pAF for the Treatment of Osteoarthritis: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for pAF for the Treatment of Osteoarthritis (NCT04886960), a randomized phase 1, phase 2 study. The primary outcome is Repeat Allogeneic Intra-articular Injection Within 6 Months..

2. Clinical Question

Statistically, the primary comparison is about the frequency of this recorded binary outcome in the two randomized arms. It is not a direct measure of pain relief, function, structural change in the knee, or the number of injections over a longer period. The secondary outcomes listed in the registry include knee injury and osteoarthritis symptoms, pain, a single-assessment rating, and physical function. Their presence gives the study a broader set of patient-reported measures, but the primary question remains the occurrence of rescue injection within the stated follow-up window. The registry record does not report further eligibility criteria or an operational definition beyond the description of rescue medication and its documentation.

3. Trial Design

The registry describes a Phase I/II, randomized, triple-masked, parallel-group trial. Participants were assigned to an amniotic fluid injection arm or a standard-of-care steroid injection arm. The record lists enrollment of 60 and gives 30 participants in each arm’s posted outcome data. The study status is completed. The start date is 2021-07-08, and the primary completion date is 2025-01-31.

The intervention descriptions specify one-time injections of 3ml: amniotic fluid in the intervention arm and corticosteroids in the standard-of-care arm. The registry calls the comparator Standard of Care Steroid Injection, while the intervention name is Amniotic Fluid Injection. The sponsor is the University of Utah. The record states triple masking but does not identify which people or roles were masked, or describe how masking was maintained. Those details are not reported in the registry record.

The primary outcome was assessed over 6 months and is recorded as a participant count. The outcome description says that participants in either arm could receive a standard-of-care rescue injection at any time when needed or requested, at the principal investigator’s discretion. Clinicians were not to know the assigned study arm, and rescue-injection information was to be recorded in the electronic medical record and the study’s electronic data capture system. Participants were not to receive additional amniotic fluid injections during the study period.

Four secondary outcomes are named: the Knee Injury and Osteoarthritis Outcome Score, Visual Analog Scale for Pain, Single Assessment Numerical Evaluation, and PROMIS Physical Function Computer Adaptive Test. The registry lists 6 outcome measures overall. Details such as the scheduled assessment visits, randomization procedure, allocation concealment, and the trial’s original sample-size rationale 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.

Before assignment: If the patient is found to be eligible for the study, research staff will approach the patient for informed consent. Patients with bi-lateral knee OA can participate but only one knee will receive the study treatment. The treating physician/principal investigator and the patient will discuss which knee should be treated with a study injection.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Repeat Allogeneic Intra-articular Injection Within 6 Months., measured over 6 months.

The primary endpoint is whether a participant received a rescue standard-of-care injection within 6 months. It is a binary outcome: each participant is classified according to whether the specified event occurred. The posted arm results report 6 participants with the event in the Amniotic Fluid Injection arm and 7 in the Standard of Care Steroid Injection arm.

The endpoint is used to capture a subsequent request for or need for standard-of-care injection during follow-up. In the registry description, rescue treatment could be given in either arm at the principal investigator’s discretion, and it was documented in the electronic medical record and the study’s electronic data capture system. This makes the measure a record of rescue treatment received, rather than a direct rating of symptoms or function. The registry does not report a separate threshold for deciding when rescue treatment was indicated.

Interpretation should stay close to that definition. The endpoint does not count additional amniotic fluid injections, since the description says participants would not receive further pAF injections during the study period. Nor does the endpoint by itself quantify the amount of pain, degree of function, or reason for a rescue injection. Those are distinct questions, with patient-reported measures listed as secondary outcomes. The registry record does not report how these secondary measures were combined or how their results were analyzed.

7. Results Posted in the Registry

• Amniotic Fluid Injection: 20.0% (6/30) versus 23.3% (7/30) on control; risk difference -3.3 percentage points (95% CI -24.2 to 17.5), risk ratio 0.86 (0.33–2.25); unadjusted two-proportion z-test p = 0.754.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary outcome is binary because it records whether each participant did or did not receive a rescue injection within the specified follow-up. A binary outcome can be summarized by the event count and the number of participants assessed in each arm. The registry lists the event count and denominator separately for each arm. This outcome format does not preserve details such as the timing, number, or clinical reason for rescue treatment beyond the fact that it occurred within 6 months.

What does a risk difference express?

A risk difference compares the event proportions between two groups by subtracting one group’s proportion from the other. It is expressed on the absolute probability scale: a value of zero represents no difference between groups, while values on opposite sides of zero indicate different directions of the contrast. The posted estimate is negative for the Amniotic Fluid Injection arm relative to the Standard of Care Steroid Injection arm. Its interval estimate crosses zero, so the range of values compatible with the data includes no difference. The interval also extends to both sides of zero, which signals uncertainty about the direction and size of the underlying contrast.

