A Study to Evaluate the Efficacy & Safety of an Intra-Articular Ampion Injection for Pain of Osteoarthritis of the Knee: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for A Study to Evaluate the Efficacy & Safety of an Intra-Articular Ampion Injection for Pain of Osteoarthritis of the Knee (NCT02556710), a randomized phase 3 study. The primary outcome is Change in Knee Pain.

2. Clinical Question

3. Trial Design

This was a phase 3 randomized, double-blind, parallel-group, placebo-controlled study. It evaluated an intra-articular AMPION™ injection in adults with pain due to osteoarthritis of the knee. The registry records enrollment of 480 and marks the study as completed. The study start is recorded as 2015-09 and primary completion as 2016-06.

The treatment groups were a 4 mL AMPION™ dose and a 4 mL saline placebo dose. The registry’s intervention descriptions also refer to the placebo as a 4 mL injection. The planned comparison is therefore between the intervention and a placebo injection, not between AMPION™ and no injection. Whether participants, clinicians, outcome assessors, or other personnel were masked in particular ways is not reported in the registry record; the record describes the study as double-blind.

Randomization is intended to create groups that are comparable on average at the start of a trial, while blinding can reduce the influence of expectations on care or outcome assessment. These are general features of trial design, not evidence that all possible sources of bias were eliminated in this study. The registry does not report the randomization procedure, allocation concealment, the precise masking arrangements, or details of the injection schedule.

The primary outcome was mean change in WOMAC A Pain score from baseline to 12 weeks, with the primary population specified as ITT. Change in knee function was listed as a secondary outcome. The registry records 3 outcome measures and 3 analyses, but detailed information about the other measures and analyses is not reported in the registry record. A sample-size justification and the protocol’s planned statistical analysis are also not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: Ability to discontinue NSAID use at Screening visit and/or 72 hours prior to the Baseline visit and for the duration of the clinical study. No analgesia (including acetaminophen \[paracetamol\]) taken 24 hours prior to an efficacy measure.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intent to Treat (ITT)

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 Change in Knee Pain, measured over Scored at Baseline and 12 weeks.

The primary endpoint was the mean change in WOMAC A Pain score from baseline to 12 weeks. WOMAC A refers to the pain component of the Western Ontario and McMaster Universities Arthritis Index. The registry describes a 5-point Likert scale, ranging from 0, meaning none, to 4, meaning extreme. The endpoint summarizes the change in pain score over the specified period; a negative change represents a decrease in pain, and a more negative value represents a greater reduction.

Using change from baseline allows the analysis to describe how scores shifted during follow-up rather than relying only on the score at the end of follow-up. Comparing average changes between randomized groups is a way to assess whether the groups’ observed score trajectories differ. This is a general explanation of a change-score endpoint; the registry record does not explain why this particular endpoint or follow-up time was selected.

The reported group means were -0.91 for AMPION™ and -0.89 for saline placebo. Their reported 95% confidence intervals were -1.03 to -0.8 and -1.01 to -0.77, respectively. These are confidence intervals for the separate group means, not a confidence interval for the difference between groups. The registry reports the primary population as ITT, but further detail on how that population was defined or handled in the analysis is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does ANCOVA do?

ANCOVA, or analysis of covariance, is a general method for comparing an outcome between groups while adjusting for one or more covariates. In a randomized trial, the adjusted comparison can account for baseline information included in the model and can sometimes improve precision. The registry identifies ANCOVA as the method for the superiority comparison. It does not report which covariates were included, how they were selected, how the model was specified, or whether assumptions were checked. Those details should not be inferred from the method name alone.

For this continuous endpoint, the outcome is mean change in WOMAC A Pain score. The ANCOVA analysis concerns a between-group contrast, whereas the registry also reports an individual mean change for each arm. The comparison estimate and its uncertainty are the most direct quantities for interpreting the size and precision of the group contrast. Neither is reported in the registry record. The reported p-value, p = 0.94, gives a test result but cannot replace an effect estimate and confidence interval.

What do the confidence intervals describe?

A confidence interval expresses uncertainty around an estimated quantity under the statistical procedure used to construct it. In general, a narrower interval indicates greater precision for that estimate, while a wider interval indicates less precision. The registry reports 95% confidence intervals around the AMPION™ and placebo mean changes. Those intervals concern the arm-specific means. They do not directly give the uncertainty around the difference between arms, and they should not be treated as if they did.

A confidence interval is not a range containing every participant’s outcome, and it is not a statement that a particular value has a specified probability of being the true value. General interpretation depends on the estimation method and its assumptions. Details of the method used to construct the arm-level intervals are not reported in the registry record.

What does the p-value contribute?

A p-value measures the degree of compatibility between observed data and a statistical model that includes a null hypothesis. A small p-value can indicate that the data would be unusual under that null model, subject to the analysis assumptions. A larger p-value does not prove that groups are identical or that a meaningful difference is absent. It also does not tell the reader how large a difference is plausible. For this trial, p = 0.94 is the reported result of the ANCOVA superiority analysis, but the underlying comparative estimate and its confidence interval are not reported in the registry record.

