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 MiDAS I (Mild® Decompression Alternative to Open Surgery): Vertos Mild Patient Evaluation Study (NCT00956631), a na phase 4 study. The primary outcome is Mean Change in Back Pain as Measured by a 10-point Visual Analog Scale (VAS)..
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT00956631 |
| Phase | Phase 4 |
| Condition | Lumbar Spinal Stenosis |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 78 |
| Arms in the primary outcome | n/a |
| Lead sponsor | Vertos Medical, Inc. |
| Results posted | Yes |
2. Clinical Question
Population
People with symptomatic lumbar spinal stenosis treated in the MiDAS I study. The registry reports 78 enrolled participants; the primary outcome population is described as all available treated patients at Month 6.
Intervention
Interlaminar decompression performed with the commercially available mild® Device Kit. The study evaluates the clinical application and outcomes of the procedure.
Comparator
There is no comparator arm in the registry record. The study is listed as a single-group design, with allocation recorded as NA and masking as none.
Primary question
What is the mean change in back pain from baseline to six months, measured on a 10-point Visual Analog Scale (VAS), among available treated patients? A positive change is defined as baseline score minus six-month score, so it represents a lower score at follow-up. The record describes mean improvement of at least 2.0 as clinically relevant, but it does not report the numerical mean change or its 95% confidence interval.
This is a question about change over time in a treated group, not a direct comparison of interlaminar decompression with another procedure or with no procedure. The registry record gives no between-group estimate. Consequently, any reported before-and-after change would describe the participants’ observed scores over the study period; by itself, it would not separate the procedure’s effect from other explanations for change over time.
The record identifies lumbar spinal stenosis as the condition and describes the study as prospective and multicenter. Its stated aim is to assess clinical application and outcomes. The primary endpoint focuses specifically on back pain, rather than on every possible aspect of the condition or procedure. The registry record does not report the numerical primary result, so the clinical question cannot be answered quantitatively from the recorded outcome information.
3. Trial Design
MiDAS I is listed as a completed Phase 4, prospective, multicenter clinical study of interlaminar decompression in people with symptomatic lumbar spinal stenosis. The listed intervention is a procedure using the commercially available mild® Device Kit. The registry reports enrollment of 78 participants. The study start is recorded as 2008-07 and primary completion as 2012-04.
The design is single-group, with allocation recorded as NA and masking recorded as none. No comparator group is listed. The registry’s design information therefore describes follow-up within a treated group, rather than a randomized allocation between treatment arms. There is no like-for-like control comparison described in the record. This distinction matters when interpreting changes from baseline: a before-and-after estimate describes the course of measured outcomes in the observed group, but does not itself provide a contrast with what would have happened under a different intervention.
The primary endpoint is mean change in back pain on a 10-point VAS from baseline to six months. The registry defines change as the baseline value minus the six-month value, making a positive value consistent with a lower follow-up score. The endpoint population is stated as all available treated patients at Month 6. That wording does not specify how many participants contributed primary-outcome data.
The registry lists 3 outcome measures and 2 analyses, but the additional outcome and analysis details are not reported in the registry record. The record also does not report a protocol description, a sample-size justification for the original study, an interim-analysis plan, or a detailed statistical analysis plan. The planning assumptions associated with sample-size illustrations are not evidence of the design rationale used for this completed study.
Because there is no randomized comparator and no masking, interpretation should remain focused on the observed outcomes in this study group. The registry record does not establish that every enrolled participant completed follow-up or that all enrolled participants were included in the primary analysis. The available-patients wording signals that the endpoint population depends on data availability at Month 6, while the number with those data is 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.
Before assignment: After enrollment and prior to surgery patient was excluded if patient had procedure or trauma at study treatment level, used acetylsalicylic acid (ASA) or non-steroidal anti-inflammatory drug (NSAID) within five days of treatment, epidural steroid injection (ESI) within 3 weeks of treatment.
Overall Study
| Stage | Mild Procedure |
|---|---|
| STARTED | 78 |
| COMPLETED | 62 |
| NOT COMPLETED | 16 |
Analysis population for the primary outcome, as defined in the registry: All available treated patients at Month 6.