How do relative measures differ?

A risk ratio compares the event risks as a ratio, and an odds ratio compares the odds of the event. These relative measures answer a different scale-based question from the risk difference. A ratio of one corresponds to no relative difference; values below or above one represent different directions. The registry reports both relative measures with interval estimates. Their intervals include the value representing no relative difference, so they do not establish a clear separation between the arms. Relative measures can look different in magnitude from absolute differences, particularly when the event is not common, so they should be interpreted on their own scales rather than treated as interchangeable.

What does the p-value tell the reader?

The registry reports an unadjusted p-value for the comparison. In general, a p-value measures how unusual data at least as inconsistent with a specified null model would be if that model and the test assumptions held. It does not measure the probability that the null model is true, and it does not tell whether an effect is clinically important. The unadjusted value is not a substitute for the estimated contrast and its interval. Here, the p-value and the interval are consistent with an uncertain comparison rather than a precise estimate that rules out meaningful differences in either direction.

Why do the intervals matter?

A confidence interval is a range calculated by a statistical procedure to reflect uncertainty in an estimate. In general, wider intervals indicate less precision, while narrower intervals indicate more precision, conditional on the method and assumptions used. Whether an interval includes the no-difference value is informative, but the whole range matters: it shows what sizes and directions of effect remain compatible with the data. The registry record does not state the confidence level or the exact statistical procedure used for the posted intervals. The intervals should therefore be described without assigning an unreported confidence level or method.

What is and is not specified about the analysis?

The registry lists the primary endpoint as a participant count and posts an unadjusted comparison. It reports 0 analyses in its analyses field. The record does not describe a statistical model, covariate adjustment, test selection, or an analysis population such as intention-to-treat or per-protocol. It also does not state whether the posted comparison was prespecified in the statistical analysis plan. Those details are not reported in the registry record, so they should not be inferred from the fact that the trial was randomized.

Randomization is intended in general to make treatment groups comparable on average, but it does not ensure that every characteristic is balanced in a particular trial. An adjusted analysis can account for selected covariates if planned and appropriately specified; no such analysis is described in this record. For this reason, the posted contrast should be read as the unadjusted comparison that appears in the results, not as an adjusted treatment effect.

Why can over-dispersion matter?

Over-dispersion is a general issue for count outcomes when observed variability exceeds what a statistical model assumes. It can lead to confidence intervals that are too narrow or tests that are too optimistic if the model does not accommodate the extra variability. It is not a central feature of this primary endpoint, which is reported as whether a participant had an event rather than as a count of repeated events per participant. The endpoint does not report the number of rescue injections each participant received. No over-dispersion assessment or model-based count analysis is reported in the registry record.

The listed secondary outcomes use different measurement scales and may require different summaries or models. Their analysis details, missing-data methods, and any multiplicity adjustment are not reported in the registry record. Thus, general statistical principles can explain how such methods work, but the specific procedures used for those outcomes cannot be determined from the posted record.

10. Confidence Intervals and Precision

The estimated primary contrast is accompanied by an interval that crosses the value corresponding to no difference. This means the posted data do not pin down the direction of the contrast: values favoring either arm remain compatible with the interval. The result is therefore uncertain, rather than evidence that the arms are exactly alike. The registry also posts intervals for the relative risk and odds ratio, and those intervals include the no-relative-difference value.

The arm counts are close, with 6 events among 30 participants in the Amniotic Fluid Injection arm and 7 among 30 in the Standard of Care Steroid Injection arm. With counts of this size, a small change in the observed event pattern can have a noticeable effect on an estimate. The interval is the important companion to the point estimate because it makes the uncertainty visible rather than presenting one value as if it were exact.

The confidence level and interval calculation method are not reported in the registry record. Accordingly, the interval can be discussed as the posted uncertainty range, but it should not be assigned a confidence level or computational method that the record does not state. Nor should the point estimate be treated as a forecast for a different population or setting. The primary endpoint concerns rescue injection within 6 months, and its interpretation is limited to that outcome and follow-up period.

Precision is distinct from statistical significance. A result can fail to show a clear difference because the estimated effect is small, because uncertainty is substantial, or both. The posted interval indicates that uncertainty remains about the magnitude and direction of the contrast. It does not establish equivalence or rule out clinically relevant differences; the registry does not report an equivalence margin or a noninferiority framework.

11. 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, not total participants and not total events. They illustrate the sample size associated with detecting different fractions of the observed effect under the stated planning assumptions. For 100% of the observed effect, the table gives 2,397 participants per arm for 80% power and 3,208 participants per arm for 90% power. For 75% of the observed effect, it gives 4,321 participants per arm for 80% power and 5,784 participants per arm for 90% power. For 50% of the observed effect, it gives 9,854 participants per arm for 80% power and 13,190 participants per arm for 90% power.

