Evaluation of Fusion Rate of Anterior Cervical Discectomy and Fusion (ACDF) Using Cervios ChronOs™ and Bonion™: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Evaluation of Fusion Rate of Anterior Cervical Discectomy and Fusion (ACDF) Using Cervios ChronOs™ and Bonion™ (NCT01615328), a randomized phase 4 study. The primary outcome is Bone Fusion With CT(Postoperative 6 Months).

2. Clinical Question

The trial addressed whether the two cage materials were associated with different bone-fusion results after ACDF. The registry summary describes b-TCP as having osteoconduction ability and HA/DBM as having osteoconduction and osteoinduction abilities. Those statements explain the rationale for comparing the devices; they are not themselves trial outcomes. The primary outcome was a participant count, rather than a direct measure of the proposed biological processes.

The registry also lists radiating-pain and neck-pain visual analogue scale (VAS) scores at six months, as well as adverse-event counts. These are additional outcomes and do not replace the primary CT assessment. The posted results can describe the observed groups and the uncertainty around their comparison, but they do not establish that the materials differ in other populations, at other follow-up times, or on outcomes not reported in the registry record.

3. Trial Design

The registry describes a phase 4, randomized, single-masked, parallel-group study sponsored by Seoul National University Hospital. The study status is completed. The recorded start was 2011-11, and primary completion was 2013-08. Enrollment is listed as 85. The registry identifies two device groups: Cervios ChronOS and Bonion.

Both groups underwent anterior cervical discectomy and fusion. The distinguishing intervention was the cage material: Cervios ChronOS is described as a PEEK cage filled with b-TCP, whereas Bonion is described as a PEEK cage with HA/DBM. The registered allocation is randomized. The record labels masking as single, but does not identify which people were masked or describe how masking was maintained. Details of the randomization sequence, allocation concealment, and treatment assignment procedures are not reported in the registry record.

The primary outcome was bone fusion with CT six months after surgery. Its description specifies evaluation of fusion between the bone substitutes and cervical vertebral endplates with three-dimensional CT. The two secondary outcomes were radiating-pain VAS and neck-pain VAS at six months after surgery. The registry also contains serious and other adverse-event counts for each group.

The primary outcome denominators are 39.0 for Cervios ChronOS and 38.0 for Bonion. These are the denominators attached to the posted primary outcome results; the record does not provide a participant-flow account explaining the relationship between those outcome denominators and the enrollment figure. The protocol’s planned sample size, its original statistical assumptions, and any changes to the design 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

Reasons for not completing this period:

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 Bone Fusion With CT(Postoperative 6 Months), measured over 6 months after surgery(ACDF).

The primary endpoint is the number of participants with bone fusion assessed by three-dimensional CT at six months after ACDF. The registry description places the assessment at the interface between the bone substitute and the cervical vertebral endplates. The outcome is binary at the participant level: the posted figures count participants with fusion, rather than giving a continuous imaging score or a time-to-fusion measure.

CT provides an imaging-based way to assess the stated fusion outcome after surgery. Using a defined six-month assessment makes the outcome comparable between the randomized groups at the same registered follow-up point. The record does not describe the exact radiographic criteria used to decide that fusion was present, who read the scans, whether readers were blinded to group, or how disagreements were handled. Those details are not reported in the registry record.

The endpoint is relevant to the trial’s stated comparison of two cage materials, but it represents only the registered CT assessment at this follow-up. It does not by itself measure pain, function, later fusion status, or the full experience of surgery. The pain scores are listed as separate secondary outcomes, and the registry does not provide a longer-term primary CT result in the posted outcomes.

7. Results Posted in the Registry

• Bonion: 73.7% (28/38) versus 66.7% (26/39) on control; risk difference 7.0 percentage points (95% CI -13.4 to 27.4), risk ratio 1.11 (0.83–1.48); unadjusted two-proportion z-test p = 0.501.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

VAS of Radiating Pain (Postoperative 6 Months)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Bonion: mean 2.90 versus 2.40 on control; difference 0.50 (95% CI -0.57 to 1.57), standardized effect d = 0.21; z-test p = 0.361.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Bonion and the control. The interval gives the range of effects that remain compatible with the data.

