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 Zip Arthroplasty Patient Satisfaction Evaluation (NCT03178266), a registered phase not stated study. The primary outcome is Patient and Observer Scar Assessment Scale (POSAS).
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03178266 |
| Phase | Phase not stated |
| Condition | Knee Arthroplasty |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 41 |
| Arms in the primary outcome | n/a |
| Lead sponsor | ZipLine Medical Inc. |
| Results posted | Yes |
2. Clinical Question
Population
People identified as candidates for knee arthroplasty who met the study selection criteria were considered for enrollment. The registry record reports enrollment of 41 participants. Further participant characteristics and the selection criteria are not reported in the registry record.
Intervention
The intervention was final skin closure after knee arthroplasty with the Zip Closure Device. The registry describes the study as evaluating the device in people undergoing the procedure.
Comparator
The comparator was final skin closure with Metal Staples after knee arthroplasty. Although the brief summary describes a randomized study, allocation details are not stated in the registry record, and the record cautions that the arms are not a like-for-like control comparison.
Primary question
The primary question concerned Patient and Observer Scar Assessment Scale scores at 6 weeks post knee arthroplasty. The score was intended to capture scar characteristics from the subject’s and investigator’s perspectives, including their overall opinion of the scar relative to normal skin. The registry record does not report the scores or a between-arm estimate.
3. Trial Design
The registry describes NCT03178266 as a prospective, randomized, single-center study evaluating the Zip Closure Device in people undergoing knee arthroplasty. It lists a planned enrollment of 40 subjects in the brief summary, with 20 assigned to ZipLine and 20 to Staples, while the recorded enrollment is 41. The arm-specific number enrolled is not reported in the registry record. The study is marked completed.
The device arm received the Zip Closure Device for final skin closure, and the comparison arm received Metal Staples for final skin closure. The registry lists knee arthroplasty as the intervention and patient satisfaction as a secondary outcome. The primary outcome was the Patient and Observer Scar Assessment Scale (POSAS) at 6 weeks post knee arthroplasty.
There is an important qualification to the randomized description: allocation is not stated in the registry record, and the record cautions that the arms are not a like-for-like control comparison. Without allocation details, the basis for comparing the groups cannot be evaluated from the registry information. The registry record also does not report the recruitment process beyond identifying candidates who met study selection criteria, the analysis population, or a detailed statistical plan. Start and primary completion dates are recorded as 2017-12-01 and 2018-05-01, respectively.
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 | Zip Closure Device | Metal Staples |
|---|---|---|
| STARTED | 21 | 20 |
| COMPLETED | 21 | 16 |
| NOT COMPLETED | 0 | 4 |
Reasons for not completing this period:
| Reason | Zip Closure Device | Metal Staples |
|---|---|---|
| Death | 0 | 1 |
| Disont. Early | 0 | 1 |
| Withdrawal by Subject | 0 | 2 |
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 | Zip Closure Device | Metal Staples | Total |
|---|---|---|---|---|
| Participants analysed | 21 | 20 | 41 | |
| Age, Continuous | years | 67 (SD 7.13) | 65 (SD 6.96) | 66 (SD 6.94) |
| Sex: Female, Male: Female | Participants | 14 | 11 | 25 |
| Sex: Female, Male: Male | Participants | 7 | 9 | 16 |
| Ethnicity (NIH/OMB): Hispanic or Latino | Participants | 0 | 0 | 0 |
| Ethnicity (NIH/OMB): Not Hispanic or Latino | Participants | 21 | 20 | 41 |
| Ethnicity (NIH/OMB): Unknown or Not Reported | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): American Indian or Alaska Native | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Asian | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Native Hawaiian or Other Pacific Islander | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Black or African American | Participants | 1 | 17 | 18 |
| Race (NIH/OMB): White | Participants | 19 | 3 | 22 |
| Race (NIH/OMB): More than one race | Participants | 0 | 0 | 0 |
| Race (NIH/OMB): Unknown or Not Reported | Participants | 1 | 0 | 1 |
| Region of Enrollment: United States | Participants | 21 | 20 | 41 |
6. Primary Endpoint
The registry lists the primary outcome as Patient and Observer Scar Assessment Scale (POSAS), measured over 6 weeks post knee arthroplasty.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | score on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint was the Patient and Observer Scar Assessment Scale (POSAS), described as a score on a scale and summarized using a mean and standard deviation. The assessment was scheduled for 6 weeks post knee arthroplasty. Its stated purpose was to collect views of scar characteristics from the subject and investigator perspectives, including each person’s overall opinion of the scar in relation to normal skin.