The test’s meaning also depends on the prespecified analysis, outcome, population, and model. The record identifies the primary endpoint, the ITT population, and ANCOVA, but does not provide the full protocol or statistical analysis plan. It is therefore not possible to verify from the registry record whether all analysis decisions followed a prespecified plan.

What is the role of the ITT population?

In general, an intention-to-treat approach analyzes participants according to their randomized assignment, regardless of whether they fully followed the assigned intervention. This preserves the comparison created by randomization, provided the analysis and missing-data handling are appropriate. The registry labels the primary population as ITT. The exact operational definition, the number of participants included in the primary analysis, and the treatment of participants with missing measurements are not reported in the registry record. The label alone does not establish how missing outcomes or deviations were handled.

What can be inferred from the posted summaries?

The means and confidence intervals describe each group’s change on the pain scale. The reported ANCOVA p-value describes the test result for the comparative analysis. These are complementary but not interchangeable forms of evidence. Without the ANCOVA contrast and its uncertainty, readers cannot directly assess the estimated size or precision of the adjusted between-group difference from the registry record.

The record indicates that values are missing or not estimable for a recalculated two-arm comparison of this continuous endpoint. This means that the posted summaries do not support an independent recalculation of the comparative effect and its uncertainty. A recalculation based only on summary statistics would also be unadjusted, whereas the sponsor’s reported analysis is ANCOVA. If a discrepancy between a recalculation and the sponsor’s analysis were identified, the sponsor’s own analysis would take precedence; the record does not flag a discrepancy.

The registry also describes a planning illustration based on the observed effect, with a two-sided significance level of 0.05, equal allocation, and a normal approximation. It considers an effect to detect expressed as a fraction of the observed effect. In general, such calculations illustrate how assumptions about effect size and statistical criteria relate to planning sample sizes. They are not evidence of the study’s observed power, and they do not replace the trial’s own design justification. That justification is not reported in the registry record.

10. Analyses Reported by the Sponsor

The registry reports the sponsor’s comparative analysis as an ANCOVA superiority test with p = 0.94. The record does not report the ANCOVA treatment contrast, its confidence interval, the model covariates, or further details of the analysis. The reported arm-level means and 95% confidence intervals describe the separate group changes, not the adjusted contrast tested by ANCOVA.

A recalculated two-arm comparison is not available from the posted summary statistics: the registry notes that values are missing or not estimable for this continuous endpoint. Therefore, there is no independent recalculated estimate to compare with the sponsor’s result. The record does not identify a discrepancy. In general, an unadjusted recalculation from summary statistics would not necessarily reproduce an adjusted ANCOVA result, because the methods may use different information and assumptions.

The sponsor’s p-value should be read as the reported test result, not as an estimate of the size of the difference or proof that the groups were identical. The absence of a comparative estimate and confidence interval limits interpretation of the magnitude and precision of the result. The full statistical analysis plan and further details of the sponsor’s model are not reported in the registry record.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists Change in Knee Function as a secondary outcome, and records 3 outcome measures and 3 analyses. It does not report the complete set of outcomes and analyses, the order in which they were tested, or whether the primary outcome was the only confirmatory test. The detailed statistical analysis plan is not reported in the registry record.

Multiplicity arises when several outcomes, time points, subgroups, or statistical tests are assessed. As a general matter, conducting multiple tests can increase the chance of at least one apparently notable result by chance. Methods such as prespecifying a hierarchy or adjusting significance criteria can address this issue, but whether any such method was planned or used in this trial is not reported in the registry record. No adjustment for multiple comparisons should be assumed from the information available.

The primary population is identified as ITT, but the registry does not report the number included in the primary analysis or the detailed rules used to define that population. It also does not report how missing baseline or follow-up measurements were handled, whether any imputation was used, or whether sensitivity analyses assessed alternative missing-data assumptions. Missing-data methods matter because analyses may depend on assumptions about why outcomes are unavailable and how those unavailable values relate to observed outcomes.

The registry’s identification of an ITT population is useful, but it does not by itself resolve questions about missing observations or protocol deviations. Details of adherence, withdrawals, exclusions from analysis, and the availability of outcome measurements by group are not reported in the registry record. The record also does not report whether interim analyses were planned or conducted. These omissions limit assessment of the complete analysis strategy, rather than changing the meaning of the posted group summaries and ANCOVA p-value.

12. 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: malignant melanoma in situ (0.4%), cholelithiasis (0.4%), intussusception (0.4%), chronic obstructive pulmonary disease (0.4%), pulmonary embolism (0.4%).

The registry records serious adverse events for 2 participants at risk in the AMPION™ group and 4 participants at risk in the saline placebo group. The corresponding groups at risk are recorded as 236 and 243. No deaths were recorded in either group. These are counts as recorded in the registry; they do not establish that an event was caused by the assigned injection.

The registry also lists serious adverse event terms, each with a reported value of 0.4%: Malignant Melanoma In Situ, Cholelithiasis, Intussusception, Chronic Obstructive Pulmonary Disease, Pulmonary Embolism, and Cerebrovascular Accident. The listing does not specify the treatment group associated with each term, so group attribution should not be inferred.