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 | Mild Procedure |
|---|---|---|
| Participants analysed | 78 | |
| Age, Categorical: <=18 years | Participants | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 23 |
| Age, Categorical: >=65 years | Participants | 55 |
| Age Continuous | years | 70 (SD 11) |
| Sex: Female, Male: Female | Participants | 46 |
| Sex: Female, Male: Male | Participants | 32 |
| Region of Enrollment: United States | participants | 78 |
6. Primary Endpoint
The registry lists the primary outcome as Mean Change in Back Pain as Measured by a 10-point Visual Analog Scale (VAS)., measured over Baseline and Six Months.
| Element | Registry entry |
|---|---|
| Result type | Mean |
| Measure of spread | 95% Confidence Interval |
| Unit | units on a scale |
| Endpoint classification | Continuous Endpoint |
The primary endpoint measures mean change in back pain using a 10-point Visual Analog Scale. The scale is described as running from zero for no pain to ten for worst pain imaginable. A VAS provides a numerical way to record a participant’s rating, allowing the study to summarize scores across the treated group and compare baseline scores with scores at six months.
The registry defines the change as the baseline score minus the six-month score. Under that convention, a positive value corresponds to a lower score at follow-up; a negative value corresponds to a higher score. The sign convention is important because reversing the subtraction would reverse the interpretation of the same numerical change.
The registry describes mean improvement of at least 2.0 as clinically relevant. This is a threshold stated in the outcome description, not a result. The numerical mean change and 95% confidence interval are not reported in the registry record, so it is not possible to assess whether the observed group mean reached that threshold or how precisely it was estimated.
Using a mean summarizes the average change across participants with outcome data. It does not show the full spread of individual experiences: participants may have changes that differ from the group average. The confidence interval, if reported, would describe uncertainty around the estimated mean under the analysis assumptions. The registry record names a 95% confidence interval as the dispersion measure but does not give its endpoints. The endpoint captures back-pain ratings specifically; it should not be treated as a measure of every clinical outcome.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The primary outcome is defined clearly enough to explain its direction: change equals baseline VAS score minus the score at six months. A positive value would indicate a lower back-pain rating at follow-up, while a negative value would indicate a higher rating. The registry record, however, does not report the actual mean change or the endpoints of the 95% confidence interval. The direction and magnitude of the observed group result therefore cannot be described from the outcome information recorded.
The stated clinical-relevance benchmark is mean improvement of at least 2.0 on the 10-point scale. Since the numerical estimate is absent, it cannot be compared with that benchmark. The absence of a reported estimate also means that the precision of the result cannot be judged. A confidence interval is useful because it shows a range of values compatible with the data and analysis assumptions; without its endpoints, readers cannot tell whether the estimate is tightly or broadly uncertain.
Even if a within-group change were available, the single-group design would limit causal interpretation. Participants were treated and followed over time, but the registry lists no comparator arm and no random allocation. A change from baseline could reflect the intervention, other changes over time, or a combination of influences. The design does not furnish a direct estimate of how outcomes would have differed under another treatment or no treatment. This is a limitation of the comparison structure, not a statement about the direction or size of any observed change.
The outcome population is described as all available treated patients at Month 6. The number contributing data is not reported in the registry record. Without that count, the extent of outcome availability cannot be assessed from the record, and the enrolled total should not be mistaken for the number necessarily included in the primary endpoint analysis. The handling of missing observations is also not reported.
The safety figures record 0 serious adverse events among 78 at risk and 0 other adverse events among 78 at risk for the listed Mild Procedure group. These are registry counts, not comparative estimates: there is no control arm against which to assess event frequency. The record does not list serious-event terms, and deaths are not reported as a numerical count. The recorded zero counts should be read within those reporting limits and not as evidence about outcomes beyond the listed group and recorded categories.
Overall, the registry provides study-design and endpoint definitions but does not provide a numerical primary outcome result. Statistical interpretation is therefore limited to explaining what the measure would mean and what the design could support, rather than drawing a conclusion about the size, precision, or clinical relevance of the observed change.
