DIAM™ Spinal Stabilization System vs. Decompression, Formerly vs. Posterolateral Fusion: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for DIAM™ Spinal Stabilization System vs. Decompression, Formerly vs. Posterolateral Fusion (NCT00627497), a randomized phase 3 study. The primary outcome is Rate of Overall Success.

2. Clinical Question

The study was designed to evaluate the safety and effectiveness of the DIAM Spinal Stabilization System for patients with degenerative lumbar spinal stenosis. Its primary outcome is not a single symptom score: success requires meeting several criteria together. These include a specified improvement in Oswestry Disability Index (ODI), maintenance or improvement in neurological status, no serious adverse event classified as associated with surgical treatment, and no additional surgical procedure classified as failure.

The posted primary comparison is between DIAM Group1 and single-level posterior decompression. The registry also lists DIAM Group2 and posterolateral interbody fusion, but no primary comparison involving those groups is reported. The reported arm results therefore address a focused comparison, rather than providing a complete set of pairwise evaluations across every listed group. The registry record does not explain the distinction between the two DIAM groups or why four groups appear in the record.

The clinical question is consequently about the proportion meeting a composite success definition at a specified follow-up point. It is not simply whether ODI improved, whether neurological status was maintained, or whether an operation was followed by an adverse event considered separately. Each component and the rule requiring all components contribute to the overall-success result.

3. Trial Design

The registry describes a prospective, randomized, controlled phase 3 clinical investigation with a parallel design and no masking. The condition is degenerative lumbar spinal stenosis. The stated trial purpose concerns patients with symptoms at a single level from L2 to L5. Enrollment is listed as 32. The study began in 2008-02, had primary completion in 2010-12, and its status is terminated.

Four groups appear in the results: DIAM Group1, single-level posterior decompression, DIAM Group2, and posterolateral interbody fusion. The primary result comparison is DIAM Group1 against single-level posterior decompression. The other two groups have primary-outcome percentages listed, but no comparison estimates involving them are reported. The record also lists procedures and devices, including single-level posterior decompression, DIAM spinal stabilization, and fusion; it does not clarify the relationship between the repeated DIAM intervention entries and the two DIAM groups.

The primary outcome is measured 24 months after operation. Secondary outcomes named in the record include ODI score and ODI success, neurological success, back pain and leg pain measures, and general health status measured with SF-36. Numerical summaries are also posted for operative time, blood loss, and hospital stay. The registry record does not report the randomization method, intended allocation ratio, eligibility details beyond the stated condition and level range, or a reason for termination.

Although the study is described as randomized and controlled, the posted arm sizes are unequal and some listed groups are small. The record does not establish why the arm sizes differ, whether all randomized participants contributed to every outcome, or what analysis population was used. These omissions matter when interpreting a trial with a composite endpoint and several groups: the design label alone does not resolve how participants were allocated, followed, or included in each analysis.

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 Rate of Overall Success, measured over 24 months after operation.

The primary endpoint is the rate of overall success, expressed as a percentage of participants, at 24 months after operation. The registry defines success as meeting all of the specified criteria. First, ODI success requires improvement in pain or disability, defined as the pretreatment ODI score minus the post-treatment score being at least 15. Second, neurological success means maintenance or improvement in the evaluated motor, sensory, reflex, and straight leg raise sections. Third, there must be no serious adverse event classified as associated with surgical treatment. Fourth, there must be no additional surgical procedure classified as failure.

A composite endpoint can capture several aspects of outcome in one result. Here, it combines patient-reported pain or disability, neurological status, serious safety events, and further surgery. Requiring every component means the overall-success percentage represents participants who satisfy the complete rule, not the percentage who meet any one component. A participant who fails any component does not meet the full definition, regardless of performance on the others.

