The Viability of Short Stems in Total Hip Arthroplasty: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Viability of Short Stems in Total Hip Arthroplasty (NCT02577822), a randomized na study. The primary outcome is Mean VR-12 Mental Composite Score Through 2 Years Post Operative.

2. Clinical Question

3. Trial Design

The registry record identifies this as NCT02577822, titled “The Viability of Short Stems in Total Hip Arthroplasty.” Northwestern University is listed as the sponsor. The condition is osteoarthritis of the hip, and the record lists enrollment as 60. The study status is completed. The recorded start is 2013-10, and primary completion is recorded as 2018-08. The phase is listed as NA.

The record classifies allocation as randomized and masking as single. It does not identify who was masked, describe the randomization method, or report how allocation was concealed. It also labels the model as single-group, despite listing a short-stem group and a long-stem group, with separate short and standard-length stem interventions. Those classifications are inconsistent in the registry record; the available information does not establish how the study should be characterized beyond the listed design fields and arms.

The primary outcome is the mean VR-12 Mental Composite Score, assessed pre-operatively and at 6 weeks, 3 months, 6 months, 12 months, and 2 years post-operatively. A secondary outcome concerns EBRA-FCA analysis of femoral component subsidence through 2 years post-operatively. The record lists 6 outcome measures, but does not provide numerical results for the primary outcome or the secondary outcome in the information available for this analysis. It records 0 outcome analyses.

The registry record describes the purpose as determining the viability of short femoral stems as an alternative to standard-length stems. That purpose is not itself a statistical result. The record does not report a protocol, detailed analysis plan, sample-size justification, or explanation of the single-group model label. The listed enrollment and completion status therefore do not, by themselves, establish how many participants were included in each analysis or whether all planned assessments were completed.

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: Discrepancies between the total number of patients analyzed and patients included in participant flow is due to patients lost to follow-up during the course of the study despite attempts to contact them by the research team

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 Mean VR-12 Mental Composite Score Through 2 Years Post Operative, measured over Assesed pre-operatively, 6 weeks post-operatively, 3 months post-operatively, 6 months post-operatively, 12 months post-operatively, and 2 years post-operatively..

The primary endpoint is the mean score on the Mental Composite Score of the Veteran's RAND 12 Item Health Survey, or VR-12, at assessments extending from before surgery through 2 years after surgery. The registry record describes the instrument as a measure of health-related quality of life that can be used to estimate disease burden and evaluate disease-specific benchmarks. The score is reported as a T-score. Its listed range is 5.2 to 76.3, with a population mean of 50 and a standard deviation of 10. Higher scores indicate improved mental wellness or function as reported by patients.

A patient-reported measure can capture aspects of health and functioning that are not fully represented by imaging or other clinical measurements. Repeated assessments can describe how scores vary over time, rather than limiting the question to a single postoperative observation. The registry record names the assessment occasions but does not report the actual means, standard deviations, participant counts at each occasion, or a statistical comparison between the stem groups. The description therefore establishes what the endpoint is intended to measure, but not the direction, size, or precision of any observed difference.

The secondary outcome concerns implant subsidence assessed with EBRA-FCA through 2 years post-operatively. Numerical results for that outcome are not reported in the registry record. It is not possible to infer a relationship between subsidence and VR-12 scores from the outcome descriptions alone.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary measure is continuous and is summarized in the registry record as a mean with a standard deviation. In general, a mean is the arithmetic average of observed scores in the analyzed group. It offers a compact description of the group’s score level, but does not show the full distribution or whether individual participants had similar experiences. The standard deviation describes the dispersion of scores around the mean; it is not the uncertainty of the mean itself.

A standard error or confidence interval is commonly used to express uncertainty around an estimated mean or contrast. In general, a confidence interval gives a range of values compatible with the data and the assumptions of the analysis. Narrower intervals indicate greater precision, while wider intervals indicate less precision. No confidence interval for the VR-12 endpoint is reported in the registry record, so the precision of the group means or any contrast cannot be assessed.

