Mobile - Bearing Knee Study: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Mobile - Bearing Knee Study (NCT00765362), a non-randomized phase 3 study. The primary outcome is Knee Society Score Evaluation.

2. Clinical Question

In statistical terms, this is a descriptive question about the recorded knee rating score in a selected group after treatment. The record does not state a comparative treatment-effect question, and no efficacy conclusion can be drawn from a score value that is not reported.

3. Trial Design

The registry identifies the study as phase 3, completed, nonrandomized, unmasked, and single-group. Its recorded enrollment is 419. The study start is listed as 2000-01, and primary completion is listed as 2008-06. These entries describe the registered study; they do not establish that every enrolled subject contributed data to the primary outcome analysis.

There is one intervention, the Encore Mobile-Bearing Knee, classified as a device. The arm description identifies subjects who were candidates for total knee replacement and met the study’s inclusion and exclusion criteria. No randomized allocation is recorded, and there is no separate comparator arm in the registry description. Masking is listed as none. The record does not report further details about how candidates were selected, how treatment was delivered, or how follow-up was organized.

The primary endpoint is listed at 2 year. Its population description gives a sequence of different analysis and completion counts: 282 subjects completed the study, while only 173 were analyzed for this endpoint because the 2 year visit was completed out of window or data were missing. The registry does not give the analysis cutoff rules, the number in each reason category, or the characteristics of subjects not included in the endpoint analysis.

The record lists three outcome measures and zero analysis entries. It does not report a statistical analysis plan, sample-size justification, interim analyses, or a plan for handling multiple outcomes. The planning assumptions recorded for a separate sample-size illustration are not a description of the study’s actual design: that illustration assumes two arms with equal allocation, whereas this study is registered as single-group. No numerical planning results are reported in the registry record.

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:

Analysis population for the primary outcome, as defined in the registry: Out of the 282 subjects who completed the study, only 173 were analyzed due to either the 2 year visit being completed out of window or missing data.

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 Knee Society Score Evaluation, measured over 2 year.

The primary endpoint is the Knee Society Score evaluation, with the reported measure specified as the average knee rating score and the statistical summary described as a mean with standard deviation. The assessment timeframe is 2 year. The registry describes the knee rating score as covering pain, stability, and range of motion, with deductions for flexion contracture, extension lag, and misalignment.

The scoring description assigns points to pain, stability, and range of motion. It states that a well-aligned knee with no pain, 125 degrees of motion, and negligible anteroposterior and mediolateral instability would receive 100 points. The listed grading categories are Excellent (90-100), Good (80-90), Fair (70-79), and Poor (<70). These categories describe how scores are classified; they do not supply the study’s observed score.

A mean can summarize the average score across the analyzed subjects, while a standard deviation describes the spread of their scores around that average. Such summaries can describe both the level and variability of the measured outcome. The registry does not report either the mean or standard deviation for this endpoint, nor does it report a confidence interval. As a result, the endpoint’s observed value and the precision of its estimate are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes the primary outcome as continuous and specifies a mean and standard deviation. These statistics answer different descriptive questions. The mean represents the average score among the observations included in an analysis. The standard deviation indicates how dispersed individual scores are around that average. Neither is reported for the primary endpoint in the registry record, so there is no numerical estimate to interpret.

What would a confidence interval convey?

In general, a confidence interval expresses the uncertainty associated with an estimated quantity under a specified statistical procedure and its assumptions. It is not a range containing a fixed proportion of individual scores; that is a different kind of interval. A narrower interval generally indicates greater precision for the target estimate, while a wider interval indicates more uncertainty. The registry does not report a confidence interval for the knee rating score, so the precision of its mean cannot be assessed from the record.

Why does the analysis population matter?

The primary outcome description says that 282 subjects completed the study, but only 173 were analyzed for this endpoint. It attributes exclusion from the analysis to a 2 year visit completed out of window or to missing data. This means the reported endpoint population, as described, is a subset of those who completed the study. In general, analyses restricted to subjects with usable, in-window measurements can be affected if availability of those measurements is related to the outcome or to participant characteristics. That possibility does not establish that bias occurred in this study; it means the completeness and selection process matter when interpreting an estimate.

The record does not give the number excluded for each reason, the timing of missingness, or the characteristics of analyzed and non-analyzed subjects. It also does not describe an imputation method or sensitivity analysis. Those details are not reported in the registry record, so the impact of missing or out-of-window visits cannot be assessed.

