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 Triathlon® Partial Knee Replacement (PKR) Outcomes Study (NCT00966979), a na na study. The primary outcome is Investigation of Clinical Performance and Patient Outcome With the Functional Knee Society Score (KSS)..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00966979 |
| Phase | NA |
| Condition | Arthroplasty, Replacement, Knee |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 111 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Stryker Orthopaedics |
| Results posted | Yes |
2. Clinical Question
The study’s stated purpose was to compare 10-year Knee Society Score (KSS) functional results for the Triathlon PKR Unicondylar Knee with results for the Triathlon Cruciate Retaining (CR) Total Knee. The primary outcome described in the registry, however, is the KSS Function Score at 10 years for participants receiving Triathlon PKR. The record identifies the study as a single-group study and lists Triathlon PKR as its intervention.
Population
The registry lists 111 enrolled participants and a condition of knee arthroplasty. Eligibility criteria and detailed participant characteristics are not reported in the registry record. For the 10-year primary outcome, only 12 prospective cases reached that time point; no retrospective cases did.
Intervention
All enrolled participants were to receive the Triathlon PKR device, described as a partial knee resurfacing unicondylar knee system. The study is prospective, post-market, and multi-center according to its official title.
Comparator
The study purpose names the Triathlon CR Total Knee as the comparison, but the registry lists no comparator intervention or second study group. A like-for-like comparative result is therefore not reported in the registry record.
Primary question
What was the mean 10-year KSS Function Score among the prospective Triathlon PKR cases who reached that follow-up point, and how precisely was it estimated? The numerical score, its standard deviation, and an inferential comparison are not reported in the registry record.
3. Trial Design
This is a prospective, post-market, multi-center study of the Triathlon PKR Unicondylar Knee System. The registry classifies it as a single-group study, with no masking and allocation marked NA. The intervention description says all enrolled participants would receive Triathlon PKR. These details describe an observational follow-up structure around a device intervention, not a randomized comparison between treatment groups.
The registry lists enrollment of 111. The study start is recorded as 2010-01, primary completion as 2022-09, and status as terminated. The record does not state why the study was terminated. It also does not report the recruitment process, participating center names, eligibility criteria, or whether the recorded enrollment represents every participant who began follow-up.
The brief summary describes a planned comparison of 10-year functional KSS results between Triathlon PKR and Triathlon CR Total Knee. Yet the listed intervention and arm description include only Triathlon PKR. No control group, external comparison source, or comparative analysis is recorded. Thus, the stated purpose should not be mistaken for evidence that a direct comparative analysis was completed.
The primary outcome is the KSS Function Score at 10 years, reported as a mean with standard deviation. The record also lists 10-years Kaplan Meier Survival Analysis as a secondary outcome. It gives two outcome measures and no analysis entries. The primary outcome was reached by only 12 prospective cases; no retrospective cases reached the 10-year time interval. The record does not describe how the prospective and retrospective cases were defined, or how participants who did not reach 10 years were handled.
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: Of the 111 participants enrolled, there were 23 cases that were censored due to not having the study device, surgery canceled or an inclusion exclusion violation. Therefore, 89 knees in 88 participants are followed who did receive the study device and met protocol criteria. Those applicable data are reflected in this record.
Overall Study
| Stage | Triathlon PKR Unicompartmental Knee |
|---|---|
| STARTED | 111 |
| COMPLETED | 13 |
| NOT COMPLETED | 98 |
Reasons for not completing this period:
| Reason | Triathlon PKR Unicompartmental Knee |
|---|---|
| Death | 1 |
| Lost to Follow-up | 6 |
| Withdrawal by Subject | 14 |
| Adverse Event | 5 |
| Sponsor terminated early | 49 |
| Censored because surgery not done | 2 |
| Censored because study device was not implanted | 14 |
| Censored because of Inclusion/exclusion violation | 7 |
Analysis population for the primary outcome, as defined in the registry: Due to early study termination the primary outcome was only reached for a minimal number of participants (12) reaching 10 years. These only included prospective cases. No retrospective cases reached the 10-year time interval.
