Precision Assessment of Platelet Rich Plasma for Joint Preservation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Precision Assessment of Platelet Rich Plasma for Joint Preservation (NCT03460236), a registered phase not stated study. The primary outcome is Number of Participants With Successful Knee Pain Improvement Over 6 Months Following PRP Injections.

2. Clinical Question

The clinical question is about a count of participants meeting a threshold, not a mean change in pain score. KOOS Pain is a patient-reported measure, and the registry explains that higher transformed scores indicate less pain. Success is defined by change exceeding the threshold selected for minimal important change after non-surgical intervention for knee pain.

The study rationale focuses on symptomatic early knee osteoarthritis, including the potential relevance of PRP to Veterans and additional women with early knee osteoarthritis. The record describes the treated group as people who elected to receive PRP. It does not establish a randomized comparison or indicate that treatment outcomes were compared with an untreated or alternative-treatment group. Thus, the primary question as recorded concerns the number reaching the improvement threshold within the PRP recipients, rather than a comparative treatment effect.

3. Trial Design

The registry lists the study as completed, with an enrollment of 90. The recorded start date is 2018-04-02 and the primary completion date is 2024-03-29. The sponsor is the VA Office of Research and Development. Osteoarthritis is the listed condition, and the study title concerns platelet-rich plasma for joint preservation.

The arm description identifies symptomatic early knee osteoarthritis subjects who elected to receive PRP treatment. The record does not describe a like-for-like control arm, and allocation is not stated. It therefore does not support interpreting the study as a randomized comparison. The status of completed indicates the study's registry status; by itself, it does not establish that results for every outcome have been posted.

The primary outcome is a count of participants meeting a knee-pain improvement criterion from baseline to 6 months. Its population description specifies the 63 participants who completed both baseline and 6-month follow-up patient-reported outcome surveys. The record lists two outcome measures and zero analyses. It does not report a protocol, a statistical analysis plan, interim analyses, or a sample-size justification. Those details are not reported in the registry record.

The registry summary explains that PRP composition differs between patients because autologous blood is used, and that the relationship between composition and clinical outcomes is unknown. This is part of the study's rationale, not a reported finding about composition or a demonstrated mechanism. The record does not supply enough information to characterize additional design features, such as masking or the exact injection schedule; those details 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: After enrollment, 16 failed radiographic screening before assignment to the study.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: The 63 participants who completed both baseline and 6-month follow-up patient reported outcome surveys.

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.

Population: Males and females with early knee osteoarthritis pain.

6. Primary Endpoint

The registry lists the primary outcome as Number of Participants With Successful Knee Pain Improvement Over 6 Months Following PRP Injections, measured over Baseline to 6 months.

The primary endpoint counts participants whose KOOS Pain change meets the registry's definition of successful improvement. KOOS Pain is assessed using a standardized questionnaire with 9 questions. Each response has an ordinal scale from 0-4, and the transformed score is oriented so that higher values indicate less pain. The registry defines success as a change exceeding the previously determined 12.4pts threshold for minimal important change after non-surgical intervention for knee pain.

A threshold-based count can be useful because it expresses the outcome as the number of participants who crossed a stated level of change, rather than describing only an average score change. It can therefore make the endpoint's intended clinical meaning explicit. As a general statistical point, however, reducing a score to whether it crosses a threshold discards information about the size of changes on either side of that cutoff. The count also depends on having the outcome measured at the relevant time points.

The stated timeframe is baseline to 6 months. The primary outcome population is defined as the 63 participants with both baseline and 6-month follow-up surveys. The registry record does not report the number who met the success threshold, the underlying score changes, or an uncertainty estimate for the count. The endpoint definition is available, but its observed result is not reported in the registry record.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry identifies the primary outcome as a count of participants with successful knee-pain improvement. This is a binary outcome at the participant level: each assessed participant is classified according to whether their KOOS Pain change exceeds the stated threshold. The outcome is not a continuous mean score, even though it is derived from a score. The registry gives the measurement scale and threshold but does not report the number classified as successful.

What does a threshold-based endpoint capture?

The KOOS Pain questionnaire consists of 9 questions, with each response valued on an ordinal scale from 0-4. The registry says transformed scores are oriented so that higher scores indicate less pain. It defines successful improvement as a change exceeding the previously determined 12.4pts threshold for minimal important change after non-surgical intervention for knee pain. In general, such a threshold aims to distinguish changes considered meaningful according to the selected criterion from changes that do not cross it.

As a general statistical consideration, categorizing a score has a trade-off. It can produce an outcome that is straightforward to describe as a count, but it loses detail about the magnitude of each participant's change. Two people on the same side of the threshold may have quite different changes, while people near either side may be classified differently despite similar score changes. The registry does not report the distribution of individual changes, so these features cannot be assessed for this study.

Why does the analysis population matter?

