Metal Ions in Ceramic on Metal Total Hip Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Metal Ions in Ceramic on Metal Total Hip Arthroplasty (NCT01437124), a registered phase not stated study. The primary outcome is Cobalt Chromium Levels.

2. Clinical Question

The study rationale focuses on measuring metal ions in people who received this bearing surface and comparing the levels with reference standards. The investigators also describe an interest in relating ion levels to function and X-ray changes. Those aims do not establish that such comparisons or analyses were completed: the registry record does not report their results or analysis methods.

The brief summary says the investigators were concerned about lessons from failures of some metal-on-metal hip replacement designs and reports that prior laboratory and case-report observations had raised questions about metal levels with this implant. These statements explain the motivation for measurement; they are not findings from the registry’s primary outcome. The record characterizes clinical results as excellent at 2 years, but does not provide a clinical measure or supporting analysis for that characterization.

3. Trial Design

The registry describes one arm, “Ceramic on Metal THA,” consisting of people who received a ceramic-on-metal total hip replacement. It records enrollment of 83 and gives no comparator arm. The study is marked completed. Its recorded start is 2011-10, and its primary completion is 2012-05.

Allocation is not stated, and the registry record does not describe randomization. It also does not report a control group or a like-for-like comparison. The study should therefore be read as a report of measurements in the listed treatment group, rather than as a randomized treatment comparison. The record does not supply enough detail to classify the design more specifically or to establish how participants were selected or followed.

The primary outcome is serum cobalt and chromium levels, with a stated measurement time of 2 years post THR. The secondary outcome is chromosomal abnormality. The registry lists two outcome measures, but reports no analysis results. It does not state whether both outcomes were measured at the same visit, how chromosomal abnormalities were defined, or how the measurements were collected.

The enrollment figure describes the registry’s study enrollment; it does not establish how many people contributed a usable primary outcome at the stated time point. The numbers included in each analysis, and how missing measurements were handled, are not reported in the registry record. The sponsor is listed as Hussain Kazi.

The brief summary describes the investigators’ aim to measure metal ion levels in their group and compare them with reference standards, with further interest in function and X-ray changes. A description of an aim is not evidence that every intended analysis was performed. No detailed protocol, study design label, follow-up schedule beyond the primary outcome time, or analytic population is 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

Analysis population for the primary outcome, as defined in the registry: metal ion levels

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 Cobalt Chromium Levels, measured over 2 years post THR.

The primary endpoint is titled “Cobalt Chromium Levels.” It is described as serum cobalt chromium levels post THR, with the unit micrograms/dl, and a measurement time of 2 years post THR. The specified summary is a mean, and its stated measure of uncertainty is a 95% confidence interval. The numerical mean and confidence limits are not reported in the registry record.

Measuring serum levels provides a quantitative way to describe metal-ion concentrations in the people included in the study. The investigators’ stated rationale is to compare levels with reference standards and to add information about this bearing surface. The endpoint itself, however, does not directly measure symptoms, function, implant failure, or long-term safety. Such outcomes would need their own definitions and reported data before they could be assessed.

In general, a mean describes the arithmetic average of measured values. A confidence interval conveys uncertainty around an estimate under the statistical method used; its width is informative about precision. The interval cannot be interpreted without its numerical limits, and neither those limits nor the mean are reported in the registry record. The record also does not specify the assay, sample handling, reference standards, or any transformation of the measurements.

The secondary outcome is chromosomal abnormality. Its definition, measurement method, timing, and results are not reported in the registry record. No conclusion about that outcome can be drawn from the primary endpoint description.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry specifies a continuous primary outcome summarized by a mean and a 95% confidence interval. It does not report the numerical estimate, the interval limits, or the method used to calculate the interval. No inferential analyses are listed. The explanations below describe general statistical concepts; they should not be read as a claim that a particular method was used in this study.

What does a mean describe?

In general, the mean is the arithmetic average of observed measurements. It gives a single summary of the central level in the measured group, but does not show how much participants’ measurements varied. Two groups of measurements can have the same mean but different distributions. A mean can also be affected by unusually high or low observations. For that reason, an outcome report is more informative when it includes a measure of variability or a distributional display alongside the mean.

For serum metal-ion measurements, the unit matters: the registry specifies micrograms/dl. Interpretation also depends on how the sample was collected and measured, whether the measurement process was consistent, and what reference values are being used. These assay and reference-standard details are not reported in the registry record. Without them, even a reported mean would need contextual information for interpretation.

What would a 95% confidence interval add?

In general, a confidence interval gives a range of values compatible with the data under the method’s assumptions and conveys uncertainty about an estimated quantity. A narrower interval indicates greater statistical precision than a wider interval, all else being comparable. The interval is not a range containing most individual measurements; it concerns uncertainty in the estimated mean. Its width can be influenced by the amount of information available and by variability in the measurements.

