OptiMesh® for Lumbar Interbody Fusion Trial (OLIF): Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for OptiMesh® for Lumbar Interbody Fusion Trial (OLIF) (NCT00764491), a randomized na study. The primary outcome is Mean Change in Low Back Pain Score at 24-months Compared to Pre-op.

2. Clinical Question

The study was a randomized, parallel-group device trial. Its stated purpose was to collect data on the safety and effectiveness of OptiMesh 1500S for containing and reinforcing bone graft materials in patients undergoing interbody fusion. The primary outcome was a change score on a visual analog scale rather than a direct count of fusion procedures or a time-to-event outcome. The scale runs from no pain to the worst possible pain, and the registry defines a reduction of 2 units at 24 months compared with preoperative assessment as clinically meaningful.

The primary comparison addresses the difference between the groups’ mean changes, not whether every participant experienced the group-average change. The registry also lists right and left leg pain changes and satisfaction as secondary outcomes. Those outcomes broaden the description of participants’ reported experiences, but they do not replace the prespecified primary question. Details on the formal analysis plan and the population intended for each analysis are not reported in the registry record.

3. Trial Design

The registry describes a randomized, single-masked, parallel-group trial of two devices for lumbar interbody fusion. One group received OptiMesh 1500S filled with a mixture of demineralized bone matrix and cortico-cancellous bone, placed through a posterior approach, with supplemental pedicle screws. The comparison group received a structural allograft spacer with pedicle screws. The record lists total enrollment as 156 and the trial status as completed.

The target clinical context was degenerative disc disease requiring an interbody spinal fusion procedure combined with posterior fixation. The registry identifies Spineology, Inc as the sponsor. The start date is recorded as 2003-07 and primary completion as 2012-11. The record does not describe the sequence-generation procedure, allocation concealment, or which party was masked. It also does not report the specific surgical or postoperative procedures beyond the arm descriptions.

The primary outcome was mean change in low back pain score at the 24-month timepoint compared with preoperative assessment. The registry describes the measure as a visual analog scale and notes that 88 investigational and 16 control subjects completed the primary question at 24 months. The endpoint-specific counts therefore describe participants contributing to that outcome, not necessarily everyone enrolled. How participants without a 24-month score were handled is not reported in the registry record.

Seven outcome measures are listed, including the primary measure and three posted secondary outcomes. No reported analyses are listed in the record. Consequently, the posted group summaries and unadjusted comparisons should not be mistaken for a complete protocol-level account of the analysis. Details about the planned sample size, the intended analysis population, and any model-based adjustment 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:

Analysis population for the primary outcome, as defined in the registry: A total of 88 investigational and 16 control subjects completed this question at the 24-month timepoint.

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 Mean Change in Low Back Pain Score at 24-months Compared to Pre-op, measured over 24 month.

The primary endpoint is mean change in low back pain score from the preoperative assessment to 24 months. The visual analog scale is described as a 10 cm pain scale, with 0 representing no pain and 10 representing the worst possible pain. A change score expresses how the assessment at follow-up differs from the preoperative score; a negative mean change in the posted results represents a reduction in the recorded score.

The registry identifies a reduction of 2 units at 24 months compared with preoperative assessment as clinically meaningful. That threshold gives readers a stated reference for interpreting the magnitude of change, while the group mean remains an average and does not describe every individual participant. A mean change can conceal variation in participants’ responses, and the registry does not post individual-level data in these results.

The primary endpoint is useful for comparing average reported pain change between the randomized groups at a specified follow-up time. It is not, by itself, a direct measure of the technical success of fusion, the frequency of every complication, or how satisfied each participant was. Those questions require other outcomes. The posted primary result gives a mean change of -4.0 units in each group, with a mean difference of 0.0 units. The registry does not report additional details about the scoring procedure, assessor, or handling of missing measurements.

7. Results Posted in the Registry

• Structural Allograft Spacer: mean -4.00 versus -4.00 on control; difference 0.00 (95% CI -3.15 to 3.15), standardized effect d = 0.00; z-test p = 1.000.

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.

