Trident® X3 Polyethylene Insert Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Trident® X3 Polyethylene Insert Study (NCT00958191), a na na study. The primary outcome is Mean Linear Wear Rate at 5 Years.

2. Clinical Question

3. Trial Design

This was an open-label, prospective, post-market, historically controlled, multicenter clinical evaluation of the Trident® X3 polyethylene acetabular inserts. The registry lists the study as a single-group model, with one intervention: the Trident® X3 Polyethylene Insert. Allocation is recorded as NA, and masking as NONE. The study status is COMPLETED. Enrollment is listed as 250.

The registry gives the study start as 2005-05 and primary completion as 2012-07. Its primary objective was to compare linear wear at 5 years postoperative with a polyethylene control-group wear rate. The comparison is described as historical rather than as a randomized or concurrent control comparison. Details about the historical control group—including how it was selected, when and where its observations were collected, and whether measurement procedures were comparable—are not reported in the registry record.

Because the record describes a single-group study, the insert recipients form the evaluated group; the historical reference is not presented as a second randomized arm. This matters when interpreting any comparison: differences could reflect features of the historical reference or measurement process as well as differences in the insert. The record does not describe allocation procedures beyond recording allocation as NA, and it does not report masking beyond recording NONE.

The listed secondary outcomes cover linear and volumetric wear, radiographic stability, Harris Hip Score measures, SF-12 Health Survey score, and Lower Extremity Activity Scale score. The record lists 11 outcome measures and 18 analyses. The specific numerical results, analysis populations, and methods used for those analyses are not reported in the registry record described by the registry record. The record also does not report a protocol, statistical analysis plan, or details of participant follow-up beyond the five-year wear assessment.

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: 250 participants/271 hips enrolled - 29 participants/31 hips censored= 221 participants/240 hips followed. There were 5 revisions, but one bilateral participant had one hip revised and the other hip completed the primary endpoint. This participant is counted as completed and not in the revision category.

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.

Population: Includes participants who received the Trident X3 polyetheylene insert and were not censored from analysis.

6. Primary Endpoint

The registry lists the primary outcome as Mean Linear Wear Rate at 5 Years, measured over 5 years.

The primary endpoint is mean linear wear rate at 5 years, measured in mm/year. The registry defines linear wear as the annual rate of polyethylene removal from the insert, determined by comparing digitized images of serial radiographs collected over 5 years. In practical terms, the endpoint turns serial imaging observations into a rate intended to describe material loss over time.

Wear rate is used because it expresses change in a form that can be related to the period of observation, rather than giving only a single image-based measurement. The endpoint is a continuous measure, and the registry specifies the mean as the summary statistic and standard deviation as the dispersion measure. In general, a mean describes the central value of observations, while a standard deviation describes their spread around that mean. These summaries can help characterize both the typical measured wear and how variable measurements are among participants.

The registry states that the primary objective was to show superiority to a polyethylene control-group wear rate at 5 years postoperative. However, a numerical result for the insert group, the control-group rate, an estimated comparison, and uncertainty around that comparison are not reported in the registry record. The endpoint definition therefore clarifies what was intended to be measured, but does not by itself establish the observed magnitude or precision of wear.

Radiographic measurement also depends on the availability and quality of serial images and on how images are digitized and compared. The specific measurement procedures, reader reproducibility, and handling of missing or unusable images are not reported in the registry record. These details would help readers judge how reliably the measured rate reflects actual material removal.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The study's primary outcome is a continuous measure, mean linear wear rate at 5 years, with units of mm/year. The registry defines it as the annual rate of polyethylene removal from the insert, estimated by comparing digitized serial radiographs over 5 years. The specified summary is a mean with standard deviation as the measure of dispersion. These choices describe the intended form of the outcome summary, but the numerical mean and standard deviation are not reported in the registry record.

What does a mean and standard deviation describe?