VAS of Neck Pain(Postoperative 6 Months)

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Bonion: mean 2.00 versus 2.30 on control; difference -0.30 (95% CI -1.37 to 0.77), standardized effect d = -0.12; z-test p = 0.583.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Bonion and the control. The interval gives the range of effects that remain compatible with the data.

Both secondary outcomes were measured at six months after surgery. The posted group means are close in scale, and the unadjusted comparisons are uncertain: the radiating-pain mean difference is 0.5 with p = 0.361, while the neck-pain mean difference is -0.3 with p = 0.583. The confidence intervals for both comparisons cross zero. Taken together, these results do not provide clear statistical evidence of a group difference on either pain score.

The secondary outcomes add context to the primary CT result, but they address different questions. CT fusion is an imaging outcome; the VAS measures are symptom scores. A pattern in one does not automatically confirm or contradict the other, and the registry does not report a formal analysis combining fusion and pain. The primary result is itself uncertain, so the secondary outcomes do not resolve whether the groups differ in fusion at six months.

These secondary comparisons are unadjusted. When multiple outcomes are examined, the chance of at least one apparently unusual result can increase if each is interpreted without accounting for the number of comparisons. In general, multiplicity procedures can control a chosen error rate across a family of tests, but the registry does not report whether such a procedure was planned or used. The secondary p-values should therefore be treated as exploratory evidence rather than as independent confirmation of a treatment difference.

The registry does not report a prespecified hierarchy among the secondary outcomes, thresholds for clinically meaningful VAS changes, or analyses of change from baseline. It also does not report how many participants posted each score beyond the group denominators shown with the posted results. Without those details, the secondary results are best read as descriptive comparisons at a single follow-up point, not as a complete account of symptom trajectories or clinical benefit.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• VAS of Radiating Pain (Postoperative 6 Months)
• VAS of Neck Pain(Postoperative 6 Months)

9. Statistical Interpretation

10. Statistical Methods Explained

The primary outcome is binary: each participant is counted according to whether bone fusion was recorded on CT. For a binary endpoint, a group’s event count is interpreted alongside its denominator. The primary results give 26.0 of 39.0 for Cervios ChronOS and 28.0 of 38.0 for Bonion. A risk difference expresses the difference between the two groups’ event proportions, with the comparison oriented as Bonion relative to Cervios ChronOS. The posted estimate is 0.070. This is an absolute contrast, not a relative ratio.

What does the p-value tell us?

The unadjusted p-value for the primary comparison is 0.501. In general, a p-value measures how incompatible the observed data are with a specified null model of no group difference, under the assumptions of the test. It is not the probability that the null hypothesis is true, and it does not measure the size or clinical importance of an effect. A comparatively large p-value does not prove no difference; interpretation also depends on the estimate, its uncertainty, the design, and the quality of the outcome data.

The registry does not identify a sponsor-reported statistical analysis for this endpoint. The posted comparison should therefore be read as an unadjusted comparison of the reported group results, rather than as evidence of a reported covariate-adjusted model. No information is reported about a stratified analysis, center adjustment, or other modeling choices. Randomization is the registered allocation method, but the record does not give enough detail to assess the allocation procedure or the handling of deviations from assigned treatment.

How should a confidence interval be read?

A confidence interval describes the precision of an estimate under the statistical method used. In general, a 95% confidence interval is constructed by a procedure that, over repeated use under its assumptions, would cover the true parameter at the stated rate. It is not a probability statement about the fixed true value after the interval has been calculated. The primary interval runs from a negative to a positive risk difference, so it includes no difference as well as possible effects in either direction. That breadth signals uncertainty about the size and direction of the comparison.

For the secondary VAS outcomes, the registry reports means and standard deviations for each group and unadjusted mean differences. A mean difference is an absolute contrast between the group averages. The radiating-pain mean difference is 0.5, with p = 0.361; the neck-pain mean difference is -0.3, with p = 0.583. Their posted confidence intervals span zero. For continuous outcomes, a standard deviation describes spread among individual scores, whereas a confidence interval for a mean difference describes uncertainty in the group contrast. These quantities answer different questions.

