This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for A Safety Follow Up Study in Australian Subjects Implanted With the SMF Short Modular Femoral Stem Hip System (NCT03646513), a registered phase not stated study. The primary outcome is Metal Ion Level.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT03646513 |
| Phase | Phase not stated |
| Condition | Total Hip Arthroplasty (THA) |
| Allocation | Not Stated |
| Design model | Not Stated |
| Masking | Not Stated |
| Enrollment | 4 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Smith & Nephew, Inc. |
| Results posted | Yes |
2. Clinical Question
The study was intended to collect clinical and radiological information from people who had received the SMF Short Modular Femoral Stem during primary total hip arthroplasty. Its primary question concerned whole-blood cobalt and chromium levels over follow-up, with measurement planned from baseline through study completion, up to 20 years after surgery. The registry record states that the study was terminated before any follow-up visits, so the available information is limited to baseline.
Population
Participants enrolled in Australia after implantation of the SMF Short Modular Femoral Stem for primary total hip arthroplasty. The record reports enrollment of 4 participants.
Intervention
Implantation of the SMF Short Modular Femoral Hip System. This was a follow-up study of people who had already received the device, rather than a trial assigning a new treatment.
Comparator
No comparator group is described. The study is single arm, so it does not provide a like-for-like comparison with another implant or with no implant.
Primary question
What whole-blood cobalt and chromium levels were observed among enrolled participants from baseline through follow-up? Because no follow-up visits occurred, longitudinal levels and changes cannot be assessed from the record.
The broader study description refers to collecting clinical and radiological data to assess safety and efficacy. Secondary outcomes include stem revision, radiographic assessments of loosening and surface wear, and the HOOS JR questionnaire. These planned measures do not create a comparison group; without one, the study is descriptive rather than a controlled estimate of relative effects.
3. Trial Design
This was a prospective, single-arm study with sequential enrollment at one site in Australia. Participants had already received the SMF Short Modular Femoral Stem as part of primary total hip arthroplasty. The registry description anticipated approximately 26 subjects, while enrollment is recorded as 4. The study status is terminated.
The planned follow-up covered baseline through study completion, up to 20 years after surgery. Whole-blood testing for cobalt and chromium was described at baseline and every three years afterward. For participants with pain, swelling, and/or functional limitations that the Principal Investigator assessed as related to the implant, annual testing was also described. These are elements of the planned monitoring schedule, not evidence that the visits or tests occurred.
The registry record states that the study was terminated before any follow-up visits and that only baseline information was available. The start date is 2019-02-14 and the primary completion date is 2020-03-12. The reason for termination is not reported in the registry record. Nor is a detailed recruitment history, the timing of each participant’s implantation, or the reason enrollment ended reported in the registry record.
There is no randomized allocation or control arm described. A single-arm follow-up can describe measurements in the enrolled group, but it cannot by itself distinguish changes associated with the implant from changes over time or other influences. The registry record does not report the protocol’s intended statistical analysis plan, a sample-size justification, or plans for interim 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: Study was prematurely terminated prior to any participants completing follow-up visits.
Overall Study
| Stage | SMF Short Modular Femoral Stem Implanted Subjects |
|---|---|
| STARTED | 4 |
| COMPLETED | 0 |
| NOT COMPLETED | 4 |
Reasons for not completing this period:
| Reason | SMF Short Modular Femoral Stem Implanted Subjects |
|---|---|
| Premature study termination | 4 |
Analysis population for the primary outcome, as defined in the registry: Participants enrolled in the study with available data at the given time point for the outcome specified. Study prematurely terminated prior to any follow-up visits. Therefore, only baseline information was available.
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.
| Characteristic | Unit | SMF Short Modular Femoral Stem Implanted Subjects |
|---|---|---|
| Participants analysed | 4 | |
| Age, Continuous | years | 59.5 (SD 59.0) |
| Sex: Female, Male: Female | Participants | 2 |
| Sex: Female, Male: Male | Participants | 2 |
| Race/Ethnicity, Customized: Race – White | Participants | 3 |
| Race/Ethnicity, Customized: Race – Asian | Participants | 1 |
| Region of Enrollment: Australia | participants | 4 |
| Body Mass Index (BMI) | kg/m^2 | 30.3 (SD 28.0) |
6. Primary Endpoint
The registry lists the primary outcome as Metal Ion Level, measured over Baseline to Study Completion, up to 20 years.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | Standard Deviation |
| Unit | Nanomoles per litre (nmol/L) |
| Endpoint classification | Continuous Endpoint |
The primary endpoint is metal ion level, measured as a mean with standard deviation and expressed in nanomoles per litre (nmol/L). The specified analytes are whole-blood cobalt (Co) and chromium (Cr). Collection was planned at baseline and then every three years through follow-up up to 20 years. Annual collection was also described for symptomatic participants when the Principal Investigator assessed the symptoms as related to the implant.