What does the design allow?

A single-group study can describe outcomes observed in its enrolled and analyzed population. A randomized comparison, by contrast, can support a direct comparison between assigned groups when its design and conduct are appropriate. This record is classified as nonrandomized and single-group, with no comparator arm recorded. Consequently, it does not provide a randomized contrast for the primary score. A change over time, if it were reported, would not by itself identify what would have happened to the same subjects under a different treatment or without the device.

Masking is recorded as none. In general, lack of masking can be relevant when outcomes involve assessment or reporting that may be influenced by awareness of treatment. The score includes evaluations of pain, stability, and range of motion, but the registry does not provide details about who assessed each element or how assessments were conducted. The possible influence of assessment procedures therefore cannot be quantified from the record.

How should planning illustrations be understood?

The registry describes planning assumptions for a separate sample-size illustration: a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect described as a fraction of the observed effect. Those are stated planning assumptions, not evidence that the trial itself used that design or that its sample size was justified by those assumptions. The registered study is single-group, and numerical planning results are not reported in the registry record. Such sample-size illustrations are planning scenarios, not observed power. The record does not report the protocol’s sample-size justification.

General statistical analyses of continuous outcomes may use models or tests to address particular questions, but the choice depends on the design, distribution, and estimand. The registry records zero analysis entries and does not report the test, model, adjustment strategy, or inferential procedure used for the primary endpoint. No recalculated estimate is available from the posted endpoint summaries because the mean and standard deviation are not reported. The registry’s own analysis, if any, cannot be compared with a recalculation when its numerical result is absent.

The registry lists three outcome measures. When several outcomes or tests are considered, multiplicity can increase the chance of at least one apparently notable result if each is tested separately. General approaches include prespecifying a primary outcome, adjusting tests, or treating additional outcomes as exploratory. Which approach was planned or used is not reported in the registry record. The primary endpoint is identified, but that alone does not establish how the other outcomes were handled statistically.

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("Mobile Bearing Knee")
n   <- c(173)
m   <- c(93.1)
sp  <- c(9.9)
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  Mobile Bearing Knee  173  93.100  9.900  91.614  94.586

11. Multiplicity, Missing Data and Analysis Populations

The registry lists three outcome measures and identifies the Knee Society Score evaluation as the primary outcome. It records zero analysis entries. The registry does not report a multiplicity strategy, including whether tests across outcomes were adjusted, ordered hierarchically, or treated as exploratory. In general, considering multiple outcomes can affect how statistical evidence is interpreted; without a stated plan and reported analyses, that issue cannot be evaluated for this study.

The primary outcome population description says that 282 subjects completed the study and that only 173 were analyzed. The stated reasons are a 2 year visit completed out of window or missing data. The record does not give separate counts for these reasons, describe a missing-data method, or report a sensitivity analysis. It also does not state whether other analysis populations were defined.

These details matter because the analyzed subset may not represent all enrolled or completing subjects in the same way. If the availability of an in-window score is related to the score itself or to participant characteristics, an analysis limited to available observations may not reflect the broader group. This is a general statistical concern, not evidence that the study’s result was biased. Since the primary numerical result is not reported, the direction or size of any potential influence cannot be assessed.

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 2% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists 419 at risk for the serious adverse-event category and 0 affected. It lists 419 at risk and 281 affected in the other adverse-event category. These are registry counts for their respective categories; they are not measures of the primary Knee Society Score outcome. The registry does not provide event descriptions under the serious-event terms, and deaths are not reported in the registry record.

A zero recorded count for serious events does not, by itself, establish that the underlying risk is zero. In general, safety interpretation depends on how events were defined, collected, followed, and attributed, as well as on the amount of observation. The registry record does not provide those details or further event-level information, so the scope of the reported counts is limited.

The 281 affected in the other category should not be interpreted as a count of serious events. Nor does the registry entry alone explain the nature, severity, timing, or relationship of those events to the device. The posted counts describe what the registry records; they do not substitute for a fuller safety analysis.

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

The study record establishes that a phase 3, nonrandomized, single-group device study was completed and that it included a primary Knee Society Score evaluation at 2 year. It also provides the score’s components and grading framework. These details clarify what the study intended to assess, but they do not show the observed score or its distribution.