Why can dispersion matter?

For a continuous outcome, greater variability among participants generally makes a group mean harder to estimate precisely when other design features are unchanged. Here, the registry reports standard deviations for both VAS outcomes. The posted comparisons use those summaries and the group denominators. The record does not report the underlying score distributions, so it is not possible to assess skewness, unusual observations, or whether the normal approximation is suitable for these scores. In general, marked departures from the assumptions of a method can affect the reliability of its interval and p-value.

For a binary endpoint, the number of events and the denominators shape the uncertainty of the estimated group contrast. The count-based outcome does not have a reported over-dispersion parameter. In general, over-dispersion refers to more variability than a chosen model expects; when it is present in a model that assumes less variability, standard errors can be too small and intervals too narrow. The registry does not report a model for over-dispersion or a reason to apply one to these results.

What is and is not reported about the analysis?

The record labels the primary outcome and gives its six-month timeframe, but the statistical plan, missing-data methods, analysis populations, and multiplicity approach are not reported in the registry record. The posted comparison is unadjusted, and no sponsor analysis is listed. The record also does not specify whether outcome assessors were masked, how CT findings were classified, or whether participants with unavailable scans were handled in a particular way. These omissions limit assessment of how the estimates were generated and how sensitive they might be to analytic choices.

11. Confidence Intervals and Precision

The primary risk-difference estimate is 0.070, with a 95% confidence interval from -0.134 to 0.274. Because the interval crosses zero, the posted data are compatible with no difference as well as with a difference favoring either group. The interval is broad enough that the observed point estimate should not be treated as a precise estimate of the underlying contrast. Its limits describe uncertainty under the comparison method; they do not account for unreported sources of bias or uncertainty in outcome classification.

The primary p-value is 0.501. It does not replace the confidence interval: the p-value addresses compatibility with a null comparison, while the interval conveys a range of effects compatible with the data under the method. Neither gives the probability that a device is better, or establishes that any difference is clinically important. The registry does not report a clinically meaningful threshold for the fusion outcome.

The secondary mean-difference intervals also cross zero: the radiating-pain interval extends from -0.574 to 1.574, and the neck-pain interval extends from -1.372 to 0.772. These intervals likewise indicate uncertainty in the direction and magnitude of the group contrasts. The pain-score scales’ possible range and thresholds for meaningful change are not reported in the registry record, so the clinical importance of these contrasts cannot be determined from the registry values alone.

Precision is affected by the observed group sizes and the variability of outcomes. The registry gives primary denominators of 39.0 and 38.0 and reports standard deviations for both pain outcomes. It does not provide a detailed account of missing observations, scan assessment reliability, or the trial’s original precision goals. Consequently, the intervals quantify sampling uncertainty under the stated comparisons, but they cannot resolve limitations due to unreported trial conduct or measurement details.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm for 80% power and participants per arm for 90% power. They are not total event counts. The stated planning assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for each illustration is the stated fraction of the observed effect. For the primary outcome, the planning rows consider 100%, 75%, and 50% of the observed effect. The same effect-fraction approach is used for each secondary outcome.

The 80% power column describes the approximate number of participants per arm under which a study would have an 80% chance of detecting the assumed effect at the stated significance level, if the planning assumptions and effect were correct. The 90% column describes a higher chance of detecting that assumed effect, under the same conditions. Neither column describes the probability that the current trial’s result is correct. These are planning illustrations based on observed effects, not the original trial design calculations; the trial’s own design assumptions are not reported in the registry record. This is not observed power.

For the primary outcome, the figures are 666 participants per arm for 80% power and 892 for 90% power when planning for 100% of the observed effect. Planning for 75% of the observed effect gives 1,205 and 1,612; planning for 50% gives 2,754 and 3,687. The corresponding figures differ for each VAS outcome because the observed means and variability differ.

