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 Scorpio Posterior Stabilised (PS) vs Scorpio NRG ("Energize") PS - Total Knee Arthroplasty (NCT02520531), a randomized na study. The primary outcome is Comparison of Maximum Passive and Active Flexion..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT02520531 |
| Phase | NA |
| Condition | Arthroplasty, Replacement, Knee |
| Allocation | Randomized |
| Design model | Parallel |
| Masking | Double |
| Enrollment | 84 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Stryker Orthopaedics |
| Results posted | Yes |
2. Clinical Question
Population
People on the waiting list for a total knee prosthesis who met the study’s inclusion and exclusion criteria were eligible to be asked to participate. The registry describes a single-centre study and reports 84 participants enrolled. At the five-year follow-up, data from 36 participants per study arm were analyzed for the primary outcome. Further details about participant characteristics and eligibility criteria are not reported in the registry record.
Intervention
The intervention was total knee replacement with the Scorpio NRG PS prosthesis, also called “Energize” in the study title. It is described as a posterior-stabilized device. The registry does not report additional details about the surgical procedure, implant positioning, or rehabilitation.
Comparator
The comparator was total knee replacement with the Scorpio PS prosthesis, also described as posterior stable. Participants were randomized to receive one of the two devices. Details about the randomization sequence and how treatment assignment was concealed are not reported in the registry record.
Primary question
The study compared maximum passive and active knee flexion between the two prosthesis groups at five years of follow-up. Flexion is the bending movement of the knee, recorded in degrees. The registry also describes tolerated ranges for active and passive flexion and for hyperextension, and states that higher scores mean a better outcome. It does not report the observed mean flexion values, their standard deviations, or a numerical estimate of the difference between groups.
3. Trial Design
This was a prospective, randomized, double-blind, parallel-group comparative study at a single centre. The study status is completed, and the registry reports enrollment of 84 participants. The listed devices were the Scorpio PS and the Scorpio NRG PS total knee replacements. Participants who met the stated eligibility criteria and were waiting for a total knee prosthesis were asked to participate and randomized to one of the devices.
The registry gives a study start of 2010-09 and a primary completion date of 2018-06-28. The primary outcome was assessed at five years of follow-up. The registry reports that data from 36 participants in each study arm were analyzed for that outcome. The serious-adverse-event record lists 42 participants at risk in each arm. These figures describe different registry entries and should not be treated as an explanation of participant flow: reasons for the difference between enrollment and the primary analysis population are not reported in the registry record.
“Randomized” describes assignment by chance rather than by a participant’s or clinician’s choice. A parallel design means that participants were assigned to one device group, rather than crossing between both devices. The registry labels the study double-blind, but does not specify which people were masked or how masking was maintained. The method used to generate the randomization sequence, allocation concealment, and any steps to reduce differences in care beyond the assigned device are not reported.
The registry names four secondary outcomes: the Knee Society Score, Chair Raise Test, WOMAC Patient Questionnaire, and EQ-5D Patient Questionnaire. It also states that complications were documented. The study phase is listed as not applicable. A protocol, detailed eligibility criteria, and a sample-size justification 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.
Overall Study
| Stage | Scorpio PS | Scorpio NRG PS |
|---|---|---|
| STARTED | 42 | 42 |
| COMPLETED | 36 | 36 |
| NOT COMPLETED | 6 | 6 |
Reasons for not completing this period:
| Reason | Scorpio PS | Scorpio NRG PS |
|---|---|---|
| Revision of study device components | 2 | 2 |
| Death | 1 | 2 |
| Lost to Follow-up | 1 | 1 |
| Meet exclusion criterion | 0 | 1 |
| Withdrawal by Subject | 1 | 0 |
| Not study device | 1 | 0 |
Analysis population for the primary outcome, as defined in the registry: At the 5 years follow-up data of 36 participants per study arm were analyzed.
