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 Post Market Clinical Follow-Up of the Zimmer Stafit Acetabular System (NCT04079114), a registered phase not stated study. The primary outcome is Implant Survival.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04079114 |
| Phase | Phase not stated |
| Condition | Osteoarthritis, Hip, Fracture of Hip, Avascular Necrosis of Hip |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 166 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Zimmer Biomet |
| Results posted | Yes |
2. Clinical Question
Population
Patients who received the Zimmer Stafit Acetabular System. The registry lists hip osteoarthritis, hip fracture, avascular necrosis of the hip, dislocated hip, osteonecrosis, post-traumatic arthrosis, rheumatoid arthritis, and hip subluxation among the conditions. It does not report how participants were distributed across these conditions.
Intervention
Receipt of the Stafit Acetabular System, a device intervention. The study is described as post-market clinical follow-up intended to confirm the device’s safety and performance.
Comparator
There is no controlled comparator in this study. The design is described as non-controlled, and the registry does not state an allocation method. The patients receiving the device therefore do not form a randomized comparison with another treatment group.
Primary question
What was the implant survival rate, defined using cup revision for any reason, at 3 years postoperatively? The registry describes the intended measure as a Kaplan-Meier survival rate. It does not report a numerical survival estimate or its uncertainty.
The clinical question is descriptive rather than a comparative treatment question. It concerns implant survival and, among the secondary outcomes, pain and functional performance measured with the Harris Hip Score and safety based on complications. The record lists 166 participants as enrolled, but does not report the number contributing data to each outcome or the results for the secondary measures.
The primary outcome timeframe is qualified in the registry as 3 years postoperatively, due to early study termination. That qualification matters: the question concerns the planned timepoint, but a stated timepoint does not establish that every participant was observed for that duration. The registry does not report individual follow-up, censoring, or the number of participants with outcome data at that time. Consequently, the central question can be described from the record, but its answer cannot be evaluated from a posted survival result.
3. Trial Design
This is a multicenter, prospective, non-controlled post-market clinical follow-up study of the Zimmer Stafit Acetabular System. Zimmer Biomet is listed as the sponsor. The stated purpose was to meet post-market surveillance obligations and collect data to confirm safety and performance. Enrollment is listed as 166.
The study is marked terminated. Its recorded start date is 2011-04-28, and its primary completion date is 2017-01-24. The primary outcome is implant survival, described as the Kaplan-Meier survival rate with cup revision for any reason. The timeframe is 3 years postoperatively, qualified as being due to early study termination. The record does not explain the circumstances or decision behind termination.
The secondary outcomes are evaluation of pain and functional performance determined by the Harris Hip Score, and confirmation of safety based on complications. Four outcome measures are listed in total, but no statistical analyses are listed. The record does not provide numerical findings for the primary or secondary outcomes.
A non-controlled study can describe outcomes among people who received a device, but it does not provide a concurrent control group for estimating a comparative effect. Because the registry does not state an allocation method and the study is explicitly non-controlled, the design should not be read as a randomized comparison. The record also does not report eligibility details, recruitment locations, participant flow, or analysis populations. These omissions limit how fully the enrolled population and the completeness of follow-up can be characterized.
The record’s prospective and multicenter labels describe the study’s stated design, but do not supply details about how assessments were scheduled or standardized across centers. Those operational details, as well as the protocol and statistical analysis plan, are not reported in the registry record. The listed design and dates therefore establish the broad study structure, not the full conduct of the study.
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 | Patients Who Received the Stafit Acetabular System |
|---|---|
| STARTED | 166 |
| COMPLETED | 0 |
| NOT COMPLETED | 166 |
Reasons for not completing this period:
| Reason | Patients Who Received the Stafit Acetabular System |
|---|---|
| Study prematuely terminated. | 166 |
Analysis population for the primary outcome, as defined in the registry: Outcome Measure Data at 3 years postoperative (Study early terminated). The Kaplan-Meier survival rate with cup revision for any reason.
