Mentor MemoryGel Post-Approval Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Mentor MemoryGel Post-Approval Study (NCT00756652), a registered phase not stated study. The primary outcome is Kaplan Meier Estimated Cumulative Incidence of Reported Complications.

2. Clinical Question

The study is a post-approval monitoring study, rather than a randomized comparison. Allocation is not stated, and the record cautions that the arms are not a like-for-like control comparison. The clinical question is consequently descriptive: what cumulative event experience was estimated for MemoryGel participants under the available follow-up and reporting? It cannot be reframed as a comparative estimate of MemoryGel versus saline from these posted outcomes.

3. Trial Design

The Mentor MemoryGel Post-Approval Study is listed as a completed post-approval study of Mentor silicone gel-filled breast implants. The registry record gives an enrollment of 42491 and identifies breast reconstruction, breast augmentation, and breast revision as conditions. Its stated purpose was to satisfy an element of FDA post-approval monitoring requirements. The study began on 2006-11-01, and its primary completion date is 2019-07-31.

The record names two device groups: MemoryGel breast implant participants and saline breast implant control participants. The MemoryGel group received Mentor silicone gel-filled implants during augmentation, reconstruction, or revision surgery; the saline group received saline-filled implants during those types of surgery. Allocation is not stated. The registry record explicitly warns that this was not a randomized comparison and that the arms are not a like-for-like control comparison.

The scope of data collection changed during the study. The record says an FDA-approved protocol amendment in January 2015 limited collection to secondary procedure and reoperation data for MemoryGel participants. It also says that no data collection was required for saline control participants and that no outcome measures are reported for that arm. Reasons for reoperations is listed as a secondary outcome.

The primary endpoint description draws on follow-up and reoperation or explantation reports from 41,452 participants in the Original study, with follow-up and additional reoperation or explantation reports on 11,101 participants in the ReOperation phase. These are descriptions of the data sources for the analysis; they should not be added or treated as mutually exclusive groups. Participants without post-operative follow-up were excluded from the Kaplan-Meier analysis. The registry record does not report further details about recruitment, allocation procedures, site structure, or the statistical plan.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: In January 2015, the FDA approved a protocol amendment that limited the scope of the study to the collection of only secondary procedure and reoperation data for the MemoryGel arm participants. No data collection is required for the Saline Breast Implant Control group participants and no outcome measures are reported for this study arm.

Original Phase

Reasons for not completing this period:

Re-Op Phase

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Per the FDA-approved protocol amendment, no data collection is required for the Saline Breast Implant Control group participants and no outcome measures are reported for this study arm. The number of participants each year is based on participants with post-op follow-up in that year

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.

6. Primary Endpoint

The registry lists the primary outcome as Kaplan Meier Estimated Cumulative Incidence of Reported Complications, measured over 10 years.

The primary endpoint is titled “Kaplan Meier Estimated Cumulative Incidence of Reported Complications.” Its unit is cumulative reoperation events, and the stated timeframe is 10 years. The description says the Kaplan-Meier estimate of cumulative incidence of reoperation and explantation was calculated on a patient-level basis using follow-up and event reports.

An event-based endpoint can describe how experience accumulates over follow-up, rather than simply counting events without regard to when they occurred. In general, Kaplan-Meier estimation uses information from participants while they are followed and accounts for participants whose follow-up ends before an event is observed. This makes it a common approach for describing time-to-event data. It does not, by itself, establish that a device caused an event or that one treatment is better than another.

Here, the endpoint’s title refers broadly to reported complications, while its description specifies reoperation and explantation. The record gives a 95% confidence interval as the dispersion measure but does not state the estimate or interval limits. It also does not report the event definition in enough detail to determine which individual procedures or clinical circumstances were counted. The posted record therefore identifies the endpoint and its general measurement approach, but does not provide a numerical estimate to interpret.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The statistical method named for the primary endpoint is Kaplan-Meier estimation. The registry record describes the result as a patient-level cumulative incidence estimate of reoperation and explantation, with a 10-year timeframe and a 95% confidence interval. It does not provide the numerical estimate, interval limits, or a detailed statistical analysis plan. The explanation below describes the method in general and distinguishes that explanation from what can be confirmed about this study.

What does Kaplan-Meier estimation do?

In general, Kaplan-Meier estimation is used to describe time from a defined starting point until an event. It uses observed event times and the follow-up available for participants who have not yet experienced the event. When a participant’s observation ends without a recorded event, that participant’s follow-up contributes information up to the point it ends; the person is not treated as having experienced the event. This is called censoring.

The approach is useful when participants have different lengths of follow-up. A simple proportion of participants with an event can be difficult to interpret if observation time differs, because participants followed longer have more opportunity for an event to be recorded. A time-to-event estimate incorporates the timing and available follow-up rather than treating every observation as equally long.