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 | Scorpio PS | Scorpio NRG PS | Total |
|---|---|---|---|---|
| Participants analysed | 42 | 42 | 84 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 19 | 15 | 34 |
| Age, Categorical: >=65 years | Participants | 23 | 27 | 50 |
| Age, Continuous | years | 65.44 (SD 8.01) | 66.22 (SD 8.09) | 65.83 (SD 8.06) |
| Sex: Female, Male: Female | Participants | 18 | 19 | 37 |
| Sex: Female, Male: Male | Participants | 24 | 23 | 47 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Region of Enrollment: Netherlands | participants | 42 | 42 | 84 |
6. Primary Endpoint
The registry lists the primary outcome as Comparison of Maximum Passive and Active Flexion., measured over 5 years follow-up.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | degree |
| Endpoint classification | Continuous Endpoint |
The primary endpoint was a comparison of maximum passive and active flexion of the knee between the Scorpio NRG PS and Scorpio PS groups at five years of follow-up. Flexion measures how far the knee can bend, expressed in degrees. Passive flexion concerns movement when the knee is moved without the participant actively producing the movement; active flexion concerns movement produced by the participant. These measures describe different aspects of knee movement, so both were included in the endpoint.
Range of motion is a continuous measure: its recorded value can vary across a scale rather than falling into only a small set of categories. The registry specifies that the result is summarized as a mean with a standard deviation. A group mean describes the average recorded flexion, while the standard deviation describes how dispersed individual measurements are around that mean. The registry says that higher scores mean a better outcome and gives tolerated ranges for active flexion, passive flexion, and hyperextension.
Flexion is relevant to a comparison of knee prostheses because it describes movement after surgery. However, an endpoint definition is not a result. The registry record does not report the mean values, standard deviations, confidence intervals, or statistical test results for passive or active flexion. It therefore does not establish how the groups’ observed measurements compared or how precisely any difference was estimated.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry identifies a randomized comparison of two knee prostheses and specifies maximum passive and active flexion at five years as the primary outcome. It also identifies 36 analyzed participants per arm for that outcome. These details describe the question and the analysis population, but they are not enough to interpret the direction or size of the observed outcome.
The outcome values needed for a numerical comparison are not reported in the registry record. In particular, the record does not give the arm-specific means or standard deviations for passive or active flexion, an estimated difference between groups, a confidence interval, or a p-value. Without those statistics, the posted record cannot show whether one group had a higher mean, how variable the measurements were, or how precisely a between-group difference was estimated. No conclusion about comparative performance follows from the allocation or study design alone.
The registry states that higher scores mean a better outcome and provides tolerated ranges for active and passive flexion and hyperextension. These descriptions help explain how the measurement is framed, but they do not substitute for the missing group results. A stated threshold or tolerated range does not reveal how many participants reached it, nor does it provide a group-level comparison.
The study was randomized, which is a design feature intended to support a fair comparison by making treatment assignment independent of participant choice. It does not guarantee that all sources of bias were eliminated, and the registry does not provide the details needed to assess sequence generation, allocation concealment, or who was masked. The five-year analysis population is reported, but the reasons that not all enrolled participants appear in that analysis are not reported in the registry record.
The registry lists secondary measures covering knee function, a chair-raise task, a patient-reported knee questionnaire, and health status. Results for these measures are not reported in the registry record. The record lists serious adverse-event counts and deaths, but without a statistical analysis or contextual information those figures should be read as descriptive reporting rather than as evidence that a device caused an event or that the groups differed reliably.
Overall, the registry record supports a description of the design, measured outcomes, and reported safety counts. It does not provide the outcome estimates required to judge the magnitude, direction, or precision of the primary comparison. The study’s completion status is administrative information, not evidence of a particular result.
9. Statistical Methods Explained
What does a randomized parallel-group comparison mean?
In a randomized study, participants are assigned to study groups by chance. This is intended to reduce systematic differences between groups at the point of assignment. Randomization does not ensure that the groups will be identical in every characteristic, especially in a study with a limited number of participants. It also does not remove the need to report how the sequence was generated and how assignment was concealed. Those details are not reported in the registry record.
A parallel-group design compares people assigned to one intervention group with people assigned to another. Here, the two groups received different knee prostheses. The registry labels the study double-blind, but does not identify who was unaware of assignment or describe how masking was implemented. These missing details limit assessment of how well expectations or knowledge of treatment could have influenced care, measurement, or reporting.
How should a mean and standard deviation be understood?