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 | Patients Who Received the Stafit Acetabular System |
|---|---|---|
| Participants analysed | 166 | |
| Age, Continuous | years | 73.9 (SD 7.9) |
| Sex: Female, Male: Female | Participants | 116 |
| Sex: Female, Male: Male | Participants | 50 |
| Race and Ethnicity Not Collected | Participants | — |
| Body Mass Index (kg/m2) | kg/m^2 | 27.0 (SD 5.2) |
6. Primary Endpoint
The registry lists the primary outcome as Implant Survival, measured over 3 years postoperatively, due to early study termination.
| Element | Registry entry |
|---|---|
| Result type | Number |
| Measure of spread | not applicable |
| Unit | percentage of implant survival |
| Endpoint classification | not reduced to a single comparison |
The primary endpoint is implant survival, expressed in the registry as a percentage of implant survival. The description defines survival by counting implants revised and specifies cup revision for any reason as the event underlying the Kaplan-Meier survival rate. The stated assessment time is 3 years postoperatively, with the qualification that the study was terminated early.
This endpoint focuses on whether an implant remained unrevised over follow-up. Revision is a clinically interpretable event, and time-to-event methods can use information from participants whose observed follow-up differs. In general, Kaplan-Meier estimation represents the probability of remaining free of an event over time while accounting for censoring, provided the method’s assumptions are appropriate. Censoring means that a participant’s event status is not observed beyond a particular point; it is not itself a revision event.
The registry does not report the estimated survival percentage, the number of cup revisions, a confidence interval, or a survival curve. It also does not give the number at risk at the 3-year timepoint or describe censoring. The endpoint definition and timeframe are therefore available, but the observed estimate and its precision are not reported in the registry record. The early-termination qualification makes details about the amount and distribution of follow-up especially relevant to interpreting a time-specific estimate.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record establishes a planned primary measure and a broad study design, but it does not provide the numerical primary result. Although implant survival is described as a Kaplan-Meier rate at 3 years, no estimate, confidence interval, number of revisions, or analysis is posted. The record lists 0 analyses. It is therefore not possible to describe the observed survival rate, judge its precision, or compare it with a benchmark from the information in the record.
The study’s non-controlled design shapes what even a complete result could establish. An outcome estimate among recipients could describe observed implant experience under the study’s follow-up conditions. Without a control group, it could not by itself isolate how outcomes would differ under another device or treatment. The record does not state an allocation method, and it should not be interpreted as evidence from a randomized comparison.
The timing also deserves care. The primary endpoint is framed at 3 years postoperatively, while the record notes early study termination. These statements do not reveal how many participants reached that timepoint, how many were censored earlier, or whether follow-up differed across participants or centers. A Kaplan-Meier estimate can incorporate censored observations, but interpreting it requires information about the observed follow-up and the assumptions behind censoring. Those details are not reported in the registry record.
The adverse-event information is descriptive and separate from a causal comparison. Among the group titled patients who received the Stafit Acetabular System, 10 of 166 participants at risk are listed as affected by serious adverse events; 11 of 166 are listed as affected by other adverse events, and 6 deaths are recorded. The most frequent serious-event terms listed are each paired with 0.6%. These counts and listed percentages do not establish comparative risk, and the record does not give enough detail to determine overlap among event categories or the timing of events.
The secondary outcomes are named, but their findings are not reported. No numerical Harris Hip Score results, complication summaries beyond the adverse-event entries, or statistical analyses are listed. As a result, the record supports a description of what investigators intended to measure and what adverse-event counts were posted, but not a quantitative conclusion about the primary endpoint, changes in pain or function, or comparative safety and performance.
9. Statistical Methods Explained
Statistical methods matter because the design and endpoint determine what conclusions an estimate can support. In this study, the registry identifies a prospective, multicenter, non-controlled design and a Kaplan-Meier implant-survival endpoint. It does not report the protocol, statistical analysis plan, model details, or any completed analyses. The explanations below describe general statistical ideas, not additional methods confirmed for this study.
What a time-to-event endpoint represents
In general, a time-to-event endpoint records the time until a defined event occurs. Here, the event named in the endpoint description is cup revision for any reason. A participant without a recorded revision during observed follow-up contributes information about remaining event-free up to the last time their status is known. That participant may be censored after that point. Censoring is a feature of incomplete observation time, not proof that the event never occurred.
