Retrospective Evaluation of Performance of Coflex® Interlaminer Technology Versus Decompression With or Without Fusion: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Retrospective Evaluation of Performance of Coflex® Interlaminer Technology Versus Decompression With or Without Fusion (NCT03041896), a registered phase not stated study. The primary outcome is Overall Duration of Follow-up Care to Evaluate Overall Effectiveness of the Use of the Coflex® Interlaminer Technology.

2. Clinical Question

3. Trial Design

The study is titled as a retrospective evaluation of coflex® Interlaminar Technology versus decompression with or without fusion. It is marked completed, with enrollment of 5050. The registry record lists a start of 2016-07 and primary completion of 2017-12. The sponsor is Paradigm Spine. These administrative details describe the registered study; they do not supply evidence about the endpoint results or how the data were analyzed.

Four arms are described: Decompression, Fusion, Coflex®, and Hybrid. Decompression is standard-of-care decompression for spinal stenosis at 1 or 2 levels. Fusion is standard pedical and rod fixation with standard decompression at 1 or 2 levels. Coflex® is decompression surgery with coflex® Interlaminar Technology at 1 or 2 levels. Hybrid is coflex and fusion at adjacent levels. The registry identifies the primary endpoint comparison as coflex® versus Decompression only. It explicitly states that those were the only arms in which the primary endpoint data were collected and compared.

The record does not describe random allocation and identifies the comparison as not randomized. It also cautions that the arms are not a like-for-like control comparison. Accordingly, the arm descriptions should not be read as evidence that participants were exchangeable at baseline or that treatment assignment was independent of participant characteristics. The record does not report the allocation process, eligibility details, baseline balance, or the reasons a participant received a particular procedure.

The stated data-collection period is up to 6 months. The study also describes secondary objectives involving clinical, radiologic, and patient-reported outcomes at baseline, interim and/or final follow-up visits. Those objectives do not establish which specific measures were analyzed or what results were found. Although 3 outcome measures are listed, the registry record reports 0 analyses. The primary endpoint’s group summaries and inferential 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: The following arms: coflex® and Decompression, were the only arms where this data was collected and compared for this 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.

6. Primary Endpoint

The registry lists the primary outcome as Overall Duration of Follow-up Care to Evaluate Overall Effectiveness of the Use of the Coflex® Interlaminer Technology, measured over Study Duration Up to 6 months for data collection.

The primary endpoint is titled overall duration of follow-up care to evaluate overall effectiveness of coflex® Interlaminar Technology. It is a continuous measure, summarized as a mean with standard deviation, and its unit is days. The timeframe is described as study duration up to 6 months for data collection. The record says the measure was collected and compared only for the coflex® and Decompression arms.

Follow-up duration can describe how long participants remained in care or how much follow-up was recorded. As a general statistical point, it can also affect how much opportunity there is to observe later outcomes. But duration of follow-up is not itself a direct measure of symptom relief, function, radiographic status, or patient experience. The registry’s broader objectives mention those clinical, radiologic, and patient-reported outcomes, but the primary endpoint as written is duration of follow-up care.

The endpoint description does not state the precise operational definition of duration, the point from which days were counted, how incomplete follow-up was handled, or whether follow-up ending for different reasons was treated differently. Those details are not reported in the registry record. Nor does the record provide the arm-specific means, standard deviations, or numbers of participants contributing observations. Without those results, the endpoint’s observed distribution and the precision of any comparison cannot be assessed from the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is a continuous measure expressed in days. The registry specifies a mean and standard deviation as its descriptive summary. As a general statistical explanation, a mean represents the arithmetic center of observed values, while a standard deviation describes how dispersed individual values are around that center. Together they can characterize a distribution, but they do not show the values themselves unless the relevant summaries are reported. For this endpoint, neither arm’s mean nor standard deviation is reported in the registry record.

What would a comparison of means describe?

In general, comparing two means describes the difference in average observed values between groups. Interpretation depends on the endpoint definition, the observations included, and whether groups are comparable. Here, the registry names coflex® and Decompression as the two arms in which follow-up-duration data were collected and compared. It does not report an estimated difference, an interval around that estimate, or a statistical test. No direction or magnitude of a mean difference can therefore be stated from the registry record.

A confidence interval, in general, gives a range of values compatible with the data and the method used, while reflecting sampling uncertainty. A narrow interval indicates greater precision than a wide interval, but an interval is not a guarantee that the true value lies within it. No confidence interval for the primary endpoint is reported in the registry record, so its precision cannot be assessed. The same applies to any uncertainty measure for the arm-specific means.

Why does the study design matter?

The registry describes a retrospective, nonrandomized comparison and says allocation is not stated. In general, random assignment can help balance measured and unmeasured characteristics across arms, whereas a retrospective comparison may retain systematic differences between groups. The record further cautions that these arms are not a like-for-like control comparison. This means a simple contrast in observed averages, if available, would not by itself establish that the procedure caused any difference. Baseline data and the analytic approach used to address potential confounding are not reported in the registry record.