In general, the mean is a measure of the center of a set of measurements. It is useful when the scientific question concerns an average rate across the evaluated group. The standard deviation describes how spread out individual measurements are around that average. A relatively wide spread can indicate that observations vary substantially, even when the average is estimated. The standard deviation is not the same as a confidence interval: it describes variation among observations, whereas a confidence interval describes uncertainty about an estimated quantity under specified assumptions. The registry does not report a confidence interval for the primary endpoint.

A mean and standard deviation are most informative when readers also know the number of observations contributing to the analysis, how missing measurements were handled, and whether the distribution was suitable for the chosen summary and analysis. These details are not reported in the registry record for the primary endpoint. The enrollment listing is 250, but the number of participants with usable five-year radiographs or included in the endpoint analysis is not reported in the registry record.

What does the historical comparison mean?

The study is described as historically controlled, and its objective compares the insert's wear rate with a polyethylene control-group wear rate. A historical comparison uses a reference measured outside a concurrent randomized comparison. In general, this can be informative when the historical data and the evaluated group are sufficiently comparable, but differences in participant characteristics, treatment context, follow-up, and measurement can influence the apparent contrast. The identity and source of the historical control, its sample size, its observed rate, and the method used to compare it with the study group are not reported in the registry record.

Because the registry identifies a single-group model and records allocation as NA, it does not describe random assignment to an insert group and a concurrent control group. Masking is recorded as NONE. Without a concurrent randomized comparison, the design does not by itself balance prognostic factors across groups. Open-label status can also matter for outcome measurement if judgments or measurement processes are influenced by knowledge of treatment, though the record does not describe whether such influence occurred. The primary endpoint is based on radiographs, but details about image reading, reader masking, and measurement reproducibility are not reported in the registry record.

How should uncertainty and statistical tests be read?

In general, a confidence interval communicates the uncertainty around an estimate by identifying a range of values compatible with the data and analysis assumptions. A p-value addresses how unusual the observed data would be under a specified null hypothesis and model; it is not a measure of effect size or clinical importance. Interpreting a superiority claim requires knowing the estimated comparison, its uncertainty, the test or model, and the prespecified criterion for success. The registry record does not report the primary endpoint estimate, confidence interval, p-value, or detailed hypothesis-testing procedure.

The record does not state whether the primary comparison was adjusted for other variables, how the historical rate was incorporated, or what assumptions were made about the distribution of wear measurements. It also does not describe whether there were interim analyses or how the analysis plan handled departures from assumptions. These items are not reported in the registry record; no particular method or assumption should be inferred from the endpoint description alone.

What role do secondary outcomes play?

The registry lists secondary measures that include linear and volumetric wear, radiographic stability, mean Harris Hip Score and its pain and range-of-motion scores, mean SF-12 Health Survey score, and mean Lower Extremity Activity Scale score. It lists 11 outcome measures and 18 analyses. Multiple outcomes can provide different perspectives on the study, but each has its own measurement and interpretation. The numerical results and detailed analysis methods for these measures are not reported in the registry record.

In general, examining many outcomes or analyses increases the chance that some results may appear notable by chance if each is interpreted without regard to the full set of analyses. Methods for addressing multiplicity may include prespecifying a primary endpoint, adjusting inferential thresholds, or treating secondary findings as exploratory. The registry identifies a primary endpoint, but multiplicity procedures and the statistical analysis plan are not reported in the registry record. The number of analyses alone does not show which tests were confirmatory or how findings were interpreted.

10. Confidence Intervals for Each Arm

No two-arm comparison is shown for this trial, but each arm's mean can be given with a t-based 95% confidence interval computed from the posted mean, spread and number of participants.

