Treatment Outcomes for Ankle Arthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Treatment Outcomes for Ankle Arthritis (NCT00391365), a registered phase not stated study. The primary outcome is Musculoskeletal Functional Assessment (MFA).

2. Clinical Question

3. Trial Design

This is a completed study of surgical treatment for ankle osteoarthritis, with outcomes assessed using surveys, step counts, and laboratory gait analysis. The registry record identifies two groups: participants undergoing ankle arthrodesis (fusion) and participants undergoing ankle arthroplasty (replacement). It lists gait analysis as a procedure. The study’s stated purpose is to determine whether functional outcomes differ between people who underwent these surgical treatments.

The record lists 368 participants enrolled. Its primary completion date is 2015-08-01, and its status is completed. The study description says recruitment was closed and follow-up procedures were completed, while data analysis was still underway as of July 2016. It also states that long-term follow-up was approved in April 2017, with contact by telephone and/or U.S. Mail and follow-up planned for up to 12 years after ankle surgery. The relationship between that later follow-up and the listed primary endpoint is not reported in the registry record.

The comparison is not described as randomized; allocation is not stated. The record therefore does not establish that the groups were comparable at baseline or that observed differences, if reported, could be attributed to the operation alone. It describes 103 participants initially in the arthrodesis group and 170 in the arthroplasty group, with Year 3 assessments completed by 78 and 151 participants, respectively. MFA data analysis is described for 99 arthrodesis participants and 165 arthroplasty participants. The registry record does not explain how those analysis counts relate to the enrollment or Year 3 assessment counts.

The registry record lists two secondary outcomes, both from the Short Form-36: Physical Function and Bodily Pain. It reports three outcome measures and zero analyses. A protocol, detailed statistical analysis plan, sample-size justification, and interim analyses are not 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: The study started with 103 subjects in the arthrodesis group, and 170 in the arthroplasty group. 78 subjects in the arthrodesis group completed the Year 3 assessment, and 151 in the arthroplasty group. Analysis was done on the MFA data collected from 99 arthrodesis subjects, and 165 arthroplasty subjects.

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 Musculoskeletal Functional Assessment (MFA), measured over Over the course of 3 years.

The primary endpoint is the Musculoskeletal Functional Assessment (MFA), a patient-reported measure intended to assess perceptions of physical, psychological, and social well-being. The record says the instrument asks participants to assess their function on 100 items. The endpoint is described as change from the pre-operative assessment to 3 years, reported as a mean in units on a scale. The scale range is 0 to 100, and a lower score implies an improved outcome.

Patient-reported functional measures can capture aspects of daily life and perceived well-being that may not be represented by a laboratory measure alone. In general, repeated assessments can describe how reported function changes over time, while a comparison between groups can address whether the average changes differ. That interpretation depends on how the measure is scored, who completed it, and how missing assessments are handled.

The registry record specifies standard error as the dispersion measure for the primary endpoint. It does not report the arm-specific mean changes, standard errors, a between-group contrast, confidence interval, or p value. Thus, the endpoint’s definition is available, but the observed direction, magnitude, and precision of the outcome are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies the primary outcome as a continuous measure, summarized by a mean, with standard error as the stated dispersion measure. In general, a mean describes the average observed score or change in a group. A standard error describes the estimated uncertainty in that mean under the analysis used; it is not the same as the spread of individual participants’ values. Neither the group means nor their standard errors are reported in the registry record, so the endpoint cannot be quantitatively interpreted from the record.

What would a group comparison estimate?

For a comparison of mean changes, the central quantity would usually be a difference between the average change in the fusion group and the average change in the replacement group. This contrast would describe the observed separation between group averages on the MFA scale. Its direction must be interpreted using the scale’s stated scoring rule: lower scores imply an improved outcome. The registry record does not report a contrast or specify the exact subtraction order used for any comparison.

In general, a confidence interval gives a range of values compatible with the data and the assumptions of the statistical method. Its width conveys precision: a narrower interval indicates less uncertainty in the estimate, while a wider interval indicates more. A confidence interval would help distinguish a relatively precise estimate from one that leaves substantial uncertainty. No confidence interval for the primary outcome is reported in the registry record, and there is no basis for reconstructing one from the information available.

A p value, in general, describes how unusual data at least as incompatible with a specified null hypothesis would be under the model’s assumptions. It does not measure the probability that the null hypothesis is true, nor does it describe the size or practical importance of a difference. A p value is not reported for the primary outcome. The registry record also does not state the test, model, or adjustment strategy that would have produced one.

Why does the allocation matter?

