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 A Retrospective Study of the Navio Robotic-assisted Surgical System (NCT03072459), a registered phase not stated study. The primary outcome is Evaluate the Navio™ System for Revisions at 2+ Years Post-surgical Implantation Survivorship.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03072459 |
| Phase | Phase not stated |
| Condition | Surgical Robotics, Knee Replacement |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 128 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Smith & Nephew, Inc. |
| Results posted | Yes |
2. Clinical Question
The study asks whether absence of device revision after implantation can be assessed over follow-up extending to 120 weeks. Its primary outcome is described as overall survivorship, evaluated from baseline through the stated postoperative time points. The registry record also lists assessments of knee function, patient-reported health, and radiographic findings.
Population
The primary analysis population is described as the Safety (SAF) population. It included subjects who received the study device and were present for follow-up visits at specified time points. The record reports enrollment of 128 participants. Further eligibility criteria and the number contributing data at each assessment are not reported in the registry record.
Intervention
The study device was the Navio Robotic-assisted Surgical System. The record describes a retrospective, multi-center cohort study with prospective follow-up. Details of how the system was used in surgery, including procedural protocols and any variation across centers, are not reported in the registry record.
Comparator
The study summary describes comparison to a historical control. The control group’s source, characteristics, size, and outcome data are not reported in the registry record. Allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison.
Primary question
The stated primary question concerns absence of device revision—overall survivorship—through 120 weeks after implantation. Although the endpoint and assessment times are described, the primary outcome estimate, the number of revisions, and an uncertainty estimate are not reported in the registry record.
3. Trial Design
The registry describes a retrospective, multi-center cohort study with prospective follow-up and comparison to a historical control. Enrollment was 128. The study status is completed; the recorded start date is 2017-07-10 and primary completion date is 2017-11-29. The sponsor is Smith & Nephew, Inc.
The design combines retrospective cohort identification with prospective follow-up, according to the brief study summary. The registry record does not report the dates or criteria used to identify the retrospective cohort, the participating centers, or how prospective follow-up was conducted. It also does not report the historical control’s source, recruitment process, or comparability with the Navio cohort.
Allocation is not stated. This is not described as a randomized comparison, and the record cautions that the arms are not a like-for-like control comparison. Without details on the historical controls or an analysis accounting for differences between groups, a direct comparative interpretation would be limited. The record does not report whether any adjustment or matching was planned or performed.
The primary endpoint is described as absence of device revision from baseline through 120 weeks, with assessments listed at 24, 48, 72, 96, and 120 weeks postoperatively. The primary population is the SAF population, defined as subjects who received the study device and were present for follow-up visits at specified time points. The number included at each visit and the handling of participants who missed a visit are not reported in the registry record.
Secondary outcomes include Knee Society Score (KSS) and Veterans RAND 12 (VR-12) assessments, preoperative radiographic findings, and postoperative radiographic evaluations at 6, 12, 18, 24, and 30 months. The registry lists 10 outcome measures and 0 analyses. It does not report a statistical analysis plan, sample-size justification, interim analyses, or results for these outcomes.
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 | Navio Robotic-assisted Surgical System |
|---|---|
| STARTED | 128 |
| COMPLETED | 126 |
| NOT COMPLETED | 2 |
Reasons for not completing this period:
| Reason | Navio Robotic-assisted Surgical System |
|---|---|
| Device revised/removed | 1 |
| Subject not able to return | 1 |
Analysis population for the primary outcome, as defined in the registry: Safety (SAF) population. The SAF population included all subjects who received the study device and were present for follow-up visits at specified time points.
