My recent PRP post sparked some critical comments. Good. That is exactly what scientific discussion should do.
But there is one rather inconvenient aspect of the PRP literature that deserves more attention.
When searching registered trials of platelet-rich plasma for osteoarthritis that were started before 2020, the overwhelming majority appear to have no publicly available results. In the search shown above, only 9 studies had results, while 92 did not.
That is roughly 90% without results.
This immediately raises an uncomfortable question: why?
PRP trials are generally initiated with an a priori hypothesis that PRP is beneficial. If the results support that hypothesis, publication is usually not particularly difficult. So what happened to the enormous number of trials that disappeared?
Perhaps some were stopped early. Perhaps some failed to recruit. Perhaps some were poorly conducted. But even if half of those 92 trials never properly got off the ground, the situation remains extraordinary.
And it matters enormously.
The published PRP literature is already weak at best: small trials, multiple outcomes, questionable blinding, and substantial methodological variation. If only a small fraction of the registered evidence actually reaches the public domain, then what we currently call “the evidence” may be little more than a drop in the ocean of the data that were actually generated.
More importantly, this is not merely a statistical problem. It is an ethical one.
Patients agree to participate in clinical trials because their participation is supposed to contribute to medical knowledge. They accept inconvenience, uncertainty, procedures, follow-up visits and sometimes risk.
If even one patient was recruited into a study that investigators subsequently decided never to report, that ethical contract has been broken.
Researchers do not own trial results.
Patients helped create them.
And negative results are still results.