In general, a laboratory measure such as a blood metal-ion level can be used to characterize participants’ measured levels over time and to monitor a safety-related outcome. Reporting a mean gives a measure of the group’s central level; the standard deviation describes how dispersed individual measurements are around that mean. Neither statistic alone indicates how precise the estimated mean is: that depends on the available data and would ordinarily be assessed with uncertainty measures such as a confidence interval.
For this study, the registry record says termination occurred before any follow-up visits, leaving baseline information only. Numeric baseline cobalt and chromium results, standard deviations, and confidence intervals are not reported in the registry record. There is therefore no longitudinal estimate or comparison of baseline with later measurements to interpret.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The central limitation for interpretation is that the study did not reach its planned follow-up. Although the primary outcome was designed to describe cobalt and chromium levels over time, the registry record says that there were no follow-up visits and only baseline information was available. The numerical baseline results are not reported in the registry record. Consequently, the record does not support a description of the observed level, variation, or trajectory of either analyte.
The planned schedule and the measurements actually available must be kept distinct. The description of collection at baseline and every three years, with additional annual testing in certain symptomatic participants, sets out the intended monitoring. It does not establish that those later collections took place. No repeated measurements are available in the record to assess within-participant change, compare time points, or evaluate whether levels were stable or changing.
The study was single arm and enrolled 4 participants. Even if follow-up results had been available, the absence of a comparator would limit conclusions about whether any observed pattern was specific to the implant rather than reflecting other influences. Here, the lack of follow-up further limits the descriptive question: there are no recorded post-baseline levels to characterize.
The registry lists secondary outcomes concerning stem revision, radiographic loosening, surface wear, and the HOOS JR questionnaire. The registry record does not report numerical results for these outcomes. The absence of reported results is not evidence that an event or change did or did not occur; it means the record does not allow those outcomes to be quantified or interpreted.
The record reports zero serious adverse events, zero other adverse events, and zero deaths among the 4 participants at risk in the listed group. These counts describe the submitted safety information, but they should be read alongside the short observed study period and the lack of follow-up visits. They do not establish that no adverse events could occur during the longer follow-up originally planned.
Overall, the posted record documents a terminated follow-up study with baseline information only, rather than a completed longitudinal assessment. It does not provide an estimate of change in metal-ion levels, a comparative effect, or a basis for conclusions about safety or efficacy over time.
9. Statistical Methods Explained
The statistical interpretation depends first on the study structure and the amount of observed data. This was a prospective, single-arm follow-up study. Prospective collection means measurements were planned at specified stages after enrollment, but the plan does not imply that those measurements were obtained. The registry record explicitly states that the study was terminated before any follow-up visits and that only baseline information was available.
What a mean and standard deviation describe
The primary outcome is a continuous measure: whole-blood cobalt and chromium levels in nmol/L. The registry specifies a mean and standard deviation. In general, the mean describes the center of a set of measurements, while the standard deviation describes their spread around that center. Both are descriptive summaries, not by themselves evidence of a treatment effect or a comparison between groups.
These summaries require observed numerical measurements. The registry record does not report numeric baseline means or standard deviations for cobalt or chromium. It therefore does not permit a reader to assess the measured levels or their variation. Because there are no follow-up measurements, means at later time points and changes from baseline cannot be estimated from the recorded information.
Uncertainty and confidence intervals
In general, a confidence interval describes the statistical uncertainty around an estimate under a specified analysis. It is distinct from the standard deviation, which describes variation among measurements. Confidence intervals for the primary outcome are not reported in the registry record. With no reported numerical estimate, there is no interval to interpret for cobalt or chromium.
More broadly, uncertainty depends on the observed data and the analysis used. A small enrolled group can yield estimates that are sensitive to individual observations, but the registry record does not provide the underlying values needed to evaluate that sensitivity. No confidence-interval method, model, or adjustment procedure is reported in the registry record.
Repeated measurements and time
The intended design involved measurements at baseline and at later scheduled visits. Repeated measurements on the same participant are not independent observations: values from one person can be related across time. General analyses of longitudinal data may account for this within-person relationship, but the particular analysis method is not reported in the registry record. In this study, the issue remains prospective rather than empirical because no follow-up visits occurred. There are no recorded repeated observations on which to fit or assess a longitudinal analysis.