The primary outcome description names the 63 participants who completed both baseline and 6-month follow-up patient-reported outcome surveys. A change from baseline requires measurements at both time points, so this population definition makes clear which participants the recorded endpoint concerns. The enrollment is 90, but the registry does not explain how participants without both surveys were handled in the endpoint analysis. Imputation, sensitivity analyses, and reasons for missing surveys are not reported in the registry record.

As a general point, an analysis restricted to people with measurements at both time points can differ from an analysis that includes everyone enrolled, especially if outcome availability is related to the outcome or to participant characteristics. This is a potential issue to evaluate, not a claim that such bias occurred. The record does not provide enough information to assess the relationship between follow-up completion and pain outcomes.

What can be inferred from an unadjusted count?

For a binary endpoint, the observed count and the number assessed describe how many people met the criterion in the analyzed group. A proportion may sometimes accompany a count, but the registry does not report the primary success count or an outcome proportion. No new proportion can be inferred from the listed enrollment or survey-completion population. An uncertainty interval would help communicate the precision of an estimate; none is reported for this endpoint.

General statistical methods for binary outcomes may include confidence intervals or models that account for design features and covariates. Those are possible approaches in general, not methods documented as used in this study. The record lists zero analyses and does not report a statistical analysis plan, adjustment variables, or inferential methods. It would therefore be inappropriate to attribute a particular model, test, or adjustment strategy to the investigators.

How should planning assumptions be understood?

The registry includes planning assumptions for a sample-size illustration: a two-sided significance level of 0.05, equal allocation between two arms, a normal approximation, and an effect defined as a stated fraction of the observed effect. The description says such calculations are planning illustrations, not the trial's own design. It does not report the resulting planning values in the registry record for interpretation, and it does not establish that this study had two arms. The arm description identifies PRP recipients, while the record says allocation is not stated and flags the absence of a like-for-like control comparison.

As a general explanation, a planning calculation asks what sample size might be needed under specified assumptions. It is not an observed result and is not observed power. A normal approximation is a way to approximate a sampling distribution; its suitability depends on the setting and assumptions. Equal allocation between two arms is a planning assumption here, not evidence of the actual design. No sample-size justification for the enrolled study is reported in the registry record.

Finally, an endpoint count and an analysis result are different things. The count describes the outcome observed among participants, while an analysis may add an estimate of uncertainty or compare groups under a statistical model. The registry gives the endpoint definition but lists zero analyses. Accordingly, statistical concepts can explain how such results are commonly read, but they do not fill in the missing result or establish which methods were applied.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("Platelet Rich Plasma (PRP) Recipients")
n      <- c(63)
events <- c(25)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  Platelet Rich Plasma (PRP) Recipients  63  25  39.7  27.6  52.8  28.5  52.0  28.5  52.1

11. Multiplicity, Missing Data and Analysis Populations

The registry lists two outcome measures and zero analyses. The primary outcome is described as a count of participants with successful knee-pain improvement from baseline to 6 months. The other outcome measure and its results are not described in the registry record; those details are not reported in the registry record. There is no reported multiplicity adjustment or statistical analysis plan.

As a general statistical issue, testing multiple outcomes can increase the chance of at least one apparently notable result when each test is considered separately. Whether an adjustment is appropriate depends on the prespecified questions and analysis plan. Since no analyses are listed and no such plan is reported, it is not possible to assess how multiplicity was handled or whether any outcome was selected for emphasis after results were known.

The primary endpoint population consists of the 63 participants who completed both baseline and 6-month follow-up surveys. The record does not state how missing follow-up data were handled, why surveys were unavailable, or whether any imputation or sensitivity analyses were conducted. It also does not report an intention-to-treat analysis population or another analysis-population definition beyond the endpoint description. These matters are not reported in the registry record.

As a general point, missing outcome data can affect both the number of participants available for analysis and the interpretation of results if missingness is related to outcomes. The record does not establish that missingness biased results; it also does not provide information to rule that out. The enrollment and survey-completion figures should be read as separate reported quantities, not as a basis for deriving an unreported missing-data count.

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 0% reporting threshold.

The registry's adverse-event entry lists 90 participants at risk for serious adverse events and 0 affected. It also lists 90 at risk for other adverse events and 0 affected, with deaths recorded as 0. No serious adverse event terms are listed. These are the safety figures recorded in the registry; they do not include event descriptions or additional analysis in the registry record.

A count of zero affected means that the registry reports no affected participants in the listed category. It does not, on its own, explain how events were collected, monitored, defined, or attributed. The record does not report the duration of safety surveillance, the method for collecting adverse events, or details about the completeness of reporting. Such details are not reported in the registry record.

As a general statistical point, a zero count does not prove that the underlying event risk is zero. It describes what is recorded in the study under the stated reporting framework, and its interpretation depends on the size and follow-up of the safety population and on how events were ascertained. The registry entries should therefore be read as reported counts, not as a guarantee about safety beyond this study's recorded observations.

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

The record establishes that the study was marked completed and that its primary endpoint was defined as a count of participants with a specified KOOS Pain improvement. It also identifies a population of participants with both baseline and 6-month follow-up surveys. These details clarify what the outcome was intended to measure and which survey completers were named for that endpoint.