Adjustment is a general method for accounting statistically for selected differences among participants, often by including measured characteristics in a model. Adjustment can address only factors that are measured and appropriately modeled; it cannot automatically remove bias from unmeasured factors. The registry record does not report whether adjusted analyses were planned or performed, which covariates might have been used, or how the retrospective data were assembled. No adjusted result should be inferred.

How should the sample-size illustrations be read?

The planning assumptions describe illustrations based on the observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They specify that the effect to detect is a stated fraction of the observed effect. These are planning illustrations, not the study’s reported design justification and not observed power. The registry record does not report a sample-size justification for the study, and the illustrative assumptions should not be attributed to the investigators as the trial’s original design.

In general, a sample-size calculation explores how many observations might be needed under stated assumptions about a target effect, variability, significance level, and allocation. It does not show that a study actually enrolled that number in the relevant comparison, that its assumptions were met, or that an effect was observed. The overall enrollment of 5050 cannot be substituted for the number of participants with endpoint data in the two compared arms. Those endpoint-specific counts are not reported in the registry record. Any planning output should be read as conditional on its stated assumptions rather than as a summary of the study’s evidential strength.

The assumptions also specify equal allocation for the illustration, but the registry does not report actual arm sizes or state that enrollment was equal. The endpoint data were collected for two named arms only; the record does not say how many participants from those arms had usable follow-up-duration observations. Accordingly, the planning illustration cannot fill gaps in observed data or precision.

What does over-dispersion mean in general?

Over-dispersion refers generally to observed variability that exceeds what a chosen statistical model expects. It matters because a model that understates variability may produce uncertainty estimates that are too small and evidence that appears more precise than it is. This concept is not a reported feature of the primary endpoint analysis. The registry specifies a mean and standard deviation for a continuous measure, but it does not report a model, a variance assessment, or an over-dispersion check.

Follow-up duration may have a distribution whose shape matters to the choice of analysis. As a general point, means and standard deviations can be affected by unusually short or long observations, and the mean alone may not capture all features of a skewed distribution. The record does not report the raw distribution, a median, a range, diagnostic checks, or any transformation or alternative model. It is therefore not possible to assess whether the chosen descriptive summary adequately represented the observed durations.

The registry lists 3 outcome measures and 0 analyses. It does not describe the statistical plan, missing-data methods, multiplicity handling, or analysis populations. In general, these choices affect how estimates and uncertainty should be interpreted. Their absence from the record means readers cannot determine whether the reported endpoint was analyzed as planned, whether other outcomes influenced interpretation, or how incomplete observations were addressed. No inferential method beyond the stated descriptive parameter can be attributed to this study from the registry record.

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("Coflex®", "Decompression")
n   <- c(2058, 1428)
m   <- c(201.26, 191.75)
sp  <- c(208.64, 247.23)
sd  <- sp      # posted standard deviations
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  Coflex®  2058  201.260  208.640  192.241  210.279
CARM  Decompression  1428  191.750  247.230  178.916  204.584

11. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when a study evaluates several outcomes, comparisons, time points, or analyses. As a general statistical issue, repeated testing can increase the chance of findings that appear notable by chance unless the analysis plan accounts for the number and structure of tests. The registry lists 3 outcome measures and describes secondary objectives spanning clinical, radiologic, and patient-reported outcomes at baseline, interim and/or final follow-up visits. It does not report a multiplicity strategy, a hierarchy of outcomes, or which outcomes were analyzed. The registry record therefore does not establish how results across endpoints or visits should be interpreted together.

Missing-data handling is also not reported. The endpoint concerns follow-up duration, and the stated data-collection period is up to 6 months, but the record does not define how incomplete records, loss to follow-up, or unavailable endpoint measurements were handled. It does not provide the number of observations missing from either compared arm or describe any imputation, exclusion, or sensitivity analysis. As a general matter, missingness can affect both the observed group summaries and their comparability, depending on why data are absent. No particular missingness pattern can be inferred.

The analysis populations are not described. The registry does not say whether all eligible participants, only participants with available endpoint data, or another set was used for any analysis. Although the primary endpoint description identifies coflex® and Decompression as the only arms with data collected and compared, endpoint-specific participant counts are not reported. The record lists 0 analyses, so no analysis population or missing-data procedure can be verified from posted results. These omissions limit assessment of completeness, representativeness, and the robustness of any comparison.

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

The registry record establishes that a retrospective study was completed and that its stated primary endpoint was overall duration of follow-up care, measured in days, with a mean and standard deviation intended for the coflex® and Decompression arms. It also describes the procedures represented by four arms, the broad secondary objectives, and a data-collection period of up to 6 months. These registry entries describe the study’s scope and intended outcome, not its comparative findings.

The record does not report the primary endpoint’s observed values, group sizes for that endpoint, or an estimate of the difference between arms. It also does not report a confidence interval or test result. Thus it does not show whether follow-up duration was longer in one arm, how large a difference might have been, or how precisely such a difference could be estimated. A missing result should not be interpreted as a null result or as evidence of equivalence.