Kaplan-Meier estimation is a nonparametric method commonly used to estimate event-free survival over time. At each event time, the estimate reflects the observed events among people still under observation and at risk immediately before that time. The estimate is updated across event times. This allows participants to contribute observed follow-up even when not all participants are observed for the same duration. The registry names this method, but it does not post the event times, numbers at risk over time, curve, or estimate.
In general, interpreting Kaplan-Meier estimates relies on assumptions about how censoring relates to the chance of the event. If participants are censored for reasons associated with their underlying event risk, a simple estimate may not represent the experience that would have been observed with complete follow-up. The registry record does not describe reasons for censoring or provide information to assess this assumption. Early termination makes the duration and completeness of observation pertinent, but the record does not report participant-level follow-up.
How to read an estimate and its precision
In general, a point estimate is a single value summarizing the data under a stated method. A confidence interval gives a range of values compatible with the data and method under repeated-sampling assumptions; it conveys precision, not a guarantee that the true value lies in that particular interval. A narrow interval usually indicates greater precision than a wide interval, while neither interval width nor the point estimate alone resolves possible bias or limitations of study design.
No survival estimate or confidence interval is reported in the registry record. Thus, neither the magnitude of implant survival nor the precision of an estimate can be assessed. The count of participants enrolled is not a substitute for the number contributing information to a time-specific estimate: the risk set can change as events and censoring accumulate. The record does not report the risk set at the 3-year timepoint.
What a non-controlled design can estimate
In general, an uncontrolled follow-up study can characterize outcomes in the observed group, subject to how participants were selected, followed, and assessed. A comparison with an external benchmark would require a suitable benchmark and attention to differences in patient mix, outcome definitions, follow-up, and care. No such benchmark or comparative analysis is reported. Without a concurrent control group, an observed outcome cannot separate the device’s contribution from other influences on outcomes.
Prospective follow-up can define measurements before outcomes occur, while a multicenter design can include experience across more than one center. Those features do not by themselves establish complete follow-up, consistent measurement, or representativeness. The registry does not provide center-level results or enough detail to assess consistency among centers.
Planning illustrations and observed results
In general, sample-size planning asks how much information may be needed to detect a chosen effect under stated assumptions. The planning illustrations associated with this record are based on the observed effect, use a two-sided significance level of 0.05, assume equal allocation between two arms, and use a normal approximation. The illustrations define the effect to detect as a stated fraction of the observed effect. For time-to-event illustrations, the displayed quantity is the total number of events; for other illustrations, it is participants per arm.
These are planning assumptions, not evidence that the study was designed or analyzed in that way. This study is non-controlled, so an equal-allocation, two-arm planning illustration should not be mistaken for the actual study structure. The registry does not report its own sample-size justification, any target based on a protocol, or an observed-effect estimate for the primary endpoint. The assumptions also do not yield observed power or establish that the study had adequate information for its outcomes. No planning sample-size results should be interpreted as participant counts actually enrolled or analyzed.
What the registry’s analysis listing establishes
The registry lists 0 analyses. This means the record does not present statistical analyses for the outcomes in the record. It does not establish whether analyses were performed outside the registry, and it does not explain why results are absent. No adjustment strategy, subgroup analysis, handling of repeated measurements, or sensitivity analysis is reported. Those methods should not be inferred from the endpoint description or from general conventions in clinical research.
10. Multiplicity, Missing Data and Analysis Populations
The record lists four outcome measures: implant survival as the primary outcome and secondary measures concerning pain and functional performance on the Harris Hip Score and safety based on complications. It does not report how many statistical tests were planned, whether a hierarchy among outcomes was specified, or whether any adjustment for multiple comparisons was used. A multiplicity strategy is not reported in the registry record.
In general, testing several outcomes or timepoints can increase the chance of at least one apparently notable result when each is assessed separately. Prespecified outcome priorities and an explicit testing strategy help readers understand which findings are confirmatory and which are exploratory. The outcome labels alone do not reveal such a strategy. Since the registry lists 0 analyses and no numerical outcome results, there are no reported tests or estimates to evaluate for multiplicity.
Missing-data procedures and analysis populations are also not reported in the registry record. The record does not say how missing Harris Hip Score observations, incomplete follow-up, withdrawals, or other unavailable measurements were handled. It does not identify an intention-to-treat, per-protocol, or safety population. The enrollment count of 166 does not establish the number included in an analysis for any particular endpoint.