This endpoint is useful for describing a broad, prespecified notion of success, but its interpretation depends on the exact definition and on how each component is assessed. The registry record does not report component-specific primary results, so the overall percentage cannot show which criterion most often determined whether a participant was classified as a success. Nor does it provide a separate estimate for each element of the composite. The posted result should therefore be read as the combined endpoint, rather than as evidence about each symptom or safety component individually.

7. Results Posted in the Registry

• Single-Level Posterior Decompression: 27.3% (3/11) versus 53.8% (7/13) on control; risk difference -26.6 percentage points (95% CI -64.3 to 11.2), risk ratio 0.51 (0.17–1.50); unadjusted two-proportion z-test p = 0.188.

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.

Operative Time

• 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:
  • Single-Level Posterior Decompression: mean 1.10 versus 1.80 on control; difference -0.70 (95% CI -1.20 to -0.20), standardized effect d = -1.07; z-test p = 0.006.
• Interpretation:
  • The 95% confidence interval excludes no difference, so the mean is statistically lower for Single-Level Posterior Decompression than for the control. This is an unadjusted, secondary comparison, so it is suggestive rather than confirmatory.

Blood Loss

• 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:
  • Single-Level Posterior Decompression: mean 77.90 versus 82.50 on control; difference -4.60 (95% CI -75.93 to 66.73), standardized effect d = -0.05; z-test p = 0.899.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Single-Level Posterior Decompression and the control. The interval gives the range of effects that remain compatible with the data.

Hospital Stay

• 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:
  • Single-Level Posterior Decompression: mean 1.60 versus 1.40 on control; difference 0.20 (95% CI -0.54 to 0.94), standardized effect d = 0.21; z-test p = 0.595.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Single-Level Posterior Decompression and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes cover several domains: disability, neurological status, pain, general health, and perioperative measures. Their scope is broader than the primary composite, but the record does not provide numerical results for every named patient-centered outcome. Numerical summaries are posted for operative time, blood loss, and hospital stay. The registry lists 12 secondary outcomes as posted, while the numerical secondary summaries available for interpretation are limited to the measures identified in the results.

The secondary results do not establish a consistent direction of difference across all perioperative measures. Their estimated differences vary, and their uncertainty differs as well. This pattern is not a substitute for the primary comparison: the primary endpoint combines ODI success, neurological success, absence of a specified serious adverse event, and absence of further surgery, whereas the perioperative outcomes measure different events and resource-use characteristics.

Secondary results can help describe trial experience and identify questions for further study, but they carry less weight than a clearly prespecified primary analysis. When many outcomes are examined, some may appear notable simply because multiple comparisons have been made. Without a reported multiplicity strategy, the chance of false-positive findings across the full set is not quantified. The record does not report a hierarchy for secondary outcomes or adjustments to account for multiple testing.

The registry record does not report numerical results for the named secondary ODI, neurological, back-pain, leg-pain, and SF-36 measures. Their absence prevents a direct assessment of whether the primary composite aligns with changes in the individual patient-centered domains. It also prevents judging how the component success criterion based on ODI relates to the separately listed ODI outcomes. No such relationship should be inferred from the primary percentage alone.

Accordingly, secondary results are best treated as descriptive context. The reported summaries can characterize aspects of the operation and discharge, but they do not resolve the uncertainty in the primary endpoint or establish a broader pattern across outcomes that are not numerically reported.

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

• Oswestry Disability Index (ODI) Score
• Success Rate of Oswestry Diability Index Scores
• Success Rate of Neurological Status
• Back Pain
• Back Pain Success Rate
• Leg Pain
• Leg Pain Success Rate
• General Health Status (SF-36)

9. Statistical Interpretation

10. Statistical Methods Explained

The main comparison is between a binary outcome in DIAM Group1 and the same binary outcome in single-level posterior decompression. A participant either meets the registry’s full overall-success definition or does not. The arm percentages describe the fraction classified as successful within each group; they do not show the component-level outcomes separately. For this comparison, the posted results list seven successes among 13 participants in DIAM Group1 and three among 11 participants in the decompression group.

What does a risk difference mean?