Even if a numerical difference were available, a nonrandomized comparison would need cautious interpretation. The record does not state allocation and warns that the arms are not a like-for-like control comparison. In general, differences in participant characteristics or clinical circumstances can affect observed outcomes, and a group contrast alone does not isolate the effect of a procedure. The registry does not report baseline comparisons or an adjustment strategy that would clarify this issue.

Follow-up duration also does not directly measure the clinical, radiologic, or patient-reported outcomes mentioned in the study objectives. It can characterize how much follow-up care was recorded, but it cannot by itself establish improvement, safety, or overall effectiveness. The adverse-event entries are zeros across the listed arms, with no serious-event terms, but the registry record does not explain the entries or provide an adverse-event analysis. They should not be treated as a definitive finding of no harm.

In short, the registry record supports a description of the study question and its limitations in reporting. It does not support a quantitative conclusion about the primary comparison or a causal conclusion about the procedures.

13. Why This Trial Matters Statistically

This study raises a useful statistical distinction between a broad clinical objective and the specific endpoint registered for comparison. The title and summary frame an evaluation of clinical, radiologic, and patient-reported performance, while the primary endpoint is duration of follow-up care. Distinguishing the measure actually specified from the broader objective helps prevent a care-duration statistic from being read as a direct measure of clinical outcome.

The record also illustrates why study design is central to interpretation. It describes a retrospective evaluation, identifies the comparison as nonrandomized, leaves allocation unstated, and cautions that the arms are not like-for-like controls. These details matter because observed group differences in nonrandomized data can reflect factors other than the intervention. Statistical adjustment can be useful in general, but the registry does not report whether adjustment was performed or what information was available for it.

Another important issue is the difference between overall enrollment and the population contributing to a particular endpoint. The record lists enrollment of 5050, yet primary endpoint data were collected only for coflex® and Decompression. Without arm-specific endpoint counts and outcome summaries, the overall enrollment cannot establish the precision of that comparison. This distinction is essential when reading study size alongside outcome reporting.

Finally, a completed record and a stated endpoint do not substitute for posted results. The absence of analyses and numerical endpoint findings leaves uncertainty about the observed effect, its precision, and the way incomplete data or multiple outcomes were handled. Clear reporting of estimates, uncertainty, analysis populations, and methods is necessary for readers to evaluate what the data show. In this record, the main statistical lesson is the boundary between a registered study objective and evidence that can be quantitatively interpreted.

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 primary limitation is that the registry record does not report numerical results for the primary endpoint. Although the endpoint is defined as a mean and standard deviation in days, neither summary is given for coflex® or Decompression. No endpoint-specific group counts, estimated contrast, confidence interval, or test result is reported. This prevents assessment of the observed difference and its precision.

The primary endpoint is described as follow-up duration, but the operational definition is not reported. The record does not specify the start and end points for counting days, how follow-up ending for different reasons was treated, or how incomplete observations were handled. The stated data-collection period of up to 6 months does not supply those details. Without them, it is difficult to determine exactly what a group mean would represent.

The design is retrospective and nonrandomized, allocation is not stated, and the registry explicitly cautions that the arms are not a like-for-like control comparison. Baseline characteristics, participant selection, treatment allocation, and any confounding adjustment are not reported. As a result, even a reported unadjusted difference would require careful interpretation, and the available record does not permit assessment of comparability between the two endpoint arms.

Although 3 outcome measures are listed, the record reports 0 analyses. It does not describe a statistical analysis plan, analysis populations, missing-data methods, or multiplicity handling. The broader objectives mention clinical, radiologic, and patient-reported outcomes, but their specific results are not reported in the registry record. Adverse-event entries also contain zeros across the listed arms without explanatory analysis, so their meaning cannot be established from the record alone.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Retrospective Evaluation of Performance of Coflex® Interlaminer Technology Versus Decompression With or Without Fusion — NCT03041896.
• Registry record last updated 2020-05-19; status last verified 2020-05.
• Results first posted 2020-05-19.
• 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

NCT03041896 is a completed retrospective evaluation sponsored by Paradigm Spine, with enrollment listed as 5050. The registry lists a start of 2016-07 and primary completion of 2017-12. The study concerns spinal stenosis and describes coflex®, Decompression, Fusion, and Hybrid arms involving procedures at 1 or 2 levels, with Hybrid described as coflex and fusion at adjacent levels.

The primary endpoint is overall duration of follow-up care in days, summarized as a mean and standard deviation, with data collected over a period of up to 6 months. The registry states that this endpoint was collected and compared only for coflex® and Decompression. It lists 3 outcome measures and 0 analyses. Numerical primary-endpoint results, endpoint-specific participant counts, analysis methods, and missing-data procedures are not reported in the registry record. The record describes the comparison as nonrandomized and cautions that the arms are not like-for-like controls.