For the overall opinion, the description defines 1 as Normal and 10 as Very Different. This anchors the meaning of that rating: lower values correspond to an opinion closer to normal skin, while higher values correspond to an opinion farther from normal skin. The registry description does not give additional detail about how individual scar characteristics were combined or how the patient and investigator ratings were represented in the primary result.
In general, a continuous score can be described by its mean to indicate the center of observed values and by its standard deviation to describe their spread. Those summaries can help readers understand both the typical rating and how much ratings varied among participants. The endpoint’s purpose is to quantify scar assessments; it does not by itself describe all aspects of recovery or establish the reason for any difference between groups. The registry record does not report endpoint values, group means, standard deviations, or a treatment contrast.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies POSAS as the primary outcome, but it does not report the observed POSAS results. There are no posted group means or standard deviations, and no estimated difference between the Zip Closure Device and Metal Staples arms. Accordingly, the registry information does not show the direction or magnitude of any difference in scar ratings at 6 weeks post knee arthroplasty.
There is also no reported confidence interval or hypothesis-test result for the primary endpoint. In general, a confidence interval communicates the range of values reasonably compatible with the data under the analysis assumptions. Its width indicates precision: a narrower interval conveys more precision than a wider interval. Without a reported estimate and interval, the precision of any arm comparison cannot be assessed. No p-value for the primary endpoint is reported in the registry record either, so the record does not support a conclusion about statistical evidence for a difference.
The registry reports enrollment of 41 and describes a plan for 20 subjects in each arm, but the actual arm-specific enrollment is not stated in the registry record. The adverse-event risk counts are 21 for the Zip Closure Device arm and 20 for the Metal Staples arm; those safety counts do not substitute for a reported endpoint analysis. The record also states that allocation is not stated and cautions against treating the arms as a like-for-like control comparison. That caveat limits the interpretation of any simple arm contrast, even if outcome summaries were available.
In general, a randomized comparison is most interpretable when allocation and analysis procedures are clear, because these details help readers assess whether observed group differences could reflect factors other than the intervention. Here, the registry summary calls the study randomized, but the allocation method and details are not reported in the registry record. The cause of the discrepancy between planned enrollment and recorded enrollment is not reported in the registry record; it should not be inferred from the counts alone.
The record lists two outcome measures and zero analyses. This does not establish that no analysis occurred outside the registry; it means that statistical analyses are not reported in the registry record. The posted information therefore supports a description of the question and design, but not a conclusion about the comparative POSAS results. Patient satisfaction is listed as a secondary outcome, but its result is not reported in the registry record.
9. Statistical Methods Explained
The registry identifies the primary outcome as a continuous measure: POSAS score, with a mean and standard deviation as the stated summary statistics. In general, a continuous outcome can take values along a scale rather than being limited to categories such as event or no event. A mean describes the center of the observed scores, while a standard deviation describes how dispersed scores are around that center. Neither summary is reported for this outcome in the registry record, so the actual score distribution and average rating cannot be assessed.
What would a group comparison mean?
In general, a comparison of mean scores describes how far apart the group averages are, on the scale used for the outcome. Such a contrast should be presented with an uncertainty measure, commonly a confidence interval, so readers can judge both its size and its precision. A confidence interval is not a guarantee that the true value lies inside a particular interval; rather, it reflects uncertainty under the statistical model and procedure used. No mean contrast or confidence interval is reported in the registry record.
When interpreting this particular scale, the endpoint description anchors the overall opinion rating at 1 for Normal and 10 for Very Different. That context is necessary before assigning meaning to a score’s direction. The record does not report the observed values, so no statement can be made about whether ratings tended toward one end of the scale or how variable they were.
How does allocation affect interpretation?
In general, random allocation can help balance known and unknown participant characteristics between treatment groups, making a comparison more credible. However, the label randomized does not provide all the details needed to assess how allocation was carried out. The brief summary calls this study randomized, while allocation is not stated in the registry record. The record also warns that the arms are not a like-for-like control comparison. The method of allocation, concealment procedures, and any other details that would clarify the comparison are not reported in the registry record.
That caution matters because an observed difference between groups, if one were reported, could not automatically be attributed to closure method without considering how participants entered and were assigned to each arm. The registry record does not provide enough detail to assess comparability of the groups at baseline or to determine whether the stated randomization was implemented as planned. Baseline characteristics are not reported in the registry record.
What do the stated planning assumptions tell readers?
The registry includes a description of a planning illustration based on an observed effect. It specifies a two-sided significance level of 0.05, equal allocation between arms, a normal approximation, and an effect to detect expressed as a fraction of the observed effect. It also distinguishes participant-per-arm planning quantities from total-event quantities for time-to-event analyses. The primary outcome is continuous, not time-to-event. Numerical planning results are not reported in the registry record.