A risk difference expresses the difference between two event proportions on the percentage-point scale. Its sign depends on the order of the groups in the comparison. The posted estimate is an unadjusted comparison of the observed proportions, rather than an estimate adjusted for participant characteristics or other covariates. The registry record does not report an adjusted primary analysis.

The risk difference is useful because it keeps the comparison in the same units as the outcome: the proportion meeting the success definition. It does not by itself indicate whether the observed difference is precise, which is why it should be read together with its confidence interval. In this trial, that interval includes no difference. The p-value is also unadjusted and is reported as 0.188. Neither the interval nor the p-value supplies a reason for the result, and neither identifies which component of the composite endpoint contributed to the observed arm percentages.

Why does a confidence interval matter?

A confidence interval describes the range of values reasonably compatible with the data under the statistical model used for the estimate. It is not a guarantee that the true effect lies in the interval, and it is not a direct probability statement about the particular trial result. A wide interval indicates that the data do not pin down the effect closely. Here, the interval extends across no difference and allows for effects on both sides. This is consistent with uncertainty, rather than a clear distinction between the groups.

General statistical explanation: small groups usually provide less information about a proportion than larger groups, particularly when the outcome can occur in only two ways. A small change in the classification of a participant can shift the observed proportion noticeably. This makes the interval and the amount of follow-up information important alongside the point estimate. It does not imply that the observed results are invalid; it means that the estimate is imprecise.

How should the p-value be read?

A p-value measures how incompatible the observed data are with a specified null model, assuming that model and the analysis assumptions hold. It is not the probability that the null hypothesis is true, nor the probability that a finding occurred by chance. The reported value, 0.188, is above the conventional 0.05 threshold used in the sample-size illustration. The registry record does not report a prespecified hypothesis-testing plan or multiplicity procedure, so the p-value should be understood as an unadjusted descriptive inferential result rather than as a complete account of the sponsor’s analysis strategy.

Statistical significance is not the same as clinical importance. A result can be uncertain even when the observed arm percentages differ, and a small p-value would not by itself establish that a difference matters to patients. The record does not provide a threshold for a clinically important difference in overall success. The composite’s definition is reported, but there is no separate assessment of the importance of different magnitudes of change.

What do the continuous summaries convey?

Operative time, blood loss, and hospital stay are reported as group means with standard deviations. A mean describes the average observed value; a standard deviation describes the spread of observations around that average. A standard deviation is not a confidence interval for the mean. The posted comparisons give unadjusted mean differences and confidence intervals. Their interpretation is limited by the group sizes and the variability in the measured values. In particular, blood-loss values have substantial dispersion relative to the difference in group means, so the estimated comparison is imprecise.

General statistical explanation: a mean-based comparison is most informative when its assumptions are reasonably suited to the data. Skewed measurements or unusually extreme values can make the mean and standard deviation less representative of a typical participant. The registry record does not report distribution checks, transformations, robust methods, or a rationale for the chosen summary. No alternative analysis is reported, so it is not possible to assess whether such choices affected the results.

Why does over-dispersion matter?

General statistical explanation: for a count or proportion, over-dispersion means that observations vary more than a model assumes. When present and unaccounted for, uncertainty estimates can be too small. The posted primary endpoint is binary and the sample is limited, but the registry record does not report a model-based analysis or a check for over-dispersion. The primary comparison is described as an unadjusted risk difference, and no additional model details are reported.

The posted analysis results are therefore best read as simple, unadjusted summaries with uncertainty, not as evidence of covariate-adjusted effects or a fully documented statistical analysis plan. The record reports no analyses in its analysis listing, and does not state how missing outcomes, protocol deviations, or multiple endpoints were handled.

11. Confidence Intervals and Precision

The primary result is not estimated with high precision. The reported confidence interval for the risk difference crosses no difference and includes values on either side of it. This means the data are compatible with a range of possible group differences, including no underlying difference; the observed percentages alone do not identify the size or direction of the underlying effect with confidence. The p-value of 0.188 is consistent with that uncertainty.