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 | Navio Robotic-assisted Surgical System |
|---|---|---|
| Participants analysed | 128 | |
| Age, Continuous | years | 64.7 (SD 9.6) |
| Age, Customized: < 60 years | Participants | 39 |
| Age, Customized: ≥ 60 years | Participants | 89 |
| Sex: Female, Male: Female | Participants | 54 |
| Sex: Female, Male: Male | Participants | 74 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 0 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 128 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 |
| 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 | 4 |
| Race (NIH/OMB): White | Participants | 122 |
| Race (NIH/OMB): More than one race | Participants | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 1 |
| Region of Enrollment: United States | participants | 128 |
| Height | centimeters (cm) | 172.1 (SD 10.8) |
| Weight | kilograms (kg) | 89.9 (SD 18.1) |
| BMI | kg/m^2 | 30.3 (SD 5.4) |
| BMI Category: < 30 kg/m^2 | Participants | 66 |
| BMI Category: ≥ 30 kg/m^2 | Participants | 61 |
| Smoking Status: Current smoker | Participants | 7 |
| Smoking Status: Previous smoker | Participants | 31 |
| Smoking Status: Never smoked | Participants | 74 |
| Smoking Status: Unknown | Participants | 16 |
| Surgical Approach: Medial parapatellar | Participants | 89 |
| Surgical Approach: Subvastus / Tissue sparing | Participants | 18 |
| Surgical Approach: Midvastus | Participants | 0 |
| Surgical Approach: Lateral parapatellar | Participants | 3 |
| Surgical Approach: Unknown | Participants | 0 |
| Surgical Approach: Other | Participants | 18 |
| Knee System Type: Missing | Participants | 3 |
| Knee System Type: Smith & Nephew | Participants | 108 |
| Knee System Type: Other - Non-Smith & Nephew | Participants | 17 |
| Unilateral Knee Replacement Type Used: Medial | Participants | 124 |
| Unilateral Knee Replacement Type Used: Lateral | Participants | 4 |
6. Primary Endpoint
The registry lists the primary outcome as Evaluate the Navio™ System for Revisions at 2+ Years Post-surgical Implantation Survivorship, measured over Preoperative (Baseline) and 24, 48, 72, 96, and 120 weeks postoperatively.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint concerns the absence of device revision after surgical implantation, described in the registry as overall survivorship. A revision is a clinically interpretable event that indicates the implanted device or procedure has required further intervention; measuring whether revision has occurred over follow-up is one way to describe how long an implant remains unrevised. This explains the endpoint’s role in the study, but does not establish what the results were.
The registry specifies assessment from baseline through 120 weeks post-surgically, including visits at 24, 48, 72, 96, and 120 weeks. The outcome is described in terms of participants and a number, but the posted results do not give the number with revisions, the number without revisions, or an estimated survivorship value. A confidence interval or other measure of uncertainty is also not reported in the registry record.
The primary population is the SAF population: subjects who received the study device and were present for follow-up visits at specified time points. This definition makes follow-up availability relevant to interpretation. The registry does not say how missing visits or incomplete follow-up were handled, nor does it provide the number of participants contributing to each time point. Consequently, the endpoint definition and schedule can be described, but the degree of observed revision-free follow-up cannot be assessed from the reported primary results.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record gives the study question, endpoint definition, follow-up schedule, and enrollment, but it does not report a primary endpoint result. In particular, it does not provide a revision count, an estimate of overall survivorship, or a confidence interval. The record therefore does not allow a reader to quantify the primary outcome or judge its precision.
The study enrolled 128 participants and describes a SAF population consisting of subjects who received the device and were present for follow-up visits at specified time points. Enrollment is not the same as the number observed at every follow-up visit. The number contributing to each assessment and the amount of missing follow-up are not reported in the registry record, so the completeness of outcome ascertainment cannot be determined.
The brief summary describes a historical control, but the comparator’s details and outcome results are not reported. Allocation is not stated, and the registry cautions that the arms are not a like-for-like control comparison. A comparison with historical participants can be affected by differences in who entered each cohort, clinical practice, outcome ascertainment, or follow-up. Whether such differences were evaluated or adjusted for is not reported in the registry record. The description alone is not evidence of a randomized or otherwise balanced comparison.
The registry lists secondary assessments of KSS, VR-12, and radiographic findings at multiple time points, but it does not report their results or analysis methods. Ten outcome measures are listed and 0 analyses are reported. The listing of outcomes does not establish that each was analyzed or that results were favorable, unfavorable, or statistically precise.
For safety, the Navio group lists 2 participants with serious adverse events and 28 with other adverse events among 128 at risk in each category; deaths are listed as 0. The record also lists Deep venous thrombosis (DVT) and Lower extremity DVT at 0.8% each among the top serious terms. These figures describe recorded events, not proof that the device caused them. The registry does not provide enough detail to determine whether the two DVT terms refer to separate participants or overlapping event coding.