In general, a sample-size illustration describes how many participants might be needed under particular assumptions about an effect, variability, allocation, and statistical procedure. It is not evidence that the study had a particular chance of detecting an effect after completion. Because the registry does not report the observed POSAS effect or its variability, the assumptions cannot be checked against posted endpoint results. The illustration should be read as planning information, not as an outcome finding.
What can be said about model assumptions?
The planning description mentions a normal approximation. In general, a normal approximation uses a mathematical distribution to estimate the behavior of a statistic, and its suitability depends on the data and analysis context. The registry record does not provide an endpoint analysis, diagnostic checks, or details of a fitted model, so the use or adequacy of any approximation for the actual POSAS analysis cannot be evaluated. For count outcomes, over-dispersion means that variability exceeds what a basic count model expects; accounting for it can affect uncertainty estimates. No such model is described for the primary endpoint in the registry record.
The registry lists a mean and standard deviation for the continuous primary outcome, but not the method used to handle missing scores, the confidence-interval method, or any adjustment variables. Those details are not reported in the registry record. The posted results therefore do not allow independent assessment of the statistical analysis or reproduction of a numerical treatment comparison.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists two outcome measures, with POSAS as the primary outcome and Patient Satisfaction as a secondary outcome. It reports zero analyses. Results for either outcome are not reported in the registry record. The record does not describe a hierarchy of outcome tests, an adjustment for multiple comparisons, or a prespecified rule for interpreting several results. Those procedures are not reported in the registry record.
In general, testing multiple outcomes or making multiple comparisons can increase the chance of finding an apparently notable result by chance. A statistical plan may address this through a prespecified hierarchy or an adjustment procedure. Without such information, readers cannot determine how the study intended to account for multiplicity. This is a limitation of the registry information, not evidence that an adjustment was or was not used outside the record.
The registry does not report how missing POSAS scores or patient-satisfaction responses were handled. The amount and pattern of missing outcome data are not reported in the registry record. In general, missingness can affect a result if participants with missing measurements differ systematically from participants whose measurements are available. The analysis population, inclusion and exclusion rules, and any imputation or sensitivity analyses are not reported in the registry record.
These omissions prevent assessment of whether the reported enrollment and analyzed population would be the same. The registry record also does not state whether analyses followed assigned groups or another population definition. No interpretation of the treatment contrast can be based on an analysis population that is not described.
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 |
|---|---|---|---|
| Zip Closure Device | 0 | 21 | 0.0% |
| Metal Staples | 1 | 20 | 5.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Zip Closure Device | 0 of 21 |
| Metal Staples | 1 of 20 |
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 |
|---|---|
| Zip Closure Device | 2 of 21 |
| Metal Staples | 0 of 20 |
Most frequent serious adverse event terms
| Event term | Organ system | Zip Closure Device | Metal Staples |
|---|---|---|---|
| Death | Cardiac disorders | 0 of 21 | 1 of 20 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Zip Closure Device | Metal Staples |
|---|---|---|---|
| Blister lateral to distal end of closure | Skin and subcutaneous tissue disorders | 1 of 21 | 0 of 20 |
| Serous Drainage | Skin and subcutaneous tissue disorders | 1 of 21 | 0 of 20 |
Serious events with the highest arm-level rate: death (5.0%).
The safety figures distinguish serious adverse events, other adverse events, and deaths. In the Zip Closure Device group, 0 serious events were reported among 21 at risk, 2 other events among 21 at risk, and 0 deaths. In the Metal Staples group, 1 serious event was reported among 20 at risk, 0 other events among 20 at risk, and 1 death. The listed top serious term is Death, at 5.0%.
These are counts from the registry record, not estimates of comparative risk adjusted for differences between groups. The event counts are small, and the record does not report an inferential comparison or confidence intervals for safety outcomes. The number at risk is the denominator stated for each category; it should not be treated as an outcome score or as proof that every event was caused by the closure method.
In general, serious events, other events, and deaths are distinct reporting categories, and their counts should not be added unless the record establishes that they are mutually exclusive. The registry does not provide event narratives, timing, relatedness assessments, or further detail about the death. The cause and relationship of the reported death to study treatment are not reported in the registry record. These figures describe what was recorded, but they do not by themselves establish causation or provide a complete safety comparison.
12. What the Result Does, and Does Not, Mean
The registry record establishes that this completed, single-center study evaluated skin closure after knee arthroplasty with the Zip Closure Device or Metal Staples. Its primary question concerned patient and observer scar ratings at 6 weeks post knee arthroplasty. It also lists patient satisfaction as a secondary outcome. The posted information does not include the endpoint results, so it cannot show the average scar ratings, their variability, or the estimated difference between arms.