A confidence interval cannot be evaluated when its limits are absent. The registry states that the mean is to be accompanied by a 95% confidence interval, but the mean and interval are not reported in the registry record. Therefore, neither the magnitude nor the precision of the primary estimate can be described. The record also does not say whether the interval was calculated using a normal approximation, a method accommodating skewness, or another approach.

Why might distributional assumptions matter?

In general, a statistical method for a mean relies on assumptions about the data or the sampling process. If measurements are strongly skewed or contain extreme values, a mean and a conventional interval may not summarize the distribution well. A transformation, robust method, or additional distributional summaries may sometimes be considered, depending on the scientific question and data. These are general options, not methods reported for this study. The registry does not report the observed distribution, diagnostic checks, transformations, or alternative summaries.

Over-dispersion is a general concern when variability is greater than a model assumes. If a model understates variability, standard errors may be too small and confidence intervals may be too narrow. The registry does not identify a model for the primary outcome, so there is no basis to say that over-dispersion was present or how it was handled. For a continuous outcome, variability in the actual measurements would be essential to evaluating precision, but that information is not reported in the registry record.

What can be learned from the planning assumptions?

The registry’s planning illustration is described as based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It describes the effect to detect as a stated fraction of the observed effect. This is a hypothetical planning exercise, not the design description for the reported single-arm cohort. The observed effect, the fractions used, and the resulting planning values are not reported in the registry record.

In general, a sample-size calculation asks what sample size might be needed to detect a specified effect under stated assumptions. It does not show the probability that a completed study has correctly detected an effect, and a planning illustration is not observed power. The registry record does not report its own sample-size justification or establish that the planning assumptions were used to design this study. Any planning values should be understood only as conditional illustrations under their stated assumptions, not as features of the observed cohort.

Equal allocation between two arms is a planning assumption in the illustration. It does not create a second arm in the registry record, which reports one arm. The distinction matters: a hypothetical two-arm calculation cannot be used to infer a comparative result from data without a reported comparison group.

What do the adverse-event entries represent statistically?

The adverse-event fields report counts of people at risk and affected in serious and other event categories. A count of zero affected is a reported count, not a precise estimate that the underlying risk is zero. In general, estimates of event frequency depend on the completeness and duration of surveillance, event definitions, and the denominator actually observed. The registry does not report event ascertainment procedures or follow-up completeness for these entries. Deaths are not reported in the registry record.

These general principles explain how the stated outcome summaries and planning assumptions are usually interpreted. They do not fill in the absent estimates, methods, or analyses. The registry record does not report enough statistical detail to assess the calculation of the primary confidence interval or to reproduce an analysis.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures: the primary cobalt and chromium levels and the secondary outcome of chromosomal abnormality. It reports no analyses. The analysis methods, including any formal tests, confidence intervals beyond the stated primary-outcome summary, or adjustments for multiple outcomes, are not reported in the registry record.

In general, multiplicity arises when several outcomes, time points, subgroups, or comparisons are examined. Considering many results can increase the chance of a seemingly notable finding arising by chance. A prespecified hierarchy or adjustment can help address that issue, but the appropriate approach depends on the study question and analysis plan. No multiplicity strategy or detailed statistical plan is reported in the registry record, so it is not possible to assess how multiple outcomes were treated.

The record gives enrollment of 83 but does not report the number with a measured primary outcome, the number assessed for chromosomal abnormality, or the analysis population for either outcome. It does not state whether all enrolled participants were intended to be analyzed, whether any participants were excluded, or why an outcome might be unavailable. Missing-data methods, if any, are not reported in the registry record.

In general, missing outcome data can affect both the precision and interpretation of an estimate, especially if the likelihood of missingness is related to the measurement or participant characteristics. The registry does not provide information to assess that possibility. There is also no reported sensitivity analysis showing how alternative assumptions about missing measurements might affect results.

11. 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.

The registry lists the ceramic-on-metal THA group as having 83 at risk and 0 affected for serious adverse events. It also lists 83 at risk and 0 affected for other adverse events. No serious adverse-event terms are listed. Deaths are not reported in the registry record.

These entries should be read as the counts recorded in the adverse-event fields, not as proof that no harm occurred. The registry record does not describe the event definitions, collection procedures, reporting window, or completeness of follow-up for these fields. It is therefore not possible to judge from these entries alone how comprehensively events were sought or captured.

In general, a zero count in a study group does not establish that the true event risk is zero. Its interpretation depends on the amount and duration of observation and on the quality of event ascertainment. The record does not provide enough detail to quantify uncertainty around the adverse-event counts or to compare safety with another treatment, because no comparator is reported.

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

The record identifies a clinical question about serum cobalt and chromium levels after ceramic-on-metal total hip replacement, with measurement specified at 2 years post THR. It describes a single reported arm and enrollment of 83. It also identifies chromosomal abnormality as a secondary outcome and lists limited adverse-event counts. These details clarify what the registry entry intended to address and what information it records.

