Torsion of the Tibial Tuberosity, a New Factor of Patellar Instability?: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Torsion of the Tibial Tuberosity, a New Factor of Patellar Instability? (NCT03304119), a registered phase not stated study. The primary outcome is Existence of Tibial Tuberosity Torsion..

2. Clinical Question

This is an anatomical association question, not a comparison of treatments. The study aims to assess whether a rotational feature of the tibial tuberosity may distinguish people with recurrent patellar dislocation from a control group. Patellar tilt and the distance between the tibial tuberosity and trochlear groove are also listed as secondary measures.

The clinical motivation in the registry is that patellar instability can occur alongside anatomical factors, and that external torsion of the tibial tuberosity had been noticed on MRI in patients with instability. The proposed analysis asks whether measuring this feature could contribute information about recurrent dislocation. However, the record does not report the frequency of torsion in either group, the group-specific measurements, or an estimate of association. It therefore describes a research question rather than an answer to it.

3. Trial Design

The registry describes an observational comparison of MRI findings in a patellar instability group and a control group. It does not describe a randomized allocation or a treatment assignment. The record explicitly indicates that allocation is not stated and that the arms are not a like-for-like control comparison. This matters because a difference between groups, if reported, could reflect differences in how participants were selected or assessed as well as a relationship between torsion and patellar instability.

The patellar instability group is described as patients with instability stemming from recurrent patellar dislocation. The control group is described as a group that has not been checked for patellar instability. That wording leaves uncertainty about whether instability was actively excluded in controls. The record does not report criteria for selecting participants, matching procedures, demographic characteristics, or other factors that might differ between the groups.

The primary outcome description refers to assessment of MRI scans by four reviewers and an analysis based on available MRI. Enrollment is listed as 92. The record does not give group-specific enrollment, the number of MRI scans available for each outcome, or the number of scans assessed by each reviewer. It also does not explain how reviewer assessments were combined or whether reviewers were blinded to group status.

The registry lists the study status as completed. It gives a start date of 2016-04-01 and a primary completion date of 2016-12-30. The outcome timeframe separately describes data collection from April 2010 until december 2016. The registry record does not reconcile these different descriptions of timing. It states that participant follow-up duration is not applicable, consistent with an MRI assessment rather than a follow-up endpoint. Statistical analyses and primary outcome results 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: Analysis based on the IRM 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.

6. Primary Endpoint

The registry lists the primary outcome as Existence of Tibial Tuberosity Torsion., measured over 4 reviewers Assessment of 92 IRM of patients. Study data collection from April 2010 until december 2016. Patient duration follow up not applicable..

The primary endpoint is the existence of tibial tuberosity torsion. The registry describes recording whether torsion is present or absent and measuring its magnitude in degrees on MRI. The endpoint is intended to represent an anatomical feature that could be associated with patellar dislocation. Its relevance in the registry is framed around whether the feature is associated with dislocation, not whether a treatment changes it.

The record specifies a median and interquartile range for the measurement. In general, the median describes the central value after ordering observations, while the interquartile range describes the spread of the middle portion of those observations. These summaries can be useful when a measurement is skewed or has values that make a mean and standard deviation less representative. They describe the distribution; by themselves, they do not establish whether groups differ or whether a difference is statistically precise.

The binary assessment of presence or absence and the measurement in degrees are related but distinct. A count or proportion with torsion would describe how often reviewers identified the feature, whereas a summary of degrees would describe its measured magnitude. The registry record does not report either kind of result, nor does it state a threshold defining torsion as present. It also does not explain how disagreements among reviewers were handled. Consequently, the endpoint is specified at a broad level, but important operational details and the observed findings are not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does the primary outcome represent?

The outcome combines a categorical assessment with a measurement. Reviewers were to identify whether tibial tuberosity torsion existed and to measure torsion in degrees on MRI. In general, categorical data are summarized by counts or proportions in each category, while a continuous measurement can be described by location and spread. The registry specifies median and interquartile range for the measurement. It does not report observed counts, medians, or interquartile ranges.

These summaries answer descriptive questions. A median indicates the middle observation in an ordered set, and the interquartile range conveys variation across the central part of the set. Neither summary alone quantifies the uncertainty in a comparison between groups. To assess an association, an analysis would ordinarily need to compare the relevant distributions or frequencies and report an estimate with uncertainty. The registry record does not state what comparative method was planned or used.

Why does the group comparison require caution?

In general, random allocation can help create groups that are comparable with respect to measured and unmeasured characteristics. This study is not described as randomized, and allocation is not stated. The registry also cautions that the arms are not a like-for-like control comparison. The control group is described as not having been checked for patellar instability, so it is unclear whether the comparison group was confirmed to be free of the condition.