The primary endpoint result itself is not reported in the registry record. There is no reported success count, estimate of uncertainty, or analysis result. Therefore, the available record does not show how many participants met the stated threshold or how precisely any such count might be estimated. The enrollment figure does not substitute for the endpoint count, and the survey-completion population does not reveal the number who met the criterion.

The design description also limits what the study can establish. PRP recipients who elected treatment are described, while a like-for-like control comparison is not. Allocation is not stated. Without a reported comparator and comparative analysis, the record cannot establish that a change was caused by PRP or that outcomes differed from those under another approach. That limitation remains even if a within-group endpoint result were available.

The registry's rationale discusses uncertainty about PRP composition and its relationship to outcomes, but no analysis of that relationship is listed. The record therefore does not establish whether composition affected pain scores or whether PRP stimulated cartilage repair. The rationale identifies questions of interest; it is not evidence that those mechanisms or effects were observed.

In short, the record documents a completed study, its treatment group, and its primary outcome definition, alongside safety counts. It does not report the primary outcome result or statistical analyses. The available information supports describing the study's question and measurement approach, but not drawing conclusions about treatment effect, comparative benefit, mechanism, or the precision of the pain-improvement outcome.

14. Why This Trial Matters Statistically

This study raises several statistically important issues that often arise in clinical research. First, it uses a threshold-based patient-reported outcome. A count of participants crossing a defined threshold is readily interpretable as a participant-level endpoint, while the underlying KOOS Pain score retains more detail about the extent of change. Reporting both the threshold count and the score distribution would address different aspects of the outcome, but the score distribution is not reported in the registry record.

Second, the endpoint population is tied to completion of surveys at both baseline and 6 months. Follow-up completeness matters because the outcome depends on paired measurements. The record identifies 63 participants in that population but does not explain how participants without both surveys were handled or describe missing-data analyses. This makes transparent reporting of analysis populations and missingness especially relevant to interpretation.

Third, the group description is not a randomized comparison. Participants elected to receive PRP, and the registry does not describe a like-for-like control arm. This means that a within-group change, if reported, would not by itself isolate the effect of PRP from other explanations. The study's stated interest in differences in PRP composition also requires an analysis relating composition to clinical outcomes; no such analysis is listed.

Finally, endpoint definitions and completion status are not substitutes for results. The record specifies the primary outcome but lists zero analyses and does not report its observed count. Statistical interpretation requires both the outcome data and information about their precision and analysis. These distinctions help readers separate what the study planned to measure from what the registry record reports as an analyzed finding.

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 primary limitation for interpreting this record is that the primary endpoint's observed count is not reported in the registry record. The number meeting the KOOS Pain threshold, an uncertainty estimate, and an inferential result are all absent. The record therefore describes the outcome definition without reporting its observed result.

The design description identifies PRP recipients who elected treatment and does not describe a like-for-like control comparison. Allocation is not stated. This prevents interpretation as a randomized comparison and limits what a within-group result could establish about effects attributable to treatment. The record also does not report whether participants or outcome assessors were masked.

The primary outcome population is defined by completion of both baseline and 6-month surveys. How missing surveys were handled, why they were missing, and whether sensitivity analyses were conducted are not reported in the registry record. The record does not provide baseline outcome distributions or individual change data that would help characterize the analyzed population.

The registry lists two outcome measures but zero analyses. It does not report a statistical analysis plan, multiplicity procedures, adjustment methods, or sample-size justification for the study. Although planning assumptions for an illustration are described, those assumptions do not establish the study's actual design or analysis. The registry also does not report analysis of PRP composition in relation to outcomes, despite that question appearing in the study rationale.

Safety information is limited to the listed counts and the absence of serious adverse-event terms. Event-collection procedures and follow-up details are not reported in the registry record. These limitations describe gaps in the available record; they do not establish that a particular bias, harm, or treatment effect occurred.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Precision Assessment of Platelet Rich Plasma for Joint Preservation — NCT03460236.
• Registry record last updated 2025-05-23; status last verified 2025-05.
• Results first posted 2025-05-23.
• 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

The registry describes a completed study of PRP in symptomatic early knee osteoarthritis, sponsored by the VA Office of Research and Development. Enrollment is 90; the recorded study dates are 2018-04-02 and 2024-03-29 for start and primary completion. The arm description concerns people who elected PRP treatment, and the record does not describe a like-for-like control comparison.

The primary outcome counts participants whose KOOS Pain change exceeded the stated 12.4pts improvement threshold from baseline to 6 months. The endpoint population is the 63 participants with both baseline and 6-month surveys. The success count and statistical analyses are not reported in the registry record. Safety entries list 0 affected for serious and other adverse events, and 0 deaths; no serious adverse event terms are listed.

The record defines the question and measurement approach but does not report the primary outcome result, an uncertainty estimate, or comparative evidence.