Retrospective Encore Reverse Shoulder Prosthesis Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Retrospective Encore Reverse Shoulder Prosthesis Study (NCT00765037), a registered phase not stated study. The primary outcome is Survivorship of the Encore Reverse Shoulder Prosthesis.

2. Clinical Question

3. Trial Design

NCT00765037 is titled Retrospective Encore Reverse Shoulder Prosthesis Study. Its official title describes it as a post-market study on the efficacy of the Encore Reverse Shoulder Prosthesis in a small group of subjects. The registry lists the study status as completed, enrollment of 19, a start date of 2008-08, and a primary completion date of 2009-05.

The registry summary says the purpose was to evaluate survivorship and efficacy in a group of no more than 50 subjects for whom data collection had already begun. That description identifies an existing-data context, but does not explain when or how the data were collected, how participants were selected, or what follow-up procedures were used. Those details are not reported in the registry record.

One intervention group is listed: subjects who needed treatment for rotator cuff deficiency or glenohumeral arthritis, received the Encore Reverse Shoulder Prosthesis, and were willing to participate. No other study arm or comparator is described. The allocation method is not stated, and the registry does not offer a like-for-like control comparison. Consequently, the record describes a treated group rather than a randomized comparison.

The primary outcome is a count of subjects who completed all study visits through the 1 year visit. Although the outcome is named prosthesis survivorship, the description does not define device failure or specify whether revision, removal, or another event would count as failure. No primary outcome result or analysis is reported in the registry record. The record lists one outcome measure and no analyses.

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

Reasons for not completing this period:

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 Survivorship of the Encore Reverse Shoulder Prosthesis, measured over 1 year.

The primary endpoint is titled survivorship of the Encore Reverse Shoulder Prosthesis. Its stated measure is the number of subjects who completed all study visits through the 1 year visit. This is a count of participants meeting a follow-up-completion criterion, with the timeframe specified as 1 year.

Completion of scheduled visits can describe whether follow-up information was obtained through the stated visit. It is not, by itself, a direct measure of whether a device remained in place, whether it functioned as intended, or whether a participant experienced a device-related event. The registry description does not state how device failure was defined or how such events would be reflected in this endpoint. That distinction matters when interpreting the word “survivorship”: the outcome’s title suggests a device-focused concept, while its operational description identifies visit completion.

Counting participants can be useful for a simple endpoint, but interpreting the count requires knowing the number assessed, the number meeting the criterion, and how participants without complete follow-up were handled. The registry record does not report the number completing all visits through the 1 year visit, an analysis population, or a missing-data approach. The endpoint is therefore identifiable from the description, but its observed result and precision are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What kind of outcome is described? The primary outcome is a count of participants who completed all study visits through the 1 year visit. A count records how many people meet a stated criterion. To interpret a count as a proportion or rate, a suitable denominator and a clearly defined observation period are also needed. The registry gives enrollment of 19 and a one-year timeframe, but does not report the number meeting the endpoint, the number included in its analysis, or any derived estimate.

General: what would an estimate and confidence interval convey? An estimate summarizes the observed result using the study data. A confidence interval describes the statistical uncertainty around an estimate under the assumptions of the analysis. A narrower interval indicates greater precision, while a wider interval indicates less precision. Neither an estimate nor a confidence interval is reported for this primary outcome in the registry record. No interval can be inferred from enrollment alone, because the endpoint count and analysis details are absent.

General: why does the endpoint definition matter? Statistical methods can only answer questions represented by the recorded outcome. Here, the stated criterion is completion of study visits. A device-survival analysis would generally require a defined failure event and information about whether and when each participant experienced that event, as well as appropriate handling of participants whose follow-up ends before failure is observed. The registry does not state such a failure definition or provide event-time information. It is therefore important not to reinterpret the visit-completion count as an unreported time-to-event estimate.

General: what does a comparator contribute? A comparator provides a reference for estimating how outcomes differ between groups. Random assignment, when used and adequately described, can help make groups comparable at the start of a study. The registry does not describe a comparator or state an allocation method for this study. It therefore provides no basis for estimating a comparative effect or separating changes associated with treatment from other explanations. A single-group count, even if reported, would describe that group rather than establish what a different group would have experienced.