These design features do not make descriptive comparisons impossible, but they affect what a difference could mean. A group contrast could reflect the anatomical feature of interest, differences in participant selection, differences in ascertainment, or other group characteristics. The registry does not report matching, adjustment, or other methods to address such possibilities. No causal interpretation is justified by the design details recorded.

What would a confidence interval add?

In general, a confidence interval communicates the precision of an estimated effect. It is more informative than a significance test alone because it shows a range of effect sizes compatible with the data and analysis assumptions. A result with substantial uncertainty may be compatible with several interpretations, even if a single point estimate appears suggestive. The registry record does not report a confidence interval or any other uncertainty measure for the primary outcome.

A p-value, if reported, would address how compatible the data are with a specified statistical model under a null hypothesis. It would not measure the probability that the hypothesis is true, the size of the association, or its practical importance. No p-value or null hypothesis test is reported in the registry record. Since no outcome estimates are reported, a recalculated comparison cannot be made from the registry information.

What do the planning assumptions mean?

The record describes a sample-size planning illustration based on an observed effect, rather than the study's own design. The stated assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation; the target effect is described as a stated fraction of the observed effect. For time-to-event settings, the stated convention is to give the total number of events; for other settings, it is to give participants per arm.

These assumptions describe a planning exercise, not evidence that the study had a particular probability of detecting an effect. Sample-size estimates calculated from an observed effect are planning illustrations and must not be interpreted as observed power. Their meaning depends on the effect used as the starting point and the assumptions adopted. The registry record does not report the observed primary effect, specific effect fractions, or statistical analysis results needed to evaluate such an illustration. It also does not report that these assumptions formed part of the original protocol or justified the enrollment.

In general, planning based on an observed effect can be uncertain because the initial estimate may be imprecise. A smaller target effect generally requires more information to distinguish it from no effect under otherwise fixed assumptions. That is a general statistical principle, not a calculated conclusion about this study. The registry record does not report an original sample-size justification, target power, or interim-analysis plan.

How should multiple outcomes be understood?

The primary endpoint is torsion, and the registry names patellar tilt and the tibial tuberosity–trochlear groove distance as secondary outcomes. Considering several outcomes can raise a multiplicity issue: when many hypotheses are tested, the chance of at least one apparently notable result can increase. Statistical plans may address this by defining a primary outcome in advance or adjusting inference across tests. The registry record does not report a multiplicity strategy or identify analyses for the secondary outcomes.

The record lists three outcome measures overall, but gives only two named secondary measures in addition to the primary endpoint. It does not explain the remaining outcome measure or provide analysis details. Without the outcome results and statistical plan, the extent to which multiplicity affected interpretation cannot be assessed. These missing details should not be filled in by assuming a conventional method.

10. Multiplicity, Missing Data and Analysis Populations

The registry identifies a primary endpoint and names patellar tilt and tibial tuberosity–trochlear groove distance as secondary outcomes. It does not report a multiplicity plan, such as whether secondary outcomes were treated as exploratory or whether any adjustment was used when interpreting several comparisons. In general, testing multiple outcomes can increase the chance of at least one result appearing notable by chance. A prespecified primary outcome can help distinguish the main question from supporting analyses, but the record does not provide enough detail to assess how that distinction was implemented.

The record states that analysis was based on available MRI. It does not report how many scans were available, how many were excluded or lacked measurements, or why information might be unavailable. It does not describe an approach to missing data or explain whether the available scans differed from those not analyzed. The enrollment of 92 therefore cannot be treated as the denominator for every endpoint.

Analysis populations are also not described in detail. The registry does not specify a participant flow, a rule for assigning participants to analysis groups, or whether every enrolled participant was included in each outcome analysis. It does not report the number of participants or scans contributing to either group. These omissions prevent assessment of how exclusions or incomplete MRI information may have affected the comparisons.

Although the status is listed as completed, the primary results and analysis methods are not reported in the registry record. The record does not state whether analyses were prespecified, whether an interim analysis occurred, or how reviewer disagreements were handled. Those details should be regarded as not reported in the registry record, rather than inferred from the outcome description.

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

The study addresses a focused anatomical question: whether external torsion of the tibial tuberosity, assessed on MRI, is associated with recurrent patellar dislocation. The registry describes the intended endpoint, the groups, and several MRI measurements. It does not report the measurements or comparisons needed to answer that question. The record therefore supports understanding what the investigators set out to examine, but not whether torsion was more common, greater in magnitude, or statistically associated with instability.

Even if outcome values were available, an association would not by itself establish that torsion causes patellar dislocation. In general, observational group comparisons can be influenced by how participants enter each group, how outcomes are assessed, and characteristics that differ between groups. Here, the registry says the arms are not a like-for-like control comparison and describes controls as not checked for patellar instability. Those features would be important when interpreting any reported contrast.