Overall, the posted information supports a description of the study design and registered outcomes, plus the reported adverse-event counts. It does not support a quantitative conclusion about revision-free survivorship or comparative efficacy. Any planning illustrations associated with the page are distinct from observed trial findings; the stated assumptions describe planning calculations, not observed power and not the study’s own design justification.
9. Statistical Methods Explained
Statistical methods determine how outcomes are summarized, how comparisons are made, and how uncertainty is represented. The registry record describes the endpoint and study population, but does not report the statistical analysis plan. The distinctions below are general explanations of concepts relevant to interpreting this type of study, not claims about procedures used by the investigators.
What does a binary outcome mean?
In general, a binary outcome classifies each participant into one of two states for a defined endpoint—for example, whether a specified event occurred or did not occur during a defined period. The primary endpoint is framed around absence of device revision. A clear analysis needs a rule for what counts as revision, the time period over which it is assessed, and how participants without complete follow-up are handled. The registry describes the endpoint and schedule but does not report a revision count or the analysis rules.
For a binary outcome, a count and the number assessed are often useful starting points. Counts alone do not show how precisely an underlying event rate is estimated. A confidence interval expresses a range of values compatible with the observed data under the assumptions of the method; a narrow interval indicates greater precision than a wide interval. No primary endpoint estimate or confidence interval is reported in the registry record, so its precision cannot be evaluated.
How does follow-up affect survivorship?
In general, time-to-event analysis is used when both whether an event occurred and when it occurred matter. Participants may have different lengths of observation, and some may leave follow-up before an event is observed. Such methods can account for differing observation times under specified assumptions. The registry uses the term overall survivorship and lists assessments through 120 weeks, but does not report the analytic method, event times, censoring rules, or follow-up completeness. It is therefore not possible to tell from the registry whether a time-to-event estimator was used or how incomplete observation was treated.
A visit-based summary and a time-to-event estimate answer related but not identical questions. A visit-based count describes the observed status at a particular assessment among those with available data. A time-to-event analysis uses the timing of events and follow-up, and may incorporate participants who have not had the event by their last observation. The record does not specify which summary supports the primary endpoint, so neither approach should be attributed to the investigators.
Why does the historical comparison need caution?
In general, randomized allocation can help make comparison groups similar in expectation, while historical comparisons rely on data collected from a different group at an earlier time or in another setting. Differences in participant characteristics, care, outcome definitions, or observation can affect apparent group differences. Statistical adjustment can address measured differences under assumptions, but cannot automatically remove unmeasured differences. The study summary mentions a historical control, while allocation is not stated and the registry explicitly says the arms are not a like-for-like control comparison. The source and characteristics of the control and any adjustment methods are not reported in the registry record.
For this reason, group contrasts should not be read as if they came from a randomized trial. A numerical difference, even if reported, would need to be interpreted alongside the design, outcome definitions, missingness, and precision. The primary comparative results are not reported, so no such contrast can be described.
What do planning assumptions represent?
General sample-size calculations estimate how many observations might be needed to detect a specified effect under chosen assumptions. They are planning exercises, not evidence that a study actually had a particular probability of detecting an effect. The planning assumptions associated with this study describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is framed as a stated fraction of the observed effect. For time-to-event tables, the stated quantity is total events using the Schoenfeld method; other tables use participants per arm.
These assumptions are expressly described as a planning illustration computed from the observed effect, not the trial’s own design. They should not be interpreted as observed power or as the original sample-size justification. The registry record does not report a sample-size justification, and no planning output should be mistaken for an observed endpoint result.
What is not available for evaluating the analysis?
The registry lists 10 outcome measures and 0 analyses. It does not report the statistical model, test, effect estimate, confidence interval, p-value, covariate strategy, or handling of missing observations. It also does not report interim analyses. Without these details and the endpoint results, readers cannot assess model assumptions, reproduce the primary analysis, or determine how much uncertainty surrounds its estimate. Those absences are limits of what the registry record reports, not proof that a particular method was or was not used outside the record.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity arises when several outcomes, time points, or comparisons are assessed. In general, the more statistical tests conducted, the greater the chance that at least one result appears noteworthy by chance if each is interpreted without accounting for the full testing plan. A prespecified hierarchy, adjustment procedure, or clearly labeled exploratory analysis can help readers understand how multiple results should be interpreted.
