. Numerical results for the specified earlier timepoints are not reported in the registry record.
The listed secondary outcomes assess clinical status and health-related quality of life using KSS, KOOS, and EQ-5D questionnaires. Their outcome values and analyses are not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record describes an observational comparison of patients eligible for different knee procedures and device systems, not a randomized trial. That design matters for interpretation: the groups may differ in ways related to eligibility, clinical circumstances, device choice, or other factors. Without random allocation, a difference between arms, if reported, could not automatically be attributed to the device or procedure alone. The record itself cautions that the arms are not a like-for-like control comparison.
The stated primary outcome is freedom from revision, estimated with Kaplan-Meier survival curves. The record identifies timepoints through 5 years and says that 10-year survivorship was unavailable because the study terminated. However, the numerical survivorship results and the number of participants free from revision at each specified timepoint are not reported in the registry record. As a result, the record does not support a numerical interpretation of survivorship or a comparison of survivorship between arms.
The registry also lists patient-reported and clinical outcomes using KSS, KOOS, and EQ-5D. The outcome values, changes over time, uncertainty estimates, and analyses for these measures are not reported in the registry record. No conclusions about the magnitude or precision of differences in these scores can be drawn from the outcome descriptions alone.
The registry lists 0 analyses. This means the record does not include a reported analysis result for interpretation. It should not be read as evidence that there were no events or no differences; those conclusions require results that are not reported. The record also lists operative and non-operative adverse-event counts, but these counts do not supply a comparative estimate of device effects. The event categories and their interpretation are addressed separately from the survivorship outcome.
Any planning illustrations based on an observed effect are not evidence of observed power and do not substitute for an analysis. In general, a confidence interval conveys the range of effect estimates compatible with the data under a specified statistical model; without reported effect estimates and intervals, precision cannot be assessed. The registry record does not report the statistical plan, adjustment methods, or details needed to evaluate assumptions behind an estimate. Overall, the posted record describes the study question and some safety counts, but does not report numerical primary efficacy results or analyzed secondary outcomes.
9. Statistical Methods Explained
The registry describes survivorship using Kaplan-Meier survival curves. This method is commonly used for time-to-event outcomes, where the event is a revision and follow-up time matters. In general, a Kaplan-Meier curve estimates the probability of remaining free of the event as follow-up progresses. It can incorporate information from participants whose follow-up ends before the event occurs, provided their event status is known up to that point. Such observations are called censored. The registry record does not report censoring rules, the number at risk over time, or the handling of participants lost to follow-up.
What does a survival estimate represent?
A survival estimate at a specified timepoint describes the estimated share of the analysis population that has not experienced the event by that time, under the method's assumptions. It is not simply a count of participants who remain in follow-up, and it is not necessarily the same as a raw proportion when follow-up differs among participants. The registry describes results as numbers of participants free from revision at specified timepoints, while also stating that survivorship is shown with Kaplan-Meier curves. The numerical estimates and supporting risk sets are not reported in the registry record, so the relationship between counts and curve estimates cannot be assessed.
Why does non-random allocation matter?
In general, random allocation helps balance measured and unmeasured characteristics between treatment groups on average. Non-random allocation does not provide that protection. Patients eligible for different procedures or devices may have different clinical characteristics or may be treated in different circumstances. Those differences can affect outcomes independently of the device or procedure. Statistical adjustment can sometimes address measured differences, but it cannot guarantee removal of confounding, especially when relevant characteristics are unmeasured. The registry record does not report an adjustment strategy. Its explicit caution that the arms are not a like-for-like control comparison is therefore important when reading any apparent difference.
What can a confidence interval add?
In general, a confidence interval communicates statistical uncertainty around an estimate. A relatively narrow interval indicates greater precision under the model used; a wide interval indicates less precision. It does not resolve bias from non-random allocation, measurement issues, or an unsuitable model. No confidence intervals or numerical outcome estimates are reported in the registry record for the primary endpoint. Consequently, neither the size nor precision of a survivorship estimate can be evaluated from the record.
How should planning illustrations be read?
The registry's sample-size assumptions describe planning illustrations based on an observed effect, not the study's own design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. For time-to-event tables, the calculation gives the total number of events using the Schoenfeld method. Other planning calculations are expressed as participants per arm. These illustrations describe hypothetical requirements under specified assumptions; they are not observed power and do not establish that the study was adequately powered. The registry record does not report the trial's own sample-size justification or a statistical design plan.
In general, over-dispersion occurs when count data vary more than a model assumes. Ignoring it can make uncertainty appear smaller than it is. Whether over-dispersion is relevant depends on the outcome and model; the registry record does not report a count-outcome analysis or the assumptions used for such an analysis. Likewise, the record does not report model diagnostics, sensitivity analyses, multiplicity procedures, or a prespecified hierarchy for outcomes. These omissions limit assessment of how robust any analysis might be, although no numerical efficacy analysis is reported to evaluate in the first place.