The endpoint's measurement also depends on MRI assessment. The record states that four reviewers assessed MRI scans, but does not report reviewer agreement, blinding, measurement procedures, or how differing assessments were resolved. These details matter because measurement variation can affect both the classification of torsion as present or absent and the measured angle. The registry does not report evidence about the reliability of this assessment.

The absence of posted results should not be interpreted as evidence that no association exists, nor as evidence that an association exists. It means that the registry record does not contain the outcome evidence required to distinguish those possibilities. Likewise, the listed enrollment does not establish that the study was sufficiently precise to identify an association. Without group-specific data and uncertainty estimates, the magnitude and precision of any relationship remain unknown.

The registry's completed status and its stated objective do not resolve these limitations. A completed study can have a fully described question while still lacking posted analyses. The appropriate interpretation is limited to the design information and planned measurements recorded; conclusions about the anatomical hypothesis are not reported in the registry record.

12. Why This Trial Matters Statistically

This study is statistically interesting because it asks whether a measurable anatomical feature on MRI can be distinguished between a clinical group and a control group. Such a question depends not only on the measurement itself, but also on reliable assessment, clear group definitions, and a comparison that supports a meaningful interpretation. The registry identifies torsion as the primary feature and names patellar tilt and tibial tuberosity–trochlear groove distance as secondary measurements.

The record also illustrates why the label “control group” does not by itself guarantee a valid control comparison. The control group is described as not having been checked for patellar instability, and the registry cautions that the arms are not a like-for-like comparison. In general, incomplete or unequal ascertainment can affect group classification and can complicate interpretation of an observed contrast. The status of controls is therefore central to the question, not just a technical detail.

Measurement procedures matter as well. Four reviewers assessed MRI scans, but the registry does not report how agreement was evaluated or how measurements were reconciled. For an anatomical measurement, variability between reviewers or ambiguity in the definition could affect the observed distribution. A clear protocol and information about measurement reliability would help readers understand how confidently the endpoint was classified and quantified.

Finally, this record demonstrates the difference between a stated research aim and an evaluable result. The objective is described, but group summaries, analysis methods, and uncertainty estimates are not reported. Without those elements, readers cannot judge whether the data support the proposed association or how precise an estimate might be. The statistical importance of the study thus lies in both its focused question and the limits of what its registry record makes available.

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 most direct limitation is that the primary outcome results are not reported in the registry record. There are no group-specific counts for torsion, degree measurements, comparative estimates, confidence intervals, or test results. The record lists zero analyses. This prevents evaluation of the main research question and prevents any independent recalculation from the posted information.

The study groups are incompletely characterized. The instability group is described as having recurrent patellar dislocation, while the control group is described as not having been checked for patellar instability. The record explicitly cautions that the arms are not a like-for-like comparison. It does not report how participants were selected, whether controls were confirmed to be free of instability, or whether groups differed in other characteristics. Any comparison would therefore require careful consideration of selection and classification.

The MRI analysis is also insufficiently detailed for assessing measurement quality. Although the record says four reviewers assessed 92 MRI scans, it does not report the number of usable scans for each outcome, the reviewers' training, blinding, agreement, or the process for resolving inconsistent readings. It does not state a threshold for classifying torsion as present. These omissions limit reproducibility and make it difficult to assess potential measurement error.

The registry gives different descriptions of study timing: a start date of 2016-04-01 and primary completion date of 2016-12-30, while the outcome timeframe describes data collection from April 2010 until december 2016. The reason for this difference is not reported in the registry record. The record also does not describe missing-data handling, analysis populations, multiplicity, model specification, or adjustment for other factors. These are additional limits on interpreting any result beyond the absence of posted outcome data.

14. Related Tutorials

15. Related Statistical Calculators

16. Sources

• ClinicalTrials.gov: Torsion of the Tibial Tuberosity, a New Factor of Patellar Instability? — NCT03304119.
• Registry record last updated 2019-03-20; status last verified 2018-02.
• Results first posted 2019-03-11.
• 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

The registry record describes a completed, MRI-based study of tibial tuberosity torsion and patellar instability, with enrollment of 92. Its primary endpoint is the existence and degree of torsion on MRI, summarized by median and interquartile range. Four reviewers are described as assessing MRI scans. Patellar tilt and tibial tuberosity–trochlear groove distance are listed as secondary outcomes.

The comparison involves a patellar instability group and a control group, but the registry cautions that the groups are not a like-for-like comparison and says allocation is not stated. The record does not report group sizes, primary or secondary outcome results, or statistical analyses. It also does not report details needed to evaluate missing data, reviewer agreement, multiplicity, or adjustment. The registry record therefore establishes the study question and broad outcome plan, but does not provide results that answer whether tibial tuberosity torsion is associated with recurrent patellar dislocation.