Prospective Multicenter Post Approval Study of the LPS-Flex Mobile Bearing Knee: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Prospective Multicenter Post Approval Study of the LPS-Flex Mobile Bearing Knee (NCT00854295), a non-randomized na study. The primary outcome is Group 2 - Total Knee Society Score (KSS).

2. Clinical Question

3. Trial Design

This is a prospective, multicenter post-approval study of the NexGen LPS-Flex Mobile Bearing Knee. The registry classifies it as nonrandomized, unmasked, and single-group, with an enrollment of 266 and completed status. The listed start is 2009-04 and primary completion is 2020-06. The record names Zimmer Biomet as sponsor.

The study descriptions distinguish two groups with different enrollment histories. Group 2 is the post-approval cohort: subjects eligible for the mobile-bearing knee were enrolled in a short-term study described as 5 years. Unilateral and bilateral subjects are included in the same arm. Group 1 consists of subjects who received either the fixed-bearing or mobile-bearing LPS Flex device in the earlier Investigational Device Exemption study. The post-approval study followed those subjects from 4 years to 10 years.

Those group labels do not make the design randomized or establish that the groups are exchangeable. Device, enrollment history, and follow-up context differ. The registry also identifies separate safety groups for unilateral and bilateral Group 2 subjects and for the two Group 1 device cohorts. These safety categories should not be mistaken for randomized treatment arms.

The primary outcome is a continuous score assessed at pre-op, 6 week, 6 month, 1 year, 2 year, 3 year, 4 year, and 5 year. The registry does not report the detailed statistical analysis plan, allocation procedures beyond the nonrandomized classification, or a sample-size justification for the original study. The record lists 8 outcome measures and 0 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.

Before assignment: All cases in "Group 1" per the protocol (subjects in the previous IDE study who were eligible to participate in the PAS) have study completed and are not included in these results. A final report for Group 1 was previously approved by FDA on June 29, 2016. Since 2016, only data from Group 2 subjects (PAS Group) was reported to FDA and are applicable to this clinicatrials.gov record.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Only subjects with an evaluable endpoint at each time frame interval were used to calculate mean and standard deviations.

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: Cases were enrolled into a short-term study (5 years) and consisted of cases eligible to receive the LPS-Flex Mobile Bearing Knee implanted by an orthopedic surgeon experienced in primary total knee replacement.

6. Primary Endpoint

The registry lists the primary outcome as Group 2 - Total Knee Society Score (KSS), measured over Pre-op, 6 week, 6 month, 1 year, 2 year, 3 year, 4 year, and 5 year.

The primary endpoint is Group 2’s Total Knee Society Score (KSS), reported as a mean with standard deviation at pre-op and the listed follow-up intervals through 5 years. The registry describes the score as assessing pain and function on a scale from 0 to 200. Lower scores indicate worse knee conditions and higher scores indicate better knee conditions.

A continuous score can describe the distribution of measured pain and function across participants without reducing each participant’s result to a simple event category. Reporting a mean gives a measure of the group’s average score at an assessment time; the standard deviation describes how dispersed individual scores are around that mean. These summaries answer different questions: the mean concerns the group average, while the standard deviation concerns variation among participants.

The registry states that only subjects with an evaluable endpoint at each time-frame interval were used to calculate the mean and standard deviation. Thus the stated analysis population may be different at different assessment times. The registry record does not report the numerical KSS means or standard deviations, nor the number of evaluable subjects at each time point. It therefore does not permit a quantitative description of the score’s observed change over follow-up.

In general, repeated assessments can help describe how a measured outcome varies over time, but a series of group means alone does not establish the within-person pattern. That interpretation also depends on who contributed data at each assessment and on how missing measurements were handled. Those details are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is continuous, and the registry specifies a mean and standard deviation at each assessment time. The study’s design and reporting details determine what these summaries can establish. Several general statistical ideas help clarify their meaning, but the registry record does not report enough numerical results to apply them to the KSS findings.

What does a mean describe?

In general, a mean is a measure of the center of a set of scores. Here, the intended mean is calculated from subjects with an evaluable KSS endpoint at a particular time-frame interval. A mean at one assessment describes that assessment’s included subjects; it does not necessarily describe every enrolled subject, or the same set of subjects as another assessment.

The registry reports no actual KSS means. It is therefore not possible to state the average score at pre-op or any follow-up time, or to describe an observed change between times. The score’s defined range and direction make interpretation possible once values are known, but do not themselves reveal the results.

What does a standard deviation describe?

In general, a standard deviation describes the spread of individual observations around their mean. A small or large standard deviation is not, by itself, evidence about whether a treatment is beneficial or harmful. It is also not the same as a confidence interval. A confidence interval is a range calculated to express uncertainty about an estimate; it depends on the estimate’s variability and the amount of information available.

The registry says that standard deviations were used but does not report their values. It also does not report confidence intervals for the primary endpoint. Consequently, the precision of the mean scores cannot be evaluated from the registry record.