For this study, the record says participants with no post-operative follow-up were excluded from the Kaplan-Meier analysis. It does not explain how other incomplete follow-up was handled, how the time origin was set, or how events and censoring were defined in detail. Those implementation choices matter for interpreting a Kaplan-Meier result and are not reported in the registry record.

How should cumulative incidence be understood?

In general, cumulative incidence describes the probability or proportion of participants estimated to have experienced an event by a specified time, under the assumptions of the analysis. The registry endpoint is labeled cumulative incidence and describes reoperation and explantation. It does not specify whether those were analyzed as a combined endpoint, as separate event types, or under another event-counting rule. Nor does the record explain whether events could recur or how repeat procedures contributed to the reported measure. The endpoint’s unit is stated as cumulative reoperation events, but the detailed operational definition is not reported in the registry record.

In time-to-event analyses, a competing event can prevent the event of interest from occurring or being observed in the usual way. Different methods can handle competing events differently. The record does not state whether competing events were present or how they were handled. It is therefore not appropriate to assume that a particular competing-risk method was used. This is a general methodological consideration, not a claim about the study’s analysis.

What does the confidence interval add?

In general, a confidence interval describes statistical uncertainty around an estimated quantity. Its width reflects precision: less precise data or greater variability can result in a wider interval. A confidence interval is not a guarantee that an individual participant’s outcome will fall within its limits, and it does not by itself establish whether an effect is clinically important.

The record specifies a 95% confidence interval but does not report its limits. Consequently, neither the estimate’s precision nor the range of values compatible with the analysis can be assessed from the posted registry information. The interval method itself is also not reported in the registry record.

What can the analysis populations tell us?

The endpoint description says the Kaplan-Meier analysis used follow-up and reoperation or explantation reports from the entire data set of 41,452 participants in the Original study, with follow-up and additional reoperation or explantation reports on 11,101 participants in the ReOperation phase. The record does not clarify the relationship between these data sources, so these figures should not be combined or interpreted as separate populations. The description also says participants with no post-operative follow-up were excluded. It does not give the number excluded, the number at risk at successive times, or the follow-up distribution.

In general, an analysis population definition is important because it states which participants contribute information and under what conditions. Excluding participants without follow-up may be necessary for a time-to-event analysis, but the amount and pattern of missing follow-up can affect how representative the analyzed experience is. The registry record does not report enough information to assess those issues for this endpoint.

Are the planning calculations trial results?

The record describes sample-size calculations as planning illustrations based on the observed effect, not as the trial’s own design. It specifies a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation; the effect to detect is a stated fraction of the observed effect. For time-to-event tables, the stated quantity is the total number of events using the Schoenfeld method; other tables are described as participants per arm. These are planning assumptions, not observed power and not evidence that the trial was designed or analyzed using those assumptions.

The registry record does not report the study’s own sample-size justification, power calculation, interim analyses, or statistical plan. Nor does it state the numerical planning outputs or the specific effect fractions in the information summarized for the endpoint. Those calculations cannot substitute for the missing endpoint estimate and confidence interval. A planning illustration addresses what a hypothetical future study might require under stated assumptions; it does not establish the precision or validity of this completed study’s reported estimate.

10. Multiplicity, Missing Data and Analysis Populations

The record lists three outcome measures and names reasons for reoperations as a secondary outcome. It does not provide the full outcome definitions or indicate how many statistical comparisons were planned. A count of outcome measures alone is not enough to determine how many hypotheses were tested, whether outcomes were analyzed separately, or whether repeated time points or subgroups were examined.

Multiplicity arises in general when several outcomes, comparisons, or analyses are considered. If many tests are performed, the chance of observing an apparently notable result by chance can increase. Prespecified procedures can address this concern, but the registry record does not report whether any multiplicity adjustment or hierarchy of outcomes was used. No hypothesis tests or numerical results are reported for interpretation in the primary endpoint description.

Missing-data information is limited. The record states that participants without post-operative follow-up were excluded from the Kaplan-Meier analysis. It does not state how many participants were excluded, why follow-up was absent, how other missing observations were handled, or whether sensitivity analyses were conducted. In general, missing follow-up can affect the interpretation of time-to-event estimates if participants with incomplete observation differ systematically from those with continued follow-up. Whether that applies cannot be assessed from the registry record.

The protocol amendment in January 2015 limited data collection to secondary procedure and reoperation data for MemoryGel participants. No data collection was required for saline control participants, and no outcome measures are reported for that arm. This limits what can be compared and means the posted record does not support a complete arm-to-arm analysis of the stated endpoint. The analysis populations, handling of missing data, multiplicity procedures, and analysis plan beyond the named Kaplan-Meier method are not reported in the registry record.

11. What the Result Does, and Does Not, Mean

The record establishes that a 10-year Kaplan-Meier estimate of reported reoperation and explantation was the primary endpoint, and it describes the data sources and an exclusion for participants without post-operative follow-up. It does not report the estimate or confidence interval values. As a result, the posted information cannot show how often the endpoint occurred, how precisely it was estimated, or how the result changed over time.