Smaller effects are harder to distinguish from random variation, so they require more participants under the stated assumptions. These illustrations should not be treated as a guarantee that a future study will achieve the stated power: the actual effect, variability, outcome completeness, and analysis method could differ. The displayed planning curve conveys the same general relationship between assumed effect size and required enrollment.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.667; treatment proportion p₁ = 0.737; average p̄ = 0.702.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6470 = 1.2681.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6451 = 0.5429.
4. n = (1.2681 + 0.5429)² / (0.0702)² = 666.0, rounded up to 666 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.666666666666667                          # control proportion
p1 <- 0.736842105263158                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(1615328)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 666 (80% power), 892 (90% power)
 75% of observed effect: n per arm = 1,205 (80% power), 1,612 (90% power)
 50% of observed effect: n per arm = 2,754 (80% power), 3,687 (90% power)
power.prop.test: 666 
Simulated power at n = 666 per arm: 0.795 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry identifies one primary outcome and two secondary outcomes. It does not report a multiplicity plan, such as an adjustment to the significance threshold or a hierarchical testing strategy. When several outcomes are tested, the chance of at least one apparently positive result can rise if each is judged separately at the same threshold. This general issue is relevant to interpreting the two unadjusted pain comparisons alongside the primary CT comparison. The registry record does not say whether any additional outcomes or analyses were planned.

The record lists no reported sponsor analyses. It gives unadjusted comparison results, but does not describe a full statistical analysis plan, prespecified covariates, subgroup analyses, sensitivity analyses, or rules for choosing among analysis populations. The planned intention-to-treat or per-protocol population, and how crossovers or protocol deviations were handled, are not reported in the registry record. Randomized allocation does not by itself establish which participants were included in each posted analysis.

The enrollment figure is 85, while the primary outcome results use denominators of 39.0 and 38.0. The registry does not provide a participant-flow explanation, reasons for unavailable outcomes, or a missing-data method. These details matter because incomplete outcome data can affect both the group estimates and their precision, depending on why data are missing and how the analysis handles them. It would be inappropriate to infer the cause of any difference between the enrollment and outcome denominators from the posted record alone.

The registry does not describe whether CT assessments were independently reviewed, whether readers were masked to assigned group, or how uncertain fusion classifications were adjudicated. Nor does it state whether VAS outcomes were analyzed using baseline adjustment or another repeated-measures method. These absences do not establish that such methods were not used; they mean the methods are not reported in the registry record. They limit reproducibility and make it harder to assess the potential influence of analytic choices.

15. 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.

The posted adverse-event figures report zero serious adverse events and zero other adverse events for Cervios ChronOS among 39 participants at risk, and zero in both categories for Bonion among 38 participants at risk. These are the event counts recorded in the registry. They describe what was posted for the groups and do not establish that no adverse events occurred outside the registry’s reporting or observation procedures.

The registry does not provide serious-event terms, event definitions, collection methods, or a timeframe for the adverse-event counts. Death counts are not reported in the registry record. No details are given about follow-up completeness or whether events were assessed for relatedness to the device or procedure. Without those details, the counts should be read as limited recorded safety information, not as a complete comparative safety analysis.

Zero reported events in both groups does not demonstrate equal safety or exclude uncommon events. The group sizes are limited, and no comparative safety model or confidence interval is reported. These figures can describe the posted record but cannot establish the frequency of events in a broader population or beyond the period captured by the study.

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

The registry results describe a randomized comparison of two PEEK cage materials used during ACDF. At the six-month CT assessment, the posted fusion counts were 26.0 of 39.0 participants with Cervios ChronOS and 28.0 of 38.0 with Bonion. The unadjusted risk-difference estimate favors Bonion numerically, but its confidence interval includes no difference and values in either direction. The comparison is therefore uncertain and does not establish a reliable group difference.

That result does not prove the devices are equivalent. The registry does not report an equivalence margin or an analysis designed to demonstrate equivalence. It also does not show that either device is superior, because the estimate is imprecise and the comparison is not statistically persuasive. The appropriate reading is limited to the observed six-month results and their uncertainty.

The pain-score comparisons do not supply clear evidence of a difference either, and they are secondary, unadjusted outcomes. The record does not report whether multiplicity was addressed, or provide a threshold for interpreting a clinically important change in VAS. The posted adverse-event counts are zero in each reported category for both groups, but limited safety reporting cannot establish that risks are absent.