The primary outcome is continuous and is specified as a mean with a standard deviation. A mean summarizes the central value of the observations in a group. The standard deviation describes how much individual measurements typically vary around that group’s mean. The two statistics convey different information: a mean alone does not show how spread out observations are, and a standard deviation alone does not show the group’s average level.
To compare groups, researchers can estimate a difference between their means. That estimate describes the observed separation in average values, while a confidence interval describes the range of values compatible with the data under the statistical model and procedure used. General statistical interpretation depends on both the estimated effect and its uncertainty; a p-value alone would not describe the size or practical meaning of an effect. The registry record does not report the group means, standard deviations, between-group estimate, confidence interval, or p-value for the primary outcome.
Why does analysis population matter?
The registry says that five-year primary-outcome data from 36 participants per arm were analyzed. That specifies the reported analysis population for the endpoint, but does not explain how participants entered or were excluded from that analysis. A reader would need the participant flow, reasons for missing follow-up, and analysis-population definition to assess whether the groups remained comparable in the analysis. Those details are not reported in the registry record.
Missing outcome data can affect interpretation if participants with unavailable measurements differ from those with observed measurements. Statistical approaches to missing data make assumptions about why values are missing and how missing values relate to observed information. The registry does not report the amount or pattern of missing primary-outcome data beyond the stated analysis population, any imputation method, or sensitivity analyses. It is therefore not possible to assess the robustness of the reported analysis to missing data from this record.
What is multiplicity, and why can it matter?
Multiplicity arises when several outcomes, comparisons, time points, or analyses are examined. When many statistical tests are conducted, the chance of finding at least one apparently unusual result by chance can increase. Common approaches include identifying a primary endpoint in advance, adjusting the testing threshold, or interpreting secondary analyses as exploratory. Which approach is appropriate depends on the study plan and the questions being addressed.
The registry identifies a primary flexion comparison and lists secondary outcomes: the Knee Society Score, Chair Raise Test, WOMAC Patient Questionnaire, and EQ-5D Patient Questionnaire. The registry also indicates five outcome measures. It does not report a statistical plan for controlling multiplicity, the planned hierarchy of outcomes, or the number of analyses conducted. No analysis count is reported. The handling of multiple outcomes and time points is therefore not reported in the registry record.
What do the planning assumptions mean?
Planning sample sizes are not findings from the trial and are not observed power. The stated planning illustration uses a two-sided significance level of 0.05, equal allocation, and a normal approximation, with the effect to detect expressed as a fraction of the observed effect. Such an illustration describes sample sizes under specified assumptions; it does not show that the study had a particular probability of detecting a true effect after the data were collected. The registry does not report its own sample-size justification or the assumptions used to plan enrollment.
In general, power depends on the assumed effect, variability, analysis method, and sample size. For a continuous outcome, over-dispersion means that the measurements vary more than an assumed model anticipates. Greater variability can make a group comparison less precise and can reduce the ability to distinguish an effect from random variation. This is a general statistical point; the registry does not report evidence of over-dispersion or an assessment of model fit for this endpoint.
The stated assumptions alone do not supply the missing outcome estimates. Because the registry does not report the observed means, variability, or inferential results, it is not possible to determine from the record whether the primary comparison was statistically distinguishable, or how narrow or wide an interval around an estimate would be.
10. Multiplicity, Missing Data and Analysis Populations
The registry identifies maximum passive and active flexion as the primary outcome and names four secondary outcomes: the Knee Society Score, Chair Raise Test, WOMAC Patient Questionnaire, and EQ-5D Patient Questionnaire. It also reports five outcome measures. Multiple outcomes can raise a multiplicity question because the chance of an apparently notable result can increase when many comparisons are tested. The registry does not report whether an adjustment was planned, whether outcomes were tested in a hierarchy, or how multiple time points or analyses were handled. The statistical plan for multiplicity is not reported in the registry record.
The record gives the number of participants whose data were analyzed for the primary endpoint at five years: 36 per arm. It does not provide a participant-flow account, the number of missing measurements, reasons for missingness, or the analysis population definition. It also does not report an imputation procedure or sensitivity analyses. Consequently, the impact of missing data on the comparison cannot be assessed from the registry record.