The symptom-triggered annual testing described in the registry would also differ from the scheduled testing planned for all participants. In general, measurements collected in response to symptoms may represent a different subset of observations than measurements obtained on a fixed schedule. The record does not report any such follow-up testing or how it would have been incorporated in an analysis.
Single-arm interpretation
A single-arm study can describe outcomes among participants in that arm. It does not provide a contemporaneous control group for estimating a contrast between the implant and another intervention. General comparisons with historical values or external populations would require suitable data and explicit analytic methods; neither is reported in the registry record. No adjusted analysis or other outcome analysis is listed in the registry.
The registry reports zero analyses. This means there are no recorded inferential analyses to interpret alongside the planned outcome measures. It is not appropriate to treat the absence of a reported test as a finding of no difference or no effect. In this study, there is also no comparator and no post-baseline outcome data from which to estimate a longitudinal difference.
Planning illustrations and power
Any sample-size illustrations associated with the statistical material are planning calculations, not the study’s observed results and not its original design. Their stated assumptions are a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the effect to detect expressed as a fraction of an observed effect. This hypothetical two-arm framework does not match the registry’s single-arm design. The registry record does not report that these assumptions were used to plan this study.
Such calculations are not observed power. In general, a planning calculation asks what sample size might be needed under specified assumptions; it does not show the probability that a completed study has established an effect. The record does not report a sample-size justification for the actual study. With no follow-up results reported, an observed effect for the primary outcome cannot be interpreted from this record.
Dispersion and model assumptions
In general, dispersion matters because a mean can conceal substantial variation across participants. If continuous outcomes are more variable than an analysis assumes, standard errors and inferential conclusions based on that assumption may be unreliable. The registry identifies standard deviation as the descriptive measure for the primary endpoint, but it does not report numerical dispersion or a model that addresses distributional assumptions. No conclusion about distribution shape, over-dispersion, or model adequacy can be drawn from the record.
10. Multiplicity, Missing Data and Analysis Populations
The registry lists a primary outcome of metal ion level and secondary outcomes concerning stem revision, radiographic loosening, radiographic surface wear, and the HOOS JR questionnaire. The record also lists 6 outcome measures overall. When multiple outcomes are assessed, general statistical practice recognizes that the chance of at least one apparently notable result can increase if each is tested separately. A prespecified approach to handling multiple comparisons can help clarify which findings are confirmatory and how uncertainty is interpreted.
The registry record does not report a multiplicity adjustment, a hierarchy among secondary outcomes, or a detailed statistical analysis plan. It also reports zero analyses. Thus, there are no reported outcome tests for which multiplicity procedures or adjusted inferences can be evaluated. The reason for any omitted plan is not reported in the registry record.
For missing data, the key fact is that termination occurred before any follow-up visits, leaving baseline information only. The registry record does not describe a missing-data method, imputation strategy, or sensitivity analysis. It does not report enough information to distinguish why particular outcome values are absent or to assess whether missingness could be related to participant characteristics or outcomes.
The primary outcome population is described as enrolled participants with available data at the given time point. The record does not describe a separate analysis population, such as an intention-to-treat or per-protocol set, and no analysis population definition is reported in the registry record. With no follow-up visits, the intended repeated-measure outcome population cannot be evaluated longitudinally. The record does not explain how baseline data were handled in an analysis.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| SMF Short Modular Femoral Stem Implanted Subjects | 0 | 4 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| SMF Short Modular Femoral Stem Implanted Subjects | 0 of 4 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| SMF Short Modular Femoral Stem Implanted Subjects | 0 of 4 |
The listed safety group is SMF Short Modular Femoral Stem Implanted Subjects, with 4 participants at risk for serious adverse events and 4 at risk for other adverse events. The recorded counts are zero serious adverse events, zero other adverse events, and zero deaths. No serious adverse-event terms are listed.
These are counts in the registry’s safety record, not estimates of long-term risk. The study was terminated before any follow-up visits, and the record states that only baseline information was available for the study’s follow-up. The counts therefore cannot be read as a completed assessment across the planned follow-up period of up to 20 years. The registry record does not report the duration of safety observation for each participant or provide event-level details beyond the listed counts.
A zero count means no events were recorded in that category in the posted safety information. In general, a zero count in a small observed group does not prove that an event is impossible or that the underlying risk is zero. No rates or comparisons with another group can be inferred from these counts, because the study has no comparator and the record does not provide the observation time needed to describe rates.
12. What the Result Does, and Does Not, Mean
The record documents a prospective study intended to follow Australian participants after implantation of the SMF Short Modular Femoral Stem. Its primary outcome was whole-blood cobalt and chromium, with clinical and radiological outcomes also listed. It records enrollment of 4 participants and states that the study was terminated before any follow-up visits. These registry entries describe the study’s status and the limits of its available observations.
