Arthroscopy in the Treatment of Degenerative Medial Meniscus Tear: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Arthroscopy in the Treatment of Degenerative Medial Meniscus Tear (NCT00549172), a randomized na study. The primary outcome is The Lysholm Knee Score.

2. Clinical Question

The study was randomized and used a parallel design. The record reports an enrollment of 146. Its description frames the comparison as a way to evaluate whether resecting the torn tissue contributes to outcomes beyond those associated with diagnostic arthroscopy. That framing describes the research question; it is not itself evidence of a difference between the groups. The posted primary results are therefore best read as separate summaries of the one-year score in each arm, not as a direct estimate of the effect of resection.

3. Trial Design

This was a randomized, parallel-group trial with an enrollment of 146. The registry record lists the study as completed, with a start date of 2007-10 and a primary completion date of 2013-03. The sponsor was Tampere University. The record lists the masking as quadruple. Its brief summary also describes a double-blind, placebo-controlled, randomized trial; the operative and conservative arm descriptions clarify that the comparator procedure was diagnostic arthroscopy.

Participants were assigned to one of two procedures. In the operative arm, the degenerative tear of the medial meniscus was partially resected. In the conservative arm, arthroscopy was diagnostic. The latter is therefore a procedural comparator, not an arm described as receiving no arthroscopy. The registry labels the arms Operative (O) and Conservative (K), and reports 70 participants for the operative primary outcome and 76 for the conservative primary outcome.

The primary outcome was the Lysholm Knee Score at one year. The registry also lists secondary outcomes concerning general quality of life, pain at rest, and cost effectiveness. It records six outcome measures but zero analyses. The results reported for the primary outcome are group means with 95% confidence intervals. Details such as the allocation procedure, masking roles, site structure, eligibility criteria, and prespecified statistical analysis are not reported in the registry record. Randomization and the masking label describe the design, but do not establish how these procedures were implemented.

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

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.

Population: Age, Sex, Weight, Height, BMI, Duration of medial knee pain, Type of onset of symptoms, Radiographic assessment (Kellfren-Lawrence), Clinical meniscal tests

6. Primary Endpoint

The registry lists the primary outcome as The Lysholm Knee Score, measured over One year.

The primary endpoint was the Lysholm Knee Score at one year, measured in units on a scale. The score is based on an eight-item questionnaire designed to assess knee function and symptoms during activities of daily living. Scores range from 0 to 100; higher scores indicate less severe symptoms. This makes the measure a summary of reported function and symptoms rather than a direct measure of the meniscal tissue or the surgical procedure itself.

A continuous score can be summarized by a mean, which describes the average observed score in a group. The posted results give a mean for each arm and a 95% confidence interval around each mean. Those intervals describe uncertainty around the corresponding group means; they are not confidence intervals for the difference between arms. A direct comparison would address how far apart the group outcomes are while accounting for uncertainty in both groups. Such a comparison is not reported as an estimable result in the registry record.

The one-year timeframe indicates when the primary outcome was assessed. The registry does not report additional details about the questionnaire administration, the handling of incomplete responses, or whether the one-year measure was analyzed under a particular population definition. Those details matter when interpreting a score as a group-level trial outcome, so the reported means should be read alongside the limits of the analysis information available.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry record identifies a randomized, parallel-group design and reports mean Lysholm scores with 95% confidence intervals for the two arms. It does not report a statistical analysis plan or a direct test or estimate comparing the arms. The following explains the statistical concepts relevant to reading the reported summaries; general explanations do not imply that a particular method was used in this trial.

What does a group mean describe?

For a continuous outcome, a mean is the arithmetic average of the observed scores in a group. It gives a compact description of the group’s central value, but it does not show how scores vary among individuals. Two groups can have similar means while having different distributions of individual scores. The registry record does not report a standard deviation or another measure of within-group spread for the primary outcome, so the individual-level variability cannot be assessed from the posted summary.

The scale’s direction is important to interpretation: higher Lysholm scores indicate less severe symptoms. The reported mean is therefore read in that context. A mean does not describe every participant, and a group average should not be treated as an individual outcome. Nor does a difference between group means, considered alone, identify a causal effect. In a randomized study, the intended comparison is between outcomes under the assigned strategies, with attention to the analysis population, follow-up, and uncertainty.

What does a 95% confidence interval convey?

A confidence interval is an uncertainty summary for an estimated quantity. In general, a 95% confidence interval is produced by a procedure that, under its assumptions, would cover the target quantity in 95% of repeated applications. It is not a statement that a particular fixed quantity has a 95% probability of lying inside the interval. The intervals reported for this trial correspond to each arm’s mean, not to the difference between arm means.

The width of a confidence interval reflects the precision of the estimate under the method used. Precision depends on factors such as the amount of information and the variability in observations. The record does not state the calculation method used for these intervals or report the underlying score distributions. Their endpoints can therefore be described as posted, but the detailed assumptions behind their construction are not reported in the registry record.