Right Leg Pain Score--Change From Preop at the 24-month Timepoint

• 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 errors.
• Result:
  • Structural Allograft Spacer: mean -2.00 versus -2.60 on control; difference 0.60 (95% CI -0.81 to 2.01), standardized effect d = 0.18; z-test p = 0.405.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Structural Allograft Spacer and the control. The interval gives the range of effects that remain compatible with the data.

Left Leg Pain--Change From Preop at the 24-month Timepoint

• 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 errors.
• Result:
  • Structural Allograft Spacer: mean -2.50 versus -2.50 on control; difference 0.00 (95% CI -1.75 to 1.75), standardized effect d = 0.00; z-test p = 1.000.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Structural Allograft Spacer and the control. The interval gives the range of effects that remain compatible with the data.

Number of Participants Rating Their Procedure as Very Satisfied or Somewhat Satisfied at 24-months Postoperative

• Endpoint type: Binary: the number of participants with the event, compared as proportions.
• Test: Unadjusted two-proportion z-test, with a Wald 95% confidence interval for the risk difference.
• Result:
  • Structural Allograft Spacer: 81.2% (13/16) versus 94.9% (37/39) on control; risk difference -13.6 percentage points (95% CI -34.0 to 6.7), risk ratio 0.86 (0.67–1.10); unadjusted two-proportion z-test p = 0.110.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Structural Allograft Spacer and the control. The interval gives the range of effects that remain compatible with the data.

The secondary outcomes extend the assessment beyond low back pain to right and left leg pain and participant satisfaction. Across these measures, the posted summaries are not a single composite result: they address different experiences, have different endpoint counts, and use different outcome scales or formats. They should be read as complementary descriptions rather than combined into one overall effect.

In broad terms, the secondary comparisons do not present a uniform pattern of clearly separated groups. The displayed estimates and intervals vary in direction and precision, and the posted unadjusted tests do not provide a multiplicity-adjusted assessment. This is consistent with treating the secondary findings as supportive context rather than as confirmation of the primary comparison. They do not overturn the primary result, which is itself an estimate with uncertainty rather than proof of equivalence.

General: when several outcomes are examined, the chance of observing at least one apparently unusual result can increase if each is assessed separately without adjustment. Multiplicity methods can address that issue, but the registry record does not report a planned adjustment or a hierarchy among the outcomes. Unadjusted secondary p-values should therefore not be interpreted as if they were the result of one prespecified, multiplicity-controlled test.

There are also differences in the number of participants contributing to each secondary measure. The record does not state whether these differences reflect missing assessments, eligibility for a particular measure, or another reason. It does not provide participant-level results or a joint analysis of the outcomes. These limitations make it difficult to determine whether apparent similarities across endpoints reflect a common underlying pattern or simply imprecision in separate comparisons.

The secondary results are most useful as additional descriptive evidence about pain scores and satisfaction at the 24-month visit. Their interpretation should remain bounded by the unadjusted nature of the comparisons, the varying endpoint counts, and the absence of a reported analysis plan. The registry does not report a prespecified multiplicity strategy or analyses that would establish how these outcomes were intended to support the primary question.

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

• Right Leg Pain Score--Change From Preop at the 24-month Timepoint
• Left Leg Pain--Change From Preop at the 24-month Timepoint
• Number of Participants Rating Their Procedure as Very Satisfied or Somewhat Satisfied at 24-months Postoperative

9. Statistical Interpretation

10. Statistical Methods Explained

The posted primary comparison is a difference between two group means. It contrasts the average change from preoperative low back pain score in the OptiMesh 1500S group with the average change in the structural allograft spacer group. The arm summaries report the mean change and standard error for each group. The comparison reports a mean difference, an interval, and an unadjusted p-value. No adjusted or model-based analysis is listed in the registry record.

What does a mean difference represent?

A mean difference expresses how far apart two group averages are on the outcome’s original scale. Here the outcome is a change in visual analog scale score, so the difference is expressed in units on that scale. A mean difference of 0.0 means that the displayed average changes are the same. It does not imply that individual participants had identical scores or changes. A group average can combine participants with quite different experiences.