Serious adverse event counts are not a complete account of safety. They do not describe event severity beyond the serious classification, timing, duration, relatedness assessments, or all non-serious events. The registry records other adverse events in the AMPION™ and placebo groups, but the counts alone do not establish causality or provide a full clinical interpretation. Further event-level information is not reported in the registry record.

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

The registry reports mean WOMAC A Pain change of -0.91 for AMPION™ and -0.89 for saline placebo, with separate 95% confidence intervals for each mean. It also reports an ANCOVA superiority-analysis p-value of 0.94. Together, these are the posted descriptive and inferential results for the primary endpoint, which assessed change from baseline to 12 weeks in the ITT population.

These figures do not provide the adjusted difference between groups or a confidence interval for that difference. The individual group intervals are not substitutes for the interval around a comparative estimate. The absence of a reported contrast limits how precisely readers can characterize the between-group effect from the registry record. The p-value is a test result, not a measure of effect size, clinical importance, or the probability that the null hypothesis is true.

These results do not establish that the treatments are equivalent, and they do not establish that either treatment does or does not work. A conclusion about equivalence would require an appropriate design and a prespecified margin, details not reported in the registry record. The results also should not be generalized beyond the study population or circumstances without considering the eligibility criteria, treatment procedures, follow-up, and other design details, several of which are not reported in the registry record.

Safety counts are similarly limited: they summarize reported serious adverse events and deaths, but do not establish causality or capture every aspect of safety. The registry record is one source of trial information; interpreting the findings fully would require additional details about the protocol, analysis plan, missing outcomes, and complete results. Those details are not reported in the registry record.

14. Why This Trial Matters Statistically

This trial illustrates why a treatment-group summary and a comparative estimate answer different statistical questions. The posted means describe average change within each group, while the ANCOVA p-value reports a test of the comparison. For interpretation, the estimated between-group contrast and its confidence interval would show the magnitude and precision of the adjusted comparison more directly. Those quantities are not reported in the registry record.

The primary endpoint is a continuous pain score measured from baseline to 12 weeks. This makes the direction of change important: negative values indicate a decrease in pain, with more negative values indicating a greater reduction. The two posted mean changes are close, but a reader should not turn that descriptive observation into a newly calculated treatment contrast. The registry indicates that the comparative values are missing or not estimable from the posted summaries.

The trial also highlights limits in what a registry result can establish. The record identifies the design, endpoint, population label, method, and p-value, but does not provide the full statistical analysis plan, the ANCOVA model details, or missing-data methods. That makes transparency about the limits of inference essential. The statistical lesson is not that one number settles the question, but that estimates, uncertainty, methods, and reporting completeness all matter when assessing clinical trial evidence.

15. 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 registry does not report the ANCOVA treatment contrast or its confidence interval. Although it reports mean change and 95% confidence intervals for each group, those summaries do not provide the uncertainty around the adjusted between-group comparison. The registry also notes that the values needed for a recalculated two-arm comparison of this continuous endpoint are missing or not estimable.

Further details of the ANCOVA model are not reported in the registry record, including its covariates and specification. The full statistical analysis plan, the trial’s sample-size justification, and any interim analyses are also not reported. The record does not describe multiplicity procedures, missing-data handling, sensitivity analyses, or the number included in the primary analysis. These gaps limit assessment of the prespecification and robustness of the reported result.

The registry describes the study as randomized, double-blind, and parallel, but does not report the randomization procedure, allocation concealment, or detailed masking arrangements. Additional eligibility criteria, injection schedule details, adherence, withdrawals, and follow-up completeness are not reported in the registry record. These details would help readers assess how the trial was conducted and how representative the results may be.

The safety summary provides serious adverse event counts and deaths but not detailed timing, duration, relatedness, or event-level group attribution for the listed terms. It therefore does not support a full comparison of safety profiles. These limitations concern what can be concluded from the registry record; they are not evidence that unreported procedures or analyses were or were not performed.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: A Study to Evaluate the Efficacy & Safety of an Intra-Articular Ampion Injection for Pain of Osteoarthritis of the Knee — NCT02556710.
• Registry record last updated 2022-08-09; status last verified 2022-08.
• Results first posted 2022-08-08.
• 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.

19. Record Summary

NCT02556710 is a completed phase 3 randomized, double-blind, parallel, placebo-controlled study of a 4 mL AMPION™ injection for adults with pain due to osteoarthritis of the knee. The registry records enrollment of 480, a study start of 2015-09, and primary completion in 2016-06.

The primary endpoint was mean change in WOMAC A Pain score from baseline to 12 weeks in the ITT population. The posted mean changes were -0.91 for AMPION™ and -0.89 for saline placebo. The reported ANCOVA superiority analysis gave p = 0.94. A comparative estimate and confidence interval are not reported in the registry record, and a recalculated comparison is not available from the posted summaries. Serious adverse event counts were 2 in the AMPION™ group and 4 in the placebo group; no deaths were recorded in either group.