The primary outcome groups are small, and the endpoint is a composite requiring all listed criteria to be met. Both features matter for precision. With few observations, each outcome classification has appreciable influence on the arm proportion. Because the registry does not report primary results for the individual components, it is also not possible to see whether uncertainty is concentrated in one part of the composite or spread across several parts.

Precision is also limited for the additional groups. DIAM Group2 and posterolateral interbody fusion have small listed groups, and no comparative confidence intervals are reported for them. Their percentages should be viewed as descriptive observations, not as precise estimates of comparative effectiveness.

The confidence intervals for secondary comparisons also convey uncertainty. For blood loss and hospital stay, the intervals include no difference. The operative-time interval does not include no difference in the posted unadjusted estimate, but it is a secondary comparison, and the registry does not report a multiplicity adjustment or a prespecified hierarchy for interpreting secondary results. These results should not be treated as interchangeable with the primary endpoint.

Confidence intervals quantify statistical uncertainty under the analysis assumptions; they do not account for every source of uncertainty. The record does not report missing-data handling, analysis-population definitions, or sensitivity analyses. Consequently, the intervals cannot show how results might change under alternative assumptions about participants with missing outcomes or about the analysis set.

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 the reported two-group comparisons, not total events. The registry’s planning illustration uses a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It considers effects equal to 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect. The original trial’s own sample-size assumptions are not reported in the registry record, so these figures should not be mistaken for the study’s design target.

The 80% power column describes the number of participants per arm that the planning calculation estimates would be needed for an 80% chance of detecting the stated effect under those assumptions. The 90% column gives the corresponding per-arm planning figure for a 90% chance. Power is a property of a study design under an assumed effect and model; it is not a measure of how likely the observed result is to be true.

For the primary overall-success comparison, the illustration gives 53 participants per arm for 80% power and 70 for 90% power when planning for 100% of the observed effect. For 75% of the observed effect, the figures are 97 and 129; for 50% of the observed effect, they are 221 and 295. Smaller effects need more participants to detect under the same assumptions, which is why the planning figures rise as the assumed effect is reduced.

These are planning illustrations based on the observed effect, not observed power. They are not evidence that the trial was or was not adequately designed, because its original assumptions are not reported. They also rely on simplified assumptions and should be read as indicative calculations rather than as a substitute for a protocol-based sample-size justification. The sample-size curve represents the same planning relationship across the assumed effect sizes; it does not add information about the trial’s actual enrollment or results.

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 = 0.538; treatment proportion p₁ = 0.273; average p̄ = 0.406.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.6944 = 1.3610.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.6685 = 0.5626.
4. n = (1.3610 + 0.5626)² / (-0.2657)² = 52.4, rounded up to 53 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 <- 0.538461538461538                          # control proportion
p1 <- 0.272727272727273                          # 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(627497)
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 = 53 (80% power), 70 (90% power)
 75% of observed effect: n per arm = 97 (80% power), 129 (90% power)
 50% of observed effect: n per arm = 221 (80% power), 295 (90% power)
power.prop.test: 52.4 
Simulated power at n = 53 per arm: 0.811 (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 record does not report a statistical analysis plan, a prespecified testing hierarchy, or an adjustment for multiple comparisons. This is important because the record names several secondary outcomes and lists four groups, while only one primary comparison is reported. Without a documented strategy, the role of each secondary outcome in formal inference is unclear, and the risk of chance findings across multiple tests cannot be quantified.

The record reports no analyses in its analysis listing. It does post arm summaries and unadjusted comparison estimates, but does not describe whether these are the complete sponsor analyses or how they relate to any protocol-defined analysis. No interim analyses or stopping rules are reported in the registry record. The reason for the terminated status is also not reported, so the relationship between termination and the available follow-up cannot be assessed.