How should repeated time points be viewed?

The KSS schedule includes pre-op and follow-up through 5 years. In general, repeated measurements can describe how an outcome is distributed at successive times. Comparing time-specific group means is not necessarily equivalent to analyzing within-subject change: the subjects contributing to a mean may vary across assessments, especially when only evaluable endpoints are included.

The registry does not report time-specific sample counts, whether the same individuals contributed at each visit, or a model for repeated measurements. It does not report whether a within-person correlation was accounted for, or whether any adjustment was made for baseline score. No such method should be assumed.

What follows from the nonrandomized structure?

In general, random assignment helps balance measured and unmeasured characteristics across comparison groups. This study is classified as nonrandomized and single-group. The primary endpoint is identified for Group 2, rather than as a randomized comparison between device groups. Group 1 comes from an earlier study and includes recipients of either the fixed-bearing or mobile-bearing device, with follow-up described from 4 years to 10 years. Differences between these cohorts could reflect factors other than device type; the record does not report an adjusted comparative analysis.

Thus, a simple contrast between Group 2 and Group 1, if one were made, would not by itself isolate a device effect. The registry’s study classification and cohort descriptions are essential context for reading any group-level summaries.

What are the planning illustrations?

The stated sample-size assumptions describe a planning illustration computed from an observed effect, not the original trial design. The assumptions specify 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 calculations, the stated output is the total number of events using the Schoenfeld approach; other calculations are expressed as participants per arm.

In general, such calculations ask how much information a hypothetical future comparison might require under chosen assumptions. They do not show that the completed nonrandomized study had a particular power, and they do not turn its design into a two-arm randomized trial. The numerical planning outputs are not reported in the registry record. The original study’s sample-size justification is also not reported.

The posted record does not identify the statistical test used for KSS, any covariate adjustment, an interim analysis, or a multiplicity procedure. These methods cannot be inferred from the fact that means and standard deviations were calculated.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists 8 outcome measures, but the primary outcome singled out for this description is Group 2’s Total Knee Society Score. The record does not report a multiplicity plan or explain whether statistical testing across outcomes or assessment times was performed. In general, when many outcomes or repeated comparisons are examined, the chance of at least one apparently unusual result can increase; a prespecified approach to multiple testing can help clarify how results should be interpreted. No such approach is reported, and no KSS tests are reported.

The registry states that only subjects with an evaluable endpoint at each time-frame interval contributed to the corresponding mean and standard deviation. This identifies an evaluable-endpoint analysis population, but does not describe the criteria for evaluability or the handling of missing measurements. The number of subjects with an evaluable KSS at each time is not reported in the registry record. It also does not report whether missing data were imputed, whether participants with missing follow-up were otherwise included, or whether sensitivity analyses were conducted.

In general, missing outcome data can affect interpretation when the people with observed measurements differ systematically from those without them. The direction and extent of any such influence cannot be determined without information about missingness and the results of appropriate analyses. No assumptions about why measurements may be unavailable should be made from the evaluable-endpoint statement alone.

The registry record lists 0 analyses, so it does not provide an inferential analysis population or a model specification for the primary endpoint. Details of a prespecified statistical plan, interim analyses, and adjustments for multiple comparisons are not reported in the registry record.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

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

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: knee pain (2.9%), tibial component loosening (2.9%), cardiac bypass (2.6%), knee joint replacement surgery (1.9%), total hip joint replacement (1.9%).

The registry lists safety information for four groups: Group 2 unilateral, Group 2 bilateral, Group 1 fixed-bearing, and Group 1 mobile-bearing. For each group it gives an at-risk count, an affected count for serious adverse events, an affected count for other adverse events, and a death count. The listed serious adverse-event counts are 17 of 106 for Group 2 unilateral, 0 of 14 for Group 2 bilateral, 8 of 77 for Group 1 fixed-bearing, and 5 of 69 for Group 1 mobile-bearing. The other adverse-event counts are 82 of 106, 14 of 14, 64 of 77, and 14 of 69, respectively. Death counts are 7, 0, 1, and 1, respectively.

These are descriptive counts as listed in the registry, not randomized comparisons. The groups differ in cohort history and include distinct device and laterality categories. The record does not report the time period attached to each safety count, provide event-level detail, or define in the posted safety summary whether affected counts represent people with one or more events or total event occurrences. The meaning of “at risk” is not further described in the registry record.

The registry also lists serious-event terms with percentages: knee pain, 2.9%; tibial component loosening, 2.9%; cardiac bypass, 2.6%; knee joint replacement surgery, 1.9%; total hip joint replacement, 1.9%; and knee arthritis, 1.4%. Their denominator and the attribution of these events are not reported. These entries alone do not establish that a device caused an event or permit a causal comparison.

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

The result that can be read from the registry is primarily a description of study design and planned measurement, rather than a numerical estimate of the primary outcome. Group 2 was assessed with the Total Knee Society Score at pre-op and at intervals through 5 years; the registry defines the scale and states that evaluable subjects contributed to each time-specific mean and standard deviation. The actual means, standard deviations, and evaluable counts are not reported in the registry record.