The posted estimate is 0.0, based on a mean of -4.0 in each group. The direction of a difference depends on which group is subtracted from which. For this primary comparison, the displayed group means are equal, so the direction convention does not alter the point estimate. In other comparisons, the sign should be read together with the group ordering and the outcome definition.

What do standard errors describe?

The primary arm summaries report standard errors of 0.578 and 1.502. General: a standard error describes the sampling uncertainty of an estimated mean, rather than the spread of individual participants’ measurements. It generally becomes smaller when an estimate is based on more information, but it does not tell the reader how widely individual outcomes varied. A standard deviation is a measure of individual-level spread; it should not be substituted for a standard error.

The registry does not post confidence limits for the arm means themselves. It posts an interval for the difference between means. The comparison also includes a pooled standard deviation, but the registry does not describe the formula or assumptions behind the interval. No details are reported about whether the comparison accounts for baseline values, clinical sites, or other variables.

How should the p-value be read?

The posted primary p-value is unadjusted. General: a p-value describes how compatible the observed data are with a specified statistical null model, assuming that model and its assumptions. It is not the probability that the null hypothesis is true, nor is it a measure of clinical importance. A p-value alone also does not show the range of effects compatible with the data; the estimate and interval provide complementary information.

The record does not report the statistical test used, whether assumptions were checked, or whether the analysis was specified before results were known. It lists no reported analyses. The recalculated comparison is therefore best treated as a simple, unadjusted comparison of posted summaries rather than as a complete account of the trial’s analysis plan. The discrepancy flag is false, so there is no noted mismatch between this recalculation and a sponsor analysis.

Why do outcome counts matter?

The primary outcome description states that 88 investigational and 16 control subjects completed the question at 24 months. The total enrollment is 156, so the primary endpoint summaries do not represent the full enrollment count. The record does not explain why endpoint counts differ from total enrollment, how missing values were treated, or whether the analysis followed an intention-to-treat principle. General: when outcome data are unavailable for some participants, the analysis population and missing-data method can affect how well a comparison represents the randomized groups.

What is the role of the planning illustrations?

The registry includes planning illustrations for two secondary comparisons, not for the primary endpoint. They use the observed effect and state a two-sided significance level of 0.05, equal allocation between groups, and a normal approximation. The illustrations show participants per arm for 80% and 90% power under the listed effect fractions. They are not the trial’s sample-size justification and do not describe observed power. The protocol’s own sample-size assumptions are not reported in the registry record.

General: planning calculations ask how much information a future study might need under specified assumptions. Their output depends on the effect chosen for detection, variability, allocation, and statistical method. When the effect is taken from an observed comparison, it can be an uncertain basis for planning; smaller assumed effects require more information to detect. The planning figures should not be read as proof that the completed trial was adequately powered for its primary question.

11. Confidence Intervals and Precision

The primary mean difference is 0.0 units, with a posted interval from -3.155 to 3.155. This interval conveys substantially more than the point estimate alone: the data are compatible with a range of possible differences around the observed estimate. In particular, the range includes differences favoring either group and is broad enough to include differences that could be clinically meaningful under the registry’s stated 2-unit threshold.

General: a confidence interval is a range produced by a statistical procedure to express uncertainty in an estimate. Its interpretation depends on the method and confidence level. The registry record does not identify the confidence level or interval-construction method, so the interval should be described as the posted interval rather than assigned an unreported confidence level. An interval is not a guarantee that the true effect lies within its limits.

The endpoint-specific sample sizes were 88 and 16, and the reported standard errors were 0.578 and 1.502. Those summaries indicate that the available information was uneven between the groups. The smaller endpoint count and larger standard error in the structural allograft group are relevant when judging precision. The record does not provide a rationale for the imbalance or details on missing outcome handling.

A point estimate of zero does not mean the trial has tightly ruled out differences. The interval’s width, the difference in group counts, and the absence of reported analysis details all matter to interpretation. Conversely, a wide interval is not proof that a meaningful difference exists; it signals uncertainty about the size and direction of the difference. The posted result supports a cautious statement about the estimated group contrast, not a definitive conclusion of sameness.