The record also cannot establish a comparative effect between MemoryGel and saline. The saline group has no reported outcome measures because the amendment required no data collection for that arm. The study is not described as randomized, allocation is not stated, and the record explicitly says the arms are not a like-for-like control comparison. The data therefore do not support an inference that one implant type caused more or fewer events than the other.

In general, a cumulative incidence estimate is a summary of observed event experience under a defined analysis. It is not by itself an explanation of why an event occurred, a prediction for every participant, or proof of a causal relationship. Interpretation also depends on the event definition, follow-up, censoring, and completeness of reporting. Several of these details are not reported in the registry record.

The adverse-event summary’s zero entries describe the fields in that record, but do not establish that no adverse events occurred. The record does not provide sufficient context about those entries to support such a conclusion. Similarly, the enrollment figure is not a substitute for the endpoint analysis population: the endpoint description identifies a data set and follow-up sources, as well as exclusion of participants without post-operative follow-up.

The appropriate conclusion is limited to the scope and reporting of the registry: the study was a post-approval monitoring study, and its posted primary endpoint was intended to summarize reoperation and explantation over 10 years. The numerical endpoint result and the information needed to judge its precision are not reported in the registry record.

12. Why This Trial Matters Statistically

This study illustrates an important distinction between a registry’s endpoint description and a reportable statistical result. Naming a Kaplan-Meier cumulative incidence endpoint and a confidence-interval measure tells readers what type of estimate was intended. Without the numerical estimate and interval limits, however, readers cannot assess event frequency or precision. A method label is not a substitute for the result itself.

The record also shows why analysis populations and follow-up descriptions matter. Its endpoint description refers to data from an Original study and a ReOperation phase, and says participants without post-operative follow-up were excluded. These details help identify the available information, but the record does not give the time-specific numbers at risk or explain the relationship between the two data sources. Those omissions constrain assessment of how the follow-up supports the estimate.

The changing scope of collection is statistically consequential for interpretation. After the January 2015 amendment, data collection was limited to secondary procedure and reoperation data for MemoryGel participants, while no outcome measures were reported for saline participants. A named control arm is not automatically a usable comparator; comparable outcome ascertainment is needed for a meaningful arm-level contrast. The registry record expressly cautions that the comparison is not like-for-like.

Finally, planning calculations and completed-study results answer different questions. The record’s sample-size assumptions describe planning illustrations based on an observed effect. They do not provide observed power or replace the primary endpoint estimate. This distinction is useful whenever readers encounter projected sample sizes alongside a study with incomplete numerical outcome reporting: projections concern hypothetical design choices, while an endpoint estimate describes the analysis actually reported.

13. 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 statistical interpretation is that the registry record does not report the numerical Kaplan-Meier estimate or the limits of its 95% confidence interval. The event definition is also incomplete: the endpoint title refers to reported complications, while the description names reoperation and explantation, without explaining the detailed event-counting rules or whether these were combined or separately analyzed.

Follow-up and analysis-population details are limited. The record says participants with no post-operative follow-up were excluded, but does not report how many were excluded, why follow-up was unavailable, how other incomplete follow-up was treated, or how many participants remained at risk over time. It describes Original study and ReOperation phase data sources but does not clarify their relationship. The reported counts should not be combined or interpreted as mutually exclusive groups.

Comparative interpretation is further limited because no outcomes are reported for the saline arm after the protocol amendment limited collection to MemoryGel secondary procedure and reoperation data. The study is not described as randomized, allocation is not stated, and the record warns that the arms are not a like-for-like comparison. No causal or comparative conclusion can be drawn from the listed arms.

The registry record does not report the detailed statistical plan, sample-size justification for the study, missing-data sensitivity analyses, multiplicity procedures, interim analyses, or methods for handling competing events. It also provides limited context for the adverse-event summary, whose fields contain zero values. These limitations concern what can be established from the record; they do not establish that an analysis or data collection was absent beyond what the record explicitly states.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: Mentor MemoryGel Post-Approval Study — NCT00756652.
• Registry record last updated 2020-06-04; status last verified 2020-06.
• Results first posted 2020-06-04.
• 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.

17. Record Summary

The Mentor MemoryGel Post-Approval Study is listed as a completed post-approval monitoring study with enrollment of 42491. The record identifies breast augmentation, breast reconstruction, and breast revision, and names MemoryGel and saline implant groups. A January 2015 protocol amendment limited data collection to secondary procedure and reoperation data for MemoryGel participants; the saline group has no reported outcome measures.

The primary endpoint is a 10-year Kaplan-Meier estimated cumulative incidence of reported complications, described as reoperation and explantation. Participants without post-operative follow-up were excluded from the analysis. The registry record does not report the endpoint estimate, its confidence interval limits, or a detailed statistical analysis plan. It cautions that the study was not randomized and the arms are not a like-for-like control comparison, limiting comparative interpretation.