R code and output

arm <- c("Trident® X3 Polyethylene Insert")
n   <- c(110)
m   <- c(0.016)
sp  <- c(0.068)
sd  <- sp      # posted standard deviations
for (i in seq_along(n)) {
  se <- sd[i] / sqrt(n[i]); h <- qt(0.975, n[i] - 1) * se
  cat(sprintf("CARM|%s|%d|%.3f|%.3f|%.3f|%.3f\n", arm[i], n[i], m[i], sd[i], m[i] - h, m[i] + h))
}

CARM  Trident® X3 Polyethylene Insert  110  0.016  0.068  0.003  0.029

11. Multiplicity, Missing Data and Analysis Populations

The registry identifies mean linear wear rate at 5 years as the primary outcome and lists 11 outcome measures and 18 analyses. It also names several secondary measures, including volumetric wear, radiographic stability, hip score measures, SF-12 Health Survey score, and Lower Extremity Activity Scale score. However, the registry record does not report a statistical analysis plan describing the order of testing, whether secondary outcomes were exploratory, or any adjustment for multiple comparisons. When many outcomes or analyses are considered, general statistical practice recognizes that unadjusted testing can increase the chance of chance findings; the record does not establish whether that issue was addressed.

The record does not describe missing-data handling, reasons for missing assessments, or the number of participants contributing data to each outcome. The enrollment listing of 250 does not establish how many had evaluable five-year radiographs or completed other assessments. It also does not report an analysis population definition, such as how participants with incomplete follow-up were handled. These details are not reported in the registry record.

For a longitudinal radiographic endpoint, missing or unusable images could affect which observations contribute to a wear estimate. In general, missingness can influence results when the availability of measurements is related to participant status or measured outcomes. This is a methodological consideration, not a claim about what occurred in this study: reasons for missing images and the methods used to address them are not reported in the registry record.

The record also does not report interim analyses, stopping rules, or a sample-size justification for the trial's own design. Those aspects should not be inferred from the enrollment listing or from planning illustrations associated with other calculations. Without the analysis plan and missing-data details, the extent to which the reported study results—if available elsewhere—would be robust to analytic choices cannot be assessed from this registry record.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: non-operative site (5.9%), operative site (4.6%).

The registry lists operative adverse events with 12 serious events among 240 at risk, and non-operative adverse events with 33 serious events among 221 at risk. These are category-specific counts as recorded in the registry; they should not be added or treated as a single participant total. The record does not explain whether an individual could contribute events to more than one category or how repeat events were counted.

The registry also lists top serious-event terms as Non-operative Site at 5.9% and Operative Site at 4.6%. These percentages are reported as terms, but the record does not provide the underlying term-level counts or explain the exact calculation and coding conventions. They should therefore be read as registry-listed percentages rather than reinterpreted into new event rates.

In general, adverse-event counts describe events observed and recorded under a study's ascertainment procedures. Interpreting them requires context about event definitions, follow-up duration, severity grading, relatedness assessment, and whether counts refer to people or events. Those details are not reported in the registry record. The deaths field is null; deaths are therefore not reported in the registry record. These safety figures do not answer the primary question about five-year linear wear and do not establish a comparison with a control group.

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

The registry record documents a prospective, post-market evaluation of the Trident® X3 Polyethylene Insert and identifies a specific primary question: whether its mean linear wear rate at 5 years was superior to a polyethylene control-group wear rate. The endpoint is defined in mm/year and based on serial radiographs. This is useful information about the intended measurement and comparison.

However, the numerical primary endpoint result is not reported in the registry record. The historical control rate, an estimated contrast, and uncertainty around that contrast are also not reported. Thus, the record does not allow readers to determine the observed wear rate, the size or direction of a difference, or how precisely the comparison was estimated. The study objective is not itself evidence that the objective was achieved.

The design also limits what a comparison can establish. This is a single-group, historically controlled study, not a randomized comparison against a concurrent control. In general, historical comparisons may be affected by differences in participants, clinical context, follow-up, or measurement procedures. The information needed to assess those sources of comparability is not reported in the registry record. The open-label design and absence of masking are also relevant design features, although the record does not establish that they changed the measurements.

The listed secondary outcomes and adverse-event counts contribute context about the study's scope and recorded safety information, but their numerical results and detailed methods are not reported in the registry record. They cannot substitute for the missing primary wear comparison. The listed serious-event counts should be interpreted within their respective categories and not as evidence about the primary wear outcome.