What analysis is reported? The registry lists one outcome measure and no analyses. It does not report a statistical model, test, effect estimate, standard error, confidence interval, or hypothesis-test result for the primary endpoint. The absence of a registry analysis does not establish that no analysis was conducted elsewhere; it means that the statistical analysis is not reported in the registry record.

General: why do missing observations matter? If participants do not complete follow-up, their endpoint status may be unknown. Excluding such participants, treating them as not meeting the endpoint, or using another method can yield different interpretations. The appropriate approach depends on the endpoint, the reasons for missingness, and the analysis plan. The registry does not report the number of participants with missing endpoint information, reasons for missingness, or a method for handling it. The completed study status does not resolve those questions.

What do the safety counts represent? The registry gives counts of participants affected, alongside counts at risk, for serious and other adverse events. These are descriptive entries, not adjusted comparisons. General statistical interpretation of event counts depends on definitions, observation time, event ascertainment, and whether participants can experience multiple events. The record does not provide event terms for serious events, event timing, or a detailed account of ascertainment, so the counts should not be extended beyond their stated meaning.

How should planning calculations be read? General sample-size calculations are planning illustrations based on assumptions; they are not evidence that a study had a particular probability of detecting an effect after completion. The stated planning assumptions specify a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of an observed effect. The assumptions distinguish participant counts per arm from total event counts for time-to-event calculations. This study’s registry description does not present two arms, and it reports no primary endpoint analysis. The planning assumptions therefore do not supply an observed result, a study-specific power assessment, or evidence of a comparative effect.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Encore RSP")
n      <- c(13)
events <- c(13)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Encore RSP  13  13  100.0  75.3  100.0  77.2  100.0  76.8  99.8

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity concerns the risk of misleading statistical conclusions when several outcomes, comparisons, or analyses are examined. The registry lists one outcome measure, titled survivorship of the Encore Reverse Shoulder Prosthesis. It does not report multiple primary outcomes or a set of secondary outcome analyses. A plan for controlling multiplicity, or a statement that such control was unnecessary, is not reported in the registry record.

The record lists no analyses. It does not state whether the primary outcome was assessed using a prespecified statistical test, whether subgroup or sensitivity analyses were planned, or whether any interim analyses were conducted. Those details are not reported in the registry record and should not be inferred from the study’s completed status.

Missing data are also relevant because the endpoint depends on completing all study visits through the 1 year visit. The registry does not report how many participants completed that follow-up, whether any endpoint information was missing, why information might be missing, or how incomplete follow-up was handled. Enrollment of 19 does not establish that all 19 contributed to the endpoint analysis.

The analysis population is not reported in the registry record. It is therefore unclear which participants, if any, were included in an analysis of the primary endpoint. The record also does not describe an intention-to-treat population, a per-protocol population, or any other analysis set. Without those details, the endpoint’s denominator and the potential effect of missing follow-up cannot be assessed from the registry entry.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry reports zero participants affected by serious adverse events among 19 at risk in the Encore RSP group. For other adverse events, it reports 11 participants affected among 19 at risk. These are participant counts in two separately labeled categories; they are not a comparison between treatments.

The registry does not list serious adverse event terms. It also does not report the death count. The other-adverse-event entry does not identify the event types, severity, timing, or relationship to the prosthesis. The counts should therefore be read only as the recorded number of participants affected in each category, not as a complete account of the nature or causes of events.

General: adverse-event counts depend on how events are defined, collected, and attributed, as well as the period during which participants are observed. The record does not provide those details beyond the listed counts and risk totals. It also does not provide a control group, so these entries cannot establish a comparative safety difference.

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

The registry record describes a completed post-market study of the Encore Reverse Shoulder Prosthesis, with enrollment of 19 and a primary outcome framed as survivorship through a 1 year visit. The operational definition is completion of all study visits through that visit. The record also reports the number of participants affected by serious and other adverse events.

The primary endpoint result itself is not reported in the registry record. Consequently, readers cannot tell from this entry how many participants completed all visits, how complete follow-up was, or how precisely the endpoint was estimated. The title of the endpoint should not be taken as evidence of a device-survival estimate, because the stated measure is visit completion and no device-failure definition or time-to-event result is reported.