The record does not provide numeric baseline metal-ion results or follow-up measurements. It therefore does not show whether cobalt or chromium levels changed over time, how much participants’ measurements varied, or how precisely a longitudinal mean could be estimated. The listed secondary outcomes also have no numerical results reported in the registry record.
The single-arm design means the study was not structured to compare the implant with another device or treatment group. More fundamentally, the lack of follow-up prevents assessment of the outcome trajectory that the study was designed to collect. No causal conclusion can be drawn from this record about the implant’s effects on metal-ion levels, revision, radiographic findings, or questionnaire scores.
The safety counts report no serious adverse events, other adverse events, or deaths among the listed participants at risk. These counts are limited to the safety information recorded and do not establish the absence of events over the planned long-term follow-up. The reason for termination and the duration of each participant’s observation are not reported in the registry record.
Thus, the record is informative about the study’s intended design, enrollment, termination, and the absence of reported follow-up data. It is not a completed estimate of long-term safety or efficacy, and it does not establish either benefit or harm.
13. Why This Trial Matters Statistically
This study illustrates why planned follow-up and observed follow-up are not interchangeable in clinical research. The registry describes repeated metal-ion testing over a period of up to 20 years, but also states that termination occurred before any follow-up visits. A long-term schedule can define the scientific question, yet only measurements that were actually collected can answer it.
It also illustrates the limits of a single-arm design. Such a design may describe outcomes within an enrolled group, but it cannot provide a direct comparison with another implant or treatment. For questions about change over time, having repeated observations is essential; for questions about relative effects, a suitable comparator and an analysis of the contrast are also needed.
Enrollment of 4 participants, compared with the planned approximately 26 subjects, places the record in the context of a study that ended before its intended scale of follow-up was reached. The record does not explain why it was terminated. Statistical interpretation should not fill that gap with speculation about recruitment, safety, feasibility, or sponsor decisions.
The entry also demonstrates the importance of separating outcome definitions from outcome results. The primary endpoint is clearly described as mean cobalt and chromium levels with standard deviations, but no numeric results or analyses are reported. Likewise, the presence of listed secondary outcomes does not mean that their results are available. This distinction helps prevent a planned measure from being mistaken for an observed finding.
For biostatistical interpretation, the record is therefore most useful as an example of how study design, data availability, and reporting completeness jointly determine what can be concluded. Its value is in documenting the planned question and the limits of the posted evidence, not in establishing a long-term clinical result.
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 trial-specific limitation is early termination before any follow-up visits. The primary outcome was intended to be measured over time, but the record states that only baseline information was available. This prevents assessment of the planned longitudinal pattern and leaves the primary question unanswered in the posted results.
Enrollment was 4, compared with the approximately 26 subjects described in the study summary. The registry record does not report why enrollment was lower than planned or why the study was terminated. It also does not report how long each participant was observed, so the extent of any safety observation cannot be characterized beyond the stated absence of follow-up visits.
The study had no comparator group. Even with complete follow-up, a single-arm design would limit the ability to attribute observed changes to the implant rather than other influences. In the available record, this limitation is compounded by the absence of post-baseline measurements and reported numeric baseline results.
The registry lists secondary outcomes, but numerical results for them are not reported in the registry record. No outcome analyses, detailed statistical analysis plan, multiplicity approach, missing-data method, or sample-size justification are reported. The reason for termination and the handling of baseline information are also not reported in the registry record.
These limitations restrict interpretation to the study’s recorded status, intended measures, enrollment, and posted safety counts. They do not explain why the study ended or imply any particular outcome.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: A Safety Follow Up Study in Australian Subjects Implanted With the SMF Short Modular Femoral Stem Hip System — NCT03646513.
- Registry record last updated 2024-03-19; status last verified 2024-01.
- Results first posted 2024-03-19.
- 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.
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18. Record Summary
NCT03646513 is a prospective, single-arm, sequential-enrollment follow-up study at one site in Australia of participants implanted with the SMF Short Modular Femoral Stem for primary total hip arthroplasty. The registry lists Smith & Nephew, Inc. as sponsor, enrollment of 4, and study status as terminated. The recorded start date is 2019-02-14 and the primary completion date is 2020-03-12.
The primary outcome is mean whole-blood cobalt and chromium, with standard deviation, measured from baseline through study completion, up to 20 years. The registry states that termination occurred before any follow-up visits, leaving baseline information only. Numeric primary outcome results and analyses are not reported in the registry record. The safety listing records zero serious adverse events, zero other adverse events, and zero deaths among 4 participants at risk.