Separate arm-level intervals are not a substitute for an interval around a between-arm contrast. Looking at whether two individual confidence intervals overlap is not a formal test of the difference between means. A direct comparison would estimate the contrast and its uncertainty using an appropriate method. The registry record explicitly indicates that values were missing or not estimable for a two-arm comparison of the continuous endpoint. Accordingly, no direct contrast should be inferred from the two arm summaries.

Why does randomization matter?

In general, random assignment is intended to make treatment groups comparable at the time of assignment, on average, including with respect to factors that may not be measured. This supports causal interpretation when the trial is conducted and analyzed appropriately. Randomization does not guarantee identical groups, eliminate missing outcomes, or settle how participants should be handled after assignment. The registry record states that the trial was randomized but does not report the sequence-generation method, allocation concealment, or analysis population. Those details are not reported in the registry record.

The parallel design means the trial assigned participants to one of the two described arms rather than describing a crossover comparison. The operative intervention was partial resection; the conservative arm received diagnostic arthroscopy. This distinction is relevant to the treatment contrast: the registry’s arm labels do not make the comparator equivalent to no procedure.

What do the planning illustrations mean?

In general, a sample-size calculation estimates how many participants may be needed to detect a specified effect under stated assumptions. The planning illustrations associated with the posted results are based on the observed effect, use a two-sided significance level of 0.05, assume equal allocation, and use a normal approximation. They consider the stated fraction of the observed effect as the effect to detect. These are planning illustrations, not evidence that the trial was designed around those assumptions, and they are not observed power. The trial’s own sample-size justification is not reported in the registry record.

Observed power is not a useful replacement for the uncertainty interval around a result: it is tied to the observed estimate and does not provide a new account of what effects remain compatible with the data. More generally, planning estimates depend on the assumed effect and method. They should not be read as evidence that a trial has established or ruled out a particular effect. The registry record does not provide a trial-specific justification or a reported analysis plan that would establish how the sample size was chosen.

Why can over-dispersion matter?

For some outcomes, especially counts, the observed variation can be greater than a simple model assumes. This is called over-dispersion. In general, ignoring it can make standard errors too small and confidence intervals too narrow, creating an overly precise impression. The primary endpoint in this trial is a continuous score, and the registry record does not report a count model or an over-dispersion assessment. This concept is relevant to statistical interpretation generally, but there is no basis to say that over-dispersion affected the reported Lysholm results.

10. Multiplicity, Missing Data and Analysis Populations

The registry record lists six outcome measures and identifies three secondary outcomes: general quality of life assessed with the 15-D, pain at rest measured using a visual analogue scale, and cost effectiveness. It records zero analyses. The posted primary results therefore do not establish how these outcomes were analyzed or whether any secondary findings were reported elsewhere in the registry.

Multiplicity arises when several outcomes, time points, or comparisons are tested. In general, conducting multiple tests can increase the chance of at least one apparently unusual result even when there is no underlying effect. Researchers may address this by specifying a primary outcome, using an adjustment method, or interpreting secondary analyses as exploratory. The record names a primary outcome and lists secondary outcomes, but does not report a multiplicity strategy, the statistical testing hierarchy, or analysis results for the secondary outcomes. No claim about multiplicity adjustment can be made from the available record.

Missing-data handling is also not reported in the registry record. The outcome summaries list 70 participants in the operative arm and 76 in the conservative arm, but the record does not say whether those counts include all randomized participants with measured outcomes, how missing scores were handled, or whether any imputation was used. It does not report reasons for missingness or a participant-flow account that would clarify outcome completeness.

The analysis populations are not reported in the registry record. In particular, it does not specify whether the primary result used an intention-to-treat population, a per-protocol population, or another definition. Without that information, the reported arm sizes should be treated as the counts accompanying the outcome summaries, not as proof of a particular analysis approach. These omissions limit assessment of bias and the robustness of the group summaries.

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.

Most frequent serious adverse event terms

Serious events with the highest arm-level rate: serious adverse event (1.4%).

The registry reports one serious adverse event in the operative arm, among 70 participants at risk, and lists the serious adverse event percentage as 1.4%. The conservative arm reports zero serious adverse events among 76 participants at risk. Other adverse events are reported as zero in both arms. These figures describe the adverse-event counts recorded in the registry; they do not provide a complete account of the event’s nature, timing, severity details, or relationship to the procedure.

The registry’s listed serious-event term is Serious adverse event. Death counts are not reported in the registry record. Definitions for serious and other adverse events, methods of collection, and the period over which participants were monitored are not reported in the registry record. The counts should therefore be read as a limited registry summary, not as a comprehensive comparison of safety.

With a small number of reported events, an absence of recorded events in one arm does not establish that the underlying risk is zero. Nor does the event count by itself show whether the arms differ in safety. A comparative safety estimate and its uncertainty are not reported. These results describe the posted counts only and should not be used as individual medical guidance.

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

The primary result gives one-year Lysholm Knee Score means for the operative and conservative arms, with a 95% confidence interval for each mean. Higher scores on this scale indicate less severe symptoms. The arm-level summaries offer a description of the observed scores, but the registry record does not report an estimable comparison between the arms. As a result, the posted data do not quantify the size or precision of a treatment contrast.