9. Statistical Methods Explained
What does the mean change represent?
The endpoint is a continuous measure: VAS scores are numerical values on the scale described in the registry. For each participant with the required measurements, the baseline score is compared with the score at six months using the specified subtraction, baseline minus six-month score. The group mean summarizes those changes. A positive mean would indicate that, on average, follow-up scores were lower than baseline scores. This interpretation depends on the stated subtraction order; it should not be inferred from the word change alone.
A group mean is a summary, not a description of every participant’s course. Different individual changes can contribute to the same average. The registry does not report the distribution of individual changes, the numerical mean, or the count contributing to the primary endpoint. No claim about the size or consistency of participant-level changes can therefore be made from the recorded primary outcome information.
How should the confidence interval be understood?
The registry names a 95% confidence interval as the measure of dispersion for the mean change. In general, a confidence interval communicates statistical uncertainty around an estimate: a narrower interval indicates greater precision under the analysis assumptions, while a wider interval indicates less precision. It does not describe the range of individual participant scores, and it does not establish that every value inside it is equally likely. The interval endpoints are not reported in the registry record, so its width and the values it includes cannot be evaluated.
In general, an interval for a mean change can help readers judge whether the estimate is compatible with a range of possible group-average changes. It can also help assess the relation between an estimate and a prespecified clinical benchmark. Here, the outcome description says mean improvement of at least 2.0 is clinically relevant, but the absent estimate and interval prevent that comparison. The benchmark is part of the endpoint description; it is not a substitute for the observed result.
What can a single-group analysis establish?
A single-group before-and-after analysis estimates change over time among the participants whose outcome data are analyzed. It does not estimate a treatment contrast between randomized groups. In general, a comparator helps distinguish changes associated with the intervention from changes that might also occur over time or under another care condition. Without a comparator in this registry record, the mean change, if reported, would remain a within-group description. It could not on its own attribute the change to the procedure.
Random allocation and masking are recorded as NA and none, respectively, and the model is listed as single group. Those design entries should not be replaced with assumptions about other methods. Details of adjustment for baseline characteristics, alternative estimators, or covariate models are not reported in the registry record. It is likewise not reported whether any hypothesis test was performed for the primary endpoint or which test, if any, was used.
What do the sample-size illustrations mean?
Planning illustrations use the observed effect as their reference and state assumptions of a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They consider effects defined as stated fractions of the observed effect. Such illustrations are planning calculations, not observed power and not a report of the original study’s design justification. The registry record does not report the numerical illustration outputs or a sample-size justification for the completed single-group study. The equal-allocation, two-arm assumptions do not describe the listed single-group design; they are assumptions for the planning exercise.
In general, a sample-size planning calculation asks how many participants would be needed to detect a specified effect under stated assumptions. Its result depends on the effect chosen and the statistical assumptions. It should not be read as evidence that a study had a particular probability of detecting an effect after the data were collected. The planning assumptions do not fill gaps in the registry’s account of how enrollment of 78 was selected.
Why can over-dispersion matter?
In general, over-dispersion means that observed variability is greater than a statistical model expects. When a model underestimates variability, standard errors and confidence intervals may be too small and statistical evidence may appear more precise than warranted. This concept is especially relevant to count or rate outcomes modeled with distributional assumptions. The primary endpoint in MiDAS I is a continuous mean change, and the registry record does not identify a model involving over-dispersion. No conclusion about an over-dispersion adjustment can be drawn for this study.
Which analysis details remain unknown?
The registry lists 2 analyses and 3 outcome measures, but details of the additional analyses and outcomes are not reported in the registry record. The record does not specify the estimation procedure for the primary mean, the treatment of outlying values, assumptions about the distribution of change scores, or any adjustment for baseline score. It also does not state whether results were adjusted for site or other characteristics. These are examples of statistical details that can affect interpretation; they should not be presumed to have been used or omitted beyond what the record states.
The primary outcome is described for all available treated patients at Month 6. A confidence interval would reflect uncertainty under the method used, but the method and the numerical interval are not given. The posted information therefore supports explaining the endpoint and design, but not reproducing or evaluating the underlying analysis.