The registry does not report the primary endpoint mean, standard deviation, confidence interval, or test result. As a result, readers cannot determine from the record whether the average score was high or low, how much scores varied, or how precise an estimate would be. The categories in the scoring description are interpretive thresholds, not reported study findings.

The outcome analysis was described as involving 173 subjects, compared with 282 subjects who completed the study. The stated reasons for exclusion from the primary analysis were an out-of-window 2 year visit or missing data. This makes the analysis population important to interpretation, but the registry does not provide additional details for assessing selection or missing-data effects.

The design also limits the kind of inference available. A single-group, nonrandomized record with no comparator does not provide a randomized estimate of how outcomes would differ under another treatment. The registry’s safety counts are descriptive entries and do not fill that gap or provide a substitute for the missing primary score results.

Accordingly, the record supports a description of the registered study, endpoint, analysis population, and posted adverse-event counts. It does not, on its own, establish a treatment effect, demonstrate efficacy, or permit a precise judgment about the primary outcome. Those conclusions would require results and analysis details that are not reported in the registry record.

14. Why This Trial Matters Statistically

This study illustrates why a clearly defined endpoint and a reported endpoint result are both needed for statistical interpretation. The registry describes the Knee Society Score’s content, scoring framework, and assessment timeframe, but gives no numerical mean or standard deviation. Without the observed estimate, neither the outcome level nor its variability can be evaluated.

It also illustrates the distinction between enrollment, completion, and analysis. Enrollment is recorded as 419, while the primary outcome description reports 282 study completers and 173 analyzed for that endpoint. These are different stages of the study population, and they should not be treated as interchangeable. The stated exclusions—an out-of-window visit or missing data—raise questions about the representativeness of the analyzed subset that cannot be resolved from the record.

The single-group, nonrandomized design is another important statistical feature. It can support a descriptive account of observed outcomes, but without a comparator it does not provide a randomized treatment contrast. The study’s phase designation does not change that basic design limitation.

Finally, the record distinguishes a serious adverse-event count from a count in the other adverse-event category, while leaving important context unreported. Understanding event definitions and ascertainment is part of interpreting safety data. Taken together, these features make the record useful for identifying the intended measurement and the limits of the available evidence, while underscoring that outcome estimates, uncertainty, and analysis methods are needed for a fuller statistical assessment.

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 central limitation for interpreting the primary endpoint is that its numerical result is not reported in the registry record. Although the outcome is described as a mean with standard deviation, neither statistic is given, and no confidence interval or test result is reported. The endpoint’s grading rules therefore cannot be connected to an observed study score.

The described analysis population is limited to 173 subjects, although the record says 282 completed the study. It attributes non-inclusion in the analysis to an out-of-window 2 year visit or missing data, but gives no reason-specific counts, missing-data strategy, or sensitivity analysis. The effect of restricting analysis to this subset is not reported.

The registered design is nonrandomized and single-group, with no comparator arm. Consequently, there is no randomized between-group estimate to distinguish the observed outcome from other possible explanations. The record also says masking was absent and does not describe the outcome-assessment procedures in enough detail to assess how the score components were measured.

The registry lists three outcome measures but no analysis entries. Statistical methods, multiplicity handling, protocol-based sample-size justification, and interim analyses are not reported in the registry record. For safety, the record gives category counts but does not provide event-level detail or deaths. These gaps limit interpretation of both the primary outcome and the adverse-event entries; they do not establish that a particular bias or problem occurred.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Mobile - Bearing Knee Study — NCT00765362.
• Registry record last updated 2011-05-11; status last verified 2011-05.
• Results first posted 2011-04-19.
• 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 describes the Mobile - Bearing Knee Study as a completed phase 3, nonrandomized, unmasked, single-group study of the Encore Mobile-Bearing Knee device. Enrollment is listed as 419; the study start is 2000-01 and primary completion is 2008-06.

The primary outcome is the average Knee Society knee rating score at 2 year, described as a continuous measure summarized by a mean and standard deviation. The registry says 282 subjects completed the study and 173 were analyzed for this outcome because of an out-of-window visit or missing data. Numerical primary outcome results and their precision are not reported in the registry record.

The registry lists 0 affected among 419 at risk for serious adverse events and 281 affected among 419 at risk in the other adverse-event category. Deaths are not reported in the registry record. The design has no comparator group, and the record does not report the statistical analysis details needed for a treatment-effect interpretation.