The record lists 0 analyses and does not provide numerical results for the named patient-reported outcomes. Thus, methods named in the registry description should not be mistaken for a complete analysis report. A method description indicates how an outcome may be represented, but interpretation also depends on the actual estimates, denominators, follow-up, uncertainty, and analysis decisions.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary survivorship outcome and secondary outcomes assessed with KSS, KOOS, and EQ-5D. It also lists 4 outcome measures and 0 analyses. The registry record does not report whether the outcomes were tested under a prespecified hierarchy, whether adjustments were planned for multiple comparisons, or how any exploratory analyses were distinguished from confirmatory ones. When multiple outcomes or timepoints are examined, the chance of a nominally unusual result can increase; in general, a prespecified multiplicity strategy helps clarify how evidence across outcomes should be interpreted. No such strategy is reported in the registry record.
Information about missing data is also not reported in the registry record. There is no description of missing questionnaire responses, incomplete follow-up, participants lost to follow-up, reasons for missingness, or imputation procedures. For a time-to-event outcome, censoring can be part of the Kaplan-Meier method, but the registry record does not describe censoring rules or whether loss to follow-up was treated in a particular way. Without these details, it is not possible to assess whether missing observations could have affected estimates.
The analysis populations are not reported in the registry record. It does not specify whether analyses included all eligible participants, participants receiving a particular device, or only participants with available follow-up. The record also does not describe exclusions from analysis or how participants who changed treatment or had incomplete assessments were handled. These details are important because the analysis population affects the interpretation of both outcome estimates and safety counts. The registry's non-randomized design makes a clear account of populations and analytic choices especially relevant to understanding any group comparisons.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Operative Adverse Events | 18 | 223 | 8.1% |
| Non-operative Adverse Events | 55 | 223 | 24.7% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Operative Adverse Events | 0 of 223 |
| Non-operative Adverse Events | 9 of 223 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 5% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Operative Adverse Events | 0 of 223 |
| Non-operative Adverse Events | 52 of 223 |
Most frequent serious adverse event terms
| Event term | Organ system | Operative Adverse Events | Non-operative Adverse Events |
|---|---|---|---|
| Non-Operative | Musculoskeletal and connective tissue disorders | 0 of 0 | 16 of 223 |
| Operative | Musculoskeletal and connective tissue disorders | 13 of 223 | 0 of 0 |
| Non-operative | Cardiac disorders | 0 of 0 | 11 of 223 |
| Non-Operative | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 0 | 9 of 223 |
| Non-Operative | Gastrointestinal disorders | 0 of 0 | 6 of 223 |
| Non-Operative | Vascular disorders | 0 of 0 | 5 of 223 |
| Non-Operative | Renal and urinary disorders | 0 of 0 | 4 of 223 |
| Operative | Injury, poisoning and procedural complications | 2 of 223 | 0 of 0 |
| Operative | Skin and subcutaneous tissue disorders | 2 of 223 | 0 of 0 |
| Non-Operative | Eye disorders | 0 of 0 | 1 of 223 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Operative Adverse Events | Non-operative Adverse Events |
|---|---|---|---|
| Elective Procedures | Musculoskeletal and connective tissue disorders | 0 of 0 | 41 of 223 |
| Non-Operative | Musculoskeletal and connective tissue disorders | 0 of 0 | 11 of 223 |
Serious events with the highest arm-level rate: non-operative (7.2%), operative (5.8%), non-operative (4.9%).
The registry reports operative adverse events among 223 participants at risk: 18 were affected by serious operative adverse events, and 0 were affected by other operative adverse events. For non-operative adverse events, 223 participants were listed as at risk; 55 were affected by serious events and 52 by other events. The non-operative group also lists 9 deaths. These are reported counts, not comparative estimates between devices or procedures.
The categories should be read as separate registry groupings: operative and non-operative events. A count of participants affected does not necessarily describe the total number of events, since one participant may experience more than one event; the registry record does not clarify this distinction. The record also does not report the timing, relatedness, event-level details, or distribution of these counts across the device arms. It therefore does not establish that an event or death was caused by a particular device or procedure.
In general, an at-risk denominator gives context for a count, but it does not by itself establish whether groups are comparable or whether follow-up was similar. No rates should be inferred without a defined analysis and follow-up basis. The record's adverse-event figures should be interpreted descriptively, alongside the absence of reported comparative analyses.
12. What the Result Does, and Does Not, Mean
The registry record establishes that a non-randomized, parallel-model study was intended to collect information on surgical and implant performance and patient clinical outcomes for people eligible for total knee arthroplasty or partial knee resurfacing. It names three device systems, gives survivorship as the primary outcome, and lists KSS, KOOS, and EQ-5D as secondary patient outcome measures. The record also contains descriptive adverse-event counts.