In general, an endpoint result, its uncertainty, and the methods used to obtain it are all needed to judge what a study's data support. The record supplies the endpoint definition and design description, but not the primary numerical result or enough analytical detail for a full appraisal. It therefore supports describing what the study set out to measure, not a conclusion about the magnitude, precision, or clinical importance of the wear comparison.

14. Why This Trial Matters Statistically

This study is statistically notable because its primary question is framed as a comparison, while the design is recorded as a single-group, historically controlled evaluation. That combination makes the source and comparability of the historical wear rate central to interpretation. A clearly defined endpoint does not remove uncertainty about whether the reference group measures the same construct under sufficiently similar conditions.

The primary outcome also illustrates the distinction between defining a measure and reporting evidence about it. The registry specifies mean linear wear rate at 5 years, its units, the radiographic basis, and a standard deviation as the dispersion measure. Yet the numerical mean and comparative estimate are not reported in the registry record. Without those estimates and their uncertainty, the statistical question cannot be evaluated from the record alone.

More broadly, this record highlights why readers need information about analysis populations, missing follow-up, measurement procedures, and prespecified testing. Serial imaging requires repeated observations, and the availability and comparability of images matter to the resulting rate. The registry record does not describe the image-reading procedures or how incomplete imaging was handled. Such details can affect both the reliability of measurement and the interpretation of a mean.

The record lists multiple secondary outcomes and analyses, which illustrates the importance of understanding how a study distinguishes its principal question from additional analyses. A primary endpoint can organize interpretation, but readers also need to know whether secondary findings were exploratory and how multiplicity was addressed. Those methods are not reported in the registry record.

These statistical considerations are useful beyond this study: study design, endpoint measurement, comparator choice, missingness, and uncertainty all shape what a result can support. Here, the registry provides substantial information about the intended evaluation but not the numerical primary results required to judge the comparison.

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 principal limitation for interpretation is that the registry record does not report the numerical result for mean linear wear rate at 5 years or the historical polyethylene control-group rate. It also does not report the comparative estimate, its uncertainty, or a statistical test for the stated superiority objective. The primary question therefore cannot be evaluated from the reported information.

The historical comparator is not described in enough detail to assess comparability. Its source, participant characteristics, follow-up, measurement procedures, and numerical results are not reported in the registry record. Since this is a single-group, historically controlled study rather than a randomized concurrent comparison, differences between the evaluated group and historical reference may complicate interpretation.

Although the endpoint is based on digitized serial radiographs, the record does not report image acquisition standards, reading procedures, reader masking, measurement reproducibility, or handling of images that were missing or unsuitable. It also does not report the number of participants with an evaluable five-year measurement, the analysis population, or how incomplete follow-up was handled. The enrollment listing of 250 should not be taken as the number contributing to the primary endpoint.

The registry lists 11 outcome measures and 18 analyses, but detailed methods for those analyses, multiplicity procedures, and a statistical analysis plan are not reported. Sample-size justification, interim analyses, and stopping rules are likewise not reported in the registry record. The safety information includes category-specific serious-event counts and listed terms, but the record does not fully describe event definitions, ascertainment, coding, or whether counts represent people or events.

These are limitations of the information available in the registry record. They do not establish that the underlying study lacked methods or data; they mean those details cannot be assessed from the record as described.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Trident® X3 Polyethylene Insert Study — NCT00958191.
• Registry record last updated 2018-02-23; status last verified 2018-01.
• Results first posted 2014-07-14.
• 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

The registry identifies NCT00958191 as the Trident® X3 Polyethylene Insert Study, a completed, prospective, open-label, post-market, multicenter, historically controlled evaluation. It lists 250 enrolled participants, a single-group model, allocation as NA, and masking as NONE. The study start is recorded as 2005-05 and primary completion as 2012-07.

The primary outcome is mean linear wear rate at 5 years, measured in mm/year from digitized serial radiographs. The stated objective was to demonstrate superiority to a polyethylene control-group wear rate. The numerical primary result and historical control rate are not reported in the registry record. The record lists 11 outcome measures and 18 analyses, along with category-specific serious adverse-event counts. Further analysis methods, missing-data handling, and details of the historical comparator are not reported in the registry record.