Missing-data methods are not reported. The record does not state how participants without a 24-month assessment were treated, whether outcome measures were imputed, or whether follow-up completeness differed by group. It also does not define an intention-to-treat, per-protocol, or other analysis population. Thus, the posted denominators cannot by themselves establish whether all randomized participants were included or whether the analyses used the same population for every outcome.

The registry also does not report sensitivity analyses to examine the effect of missing observations, alternative endpoint definitions, or different analysis assumptions. For a composite endpoint, information about each component and its missingness can be important because the overall classification depends on all criteria. Those details are not reported in the registry record.

These omissions do not prove that appropriate methods were not used; they mean that those methods cannot be evaluated from the registry record. The result should be interpreted as a posted, unadjusted comparison with limited documentation about multiplicity, missing data, analysis populations, and interim monitoring.

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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: urogenital (50.0%), spinal event at target level (25.0%), dural injury (16.7%), neurological (14.3%), accidental injury/ muscle strain (8.3%).

The safety summaries report counts of participants affected by serious and other adverse events within each group. For DIAM Group1, serious events affected 5 of 14 participants at risk, and other events affected 12 of 14. For single-level posterior decompression, the corresponding counts are 7 of 12 and 11 of 12. For DIAM Group2, they are 1 of 4 and 4 of 4; for posterolateral interbody fusion, 1 of 2 and 1 of 2. These are group-level counts, not counts of unique event types or an adjusted comparison.

The registry lists serious-event terms with percentages, including urogenital, spinal event at target level, dural injury, neurological, accidental injury/muscle strain, and cardiovascular categories. The record does not explain the denominator for these term percentages or whether a participant could contribute to more than one term. They should not be added or interpreted as mutually exclusive categories. Death counts are not reported in the registry record.

These figures are descriptive and should not be used to rank groups, particularly given the small group sizes and lack of comparative safety estimates. The primary success definition excludes serious adverse events classified as associated with surgical treatment, but the record does not provide the component-level results needed to connect that criterion to the overall-success percentages.

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

The posted primary results describe the proportion meeting the registry’s combined definition of overall success 24 months after operation. The observed proportion is higher in DIAM Group1 than in the single-level posterior decompression group, but the comparison is imprecise: its confidence interval includes no difference, and the reported unadjusted p-value is 0.188. These data do not establish a clear difference between those groups, and they do not establish that the groups are equivalent.

The result also does not show that DIAM spinal stabilization works or does not work. A statistical comparison from a small set of posted outcomes is not by itself a determination of clinical benefit. The record does not report a threshold for a clinically important difference, the numerical results for several named secondary patient outcomes, or component-specific primary results. It therefore cannot establish how the composite result relates to each symptom, neurological measure, serious-event criterion, or further-surgery criterion.

Percentages in the other listed groups are based on small groups and lack reported comparative estimates. They cannot support a reliable ordering of all four groups. The registry record does not describe why there are two DIAM groups, nor does it give enough information to explain group allocation or the differences between them.

The secondary perioperative summaries provide additional description but do not replace the primary endpoint. Their unadjusted nature, multiple outcome domains, and lack of reported multiplicity handling limit confirmatory interpretation. Likewise, the adverse-event counts are descriptive and do not establish comparative safety. The reason for trial termination, missing-data procedures, and analysis populations are not reported in the registry record.

The defensible conclusion is limited: the record posts an uncertain primary comparison and descriptive results for selected secondary and safety measures. It does not provide enough precision or analysis detail to support a definitive claim about comparative effects, and absence of a statistically clear difference should not be interpreted as proof of no difference.

17. Why This Trial Matters Statistically

This trial is statistically instructive because its primary outcome compresses several clinically distinct dimensions into a single all-criteria success measure. Such a composite can provide a broad summary, but interpretation depends on its components, their relative frequency, and the rule that every criterion must be satisfied. Here, the registry reports the overall success rate but not the separate primary-component results, so readers cannot determine which elements drove the final classifications.