This distinction matters because descriptive summaries and comparative conclusions answer different questions. A mean characterizes a group; a randomized trial’s central comparative question concerns the difference between assigned strategies. The registry’s statement that the two-arm continuous comparison was missing or not estimable means that the available results do not support a formal claim about the direction, magnitude, or statistical significance of that contrast.

The result does not establish equivalence. Similar group means, or overlapping confidence intervals around those means, are not enough to show that two procedures have equivalent outcomes. Equivalence requires a prespecified margin and an analysis designed to assess whether the difference lies within that margin. Such a margin and analysis are not reported in the registry record. The posted result also does not establish that either approach succeeds or fails, and it does not show what an individual participant would experience.

The comparison is specifically between partial resection and diagnostic arthroscopy. It should not be reframed as partial resection versus no procedure. The registry lists the condition as knee osteoarthritis and describes the clinical focus as degenerative medial meniscal tears, but does not provide detailed eligibility criteria or a fuller account of the population represented in the analysis. That limits how precisely the results can be generalized.

Other information needed for a fuller interpretation—such as the analysis population, missing-data methods, direct comparative estimate, and results for secondary outcomes—is not reported in the registry record. The most defensible reading is therefore narrow: the registry records the arm-specific one-year means and confidence intervals, but not the direct statistical comparison required to answer the central comparative question.

13. Why This Trial Matters Statistically

This trial is statistically notable because its question concerns the added contribution of partial resection when both arms undergo arthroscopy. The operative arm received partial resection, while the conservative arm received diagnostic arthroscopy. That comparator helps define what the randomized contrast was intended to address: the registry does not describe a comparison between surgery and no procedure.

Randomization is an important design feature because it is intended to support a fair comparison of assigned strategies. Yet a randomized design does not, by itself, supply an interpretable treatment-effect estimate. The posted primary results provide a mean and confidence interval for each arm, while the registry record reports that a two-arm comparison for this continuous endpoint was missing or not estimable. This illustrates why group summaries should not be mistaken for the comparative analysis that answers a trial question.

The distinction between arm-level uncertainty and uncertainty around a treatment contrast is useful beyond this study. Separate confidence intervals describe each group mean; a direct contrast requires its own estimate and interval or other appropriate inferential result. Without that comparison, readers cannot assess the estimated magnitude and precision of the randomized effect from the registry results.

The registry also names secondary outcomes and records zero analyses. That gap underscores the role of transparent reporting: naming an outcome is not the same as reporting its result, analysis method, or relationship to a prespecified testing plan. Likewise, reporting the number of participants alongside a mean does not explain missing outcomes or define the analysis population.

These points make the record valuable as an example of how design descriptions and results reporting must be read together. The randomized design and one-year score summaries provide useful context, while the absent direct comparison and analysis details constrain the conclusions that can be drawn.

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 of the posted primary results is that they do not include an estimable two-arm comparison for the continuous endpoint. Arm means and confidence intervals can describe each group, but they do not provide the treatment-effect estimate and uncertainty needed to answer the comparative question directly. A between-arm p-value or confidence interval is not reported in the registry record.

The registry record does not report a statistical analysis plan, sample-size justification, analysis population, or method for handling missing primary outcome data. The outcome counts are listed, but participant flow and reasons for any missing scores are not described. These omissions make it difficult to evaluate whether the analyzed participants represent those randomized or whether the primary analysis followed a prespecified approach.

The record names secondary outcomes but reports zero analyses. Results for those outcomes, their assessment timeframes, and any multiplicity strategy are not reported in the registry record. The record also gives limited detail about eligibility criteria, recruitment setting, allocation procedures, and the roles involved in masking. The masking field says quadruple, while the brief summary describes the trial as double-blind; further operational detail is not reported in the registry record.

The primary endpoint is reported at one year, so the posted result does not describe outcomes at other time points. The adverse-event summary is also limited: one serious adverse event is reported in the operative arm and none in the conservative arm, but event details, monitoring duration, and death counts are not reported in the registry record.

These limitations concern the information available in the registry record. They do not establish that an omitted procedure or analysis was absent from the trial itself; they mean that it cannot be evaluated from the recorded information. The results should therefore be interpreted as a limited set of posted summaries rather than a complete report of the trial’s conduct and analysis.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Arthroscopy in the Treatment of Degenerative Medial Meniscus Tear — NCT00549172.
• Registry record last updated 2023-01-13; status last verified 2022-12.
• Results first posted 2015-03-23.
• 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 registry record describes a completed, randomized, parallel-group trial sponsored by Tampere University, with an enrollment of 146. It compares partial resection of a degenerative medial meniscal tear with diagnostic arthroscopy. The primary outcome is the Lysholm Knee Score at one year, for which higher scores indicate less severe symptoms.

The posted primary outcome results give arm-specific means and 95% confidence intervals: 82.2, with an interval from 78.4 to 85.9, for the operative arm; and 83.4, with an interval from 80.3 to 86.5, for the conservative arm. The registry record indicates that an estimable two-arm comparison for this continuous outcome is missing. It also lists secondary outcomes but records zero analyses. Direct comparative results, analysis populations, and missing-data methods are not reported in the registry record.