The principal result needed to interpret the primary endpoint—the mean serum level and its 95% confidence interval—is not reported in the registry record. Without those values, it is not possible to describe the level observed, how precise its estimate was, or how it related to a reference standard. The record also does not provide the secondary-outcome findings or results relating ion levels to function or X-ray changes.

The one-arm record cannot establish how the outcome would compare with another bearing surface or with a different treatment group. It does not report a like-for-like control group, and allocation is not stated. The brief summary’s statement about clinical results is not accompanied by a defined clinical outcome or analysis in the registry record. It should not be mistaken for a quantified result on metal ions or long-term safety.

In general, a measurement study can describe levels in the people assessed, but claims about clinical benefit, comparative safety, or long-term effects require appropriately defined outcomes and evidence suited to those questions. The registry record does not report the detailed methods or results needed to make those assessments. In particular, a measurement at the stated time point does not by itself establish what happens over a longer period.

The appropriate conclusion from this entry is limited: it records the study’s aim, one treatment group, the primary outcome definition, and some adverse-event fields, while leaving the primary numerical result and analysis unreported. Missing results should not be interpreted as normal measurements, absence of chromosomal abnormalities, or evidence that the implant is safe or unsafe.

13. Why This Trial Matters Statistically

This study raises a useful statistical distinction between a research question and an answer supported by reported results. The registry gives a specific continuous outcome—serum cobalt and chromium levels—and states that it is to be summarized as a mean with a 95% confidence interval. That is a meaningful framework for describing a group’s measured levels, but the estimate and interval are not reported. A clearly defined endpoint cannot substitute for its numerical findings.

The single reported arm also matters. Measurements from a cohort can describe that cohort if results and methods are available, but they cannot provide a direct comparison with a different bearing surface when no comparator is reported. The registry’s planning assumptions refer to equal allocation between two arms, but those assumptions belong to a hypothetical planning illustration and do not change the listed one-arm study record.

Precision is important for continuous outcomes. A mean without information about variability or a confidence interval gives limited information about how stable the estimate might be. Here, neither the primary mean nor its interval is reported, and the available record does not identify how many observations contributed. This prevents an assessment of precision as well as magnitude.

The entry also illustrates why outcomes, missingness, and analysis plans need to be reported together. The registry lists a secondary chromosomal-abnormality outcome, but its definition and results are absent. It does not report analysis populations, missing-data handling, or multiplicity methods. Those omissions restrict interpretation even before considering the lack of primary results.

Finally, adverse-event counts must be interpreted in context. Zero affected is a reported count for the listed categories, not a complete safety conclusion. Event definitions and ascertainment details are not reported. Taken together, the record is statistically informative about intended measurement and important limits, but it does not provide the numerical outcome evidence needed to evaluate the primary question.

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 primary limitation is the absence of the primary outcome estimate. Although the registry specifies a mean and 95% confidence interval for cobalt and chromium levels, neither the mean nor the interval is reported in the registry record. There are also no reported values for the secondary chromosomal-abnormality outcome.

The reported cohort has no comparator arm. Allocation is not stated, and the registry record does not describe a randomized comparison. As a result, it cannot support a treatment contrast or show whether levels differed from those under another bearing surface. The reference standards mentioned in the brief summary, and any results of comparisons with them, are not reported in the registry record.

Further details needed to assess the outcome are also absent. The record does not report the assay method, sample collection procedures, distribution of measurements, observed variability, number with available measurements, or analysis population. It does not specify how missing measurements were handled, whether measurements were transformed, or how the confidence interval was calculated. No analyses are listed.

The registry identifies chromosomal abnormality as a secondary outcome but does not define the outcome or report how it was measured. It also does not report results relating ion levels to function or X-ray changes, despite mentioning those aims in the brief summary. The clinical characterization in that summary is not accompanied by a specified measure or supporting analysis.

The adverse-event fields list zero affected in the reported categories, but event definitions, surveillance procedures, and follow-up completeness are not described. Deaths are not reported in the registry record. These limitations mean that the adverse-event entries cannot be treated as a comprehensive safety assessment. The record’s stated completion status does not resolve these reporting gaps.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Metal Ions in Ceramic on Metal Total Hip Arthroplasty — NCT01437124.
• Registry record last updated 2016-06-06; status last verified 2016-04.
• Results first posted 2016-06-06.
• 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

NCT01437124 is titled “Metal Ions in Ceramic on Metal Total Hip Arthroplasty.” The registry lists Hussain Kazi as sponsor and marks the study completed. The recorded start is 2011-10 and primary completion is 2012-05. Enrollment is 83.

The record describes one arm of people who received ceramic-on-metal total hip arthroplasty, with no comparator reported. The primary outcome is serum cobalt and chromium levels in micrograms/dl at 2 years post THR, summarized as a mean with a 95% confidence interval. Chromosomal abnormality is listed as a secondary outcome.

No analyses are listed, and the primary estimate, confidence interval, and secondary-outcome results are not reported in the registry record. Serious and other adverse-event fields each list 83 at risk and 0 affected. Deaths are not reported in the registry record.