The comparison also illustrates why a difference in observed percentages is not sufficient by itself. The primary arm estimates differ, yet the confidence interval includes no difference and the p-value is 0.188. Small groups leave substantial uncertainty around the observed proportions. Reporting an estimate with its interval helps distinguish the observed pattern from a precise conclusion about the underlying comparison.

Another statistical issue is the presence of four listed groups alongside a single reported primary comparison. The record does not explain the relationship among all groups or provide pairwise comparisons for the additional groups. This makes it important not to treat all arm percentages as if they came from a fully analyzed multi-group comparison.

The record also shows how exploratory secondary outcomes and safety counts need careful framing. Numerous domains are named, but numerical results are not available for every outcome, and no multiplicity procedure is reported. Differences in perioperative summaries can suggest areas for further examination, but they should not be elevated to confirmatory findings without a documented plan and appropriate uncertainty assessment.

Finally, the sample-size illustration is distinct from the trial’s original design rationale. It uses the observed effect and stated simplifying assumptions to show how planning needs vary with the target effect. Because the trial’s own sample-size assumptions are not reported, that illustration cannot establish what the investigators intended to detect. Together, these features make the study a useful example of why endpoint definition, precision, analysis transparency, and cautious interpretation must be considered together.

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.
• Participant counts were reconstructed from posted percentages and arm sizes, so small rounding differences are possible.

Several features specific to this record restrict interpretation. The trial is marked terminated, but the reason for termination is not reported in the registry record. The record therefore does not clarify whether termination affected recruitment, follow-up, outcome availability, or the planned analysis. Enrollment is listed as 32, while outcome group sizes vary, and the record does not explain the differences or establish which participants were included in each analysis.

The primary endpoint is a composite, but only the overall-success percentages are posted. Component-level results are not reported, so it is not possible to assess whether the observed composite pattern reflects ODI, neurological status, serious adverse events, additional surgery, or a combination. The record also does not report the basis for distinguishing DIAM Group1 from DIAM Group2, nor does it provide primary comparative estimates for the latter group or the fusion group.

Several design and analysis details are absent: the randomization method, allocation ratio, analysis population, missing-data handling, multiplicity approach, interim monitoring, and original sample-size assumptions are not reported in the registry record. No analysis listing is reported, despite the presence of posted summaries and unadjusted comparisons. This limits assessment of how the posted results relate to the planned analyses.

The primary comparison is imprecise, and the additional groups are small. Safety counts are descriptive, with no reported adjusted comparisons; the denominator behind the listed serious-event term percentages is not explained. Numerical results for several named secondary outcomes are also not reported. These limitations mean that conclusions should remain confined to the observed summaries and their uncertainty, without extrapolating to unreported outcomes or analysis choices.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: DIAM™ Spinal Stabilization System vs. Decompression, Formerly vs. Posterolateral Fusion — NCT00627497.
• Registry record last updated 2021-01-05; status last verified 2012-04.
• Results first posted 2012-04-24.
• 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

This prospective, randomized, controlled phase 3 trial evaluated DIAM spinal stabilization in degenerative lumbar spinal stenosis, with a parallel design and no masking. The registry lists enrollment of 32, a start in 2008-02, primary completion in 2010-12, and terminated status. The primary endpoint was the rate of overall success 24 months after operation, defined by combined ODI, neurological, serious adverse-event, and further-surgery criteria.

The reported primary comparison is DIAM Group1 versus single-level posterior decompression. Their overall-success results are 53.8% and 27.3%, respectively; the unadjusted p-value is 0.188, and the interval includes no difference. Other listed groups have descriptive primary percentages but no reported comparisons. Secondary summaries cover selected perioperative measures, while numerical results for several named patient-centered outcomes are not reported in the registry record.

Interpretation is limited by the small outcome groups, imprecision, and absent reporting on the termination reason, analysis populations, missing data, multiplicity, and original sample-size assumptions. The posted findings are descriptive and do not establish a definitive comparative effect.