The VR-12 outcome is measured repeatedly, at pre-operative and postoperative assessments through 2 years. Repeated measurements from the same participant are generally correlated: a participant's scores over time are not independent observations. Statistical approaches for longitudinal data account for this within-participant relationship when estimating group patterns or comparisons. The registry record does not identify an analysis method, covariance structure, or specific contrast for the repeated assessments. It is therefore not possible to determine how correlation across visits was handled.

A comparison across randomized groups could be expressed in several ways, including a difference at a particular follow-up assessment or a difference in score change over time. These answer different questions. A comparison of changes also depends on how baseline scores are incorporated. The registry record does not specify a primary contrast, baseline adjustment, or whether analyses were intended at each visit or across the full trajectory. Without those details and numerical results, the listed assessment schedule should not be mistaken for a complete statistical analysis plan.

The measure is reported on a T-score scale, with a stated population mean of 50 and standard deviation of 10, and higher scores indicating improved mental wellness or function. These features help describe the instrument's scale and direction. They do not establish a threshold for an important change in this particular study. A clinically meaningful difference, if one was defined, is not reported in the registry record.

The record includes a planning-illustration description based on a fraction of an observed effect, a two-sided significance level of 0.05, equal allocation, and a normal approximation. Such an illustration is a hypothetical sample-size calculation: it estimates the participants per arm that would be needed under its stated assumptions to detect a specified fraction of an effect. It is not observed power, does not show that the study was designed using those assumptions, and does not establish that the target was met. The registry record does not report the trial's own sample-size justification or numerical planning inputs. Because no primary effect estimate is reported in the information available, the planning illustration cannot be interpreted as evidence about the outcome.

In general, over-dispersion means that the observed variability is greater than a statistical model assumes. When a model underestimates variability, standard errors may be too small and confidence intervals too narrow. The registry record does not report a distributional model or indicate that over-dispersion was relevant to the continuous VR-12 outcome. This concept is therefore a general statistical consideration, not a reported feature of this study.

The registry record lists 0 outcome analyses. This does not establish that no analyses were performed outside the registry; it means that analysis entries are not reported in the registry record. The statistical method, handling of repeated measures, model diagnostics, and any adjustment for baseline values or other covariates are not reported in the registry record.

10. Multiplicity, Missing Data and Analysis Populations

The primary outcome is assessed at multiple occasions, and the registry record lists 6 outcome measures. Testing or estimating numerous outcomes and time-specific contrasts can raise multiplicity concerns. In general, when many hypotheses are tested, the chance of at least one apparently unusual result can increase. A prespecified analysis plan can identify which outcomes and contrasts are primary and whether adjustments or a hierarchical testing strategy will be used. The registry record does not report a multiplicity strategy or specify how the repeated time points were to be treated statistically.

Missing follow-up is directly relevant because the record states that some patients were lost to follow-up despite attempts to contact them. It further explains that discrepancies between total patients analyzed and those included in participant flow arose from patients lost during the study. The number lost, timing of losses, group-specific missingness, and reasons beyond that general description are not reported in the registry record. Assessment-specific denominators are also not reported.

In general, missing-data methods rely on assumptions about why observations are unavailable. Complete-case analysis uses only participants with the required observations, while longitudinal models may use available measurements under specified assumptions. Other approaches may be needed when missingness depends on unobserved outcomes. The registry record does not say which approach was used or whether sensitivity analyses were conducted. It also does not report analysis populations, such as intention-to-treat or per-protocol groups. Those omissions limit assessment of both potential selection bias and the robustness of any result.

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

The registry record identifies a study intended to examine short femoral stems as an alternative to standard-length stems in total hip arthroplasty. It lists randomized allocation, a short-stem group, a long-stem group, and a primary patient-reported outcome assessed repeatedly. These descriptions establish the topic and measurement schedule, but they do not provide evidence about the relative outcome in the groups.

Numerical primary outcome results are not reported in the registry record. Without group summaries or an estimated contrast, it is not possible to describe whether scores rose, fell, or differed between groups. Without a confidence interval or other uncertainty measure, the precision of a comparison cannot be judged. The completed status and enrollment listing do not substitute for outcome results.