In general, the presence of a study design and a defined outcome does not establish what the study found. To interpret a comparative result, readers need the observed outcome summaries, the estimated contrast, and an indication of uncertainty. The registry record does not report these for POSAS. It also does not report a statistical analysis of patient satisfaction. As a result, neither a favorable nor an unfavorable comparative conclusion follows from the outcome information in this record.
The adverse-event counts provide descriptive information: the registry reports serious events, other events, and deaths by group. Those counts do not establish that a closure method caused an event, and no comparative safety analysis is reported. The separate risk denominators and small event counts should be read as recorded observations rather than as a complete measure of relative safety.
The brief summary describes randomized assignment, but allocation is not stated in the registry record, which also cautions that the arms are not a like-for-like control comparison. This uncertainty further limits causal interpretation. The record is useful for identifying the study question, interventions, outcome timing, and some safety counts; it is not sufficient to determine the comparative POSAS result or the precision of such a result.
13. Why This Trial Matters Statistically
This study raises statistical questions that commonly arise when a clinical comparison has a defined outcome but limited posted analysis. The primary endpoint is a continuous scar-assessment score, and its interpretation depends on knowing the group summaries, the contrast between groups, and the uncertainty around that contrast. Those results are not reported in the registry record. Without them, readers cannot judge the magnitude or precision of the primary comparison.
The registry’s description also illustrates why design labels need supporting detail. The brief summary calls the study randomized, but allocation is not stated in the registry record, and the record cautions that the arms are not a like-for-like control comparison. In general, readers need enough information about assignment and analysis to decide whether differences between groups can reasonably be interpreted as treatment effects. The registry does not give that information.
Enrollment is recorded as 41, while the brief summary describes a plan for 20 subjects per arm. This makes it important to distinguish planned enrollment from the participants represented in each analysis. The actual arm-specific enrollment and analysis population are not reported in the registry record. The safety denominators are reported, but they cannot fill in the missing details for the primary outcome.
Finally, the record demonstrates the difference between a planning illustration and an analysis result. The planning description states assumptions, but numerical planning results and the endpoint analysis are not reported in the registry record. A reader should not treat planning assumptions as evidence about what the trial observed. Clear reporting of outcome estimates, uncertainty, missing data, and analysis populations is necessary for a statistical interpretation of the study’s comparative findings.
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.
Several trial-specific limitations constrain interpretation of the registry record. The primary endpoint is named and its assessment time is stated, but POSAS values, group means, standard deviations, and a between-group estimate are not reported in the registry record. Patient satisfaction is listed as a secondary outcome, but its results are also not reported in the registry record. Thus, the central comparative question cannot be answered from the posted outcomes.
The brief summary calls the study randomized, yet allocation is not stated in the registry record. The record further cautions that the arms are not a like-for-like control comparison. The reason for that caution and the details of group assignment are not reported in the registry record. Baseline characteristics are not reported in the registry record, so group comparability cannot be assessed from the recorded information.
The recorded enrollment is 41, while the study summary describes a plan for 20 participants in each arm. Actual arm-specific enrollment for the primary analysis is not reported in the registry record. The analysis population, missing outcome data, and rules for handling incomplete measurements are not reported in the registry record either. These details matter because the analyzed participants may not be identical to those enrolled.
The primary endpoint is specified at 6 weeks post knee arthroplasty; additional primary outcome time points are not reported in the registry record. The record lists zero analyses and does not provide inferential results, multiplicity procedures, or details of the statistical model. The safety information is limited to event counts and denominators, without narratives, timing, relatedness assessments, or comparative uncertainty. These gaps mean that the registry supports a description of the study structure and recorded safety counts, but not a complete appraisal of efficacy or safety findings.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Zip Arthroplasty Patient Satisfaction Evaluation — NCT03178266.
- Registry record last updated 2019-05-15; status last verified 2019-05.
- Results first posted 2019-05-15.
- 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
NCT03178266, titled Zip Arthroplasty Patient Satisfaction Evaluation, is marked completed. The sponsor is ZipLine Medical Inc. The registry describes a prospective, randomized, single-center evaluation of final skin closure after knee arthroplasty, comparing the Zip Closure Device with Metal Staples. Recorded enrollment is 41. The study summary describes a plan for 20 subjects per arm.
The primary outcome was POSAS score at 6 weeks post knee arthroplasty, summarized as a mean and standard deviation. Patient satisfaction was listed as a secondary outcome. The record lists two outcome measures and zero analyses. POSAS and patient-satisfaction results are not reported in the registry record.
The registry reports safety counts by arm: serious events, other events, and deaths. It also states that allocation is not stated and cautions that the arms are not a like-for-like control comparison. The posted information identifies the study question and some design details, but does not provide a statistical result for the primary comparison.