The registry reports no analysis count. That does not establish that no analyses were performed; it means analysis details are not reported in the registry record. The approach to intention-to-treat or per-protocol analysis, covariate adjustment, outlier handling, and model checking is also not reported. These omissions prevent a full assessment of how the endpoint data were handled and how robust the comparison would be to alternative reasonable analysis choices.
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 |
|---|---|---|---|
| Scorpio PS | 10 | 42 | 23.8% |
| Scorpio NRG PS | 13 | 42 | 31.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Scorpio PS | 1 of 42 |
| Scorpio NRG PS | 2 of 42 |
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 |
|---|---|
| Scorpio PS | 0 of 42 |
| Scorpio NRG PS | 0 of 42 |
Most frequent serious adverse event terms
| Event term | Organ system | Scorpio PS | Scorpio NRG PS |
|---|---|---|---|
| Placement of patella prosthesis | Musculoskeletal and connective tissue disorders | 2 of 42 | 1 of 42 |
| Patella resurfacing | Musculoskeletal and connective tissue disorders | 3 of 42 | 0 of 42 |
| Cardiac Complaints | Cardiac disorders | 2 of 42 | 0 of 42 |
| Arthroscopic Nettoyage of Knee | Musculoskeletal and connective tissue disorders | 2 of 42 | 0 of 42 |
| Lung Cancer | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 1 of 42 | 0 of 42 |
| Hypopharinx Carcinoma | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 42 | 1 of 42 |
| Squamous Cell Cancer | Neoplasms benign, malignant and unspecified (incl cysts and polyps) | 0 of 42 | 1 of 42 |
| Cardiac Collapse | Cardiac disorders | 1 of 42 | 0 of 42 |
| Myocardial Infarction | Cardiac disorders | 0 of 42 | 1 of 42 |
| Urinary Tract Infection | Infections and infestations | 0 of 42 | 1 of 42 |
Serious events with the highest arm-level rate: patella resurfacing (7.1%), cardiac complaints (4.8%), arthroscopic nettoyage of knee (4.8%), placement of patella prosthesis (4.8%), lung cancer (2.4%).
The registry lists 42 participants at risk for serious adverse events in each group. It reports serious adverse events affecting 10 participants in the Scorpio PS group and 13 in the Scorpio NRG PS group. It reports zero participants affected by other adverse events in each group, and deaths of 1 and 2, respectively. These are descriptive counts as entered in the registry; they are not a statistical comparison and do not establish that a device caused an event.
The serious-event terms listed include Patella resurfacing (7.1%), Cardiac Complaints (4.8%), Arthroscopic Nettoyage of Knee (4.8%), Placement of patella prosthesis (4.8%), Lung Cancer (2.4%), and Hypopharinx Carcinoma (2.4%). The registry excerpt does not assign these terms to a particular treatment group or explain whether they refer to participants, event episodes, or a specific follow-up period. It also does not report event timing, severity criteria, relatedness assessments, or confidence intervals for these counts.
Safety counts need context to support comparison, including how events were defined and collected and whether participants could experience more than one event. Without those details, the figures should be read as registry-reported descriptive information, not as evidence of a causal effect or a reliable difference between groups.
12. What the Result Does, and Does Not, Mean
The registry record describes a randomized study comparing two posterior-stabilized knee prostheses and names maximum passive and active flexion at five years as the primary outcome. It reports that five-year data from 36 participants per arm were analyzed. This establishes the study question and the size of the stated analysis population, but the record does not include the numerical results required to answer the comparison.
In particular, the group means and standard deviations, a difference between groups, confidence intervals, and p-values are not reported in the registry record. The direction and size of any observed difference, and the precision with which it was estimated, therefore cannot be determined from the record. The listed tolerated ranges and the statement that higher scores are better help define the outcome but do not reveal the measurements participants achieved.
The same caution applies to the secondary outcomes. Their names are listed, but results are not reported in the registry record. The serious adverse-event counts and deaths are useful descriptive entries, but they do not by themselves show that an event was caused by either device or that the groups differed beyond what might arise from chance. No inference about comparative benefit or harm should be drawn from those counts alone.