The record also does not report numerical results for the secondary implant-subsidence outcome. It lists zeros for serious events, other events, and deaths in both groups, alongside zero participants at risk in the adverse-event entries. Those registry entries should be read as recorded fields, not as proof that no events occurred among all study participants: the record does not provide an exposed denominator for those entries, and the listed values do not establish complete adverse-event ascertainment.

Even if a numerical difference were available, statistical evidence and clinical importance would be distinct considerations. A small uncertainty interval could indicate a precisely estimated difference without establishing that the difference matters to patients; a broad interval could leave a range of effects compatible with the data. The registry record does not report an importance threshold for VR-12 change. No claim that one stem is better, worse, or equivalent to the other is supported by the information reported in the registry record.

12. Why This Trial Matters Statistically

This study raises a useful statistical question because it combines a comparison of two device groups with a patient-reported outcome measured repeatedly after surgery. The VR-12 Mental Composite Score represents mental wellness or function as reported by patients, while the secondary outcome addresses implant subsidence. These are different kinds of measurements and require distinct interpretations; one cannot stand in for the other.

Repeated assessment can reveal whether average scores follow different patterns over time, but it also requires careful attention to within-participant correlation, the choice of comparison, and incomplete follow-up. The registry record explicitly notes patients lost to follow-up and a discrepancy between analyzed patients and participant flow. Those details make denominator reporting and a clear missing-data strategy important for judging how representative the observed results may be.

The record also illustrates why design labels and outcome reporting need to be read together. It lists randomized allocation and separate short-stem and long-stem groups, but classifies the model as single-group. The inconsistency is not explained. In addition, the absence of outcome analyses and numerical primary results in the registry record prevents readers from evaluating effect size, uncertainty, or the relationship between the stated study purpose and the observed data.

Statistically, a well-defined contrast, complete reporting of group-specific summaries, and transparent handling of repeated and missing observations would be needed to evaluate the comparison. The record identifies the central measures and timing, but does not report those analysis details or results. The value of the record is therefore primarily in describing the intended question and highlighting what information is needed for a rigorous interpretation, rather than establishing a comparative conclusion.

13. 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 interpreting this trial from the registry record is the absence of numerical primary outcome results. Group means, standard deviations, participant counts at each assessment, between-group estimates, confidence intervals, and p-values are not reported in the record. The listed analysis count is 0. As a result, neither the size nor the precision of any observed contrast can be evaluated.

The study classification is internally inconsistent: allocation is listed as randomized, the model is listed as single-group, and the record also describes short-stem and long-stem groups with separate interventions. The record does not explain this discrepancy. It also does not identify who was masked, how randomization was implemented, or whether allocation was concealed.

Follow-up loss is acknowledged, but the record does not provide counts by group or assessment, participant characteristics for those lost, or the statistical approach used to address missing data. It does not report the analysis population or a sensitivity analysis. These gaps make it difficult to assess whether available outcome data could represent the enrolled groups.

The registry record does not report the trial's statistical analysis plan, a sample-size justification, a defined primary contrast across repeated assessments, or a multiplicity strategy. It also does not provide numerical results for the listed secondary subsidence outcome. The adverse-event entries list zero participants at risk and zero affected participants in each group, so they do not provide an interpretable event rate for the enrolled population. These limitations concern what can be assessed from the registry record and should not be taken as proof that further analyses or information do not exist elsewhere.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: The Viability of Short Stems in Total Hip Arthroplasty — NCT02577822.
• Registry record last updated 2020-01-09; status last verified 2020-01.
• Results first posted 2019-08-26.
• 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.

17. Record Summary

NCT02577822 is a completed study sponsored by Northwestern University, with osteoarthritis of the hip listed as the condition and enrollment recorded as 60. The registry record lists randomized allocation, single masking, and a single-group model, although it also describes short-stem and long-stem groups and two corresponding Taperloc stem interventions. The record does not resolve that design-label inconsistency.

The primary outcome is the mean VR-12 Mental Composite Score, assessed before surgery and at postoperative visits through 2 years. EBRA-FCA assessment of implant subsidence through 2 years is listed as a secondary outcome. The record lists 6 outcome measures and 0 outcome analyses. Numerical results for the primary and secondary outcomes, details of the statistical analysis, and the handling of missing data are not reported in the registry record. The record notes loss to follow-up despite attempts at contact.