It does not report a numerical primary outcome analysis. The registry states that the 10-year survivorship outcome was not analyzed because the study terminated, and numerical results for earlier timepoints are not reported in the registry record. It also does not report analyzed results for the secondary measures. Thus, the record cannot establish the magnitude, precision, or direction of a clinical difference in survivorship or patient-reported outcomes.
Even if group estimates were available, non-random allocation would limit causal interpretation. Differences between the arms could reflect differences in eligibility or other characteristics as well as differences associated with a device or procedure. The record cautions that the arms are not a like-for-like control comparison. No adjustment plan or sensitivity analysis is reported to clarify how such differences were addressed.
The adverse-event counts provide descriptive safety information, but do not identify whether events were related to a device or procedure or whether their frequency differed between arms. The listed number of deaths is not accompanied by causal attribution or further event details. These counts should not be treated as proof for or against safety.
In short, the registry describes the study's purpose, design, endpoints, and some adverse-event counts, but it does not report analyzed clinical outcome results. It therefore does not support a conclusion that any named system or procedure is superior, equivalent, or inferior. It also does not establish long-term survivorship at 10 years.
13. Why This Trial Matters Statistically
This record is statistically instructive because it distinguishes an outcome definition from an outcome result. A registry can specify survivorship, its follow-up timepoints, and a Kaplan-Meier method without reporting the estimates needed to interpret survivorship. Readers need the estimates, analysis populations, uncertainty, and follow-up details to assess what the observed data say. Those numerical primary results are not reported in the registry record.
The non-randomized design is another important feature. In general, comparisons between non-randomized groups can be affected by differences in who receives each procedure or device. A parallel layout does not itself make groups comparable. The registry explicitly notes that the arms are not a like-for-like control comparison, a caution that should guide interpretation of any apparent contrast.
The record also illustrates why planning calculations must be distinguished from evidence observed in a study. The stated sample-size assumptions generate planning illustrations based on an observed effect; they are not observed power and do not replace the trial's own design justification. The registry does not report that justification or a detailed statistical plan.
Finally, endpoint follow-up and study status matter. The intended survivorship measure includes timepoints through 5 years, while the 10-year outcome was unavailable because the study terminated. A registry entry can therefore preserve the research question and some descriptive safety information even when it does not provide a complete outcome analysis. For statisticians and clinical researchers, this is a reminder to separate the stated aims, available counts, and analyzed estimates rather than treating them as interchangeable 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 most consequential limitation of the registry record is the absence of numerical efficacy results. It describes survivorship and patient-reported outcomes but does not report the estimates, uncertainty, or analyses needed to evaluate them. The 10-year survivorship outcome was explicitly not analyzed because the study terminated. Although earlier follow-up timepoints are named, their numerical results are not reported in the registry record.
Non-random allocation limits interpretation of comparisons. Patients were described as eligible for different devices or procedures, and the registry states that the arms are not a like-for-like control comparison. The record does not report eligibility details, baseline characteristics, reasons for device selection, or an adjustment strategy. It is therefore not possible to determine how well groups were comparable or how potential confounding was addressed.
Further limitations arise from incomplete reporting of analytic details. The statistical plan, analysis populations, handling of missing data, censoring rules, multiplicity procedures, and sensitivity analyses are not reported in the registry record. These omissions prevent a detailed assessment of the assumptions and robustness of any estimates. The listed adverse-event counts are not accompanied by arm-specific results, event timing, relatedness, or definitions beyond the operative and non-operative categories. The record does not clarify whether counts represent participants with events or the number of individual events in every category.
The registry lists enrollment of 237 and a terminated status, but does not report the reasons for termination or whether recruitment and follow-up proceeded as planned. It also does not report a sample-size justification for the study. These gaps constrain assessment of the study's completeness and precision, independently of the non-randomized design.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Stryker NTX Registry Scorpio NRG (Re-"Energize"), Triathlon Total Knee, Triathlon Partial Knee Resurfacing (PKR) With X3 Polyethylene Insert — NCT02525562.
- Registry record last updated 2024-02-22; status last verified 2024-02.
- Results first posted 2023-03-14.
- 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.
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18. Record Summary
NCT02525562 is a terminated, non-randomized, parallel-model registry study sponsored by Stryker Orthopaedics. Its listed enrollment is 237, and the record names total knee replacement and partial knee resurfacing systems with X3 inserts. The primary outcome is device survivorship, defined as participants free from revision, with follow-up described through 5 years. The 10-year survivorship outcome was not analyzed because the study terminated. Secondary outcomes include KSS, KOOS, and EQ-5D. The record lists operative and non-operative adverse-event counts, but does not report numerical primary outcome analyses or analyzed secondary results. It cautions that the arms are not a like-for-like control comparison.