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.
| Characteristic | Unit | Triathlon PKR |
|---|---|---|
| Participants analysed | 88 | |
| Age, Continuous | years | 61.83 (44 to 76) |
| Sex: Female, Male: Female | Participants | 39 |
| Sex: Female, Male: Male | Participants | 49 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 1 |
| Race (NIH/OMB): Asian | Participants | 1 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 |
| Race (NIH/OMB): Black or African American | Participants | 0 |
| Race (NIH/OMB): White | Participants | 86 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 0 |
6. Primary Endpoint
The registry lists the primary outcome as Investigation of Clinical Performance and Patient Outcome With the Functional Knee Society Score (KSS)., measured over 10 years.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | units on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is the KSS Function Score at 10 years. The registry describes the broader Knee Society Score as having distinct components: a Pain/Motion KSS covering pain, range of motion, joint stability, and alignment, and a Functional KSS covering distance walked, stair climbing, and use of walking aids. The endpoint specified for this study is the Function Score, rather than a combined score or the Pain/Motion component.
The Function Score runs from 0 to 100, with 100 representing a better outcome. The record says scores are not classified into categories such as excellent, good, fair, or poor; interpretation is based on the score value, with higher values representing a better outcome. The planned summary measure is the mean, accompanied by a standard deviation. The mean describes the average score among the analyzed observations, while the standard deviation describes how spread out individual scores are around that average.
Functional status is a relevant way to describe what participants can do in daily mobility tasks after knee replacement. It captures walking distance, stair climbing, and walking-aid use, rather than focusing solely on joint symptoms or structural features. The endpoint can therefore characterize function in participants assessed at the specified follow-up. However, its meaning depends on who was assessed and how complete follow-up was. The registry reports that only 12 prospective cases reached the 10-year point and gives no numerical mean or standard deviation. The actual functional result and its precision are consequently not reported in the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies a clinically interpretable outcome: the 10-year KSS Function Score, on a scale where higher scores represent better function. But the record does not give the observed mean, standard deviation, confidence interval, or test result. It is therefore not possible to describe the level of function observed at 10 years, how variable the scores were, or how precisely the mean was estimated from this record.
The follow-up information is important to interpretation. The record states that only 12 prospective cases reached the primary outcome time point because of early termination, and that no retrospective cases reached 10 years. This makes the reported endpoint applicable only to the small subset of prospective cases that reached that assessment, not automatically to all enrolled participants. The registry does not report reasons participants failed to reach the time point, or whether those who did differed from those who did not.
The study’s stated purpose refers to comparison with Triathlon CR Total Knee, but the listed design is single-group and the intervention description includes Triathlon PKR only. No comparator group or comparative result is recorded. Consequently, the registry record cannot establish a difference between the two systems. Nor can an uncontrolled mean, if reported elsewhere, by itself separate device outcomes from changes over time, participant characteristics, or other influences.
The registry lists a Kaplan-Meier survival analysis as a secondary outcome, but no survival estimates or analysis entries appear in the record details available for this analysis. The time-to-event result, definition of survival, event counts used for that outcome, and handling of censoring are not reported in the registry record. Those omissions prevent interpretation of long-term survival from the stated outcome title alone.
Likewise, the record’s adverse-event counts describe reported events in operative and non-operative categories, but do not establish whether events were caused by the device or procedure. The counts should be read alongside their at-risk denominators and category labels, not as a comparative safety estimate. Overall, the registry supports a description of the planned endpoint, design, and follow-up limitation, but not a conclusion about the magnitude or certainty of a 10-year outcome or a comparative effect.
9. Statistical Methods Explained
The statistical methods that were actually used are not reported in the registry record. The outcome description specifies a mean and standard deviation for a continuous score, but that does not reveal the analysis population, treatment of incomplete observations, confidence interval method, or any hypothesis test. The registry lists no analysis entries. The following concepts explain how such methods are generally interpreted; they do not assert that the study used them.
What does a mean and standard deviation describe?
For a continuous measure such as the KSS Function Score, a mean is an average across the observations included in an analysis. It provides a concise description of the group’s central score, but does not show the individual score distribution. The standard deviation describes variability among observations around the mean. A larger standard deviation indicates more spread in scores, while a smaller one indicates scores are more concentrated. Neither statistic alone establishes how precisely the mean estimates a broader population value.