Random allocation, when used and implemented appropriately, can help balance measured and unmeasured characteristics between treatment groups on average. This record does not describe randomization; allocation is not stated, and the groups are defined by the surgery participants underwent. In general, people receiving different procedures may differ in ways that also relate to functional outcomes. A comparison of their observed averages can describe an association, but without adequate design or adjustment information it cannot isolate the effect of the procedure from other group differences.

Adjustment methods can account for measured participant characteristics when estimating a group contrast. The choice of variables and model matters, and adjustment cannot automatically remove bias from characteristics that were not measured or appropriately modeled. No adjusted analysis, covariate set, or model specification is reported in the registry record. It is therefore not possible to determine whether the posted comparison, if any, accounted for differences between groups.

How should the planning assumptions be read?

The record describes planning illustrations based on a fraction of the observed effect, with a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. In general, a sample-size calculation estimates the number of participants needed under assumptions about the target effect, variability, significance level, and desired power. Such a calculation is a planning exercise, not a description of the study’s actual observed power. The record does not report a design justification or the calculated participant requirements, and the primary outcome estimates needed to evaluate an observed effect are not reported. The planning assumptions therefore should not be treated as evidence that the study was designed to detect a particular effect.

Over-dispersion is relevant in models for count outcomes when the observed variability exceeds what a model assumes. In general, failing to account for such extra variability can make uncertainty appear too small. The primary outcome is described as a continuous mean, not a count, and the registry record does not specify a model for the secondary measures. Over-dispersion is not a reported feature of the primary endpoint analysis.

Multiplicity concerns arise when several outcomes, time points, or comparisons are tested. In general, conducting many tests can increase the chance of finding at least one apparently notable result by chance, depending on the testing strategy. The record lists three outcome measures, including the primary MFA outcome and two secondary Short Form-36 outcomes. It does not report a multiplicity plan, the analysis details for those measures, or results for them. No adjustment procedure should be presumed.

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("Ankle Arthrodesis (Fusion)", "Ankle Arthroplasty (Replacement)")
n   <- c(99, 165)
m   <- c(-12.5, -15)
sp  <- c(1.4, 0.9)
sd  <- sp * sqrt(n)      # standard errors converted to SDs
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  Ankle Arthrodesis (Fusion)  99  -12.500  13.930  -15.278  -9.722
CARM  Ankle Arthroplasty (Replacement)  165  -15.000  11.561  -16.777  -13.223

11. Multiplicity, Missing Data and Analysis Populations

The record identifies the MFA as the primary outcome and lists the Physical Function and Bodily Pain sections of the Short Form-36 as secondary outcomes. It reports three outcome measures in total and zero analyses. A plan for controlling multiplicity across outcomes, time points, or comparisons is not reported in the registry record. Without that information, the handling of multiple statistical questions cannot be assessed.

The population description gives different counts for initial group membership, Year 3 assessment completion, and MFA data analysis. Specifically, the record describes 103 participants initially in the fusion group and 170 in the replacement group; Year 3 assessment completion is described for 78 and 151 participants; and MFA analysis is described for 99 and 165 participants. The record does not explain these count differences, identify the analysis population in detail, or state whether the analysis used all available observations or a restricted set.

Missing-data methods are not reported in the registry record. It is not stated whether missing MFA values were handled through complete-case analysis, imputation, a repeated-measures model, or another approach. The reasons for noncompletion and the relationship between missingness and participants’ outcomes are also not reported. In general, conclusions can depend on these choices when outcome availability differs between groups or is related to participant characteristics or outcomes.

The record does not report an interim analysis plan, stopping rules, or a statistical analysis plan. It also does not provide a flow of participants through follow-up or analysis. These omissions limit assessment of how the analysis populations were formed and whether the reported estimates, if available, would represent all enrolled participants or a subset.

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

The registry record establishes the study question, the two surgical groups, and the primary outcome definition. It says the primary endpoint is mean change in MFA from before surgery to 3 years, and that lower scores imply improvement. It also reports participant counts for initial group membership, Year 3 assessment completion, and MFA analysis. These registry entries describe the intended comparison and some aspects of the study population.

The record does not report the primary outcome values or a statistical comparison between groups. It therefore cannot establish whether the observed mean changes differed, which group had the lower change, how large any difference was, or how precise an estimate would be. The absence of reported results should not be mistaken for evidence of no difference. It leaves the result unknown in the registry record.