In plain terms, the 80% power column describes a planning scenario with an 80% chance of detecting the specified effect under the assumptions if that effect is real; the 90% column describes the corresponding scenario with a higher target chance of detection. Greater power generally requires more participants when the other assumptions are held fixed. The planning assumptions listed are a two-sided significance level of 0.05, equal allocation between the two arms, a normal approximation, and an effect to detect set to the stated fraction of the observed effect. Smaller effects need more participants to detect than larger effects under those assumptions.

These figures are planning illustrations based on the observed effect, not the original trial’s design rationale. The trial’s own original sample-size assumptions are not reported in the registry record. This is not observed power: it does not describe the chance that the completed trial succeeded in detecting an effect, and it does not change the interpretation of the observed comparison. The accompanying curve should be read as another representation of the same planning relationship, not as additional trial outcome data.

12. 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 = 0.233; treatment proportion p₁ = 0.200; average p̄ = 0.217.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.5826 = 1.1419.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.5821 = 0.4899.
4. n = (1.1419 + 0.4899)² / (-0.0333)² = 2,396.7, rounded up to 2,397 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 <- 0.233333333333333                          # control proportion
p1 <- 0.2                          # 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(4886960)
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 = 2,397 (80% power), 3,208 (90% power)
 75% of observed effect: n per arm = 4,321 (80% power), 5,784 (90% power)
 50% of observed effect: n per arm = 9,854 (80% power), 13,190 (90% power)
power.prop.test: 2396.7 
Simulated power at n = 2,397 per arm: 0.800 (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.

13. Multiplicity, Missing Data and Analysis Populations

The registry names 4 secondary outcomes: the Knee Injury and Osteoarthritis Outcome Score, Visual Analog Scale for Pain, Single Assessment Numerical Evaluation, and PROMIS Physical Function Computer Adaptive Test. It also lists 6 outcome measures overall. These measures address related but distinct aspects of knee symptoms, pain, self-assessment, and physical function. The primary endpoint remains the occurrence of a rescue standard-of-care injection within 6 months.

When a study evaluates multiple outcomes, the chance of at least one apparently unusual result can increase if each is tested separately without an adjustment. Multiplicity methods are general statistical approaches for managing this issue, but the registry record does not report whether a correction was planned or applied. It does not state which secondary outcome was prioritized, whether any outcome hierarchy was used, or how repeated assessments were handled. Secondary results should therefore not be interpreted as if a particular multiplicity strategy were documented.

The analyses field reports 0 analyses, and the registry record does not report results for the named secondary outcomes in the posted outcome data. This does not establish that no analyses were performed; it means that analyses are not reported in the registry record. A statistical analysis plan, including prespecified hypotheses and multiplicity procedures, is not reported in the registry record.

Missing-data handling and analysis populations are also not reported in the registry record. The record does not describe whether all randomized participants were included, how missing outcome assessments were handled, or whether any sensitivity analyses were conducted. The outcome counts have denominators of 30 in each arm, but those posted values alone do not explain how the denominators were determined or whether every randomized participant contributed to the endpoint.

Without these details, readers cannot assess whether missingness could have affected the comparison or whether the full set of outcomes was analyzed as planned. These are reporting limitations, not evidence that the analyses were inappropriate. The primary result can still be described as posted, while conclusions about unreported secondary analyses, missing-data procedures, or multiplicity control remain unavailable.

14. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: gastrointestinal bleed (3.3%), myocardial infarction (3.3%).

The registry reports serious adverse events for 1 participant in the Amniotic Fluid Injection arm and 1 participant in the Standard of Care Steroid Injection arm. The at-risk count is 30 in each arm. It lists other adverse events for 1 participant in the amniotic-fluid arm and 4 participants in the steroid-injection arm. The registry reports 0 deaths in each arm.

The serious-event terms listed are Gastrointestinal bleed and Myocardial Infarction, each reported as 3.3%. The record does not specify the denominator used for these percentages or give enough detail to infer how the event terms relate to participants or event counts. These terms should be read as the registry’s listed serious adverse event categories, not as a complete description of severity, timing, or attribution.

These figures are descriptive counts. They do not by themselves establish that an event was caused by a treatment, and they do not provide a precise comparison of safety between arms. The registry record does not report event definitions, relatedness assessments, exposure-adjusted rates, or additional detail about timing. The absence of reported deaths does not address other safety outcomes. Safety interpretation is limited to the adverse-event information posted in the registry.

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

The posted primary data show that 6 participants in the Amniotic Fluid Injection arm and 7 in the Standard of Care Steroid Injection arm received a rescue injection within 6 months. The unadjusted comparison has an interval that includes no difference, and the registry reports a p-value of 0.754. The estimate is uncertain: the observed counts are close, but the interval does not establish that the underlying event frequency is the same in both arms.