12. Multiplicity, Missing Data and Analysis Populations

The registry lists seven outcome measures and three posted secondary outcomes, but it does not report a multiplicity strategy, outcome hierarchy, or adjustment across comparisons. The primary comparison is presented with an unadjusted p-value, and the secondary comparisons are also unadjusted. When multiple outcomes are tested, separate unadjusted p-values do not account for the total set of questions examined. The registry record does not report whether other analyses were conducted beyond those posted.

The analysis population is not described in enough detail to identify whether the primary result follows an intention-to-treat, per-protocol, or other approach. The primary endpoint description says that 88 investigational and 16 control subjects completed the 24-month question, while total enrollment is 156. The record does not explain the difference between enrollment and outcome counts, identify reasons for unavailable outcomes, or state how missing observations were handled. It also does not describe imputation, sensitivity analyses, or a missing-data assumption.

General: missing outcome data can affect interpretation when the availability of measurements is related to participants’ outcomes or group assignment. Complete-case summaries describe those with recorded data; whether they represent all randomized participants depends on the reasons data are missing and the analysis assumptions. Without information on those reasons and methods, the extent and direction of any effect on the comparison cannot be determined.

No reported analyses are listed, and details of the statistical analysis plan are not reported in the registry record. This absence does not establish that no analysis plan or additional analyses existed; it means the record does not document them. The registry also does not report interim analyses, rules for stopping, or a protocol-based sample-size justification. The secondary planning illustrations are not a substitute for those design details because they are calculated from observed effects.

13. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 2% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: disc herniation (100.0%), adjacent level degeneration (6.1%), spinal stenosis (6.1%), pseudoarthrosis (5.7%), infection (3.0%).

The registry reports serious adverse events for 14 participants among 123 at risk in the OptiMesh 1500S group and 6 among 33 at risk in the structural allograft spacer group. Other adverse events are reported for 19 participants among 123 at risk in the OptiMesh 1500S group and 6 among 33 at risk in the structural allograft spacer group. Deaths are listed as 3 and 0, respectively. These are descriptive counts, not adjusted comparisons of safety.

The record lists serious adverse event terms including Disc Herniation, Adjacent Level Degeneration, Spinal Stenosis, Pseudoarthrosis, Infection, and Screw Irritation, with percentages attached to the terms. The denominator and counting method for those percentages are not described in the record, so they should not be interpreted as group-specific risks without further information. The registry also does not provide details on event timing, severity grading, relatedness to the device or procedure, or whether participants could have more than one event.

General: adverse-event counts require context about follow-up, ascertainment, and the population at risk. Differences in counts alone do not establish a causal safety difference between groups. The posted figures should be read as the registry’s reported safety summaries, not as a complete account of all clinical events or a comparative safety analysis.

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

The primary result describes average low back pain score change among participants with a recorded 24-month response. The two posted group means are -4.0 units, producing a mean difference of 0.0 units. The accompanying interval extends from -3.155 to 3.155, so the estimate does not narrowly rule out differences in either direction. The result is a summary of the endpoint data, not a statement about each participant’s experience.

The registry defines a 2-unit reduction at 24 months compared with preoperative assessment as clinically meaningful. Both posted group mean changes have a magnitude greater than that threshold. This descriptive fact does not establish that either device caused the observed changes, because both groups received fusion procedures with posterior fixation and the record does not include an untreated comparison. It also does not show that every participant experienced a change of that magnitude.

The comparison does not establish equivalence, non-inferiority, or absence of a clinically important difference. Such conclusions require a suitable design, prespecified margins or hypotheses, and an analysis appropriate to those questions. Those details are not reported in the registry record. A nonsignificant or zero point estimate alone cannot prove that two interventions have the same effects.

The secondary pain and satisfaction outcomes and the adverse-event summaries provide additional descriptive context, but their counts and analyses are not a substitute for a full protocol-level assessment. The secondary results are unadjusted, and the registry does not report how multiple outcomes were handled. Safety counts are not adjusted comparisons and lack details on event timing and attribution.