Even if group-specific estimates were available, the nonrandomized design information would matter. The record does not state how participants came to undergo fusion or replacement, whether the groups were similar before surgery, or whether statistical adjustment was used. In general, a difference between groups in an observational comparison can reflect both treatment and pre-existing differences between the people receiving each treatment. A registry entry alone, without the missing design and analysis details, cannot resolve that issue.

The record lists zero serious and non-serious adverse events as at risk and affected in each surgical group, while death entries are null. These registry fields do not establish that no events occurred; they show that the displayed fields contain zeros or no death value. Event definitions, collection methods, follow-up coverage, and explanations for the entries are not reported in the registry record.

Accordingly, the information supports describing the study’s design and endpoint, but not an assessment of comparative functional outcomes, statistical significance, or clinical importance. It also does not support a treatment recommendation. The reported endpoint definitions and participant counts should be interpreted alongside the substantial gaps in outcome estimates, analysis methods, and missing-data reporting.

13. Why This Trial Matters Statistically

This study addresses a useful statistical distinction: a comparison between groups defined by the procedures participants underwent is not automatically equivalent to a randomized treatment comparison. The registry describes fusion and replacement groups, but allocation is not stated. That distinction affects what an estimated group difference could mean. Without information about treatment selection, baseline characteristics, and adjustment, a difference in outcomes could reflect factors beyond the procedures themselves.

The endpoint also illustrates why outcome definitions and results need to be read together. The MFA is a patient-reported measure intended to assess physical, psychological, and social well-being, and the record specifies a change from before surgery to 3 years. It states the scale direction and range, but does not give the group changes or their uncertainty. A clear endpoint definition makes the intended estimand more understandable; it cannot substitute for the estimates needed to judge the observed data.

The different counts for initial group membership, Year 3 assessments, and MFA analysis make the analysis population an important issue. Readers need to know which participants contributed to the outcome analysis and how missing assessments were handled to understand the scope and potential bias of an estimate. Those details are not reported in the registry record. The counts alone cannot explain why the analysis numbers differ.

Finally, the registry shows the difference between a study status and an interpretable statistical result. It is marked completed and includes an endpoint description, but it reports zero analyses and no arm-level outcome estimates. For statistical interpretation, a completed record without results still leaves the central comparison unanswered. This is important when evaluating what registry information can support: study characteristics may be documented even when the quantitative evidence required to assess the outcome is absent.

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 principal limitation is that the registry record does not report the primary outcome estimates or any analyses. Mean changes, standard errors, between-group comparisons, confidence intervals, and p values are not reported in the registry record. The endpoint can be described, but its observed magnitude, direction, and precision cannot be evaluated.

Allocation is not stated, and the comparison is not identified as randomized. The record does not describe how the surgical procedure was selected, whether the groups differed at baseline, or whether confounding was addressed. Without those details, even a reported group difference would require careful interpretation as an association rather than an established causal effect.

The participant counts are not reconciled. The record gives initial group counts, Year 3 assessment counts, and MFA analysis counts, but does not explain how these populations relate. Reasons for missing assessments, outcome availability, exclusions, and the approach to missing data are not reported in the registry record. This limits assessment of attrition and the population represented by the analysis.

Other important analysis details are also absent: the statistical model, analysis population definition, adjustment variables, multiplicity plan, and interim analysis procedures are not reported in the registry record. The record does not provide a sample-size justification or calculated planning requirements. Although it describes planning assumptions for illustrations, those assumptions do not establish the original design rationale or the study’s ability to detect a particular effect.

The safety entries require caution as well. The event fields contain zeros for both groups, while death entries are null; the record does not explain these entries or provide event definitions and collection methods. They should not be interpreted as evidence that no adverse events occurred.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Treatment Outcomes for Ankle Arthritis — NCT00391365.
• Registry record last updated 2026-01-26; status last verified 2026-01.
• Results first posted 2016-12-21.
• 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 record describes a completed study of surgical treatment for ankle osteoarthritis, comparing participants who underwent ankle arthrodesis (fusion) with those who underwent ankle arthroplasty (replacement). Enrollment is listed as 368. The primary outcome is mean change in the Musculoskeletal Functional Assessment from before surgery to 3 years; lower scores imply an improved outcome on a scale ranging from 0 to 100. The registry also lists Short Form-36 Physical Function and Bodily Pain outcomes.

The record describes initial group counts of 103 and 170, Year 3 assessment counts of 78 and 151, and MFA analysis counts of 99 and 165. It lists zero analyses and does not report outcome estimates, statistical comparisons, missing-data methods, or a multiplicity plan. Allocation is not stated. The record describes later approval for long-term follow-up of up to 12 years after surgery. These entries define the study question and some design features, but do not report the comparative functional outcome result.