The result applies to the registry’s defined endpoint: receipt of a rescue standard-of-care injection during the stated follow-up. It does not directly answer whether symptoms, pain, physical function, or structural features of osteoarthritis changed. The registry lists patient-reported secondary outcomes for some of these domains, but their results are not reported in the posted outcome data. It also does not report a longer-term primary comparison.

The comparison does not prove equivalence, nor does it rule out effects in either direction. No equivalence margin or noninferiority framework is reported in the registry record. A nonsignificant p-value is not proof that there is no effect. The interval’s uncertainty is central: the available data are compatible with no difference as well as with differences favoring either arm.

The endpoint also reflects clinical decision-making. The registry says rescue injections could be given as needed or requested, at the principal investigator’s discretion, and that clinicians were not to know the assigned arm. It does not report a standardized threshold for rescue treatment. Thus, the endpoint should be understood as a recorded treatment event, not as an independent symptom scale or a complete measure of disease status.

Finally, the posted comparison does not resolve questions about the full analysis plan, missing data, or secondary outcomes. Those details are not reported in the registry record. The appropriate conclusion is limited: the posted primary outcome counts and unadjusted comparison do not provide a precise separation between the arms for rescue injection within 6 months.

16. Why This Trial Matters Statistically

This trial’s primary endpoint illustrates why a clear outcome definition matters in clinical research. A rescue injection is an observable event that can be recorded in medical records and a study data system. It is also a measure shaped by care decisions, participant requests, and the clinician’s discretion, rather than a direct measurement of pain or function. Keeping that distinction clear helps prevent an event-count comparison from being interpreted as if it answered every question about osteoarthritis symptoms.

The posted data also show why an estimate should be read together with its uncertainty. The arm counts are close, the unadjusted p-value is 0.754, and the interval includes no difference. A point estimate alone could suggest a direction, but it cannot show how uncertain that direction is. The interval communicates that the data do not tightly determine the magnitude or direction of the comparison.

Randomized, triple-masked, parallel-group design is relevant context for interpreting a comparison, but those labels do not replace details about allocation, masking procedures, follow-up, or analysis. The registry identifies the broad design while leaving several operational and statistical details unreported. Distinguishing what the record states from what it does not state is important when assessing the strength of conclusions.

The sample-size illustrations offer another statistical lesson: planning depends on the effect a study is intended to detect. The posted scenarios show that smaller target effects require larger planned group sizes under the stated assumptions. These illustrations are not the original trial rationale and do not alter the observed result. Together, the outcome definition, uncertainty, and planning assumptions make this record useful for understanding how design and analysis constrain what can be concluded from a clinical trial comparison.

17. 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 outcome is specifically receipt of a rescue standard-of-care injection within 6 months. It does not quantify symptoms, pain intensity, physical function, or the number of rescue injections. The outcome description allows treatment at the principal investigator’s discretion and does not report a standardized decision threshold. This limits how directly the event count can be interpreted as a measure of disease severity or treatment response.

The record does not report detailed eligibility criteria, randomization methods, allocation concealment, or which roles were masked under the triple-masked designation. It also does not report the confidence level or calculation method for the interval estimates. These omissions make it difficult to evaluate aspects of trial conduct and statistical implementation from the registry record alone.

The registry reports 0 analyses and does not post results for the named secondary outcomes in the outcome data. Missing-data procedures, analysis populations, multiplicity handling, and a statistical analysis plan are not reported in the registry record. The original sample-size justification is also not reported; the available sample-size figures are planning illustrations based on the observed effect, not evidence about the trial’s original design assumptions.

Safety information is limited to the posted serious-event and other-event counts, listed serious-event terms, and death counts. The record does not provide detailed event timing, attribution, or the denominator for the listed serious-event percentages. These limitations restrict interpretation to the information recorded and should not be filled in by assumption.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: pAF for the Treatment of Osteoarthritis — NCT04886960.
• Registry record last updated 2026-03-27; status last verified 2026-02.
• Results first posted 2026-03-27.
• 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.

21. Record Summary

The registry describes NCT04886960, titled pAF for the Treatment of Osteoarthritis, as a completed Phase I/II randomized, triple-masked, parallel-group study sponsored by the University of Utah. It lists enrollment of 60, with an Amniotic Fluid Injection arm and a Standard of Care Steroid Injection arm. Each arm’s posted primary outcome denominator is 30.

The primary outcome was receipt of a rescue standard-of-care injection within 6 months. The posted counts are 6 in the amniotic-fluid arm and 7 in the steroid-injection arm; the unadjusted p-value is 0.754, and the interval estimate includes no difference. The registry lists 4 secondary outcomes but reports 0 analyses. The primary completion date is 2025-01-31, and the study status is completed.