Without those outcome values, it is not possible to say how the average score changed, how variable scores were, or how precisely any estimated mean was determined. It is also not possible to judge whether score differences were statistically distinguishable from chance or whether they were clinically important. The registry does not report an inferential analysis for the primary endpoint.

The study’s nonrandomized, single-group classification also constrains comparative interpretation. Group 1 contains subjects from a previous Investigational Device Exemption study who received either the fixed-bearing or mobile-bearing device. That history differs from Group 2’s post-approval enrollment, and the registry does not establish these cohorts as randomized controls. Any difference between their descriptive outcomes would not, by itself, establish that the device caused the difference.

The safety entries provide counts by group and selected serious-event terms, but do not establish causation. The record does not specify the relevant time periods or provide enough detail to interpret the counts as comparable event rates. Death counts are listed, but their causes and relationship to device or procedure are not reported.

In general, a registry record can document study conduct and posted outcome summaries, but causal conclusions depend on the design, the completeness of the data, and the analysis. In this case, the record supports a description of the intended KSS endpoint, follow-up schedule, cohort structure, and listed safety counts. It does not support a numerical conclusion about the primary score or a causal comparison between devices.

13. Why This Trial Matters Statistically

This study illustrates an important distinction between a planned endpoint and a reportable result. The registry identifies a continuous primary measure, its interpretation, the intended assessment schedule, and the population used for each summary. Yet it does not report the primary endpoint’s numerical means, standard deviations, or time-specific evaluable counts. Readers therefore cannot assess the magnitude or precision of the outcome from the record.

It also illustrates why design labels matter. A study can contain several device groups without being a randomized comparison. Here, the registry classifies the study as nonrandomized and single-group, while describing Group 1 as subjects from an earlier study and Group 2 as the post-approval cohort. The different enrollment histories and follow-up contexts are relevant when interpreting any descriptive contrast.

Statistical summaries also depend on who contributes data. The registry specifies that KSS summaries use subjects with evaluable endpoints at each interval, but does not give the corresponding counts or explain missing-data handling. A mean at a given time is informative about the included observations; without the denominators and missingness details, its relationship to the enrolled cohort is less clear.

Finally, the record’s planning assumptions should be distinguished from the design and analysis of the completed study. A sample-size illustration based on an observed effect and hypothetical two-arm assumptions is a planning exercise, not evidence that the original study was randomized or that it had a specified level of power. This distinction is especially useful when registry records combine descriptive follow-up, historical groups, safety listings, and planning calculations.

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.

The main limitation for statistical interpretation is that numerical KSS results are not reported in the registry record. Without the means, standard deviations, and evaluable counts at each assessment, readers cannot quantify the observed outcome or its precision. The registry describes the scoring scale and schedule, but not the results needed to evaluate score trajectories.

The study is nonrandomized and classified as single-group. Group 1 comes from an earlier Investigational Device Exemption study, whereas Group 2 is the post-approval cohort. The record does not describe a randomized comparison or report an adjusted comparative analysis. The two cohorts therefore should not be treated as interchangeable controls.

Group 2 combines unilateral and bilateral subjects in the same arm, and the registry does not report separate primary-outcome summaries for those categories. It also does not report detailed participant characteristics, baseline KSS values, or the time-specific number of participants contributing to each score summary. Their absence limits assessment of cohort composition and the comparability of measurements over time.

Although the record states that only evaluable endpoints were included at each interval, it does not report criteria for evaluability, missing-data methods, imputation, or sensitivity analyses. Statistical tests, covariate adjustment, handling of repeated observations, multiplicity control, and interim analyses are not reported in the registry record.

The safety information is limited to listed group counts and selected event terms. The registry does not report the period covered by each count, the event definitions in detail, or whether listed events were attributed to the device. The group structures and histories also differ, limiting direct comparison of these descriptive entries.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Prospective Multicenter Post Approval Study of the LPS-Flex Mobile Bearing Knee — NCT00854295.
• Registry record last updated 2023-02-14; status last verified 2023-01.
• Results first posted 2023-02-14.
• 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.

18. Record Summary

The registry describes a completed, prospective, multicenter, nonrandomized, single-group post-approval study of the NexGen LPS-Flex Mobile Bearing Knee, with enrollment of 266. Group 2 is the post-approval cohort of unilateral and bilateral recipients; Group 1 comprises subjects from an earlier Investigational Device Exemption study who received either a fixed-bearing or mobile-bearing device.

The primary outcome is Group 2’s mean Total Knee Society Score with standard deviation, assessed from pre-op through 5 years among subjects with evaluable endpoints at each interval. The scale ranges from 0 to 200, with higher scores indicating better knee conditions. Numerical primary-outcome results and time-specific evaluable counts are not reported in the registry record. Safety counts and selected serious-event terms are listed, but the record does not establish causation or a randomized comparison.