For the time-to-event endpoint, censoring is a general feature of survival analysis, but the registry does not report censoring counts, reasons, or an approach to sensitivity analysis. The endpoint’s 3-year timeframe and the early-termination qualification do not by themselves establish which participants contributed data at that time. These absences limit assessment of completeness and the relationship between the enrolled group and any outcome estimate.
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 |
|---|---|---|---|
| Patients Who Received the Stafit Acetabular System | 10 | 166 | 6.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Patients Who Received the Stafit Acetabular System | 6 of 166 |
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 |
|---|---|
| Patients Who Received the Stafit Acetabular System | 11 of 166 |
Most frequent serious adverse event terms
| Event term | Organ system | Patients Who Received the Stafit Acetabular System |
|---|---|---|
| Femoral Implant Fracture | Surgical and medical procedures | 1 of 166 |
| Death (Stroke) | Blood and lymphatic system disorders | 1 of 166 |
| Death | General disorders | 1 of 166 |
| Infection | Infections and infestations | 1 of 166 |
| Deep Infection <6 Weeks | Infections and infestations | 1 of 166 |
| Infection | Infections and infestations | 1 of 166 |
Most frequent non-serious adverse event terms
| Event term | Organ system | Patients Who Received the Stafit Acetabular System |
|---|---|---|
| Deep Infection <6 Weeks | Infections and infestations | 1 of 166 |
| Stroke | Blood and lymphatic system disorders | 1 of 166 |
| Peroperative fracture of the femur | Surgical and medical procedures | 1 of 166 |
| Vascular Injury | Vascular disorders | 1 of 166 |
| Fracture femur | Surgical and medical procedures | 1 of 166 |
| Pseudoarthrosis | Musculoskeletal and connective tissue disorders | 1 of 166 |
| Suspicion infection | Infections and infestations | 1 of 166 |
| Axonal mononeuropathy | Nervous system disorders | 1 of 166 |
| Total Knee Arthroplasty Left | Surgical and medical procedures | 1 of 166 |
| Fall | Social circumstances | 1 of 166 |
Serious events with the highest arm-level rate: femoral implant fracture (0.6%), death (stroke) (0.6%), death (0.6%), infection (0.6%), deep infection <6 weeks (0.6%).
The safety entries are counts for the group titled patients who received the Stafit Acetabular System. The registry lists 166 participants at risk for serious adverse events, with 10 affected. It also lists 166 at risk for other adverse events, with 11 affected, and records 6 deaths. These are descriptive figures, not results from a comparison with another group.
The listed serious adverse-event terms include Femoral Implant Fracture, Death (Stroke), Death, Infection, and Deep Infection <6 Weeks; each is paired with 0.6%. The registry does not provide event-level details in these entries, so the terms and percentages should be read as the reported listings rather than as a complete account of clinical context, timing, severity, or relatedness to the device.
Counts of affected participants are not necessarily counts of distinct events: one participant may experience more than one event, but the record does not report whether this occurred. The relationship between the death count and the listed death terms is also not explained. The registry does not report a comparator, event rates over person-time, or an attribution assessment. Therefore, these entries describe what was recorded, but do not by themselves establish a causal link or a comparative safety effect.
12. What the Result Does, and Does Not, Mean
The record supports several clear descriptive statements. The study was a prospective, multicenter, non-controlled post-market follow-up study of the Zimmer Stafit Acetabular System, with 166 participants enrolled. It was terminated, and the primary endpoint was defined as a Kaplan-Meier implant-survival rate based on cup revision for any reason at 3 years postoperatively, qualified because of early study termination. The registry also lists secondary measures related to pain, function, and complications.
The record does not report the numerical primary endpoint result, a confidence interval, the number of revisions, or results for the secondary measures. It lists 0 analyses. Consequently, readers cannot use this record to quantify implant survival at the stated timepoint, evaluate statistical precision, or determine whether pain or functional performance changed. The safety counts can be described as posted, but they do not provide a comparison or establish causality.
The non-controlled design is a central boundary on interpretation. Even if an outcome estimate were available, it would describe the observed group rather than estimate a difference against another treatment group. No randomized comparison is described. The record also lacks information on analysis populations, participant-level follow-up, missing data, and the handling of censoring. These gaps prevent a full appraisal of who contributed to each result and how complete the observations were.