The safety entries are descriptive counts. Zero participants were recorded as affected by serious adverse events among 19 at risk, while 11 were recorded as affected by other adverse events among 19 at risk. The record does not list the serious event terms, provide the death count, or identify the other events. Without a comparator and fuller event details, these counts do not establish a comparative safety effect.

More generally, a completed registry status does not mean that every planned result is present in the registry entry. Enrollment is not the same as an analysis population, and a count of participants at risk does not establish how many had complete endpoint data. The record does not report the analysis method, confidence interval, hypothesis test, missing-data handling, or a comparative estimate.

The defensible interpretation is therefore narrow: the registry describes the study’s purpose, group, primary outcome definition, and selected safety counts, but it does not report the primary outcome result or statistical analysis. These omissions limit what can be concluded from the registry record. They do not establish whether additional data or analyses exist elsewhere.

14. Why This Trial Matters Statistically

This study illustrates why the operational definition of an endpoint matters as much as its label. “Survivorship” can suggest that a device remained in use without failure, but the registry defines the primary measure as completing all study visits through the 1 year visit. Those concepts are not interchangeable. A reader needs the actual endpoint definition to understand what a reported count would represent.

The record also illustrates the difference between enrollment and an analysis denominator. Enrollment is 19, while the primary endpoint is not reported. Without knowing how many participants completed follow-up or were included in an analysis, the outcome cannot be interpreted as a complete summary of the enrolled group. This distinction is especially important for an endpoint that depends on attending all scheduled visits.

A single treated group can describe what was recorded among participants who received the device, but it does not provide a direct comparison with another treatment. The registry does not describe a comparator or allocation method. A comparative claim would require information that this record does not report.

Finally, safety counts need context. The registry records counts affected by serious and other adverse events, but gives limited detail about the events themselves. Counts are useful descriptive information, yet they do not by themselves explain event type, timing, cause, or comparative risk. Together, these features make the record a useful example of how endpoint definition, analysis populations, follow-up completeness, and study design constrain statistical interpretation.

15. 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 main limitation of interpretation is that the primary outcome result is not reported in the registry record. Although the outcome is defined as the number of subjects completing all visits through the 1 year visit, the record does not give that number or explain who contributed to the endpoint assessment. The endpoint’s name refers to prosthesis survivorship, but the record does not define device failure or report a device-survival analysis.

The registry describes one treated group and no comparator. It does not state an allocation method, and it provides no basis for a like-for-like comparison. The group’s clinical characteristics beyond the listed conditions and treatment context are not reported in the registry record. Further eligibility criteria and the method used to identify or select participants are also not reported.

Follow-up and analysis details are limited. The record does not report the number with complete follow-up, how missing information was handled, the analysis population, or a statistical method for the primary outcome. It lists no analyses. These omissions prevent assessment of endpoint precision and of how incomplete follow-up might affect interpretation.

Safety information is also incomplete: serious adverse event terms are not listed, the death count is not reported, and the other-adverse-event count is not accompanied by event descriptions. The record does not provide a detailed account of event timing or attribution. These limitations describe the registry entry and do not establish whether more information exists outside it.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Retrospective Encore Reverse Shoulder Prosthesis Study — NCT00765037.
• Registry record last updated 2010-08-25; status last verified 2010-08.
• Results first posted 2010-08-25.
• 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.

19. Record Summary

NCT00765037 is the Retrospective Encore Reverse Shoulder Prosthesis Study, described in its official title as a post-market study. The registry lists the study as completed, with enrollment of 19, a start date of 2008-08, and a primary completion date of 2009-05. The study concerns subjects with rotator cuff deficiency or glenohumeral arthritis who received the Encore Reverse Shoulder Prosthesis.

The primary outcome is titled survivorship and is defined as the number of subjects completing all study visits through the 1 year visit. The endpoint result and analyses are not reported in the registry record. The safety entries list zero participants affected by serious adverse events among 19 at risk and 11 affected by other adverse events among 19 at risk. Serious event terms and the death count are not reported. No comparator or allocation method is described.