That precision is commonly conveyed with a confidence interval. In general, a confidence interval gives a range of values compatible with the observed data under a specified statistical procedure and assumptions. Its width depends on factors such as variability and the amount of usable information. A confidence interval for a mean would help readers judge the estimate’s precision, but no such interval is reported in the registry record. A p-value, if used, would address compatibility with a specified null hypothesis under the test assumptions; it would not measure clinical importance or prove that a result is true. No p-value is reported.
What would a group comparison require?
A direct comparison of PKR and CR Total Knee outcomes requires outcome data for both groups and a defined contrast between them. The registry describes only one intervention group. Even if an external or historical comparator had been used, the source and methods for that comparison would need to be stated to assess comparability and bias. They are not reported in the registry record. The study’s purpose statement alone does not establish that a comparison was conducted.
How should a survival analysis be understood?
Kaplan-Meier analysis is a general method for describing the time until an event, while allowing for participants whose event status is not known through the end of observation. Such participants contribute information until their last known follow-up and are then censored. Interpretation depends on a clearly defined event, follow-up start, censoring rules, and sufficient follow-up. The registry names a 10-years Kaplan Meier Survival Analysis as a secondary outcome, but the event definition, survival estimate, uncertainty interval, and details of censoring are not reported in the registry record. The outcome name alone cannot establish the method’s implementation or result.
What do planning calculations mean?
Sample-size planning uses assumptions about the target effect, variability, significance level, allocation, and analysis method to illustrate how much information a future study might need. The planning assumptions associated with this record describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They describe an illustration based on a fraction of the observed effect, not the trial’s own design. They cannot be interpreted as observed power, and they do not show that the completed study was planned or conducted as a two-arm comparison. The planning outputs and the trial’s own sample-size justification are not reported in the registry record.
For a time-to-event planning calculation, the assumptions state that the total number of events is used; other planning illustrations express participants per arm. These conventions are relevant to understanding any such estimates, but the actual planning values are not reported in the registry record. In general, planning results are conditional on their assumptions and should not be treated as observed trial findings.
Why does over-dispersion matter?
Over-dispersion is a general concern when the variability in observed data is greater than a model assumes. If a statistical model understates variability, standard errors may be too small and confidence intervals too narrow, making results appear more precise than warranted. For a continuous score, the observed standard deviation helps describe variation, while the choice of model and any adjustments depend on the data and design. The registry does not report an over-dispersion assessment or any model-based adjustment. It would be inappropriate to infer that such a concern was present or addressed.
Finally, interpretation of any analysis depends on who contributed outcome data and how missing follow-up was handled. The registry notes limited availability at the 10-year endpoint but does not give participant-level follow-up patterns, reasons for missingness, or an analysis strategy. Those details are necessary for assessing possible selection effects and the reliability of an endpoint estimate.
10. Confidence Intervals for Each Arm
No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.
| Arm | Participants | Mean | Standard deviation | 95% CI for the mean |
|---|---|---|---|---|
| Triathlon PKR Unicompartmental Knee | 12 | 98.330 | 5.770 | 94.664 to 101.996 |
R code and output
arm <- c("Triathlon PKR Unicompartmental Knee")
n <- c(12)
m <- c(98.33)
sp <- c(5.77)
sd <- sp # posted standard deviations
for (i in seq_along(n)) {
se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}
CARM Triathlon PKR Unicompartmental Knee 12 98.330 5.770 94.664 101.99611. Multiplicity, Missing Data and Analysis Populations
The registry lists two outcome measures: the 10-year KSS Function Score as the primary outcome and 10-years Kaplan Meier Survival Analysis as a secondary outcome. It does not report a statistical analysis plan, a hierarchy for testing outcomes, an adjustment for multiple comparisons, or whether any outcomes were added or changed after study initiation. A multiplicity strategy is therefore not reported in the registry record. Without that information, the record does not show how the chance of false-positive findings across multiple analyses would have been addressed.