The registry lists 10 outcome measures. These include the primary revision-free survivorship outcome and secondary KSS, VR-12, and radiographic assessments. It does not report whether outcomes were ranked in a testing hierarchy, whether a multiplicity adjustment was planned, or whether the listed secondary outcomes were treated as exploratory. The statistical analysis plan is not reported in the registry record. The number of listed outcomes alone does not show how many statistical tests were performed; the record reports 0 analyses.
Missing data are also important when follow-up is needed to establish whether a revision occurred. The SAF population includes subjects who received the device and were present for follow-up visits at specified time points. The number followed at each visit, reasons for missed visits, and rules for handling incomplete data are not reported in the registry record. Without those details, the potential effect of incomplete follow-up on the estimates cannot be evaluated.
The record does not report whether participants with missing assessments were excluded, whether missing values were imputed, or whether sensitivity analyses were performed. These are unknowns, not evidence that a specific approach was used. The record’s population definition should therefore be read alongside the absence of reported follow-up counts and missing-data methods.
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 |
|---|---|---|---|
| Navio Robotic-assisted Surgical System | 2 | 128 | 1.6% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Navio Robotic-assisted Surgical System | 0 of 128 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Navio Robotic-assisted Surgical System | 28 of 128 |
Most frequent serious adverse event terms
| Event term | Organ system | Navio Robotic-assisted Surgical System |
|---|---|---|
| Deep venous thrombosis (DVT) | Vascular disorders | 1 of 128 |
| Lower extremity DVT | Vascular disorders | 1 of 128 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Navio Robotic-assisted Surgical System |
|---|---|---|
| Radiolucent lines | Musculoskeletal and connective tissue disorders | 7 of 128 |
| Radiolucency line tibial ML zone | Musculoskeletal and connective tissue disorders | 5 of 128 |
| Redness, burning, itchiness | Skin and subcutaneous tissue disorders | 1 of 128 |
| Effusion | Skin and subcutaneous tissue disorders | 1 of 128 |
| Swelling and discomfort | Skin and subcutaneous tissue disorders | 1 of 128 |
| Slight swelling and edema | Skin and subcutaneous tissue disorders | 1 of 128 |
| Knee pain due to mild iliotibial band tendonitis | Musculoskeletal and connective tissue disorders | 1 of 128 |
| Pain in quadriceps | Musculoskeletal and connective tissue disorders | 1 of 128 |
| Knee pain with 50 mL of blood aspiration | Musculoskeletal and connective tissue disorders | 1 of 128 |
| Possible cellulitis - not life threatening | Skin and subcutaneous tissue disorders | 1 of 128 |
Serious events with the highest arm-level rate: deep venous thrombosis (dvt) (0.8%), lower extremity dvt (0.8%).
The registry lists the Navio Robotic-assisted Surgical System group with 128 participants at risk for serious adverse events and 2 participants affected. It also lists 128 at risk for other adverse events and 28 affected. Deaths are listed as 0. These are the recorded counts in the registry; the entry does not give further detail about event timing, duration, severity grading, or participant-level overlap between categories.
The top serious-event terms are Deep venous thrombosis (DVT) and Lower extremity DVT, each listed at 0.8%. Because both terms appear in the same list, they should not automatically be counted as distinct participants or as separate episodes. The registry record does not explain whether the terms overlap, how events were coded, or the denominator used for these term-specific percentages beyond the group information.
Adverse-event counts describe events observed and recorded during the study; by themselves, they do not establish causation. The record does not report an attribution assessment, a comparison suitable for estimating excess risk, or additional context needed to interpret the events. The historical-control description does not establish a like-for-like safety comparison, and the registry cautions that the arms are not like-for-like. The listed counts should therefore be read as descriptive safety information rather than as a causal comparison.
12. What the Result Does, and Does Not, Mean
The registry record identifies a retrospective, multi-center cohort study with prospective follow-up and comparison to a historical control. It describes a primary question about absence of device revision through 120 weeks and provides an operational definition of the SAF population. It also records adverse-event counts for the Navio group. These details clarify what the study set out to assess and what safety counts were posted.
The primary endpoint results are not reported in the registry record. There is no reported number of revisions, estimate of overall survivorship, or confidence interval. As a result, the registered question cannot be answered quantitatively from the posted primary results. Enrollment of 128 participants does not establish that all had complete follow-up through each assessment.