More generally, a randomized design can strengthen a comparison when allocation, follow-up, and analysis are conducted and reported appropriately. The record does not provide enough information to assess all of those features, including allocation procedures, participant flow, missing-data handling, and the statistical plan. The completed status indicates that the study is recorded as completed; it does not supply a result or establish a particular conclusion.
The appropriate reading is therefore limited: the registry describes a planned and completed comparison, identifies the primary measurement and analysis population, and records selected safety counts. It does not report enough outcome or inferential information to determine what the primary comparison found or how uncertain that finding was.
13. Why This Trial Matters Statistically
This trial is statistically informative as an example of the difference between a clearly named research question and a fully interpretable result. The registry identifies a randomized, double-blind, parallel comparison of two knee prostheses and specifies a continuous primary outcome at five years. It also states that the outcome is summarized by a mean and standard deviation. These elements help readers understand what the investigators intended to compare.
At the same time, a study design cannot replace outcome reporting. Without the arm-specific means and variability, readers cannot judge the observed flexion values or calculate an interpretable group contrast. Without an estimate and its uncertainty, the magnitude and precision of any comparison remain unknown. The registry’s analysis-population count is useful context, but participant numbers alone do not reveal the outcome distribution or the reliability of a result.
The record also illustrates why reporting the analysis plan matters when several outcomes are named. A primary endpoint is distinguishable from secondary measures, but the registry does not say how multiplicity was handled or how missing data were addressed. Those decisions influence how results should be interpreted and how confidently they can be compared across endpoints.
Finally, descriptive safety counts should be separated from causal conclusions. Counts of serious adverse events and deaths can help characterize what was recorded, but without definitions, timing, group-specific event details, and inferential analysis, they do not establish a difference attributable to a device. The statistical value of the record lies in its design and outcome definitions, while its limits lie in the absence of the estimates and analysis details needed to evaluate the comparison.
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 direct limitation is that the registry record does not report numerical results for the primary outcome. It names maximum passive and active flexion at five years, specifies a mean and standard deviation, and reports 36 analyzed participants per arm, but does not give the means, standard deviations, between-group estimates, confidence intervals, or p-values. The comparative result and its precision therefore cannot be assessed.
The record describes the study as single-centre, which limits the settings represented in the study record. It reports enrollment of 84 participants, while the primary analysis population is reported as 36 participants per arm. Reasons for the difference between these entries, the number of participants with missing follow-up, and the pattern of missing measurements are not reported in the registry record. Generalizability and possible effects of attrition cannot be evaluated from the available details.
Important design and analysis details are also absent. The registry does not describe the randomization sequence, allocation concealment, which groups of people were masked, or how masking was maintained. It does not report the statistical analysis plan, a sample-size justification, the handling of multiplicity, missing-data methods, or sensitivity analyses. The record lists secondary outcomes but does not report their results.
The safety information is limited to summary counts and a list of serious-event terms with percentages. Definitions, timing, relatedness to the devices, group assignment for the listed terms, and methods for collecting events are not reported. These limitations mean the counts cannot support a detailed comparative safety assessment. Taken together, the registry record supports a description of the study but not a comprehensive evaluation of its primary or secondary findings.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Scorpio Posterior Stabilised (PS) vs Scorpio NRG ("Energize") PS - Total Knee Arthroplasty — NCT02520531.
- Registry record last updated 2024-02-22; status last verified 2024-02.
- Results first posted 2019-09-20.
- 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
This completed, single-centre, prospective, randomized, double-blind, parallel-group study compared the Scorpio PS and Scorpio NRG PS total knee prostheses. Enrollment was 84. The primary outcome was maximum passive and active flexion at five years, summarized as a mean and standard deviation; 36 participants per arm were analyzed for this outcome. The registry lists the Knee Society Score, Chair Raise Test, WOMAC Patient Questionnaire, and EQ-5D Patient Questionnaire as secondary outcomes.
The registry reports serious adverse events affecting 10 participants in the Scorpio PS group and 13 in the Scorpio NRG PS group, zero other adverse events affecting participants in either group, and deaths of 1 and 2, respectively. Numerical results for the primary and secondary outcomes, inferential comparisons, and key details of missing-data and multiplicity handling are not reported in the registry record. The design and descriptive entries can be summarized, but the comparative outcome and its precision cannot be determined.