The record lists no analysis entries. It also does not report endpoint estimates, confidence intervals, p-values, or a detailed description of which participants contributed to each outcome. The primary outcome population is described as only 12 prospective cases reaching 10 years, with no retrospective cases reaching that time point. The handling of participants without a 10-year assessment is not reported in the registry record.
Missing-data methods matter because participants who are not observed at long-term follow-up may differ from those who are observed. In general, an analysis limited to observed follow-up can be vulnerable to selection if the probability of being observed is related to outcomes or participant characteristics. Other approaches require assumptions about missingness and should be explicitly described. No missing-data assumptions, imputation, sensitivity analysis, or follow-up accounting are reported in the registry record.
The record also does not identify an intention-to-treat population, a per-protocol population, or another analysis population for the primary endpoint. The phrase “prospective cases” identifies the cases that reached the time point, but does not specify all inclusion rules. As a result, the generalizability and potential selection effects of any endpoint summary cannot be evaluated from the registry description alone.
12. 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 | 11 | 89 | 12.4% |
| Non-Operative Adverse Events | 20 | 88 | 22.7% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Operative Adverse Events | 0 of 89 |
| Non-Operative Adverse Events | 1 of 88 |
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 | 26 of 89 |
| Non-Operative Adverse Events | 0 of 88 |
Most frequent serious adverse event terms
| Event term | Organ system | Operative Adverse Events | Non-Operative Adverse Events |
|---|---|---|---|
| Operative site | Musculoskeletal and connective tissue disorders | 10 of 89 | 0 of 0 |
| Non-operative | Cardiac disorders | 0 of 0 | 6 of 88 |
| Non-operative | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 0 | 4 of 88 |
| Non-operative | Gastrointestinal disorders | 0 of 0 | 3 of 88 |
| Non-operative | General disorders | 0 of 0 | 2 of 88 |
| Non-operative | Renal and urinary disorders | 0 of 0 | 2 of 88 |
| Operative site | Injury, poisoning and procedural complications | 1 of 89 | 0 of 0 |
| Non-operative site | Psychiatric disorders | 0 of 0 | 1 of 88 |
| Non-operative | Respiratory, thoracic and mediastinal disorders | 0 of 0 | 1 of 88 |
| Non-operative | Vascular disorders | 0 of 0 | 1 of 88 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Operative Adverse Events | Non-Operative Adverse Events |
|---|---|---|---|
| Operative | Musculoskeletal and connective tissue disorders | 26 of 89 | 0 of 88 |
Serious events with the highest arm-level rate: operative site (11.2%), non-operative (6.8%), non-operative site (1.1%).
The registry separates adverse events into operative and non-operative categories and reports serious events, other events, and deaths. For operative adverse events, it lists 89 at risk, 11 serious affected, 26 other affected, and 0 deaths. For non-operative adverse events, it lists 88 at risk, 20 serious affected, 0 other affected, and 1 death. These are category-specific entries; they should not be added together to create an overall count because the record does not explain whether categories or event reports can overlap.
The registry also identifies the leading serious-event terms as Operative site at 11.2%, Non-operative at 6.8%, and Non-operative site at 1.1%. These entries describe the terms and percentages as recorded, but the record does not explain the calculation details or provide a comparative safety analysis. The percentages should not be interpreted as a comparison between devices, since the listed design has one intervention group and no comparator.
Serious-event counts do not by themselves establish causation. The registry entries do not report whether events were judged related to the device or procedure, how severity was defined, how long each participant was observed for safety, or how repeated events were handled. The death entry is a reported count, not an attribution. Accordingly, these figures describe recorded safety categories and require caution; they do not establish that the device caused or prevented any event.
13. What the Result Does, and Does Not, Mean
The registry record documents a prospective, post-market study of Triathlon PKR with a planned 10-year functional outcome. It identifies the KSS Function Score, explains what the score covers, and states that higher scores represent better function. It also reports that early termination limited the primary outcome follow-up: only 12 prospective cases reached 10 years, and no retrospective cases reached that interval.
Those details do not reveal the observed 10-year functional score. The numerical mean and standard deviation are not reported in the registry record, nor are confidence intervals or a test result. Without those statistics, the endpoint’s value, variability, and precision cannot be described. The limited number of prospective cases reaching the time point also means that any result based on them would need to be interpreted as a result for the observed follow-up subset, rather than assumed to represent all enrolled participants.