The record also does not provide results for the listed KSS, VR-12, or radiographic outcomes. Nor does it provide the historical control’s details or results. Allocation is not stated, and the registry warns that the arms are not a like-for-like control comparison. The study description therefore does not establish a causal effect or permit a robust comparative conclusion.
The posted safety figures—2 participants with serious adverse events, 28 with other adverse events, and 0 deaths—are descriptive. They do not establish that the device caused or prevented an event, and the registry does not provide the comparative and attribution details needed for such an interpretation.
In general, conclusions about an estimate depend on the outcome definition, completeness of follow-up, analysis method, and statistical uncertainty. Those elements are not fully reported for the primary result. The appropriate reading is therefore bounded: the registry documents the study design, its stated outcomes, and certain safety counts, while leaving the primary effectiveness estimate and its precision unreported. This absence should not be converted into a claim of benefit, lack of benefit, or equivalence.
13. Why This Trial Matters Statistically
This study is statistically informative as an example of why design and outcome reporting matter as much as the endpoint label. “Overall survivorship” can sound like a single, self-explanatory result, but interpretation depends on how revision is defined, how follow-up time is handled, and which participants contribute data. The registry gives the primary outcome description and assessment schedule, but not the resulting estimate or the methods used to obtain it.
The retrospective cohort design and historical comparison also matter. In general, a comparison with historical controls can be affected by differences between groups that arise from selection, setting, or data collection. Here, allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. These features make it important not to treat the design as randomized or to infer a causal comparative effect from the study description.
Outcome multiplicity and follow-up completeness are relevant because the registry lists several secondary outcome domains and multiple assessment times, while the analysis plan and missing-data methods are not reported. Those omissions limit the ability to evaluate how results were selected, how uncertainty was handled, and whether participants with incomplete follow-up could affect the findings.
The record demonstrates a further distinction: an adverse-event count can be reported even when the primary effectiveness result is not. Safety counts are useful descriptive information, but they do not substitute for a primary endpoint estimate or a suitable comparison. The registry lists 10 outcome measures and 0 analyses, so readers should separate registered intentions and descriptive counts from statistical results. This is important for biostatisticians and clinical researchers assessing whether a registry entry permits a conclusion, or only a description of what was planned and recorded.
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 primary limitation for interpretation is that the registry record does not report the primary endpoint result. It gives no count of revisions, survivorship estimate, or confidence interval. The number of participants contributing to each follow-up assessment is also not reported, despite the SAF population definition depending on presence at specified visits.
The control group is insufficiently described for comparative interpretation. The study summary mentions a historical control, but its source, size, characteristics, and outcome data are not reported in the registry record. Allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. Any group comparison would need to account for the possibility of differences in participants, care, or outcome ascertainment; methods for doing so are not reported.
The registry does not report the primary analysis method, statistical model, uncertainty estimates, or handling of missing data. It also does not report a sample-size justification, interim analyses, or a multiplicity plan. The listed secondary outcomes and time points therefore cannot be evaluated for the analysis strategy or the degree of uncertainty in any estimate.
Further details of the retrospective cohort criteria, participating centers, surgical procedures, event definitions, and follow-up conduct are not reported in the registry record. For safety, event timing, attribution, and possible overlap between the listed DVT terms are not explained. These omissions limit assessment of representativeness, follow-up completeness, analytic reproducibility, and causal interpretation. They do not establish that a particular method or procedure was absent; they identify information not reported in the registry record.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Retrospective Study of the Navio Robotic-assisted Surgical System — NCT03072459.
- Registry record last updated 2022-05-25; status last verified 2021-12.
- Results first posted 2022-05-02.
- 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
NCT03072459 is a completed retrospective, multi-center cohort study of the Navio Robotic-assisted Surgical System, described as having prospective follow-up and comparison to a historical control. The registry reports enrollment of 128, a start date of 2017-07-10, primary completion on 2017-11-29, and Smith & Nephew, Inc. as sponsor.
The primary outcome concerns absence of device revision through 120 weeks, with assessments at 24, 48, 72, 96, and 120 weeks postoperatively. Secondary outcomes include KSS, VR-12, and radiographic assessments. The registry lists 10 outcome measures and 0 analyses; primary and secondary outcome results are not reported in the registry record.
For the Navio group, the record lists 2 participants with serious adverse events, 28 with other adverse events, and 0 deaths. The record cautions that the historical arms are not a like-for-like control comparison.