10. Multiplicity, Missing Data and Analysis Populations
Multiplicity arises when several outcomes, time points, comparisons, or analyses are examined. In general, making many statistical tests can increase the chance that at least one appears noteworthy by chance if no adjustment or prespecified strategy is used. A multiplicity plan may identify a primary outcome, set an order for testing, or adjust inference across tests. The registry identifies a primary back-pain endpoint and lists 3 outcome measures and 2 analyses. The details needed to determine how those outcomes and analyses relate, and whether multiplicity was addressed, are not reported in the registry record. No adjustment or testing hierarchy should be assumed.
The primary endpoint population is described as all available treated patients at Month 6. This identifies an availability-based analysis population, but the number with outcome data is not reported. The record does not state how many participants lacked baseline or follow-up VAS measurements, why any measurements were unavailable, or whether participants were excluded from the analysis. It also does not describe imputation, weighting, or another missing-data procedure. Without those details, the potential influence of missing outcomes on the estimated mean cannot be assessed.
The enrollment count of 78 is not necessarily the primary endpoint denominator: the record’s wording refers to available treated patients, and it gives no separate denominator for the outcome. The registry does not report whether all enrolled participants received the procedure, whether follow-up was attempted for everyone, or how the analysis population was defined beyond the available-patients description. Those matters remain unknown rather than evidence of attrition or complete follow-up.
The registry record also does not report a protocol-based analysis plan, an interim-analysis plan, or a detailed account of how analysis decisions were made. Consequently, readers cannot establish from this record whether outcome selection, missing-data handling, or multiplicity procedures were prespecified. These omissions constrain reproducibility and interpretation, but they do not establish that a particular analysis choice was made.
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 |
|---|---|---|---|
| Mild Procedure | 0 | 78 | 0.0% |
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 |
|---|---|
| Mild Procedure | 0 of 78 |
For the Mild Procedure group, the registry records 78 participants at risk for serious adverse events and 0 affected. It also records 78 at risk for other adverse events and 0 affected. These are the posted counts for the categories listed; they are not comparisons with an untreated or alternative-treatment group. The registry lists no serious adverse-event terms.
The death count is not reported in the registry record: its entry is null, which should not be converted into a zero. The record also does not describe the adverse-event observation window, event definitions, ascertainment procedures, or whether the listed counts cover all follow-up. Thus, the zero event counts should be interpreted as the registry’s reported counts for the listed categories, without extending them to unreported categories or periods.
In general, a zero count in a study group does not prove that an event is impossible or establish comparative safety. Event counts provide descriptive information, while a comparative safety estimate requires a suitable comparator and clear information about follow-up and event ascertainment. Neither a control group nor those additional reporting details are present in the registry record. The figures therefore describe the recorded group counts only.
12. What the Result Does, and Does Not, Mean
The registry record establishes that MiDAS I was a completed, prospective, multicenter, single-group study of interlaminar decompression in people with symptomatic lumbar spinal stenosis. It describes a primary endpoint based on mean back-pain change from baseline to six months and specifies how to interpret the sign of that change. It also records the stated clinical-relevance benchmark and the serious and other adverse-event counts for the procedure group.
The record does not report the numerical mean change or its 95% confidence interval. It therefore does not show how large the observed average change was, how precise an estimate would be, or whether the result met the stated benchmark of mean improvement of at least 2.0. No conclusion about the primary outcome’s magnitude or statistical significance can be drawn from the endpoint definition alone.
Even with a numerical before-and-after estimate, the study design would support a description of change in the treated group rather than a randomized comparison. The registry lists no comparator arm and no random allocation. The estimate would not by itself show what would have happened to similar participants under a different treatment or without the procedure. This limits causal interpretation; it does not establish that the procedure did or did not cause any particular outcome.
The safety entries report 0 serious and 0 other adverse events among 78 at risk in the listed group. These counts do not establish comparative safety, and the death count is not reported in the registry record. The available information also does not identify the number contributing to the primary outcome, the handling of missing data, or the detailed statistical plan.