The stated aim of comparing PKR with CR Total Knee does not establish a comparative finding. The registry lists a single-group design and Triathlon PKR as the intervention, with no comparator group or comparison result recorded. The registry therefore does not show whether outcomes differed between the named systems.
Nor do the adverse-event figures establish a causal safety effect. They are descriptive entries without reported attribution or a comparison group. The secondary survival outcome is named, but its estimates and methods are not reported. Taken together, the record documents the research question and important limitations, but it does not provide enough statistical results to determine the size, precision, or comparative meaning of the primary outcome.
14. Why This Trial Matters Statistically
This study illustrates the distinction between a planned clinical question and the evidence available to answer it. The brief summary describes a comparison of 10-year functional results, while the registered design lists one intervention group. Statistical interpretation must follow the data structure actually recorded, not infer a controlled comparison from the stated purpose.
Long-term outcomes also depend on follow-up completeness. The primary endpoint is intended for 10 years, but the registry says only 12 prospective cases reached that time point and no retrospective cases did. Such attrition can limit precision and can affect representativeness if those with follow-up differ from those without it. Without participant flow and missing-data methods, readers cannot assess the direction or extent of potential selection effects.
The record further shows why an endpoint definition is not a result. The KSS Function Score is described clearly, including its scale and the activities it measures, but the numerical endpoint summary is not reported. Understanding the scale is useful, but it cannot substitute for the observed mean, variability, and uncertainty.
Finally, the registry’s listed secondary survival outcome and safety categories require their own definitions and analysis details. An outcome label, an event count, or a percentage is not enough to support a causal or comparative interpretation. The statistical value of this record is therefore in clarifying the intended endpoint and identifying important gaps—especially the single-group structure, limited long-term follow-up, and absence of reported analysis results.
15. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
The most direct limitation is that the registry reports no numerical primary-outcome result. The mean KSS Function Score, its standard deviation, and any estimate of uncertainty are not reported in the registry record. The stated primary endpoint can therefore be described, but its observed level and precision cannot be evaluated from this record.
Early termination curtailed long-term follow-up. Only 12 prospective cases reached 10 years, and no retrospective cases did. The registry does not explain why termination occurred, why participants did not reach the endpoint, or whether missing follow-up was related to participant status or outcome. It also does not give a participant-flow account or an analysis population definition.
The design information limits comparative conclusions. Although the study purpose names the Triathlon CR Total Knee as a comparator, the registry records a single group receiving Triathlon PKR and provides no comparator arm or comparative results. The record does not explain whether the stated comparison was pursued through another data source or a separate study.
Further limitations include the absence of analysis details, confidence intervals, p-values, a statistical analysis plan, and methods for multiplicity or missing data. The secondary survival outcome is named without a reported event definition, estimate, or censoring details. Safety entries lack reported attribution and a comparative context. These omissions mean that the registered descriptions cannot be used to establish either a device effect or a causal explanation for adverse events.
16. Related Tutorials
17. Related Statistical Calculators
18. Sources
- ClinicalTrials.gov: Triathlon® Partial Knee Replacement (PKR) Outcomes Study — NCT00966979.
- Registry record last updated 2023-09-13; status last verified 2023-08.
- Results first posted 2023-09-13.
- 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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19. Record Summary
NCT00966979 is a prospective, post-market, multi-center study of Triathlon PKR, listed as a single-group study with 111 enrolled participants. Its primary outcome is the mean KSS Function Score at 10 years, with standard deviation; higher scores on the 0-100 scale represent better function. The study status is terminated, and the registry records primary completion as 2022-09.
The registry states that only 12 prospective cases reached the primary outcome time point and that no retrospective cases reached 10 years. It describes a planned comparison with Triathlon CR Total Knee, but lists no comparator group or comparative result. Numerical primary-outcome results and analysis entries are not reported in the registry record. A Kaplan-Meier survival analysis is listed as a secondary outcome, and adverse-event entries are reported in operative and non-operative categories.