Overall, the posted information permits a careful reading of the reported means, intervals, endpoint counts, and adverse-event summaries. It does not support conclusions beyond those measures and the participants represented in them. Missing-data methods, analysis populations, and several statistical design details are not reported in the registry record.

15. Why This Trial Matters Statistically

This trial illustrates why a point estimate, an uncertainty interval, and the endpoint count need to be read together. The primary mean difference is exactly 0.0 at the displayed precision, yet the posted interval extends from -3.155 to 3.155. The point estimate alone could suggest no observed separation, but the interval shows that the comparison remains compatible with a range of effects. A zero estimate is not, by itself, evidence of equivalence.

The endpoint counts also matter. The primary analysis includes 88 investigational and 16 control subjects, against a total enrollment of 156. The registry does not report why not all enrolled participants appear in the endpoint summaries or how unavailable outcomes were handled. Unequal group information affects the precision of a comparison and raises questions about which participants the result represents.

The record also distinguishes descriptive outcome results from a reported analysis plan. Although it lists multiple outcomes and posts unadjusted comparisons, no reported analyses are listed. The intended multiplicity approach, analysis population, and sample-size rationale are not reported. The planning illustrations based on observed secondary effects should not be mistaken for evidence about the trial’s design adequacy or observed power.

For clinical researchers and biostatisticians, the central statistical lesson is interpretive restraint: a numerical estimate can be straightforward while the limits on its interpretation remain substantial. The posted means and safety counts are useful descriptive evidence, but conclusions about equivalence, causal effects, or comparative safety require design and analysis information that is not documented in the registry record.

16. 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 endpoint result is based on 88 investigational and 16 control subjects who completed the 24-month question, while total enrollment is 156. The registry does not explain the difference in counts, describe reasons for missing outcomes, or state how missing data were handled. The result may therefore represent participants with a recorded assessment rather than the entire enrolled population; the exact analysis population is not reported.

The record does not identify which party was masked, describe allocation concealment, or provide details of the statistical analysis plan. It does not report the test or model used for the primary comparison, adjustment for baseline measurements or other factors, confidence level for the posted interval, or a sample-size justification. No reported analyses are listed. These omissions limit assessment of how the posted calculations relate to the planned trial analysis.

Multiple outcomes are listed, but no multiplicity strategy is reported. The secondary comparisons are unadjusted, and outcome counts vary across endpoints. The registry does not clarify whether this variation reflects missing data, measure-specific participation, or another cause. The planning illustrations concern secondary endpoints and are derived from observed effects; they do not establish the original design assumptions.

The safety summaries lack details on event timing, severity, relationship to the device or procedure, and the denominator used for the listed adverse-event term percentages. The record also does not describe the process for event ascertainment. Thus, the safety information is best interpreted as a set of posted counts rather than a complete comparative safety analysis. Finally, the trial concerns a specific pair of device strategies and clinical context, so the registry results do not directly describe other procedures or populations.

17. Related Tutorials

18. Related Statistical Calculators

19. Sources

• ClinicalTrials.gov: OptiMesh® for Lumbar Interbody Fusion Trial (OLIF) — NCT00764491.
• Registry record last updated 2021-09-16; status last verified 2021-08.
• Results first posted 2021-09-16.
• 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.

20. Record Summary

The completed randomized, single-masked, parallel-group OLIF trial compared OptiMesh 1500S with a structural allograft spacer for lumbar interbody fusion. Total enrollment was 156. The primary endpoint was mean change in low back pain score at 24 months compared with preoperative assessment.

The posted primary means were -4.0 units in each group, with a mean difference of 0.0 and an interval from -3.155 to 3.155. The endpoint description reports 88 investigational and 16 control subjects completing that question. The registry also lists secondary pain and satisfaction outcomes and adverse-event counts.

The record does not report the analysis plan, missing-data methods, multiplicity approach, or a sample-size justification. The secondary comparisons are unadjusted, and the posted safety information is descriptive. These limits should shape interpretation of the numerical summaries.