The early-termination note gives important context but does not specify the circumstances, consequences for follow-up, or reasons for stopping. The registered timeframe should not be confused with proof that all participants were observed through the full period. The record does not report enough detail to resolve that question.
Accordingly, the evidence recorded is best understood as an incomplete registry account of a post-market follow-up study, not as a comparative estimate of device effects. Missing results should not be interpreted as evidence for or against a particular outcome. The registry’s stated study purpose and endpoint tell readers what was to be assessed; the absent analyses mean the posted record does not answer those outcome questions quantitatively.
13. Why This Trial Matters Statistically
This study illustrates a distinction central to clinical statistics: defining an outcome is not the same as reporting its estimate. The registry gives a specific primary endpoint—implant survival measured with a Kaplan-Meier rate for cup revision for any reason—and a stated timepoint of 3 years. Yet it does not report the survival estimate, its uncertainty, or the number of revisions. Without those results, readers cannot assess the observed magnitude or precision.
The design also illustrates why an outcome and a treatment comparison are different statistical questions. A non-controlled follow-up study can describe experience among device recipients, but does not create a concurrent counterfactual group. The record’s post-market purpose is clear, while a comparative effect is not estimable from the design described. The listed adverse-event counts likewise remain descriptive without a comparator.
Time-to-event analysis is particularly sensitive to how observation time is represented. Kaplan-Meier methods are useful when participants have differing follow-up, but interpretation depends on events, risk sets, censoring, and assumptions. The early-termination qualification makes these details important, while the registry does not report them. This shows why a method name alone is not enough to assess an analysis.
Finally, the absence of analyses and outcome results demonstrates the importance of complete registry reporting. A clearly stated endpoint and enrollment count support understanding of the study’s intent and broad scale, but cannot substitute for results, uncertainty, analysis populations, or missing-data methods. Statistical interpretation depends on both the design and a transparent account of what was observed and analyzed.
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 limitations specific to this record constrain interpretation. The study is marked terminated, and the primary outcome description explicitly links its 3-year postoperative timeframe to early study termination. The registry does not explain why the study ended early, how termination affected planned follow-up, or how many participants remained under observation at relevant times.
No numerical implant-survival result is reported. The record also lacks the number of cup revisions, a confidence interval, a survival curve, and risk-set information. Although Kaplan-Meier estimation is named, the record does not report censoring patterns or how censoring was handled in practice. These omissions prevent assessment of both the outcome magnitude and its precision.
The non-controlled design provides no concurrent comparison group. Allocation is not stated, and the study should not be treated as randomized. The record does not provide enough detail about eligibility, recruitment, centers, participant flow, or analysis populations to judge how the enrolled group relates to the population of interest or to determine who contributed to each outcome.
The secondary outcomes are named without numerical findings. The registry lists 0 analyses, and does not report a statistical analysis plan, multiplicity approach, missing-data procedures, or sensitivity analyses. The adverse-event entries give counts and selected terms, but not event timing, relatedness, participant-level overlap, or a comparative assessment. These are limitations of the available registry record; the record does not establish whether additional material exists elsewhere.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Post Market Clinical Follow-Up of the Zimmer Stafit Acetabular System — NCT04079114.
- Registry record last updated 2020-06-30; status last verified 2020-06.
- Results first posted 2020-06-30.
- 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.
Continue through the Clinical Biostats statistical pathway
Use this trial's endpoint as a starting point for deeper study of effect measures, confidence intervals, and sample-size planning.
18. Record Summary
NCT04079114 is a post-market clinical follow-up study of the Zimmer Stafit Acetabular System sponsored by Zimmer Biomet. It is described as prospective, multicenter, and non-controlled, with 166 participants enrolled. The recorded start date is 2011-04-28, the primary completion date is 2017-01-24, and the status is terminated.
The primary endpoint is a Kaplan-Meier implant-survival rate based on cup revision for any reason at 3 years postoperatively, with the timeframe qualified because of early study termination. Secondary outcomes concern the Harris Hip Score and complications. The registry lists 0 analyses and does not report numerical outcome results. It records 10 participants affected by serious adverse events, 11 by other adverse events, and 6 deaths in the device-recipient group.