These findings do not answer questions about longer-term fusion, other clinical outcomes, different patient groups, or other surgical techniques. The registry record also lacks detail about missing data, endpoint classification, analysis populations, and the original study assumptions. Those limitations matter when considering how broadly to interpret the results. The reported estimates are evidence about this trial’s posted outcomes, not a prediction for an individual or a recommendation about device selection.

17. Why This Trial Matters Statistically

This trial is statistically informative because it places an imaging-based endpoint at the center of a randomized comparison between two cage materials. The outcome is a participant count with CT-assessed fusion at a specified follow-up, allowing the comparison to be expressed as an absolute difference between groups. The registry also reports pain outcomes, making it possible to distinguish an imaging endpoint from symptom scores rather than treating them as interchangeable measures.

The results illustrate why the point estimate and its uncertainty should be read together. The observed primary counts differ, but the confidence interval includes both no difference and effects in either direction. A single estimate cannot convey this uncertainty on its own, while a p-value alone does not show the range of effects compatible with the data. The posted results therefore offer a clear example of why absence of strong statistical evidence is not proof of no effect or proof of equivalence.

The registry also enables a careful look at the limits of trial interpretation. Randomized allocation is documented, but important analytic and operational details are not: the masking target, the original design assumptions, missing-data handling, analysis populations, and multiplicity strategy are not reported. A statistically responsible reading separates what the record does show from what it leaves unresolved.

Finally, the planning illustrations make the relationship between effect size and enrollment concrete. They use observed effects and stated planning assumptions, not the trial’s original design calculations. This distinction matters: planning exercises can inform future study design, but they cannot retroactively measure the probability that the completed trial detected an effect.

18. 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.

Several trial-specific limitations constrain interpretation. The primary endpoint is assessed at six months, and no later CT outcome is posted. The registry does not describe the radiographic criteria for fusion, the identity or masking of scan readers, or how borderline assessments were handled. The primary comparison therefore cannot be independently evaluated for outcome classification procedures from the registry record.

Enrollment is listed as 85, while the primary outcome denominators are 39.0 and 38.0. The record does not explain participant flow, missing CT scans, withdrawals, or exclusions from the analysis. It is not possible to determine from the posted results why those denominators appear as they do or what effect any missing observations may have had.

The registry reports no sponsor analyses, and important statistical details are absent, including the original sample-size rationale, analysis populations, missing-data methods, multiplicity approach, and adjusted analyses. The registered single masking is not further specified. These omissions limit assessment of potential bias, the reproducibility of the analysis, and the interpretation of secondary outcomes.

The registry also provides limited safety detail: adverse-event definitions, collection period, event terms, and death counts are not available. The pain outcomes are single follow-up comparisons, without posted baseline scores or a stated threshold for clinically meaningful change. The findings should consequently be read as a narrow account of posted six-month outcomes rather than a complete assessment of longer-term effectiveness, symptoms, or safety.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Evaluation of Fusion Rate of Anterior Cervical Discectomy and Fusion (ACDF) Using Cervios ChronOs™ and Bonion™ — NCT01615328.
• Registry record last updated 2014-07-23; status last verified 2014-07.
• Results first posted 2013-11-18.
• 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.

22. Record Summary

NCT01615328 is a completed phase 4 randomized, single-masked, parallel-group trial sponsored by Seoul National University Hospital. Enrollment is listed as 85, with the recorded start in 2011-11 and primary completion in 2013-08. The study compared ACDF using Cervios ChronOS, a PEEK cage filled with b-TCP, with Bonion, a PEEK cage with HA/DBM.

The primary outcome was CT-assessed bone fusion six months after surgery. Posted counts were 26.0 of 39.0 for Cervios ChronOS and 28.0 of 38.0 for Bonion; the unadjusted comparison is uncertain, with a confidence interval spanning no difference. Secondary outcomes were radiating-pain and neck-pain VAS scores at six months. The registry also records zero serious and zero other adverse events in each group. Details of the analysis plan, missing data, and outcome assessment procedures are not reported in the registry record.