Accordingly, the registry supports understanding the study question, design, endpoint definition, and recorded safety counts. It does not support a quantitative conclusion about the primary result or a controlled estimate of the procedure’s effect. Those boundaries are important: an unreported result is not a zero result, and a within-group observation is not a treatment comparison.
13. Why This Trial Matters Statistically
This study is statistically informative as an example of how a prospective clinical study can define a measurable outcome while still leaving important inferential questions dependent on design and reporting. The primary outcome specifies the measure, time points, direction of subtraction, dispersion measure, and a clinical-relevance benchmark. Those details make the intended interpretation of a numerical result understandable. Yet the numerical estimate and interval are not reported in the registry record, so the endpoint definition cannot substitute for the result.
The single-group structure highlights the difference between describing change and estimating a comparative effect. Repeated measurements in treated participants can answer whether their recorded scores changed over time, if results are reported. Without a comparator, that change does not separate the intervention from other influences on outcomes. This distinction is central when interpreting prospective studies and should remain explicit even when an endpoint has a clear clinical meaning.
The record also illustrates why analysis population and missing-data reporting matter. The primary outcome is defined for all available treated patients at Month 6, but the number available is not stated. Enrollment alone does not identify the outcome denominator. Without that denominator and a description of missing-data handling, readers cannot assess how complete the endpoint information was or how the analysis addressed unavailable measurements.
Finally, the event counts are descriptive and belong to a single listed group. Zero recorded events in the listed categories are not a comparison and cannot answer a comparative safety question. Taken together, the study details show why statistical interpretation depends not only on the endpoint but also on a reported estimate, its precision, the analysis population, and a design capable of addressing the intended comparison.
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 trial-specific limitation is the single-group design. The registry lists no comparator arm, with allocation recorded as NA and masking as none. A change from baseline to six months would therefore describe the treated group over time, not a randomized contrast. The registry record cannot establish how outcomes would have differed under another intervention or without the procedure.
The primary endpoint result is not reported numerically. Although the outcome description names a mean change and a 95% confidence interval, neither the estimate nor the interval endpoints appear in the registry record. The stated benchmark of mean improvement of at least 2.0 therefore cannot be assessed against an observed result. The absence of a numerical result is a reporting limitation; it should not be interpreted as no change.
The outcome population is all available treated patients at Month 6, but the number contributing data is not given. The record does not explain missing measurements, provide the outcome denominator, or describe missing-data methods. It is therefore not possible to assess completeness of follow-up or the possible effect of unavailable data on the mean.
Other analysis details are also not reported in the registry record, including the method used to estimate the mean and interval, the handling of multiple outcomes or analyses, and the details of any statistical analysis plan. The registry lists 3 outcome measures and 2 analyses, but does not describe the additional outcomes and analyses in the information recorded.
For safety, the record gives zero serious and zero other adverse events among 78 at risk in the listed group, but it does not report the death count, event terms, or observation window. Those omissions limit interpretation of the counts. The prospective, multicenter description and enrollment of 78 provide context, but they do not resolve these reporting and design constraints.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: MiDAS I (Mild® Decompression Alternative to Open Surgery): Vertos Mild Patient Evaluation Study — NCT00956631.
- Registry record last updated 2013-04-04; status last verified 2013-02.
- Results first posted 2013-04-04.
- 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
MiDAS I (NCT00956631) is a completed Phase 4, prospective, multicenter, single-group study of interlaminar decompression for symptomatic lumbar spinal stenosis. Enrollment is recorded as 78. The study start is 2008-07, and primary completion is 2012-04. The intervention is listed as a procedure using the commercially available mild® Device Kit.
The primary outcome is mean change in back pain on a 10-point VAS from baseline to six months, defined as baseline score minus six-month score. The registry describes mean improvement of at least 2.0 as clinically relevant and names a 95% confidence interval, but does not report the numerical mean change or interval endpoints. The primary population is all available treated patients at Month 6; its size is not reported.
The registry records 0 serious and 0 other adverse events among 78 at risk in the Mild Procedure group. Deaths are not reported as a numerical count. No comparator arm is listed, and details of missing-data handling, multiplicity, and the statistical analysis plan are not reported in the registry record.