The two least lousy trials of PRP for plantar fasciitis

I’m working through a big update to my plantar fasciitis book chapter on “regenerative” treatments, especially autologous whole blood (AWB) and platelet-rich plasma (PRP) therapy — literally withdrawing blood from a patient and then re-injecting it, or just the platelets. The idea is to stimulate healing by putting more of the active ingredients of blood right where they are most needed.

“Increased circulation,” the hard way!

Give blood! To … yourself?!

(Reminder: I have a salamander logo/mascot because salamanders demonstrate the genuine biological marvel of actual regeneration. It can be done! By salamanders.)

I started my update journey by cracking open a new 2025 trial of AWB that reports better results with some extra rest in the first few days after the injection. But I couldn’t put it context with any broad statements about the state of AWB/PRP science because (I realized) I haven’t checked up on the science of blood-injecting in quite a long time. And so I dove down the PubMed rabbit hole! Dozens of browser tabs later (most of them still open now)…

I have two older trials for you today, 9 and 6 years old, and interesting pair that was quite challenging to digest. These are two of the only placebo-controlled trials of PRP for plantar fasciitis that exist — which is the only kind of trial that matters if you really want to know what works. Big scientific reviews are relatively useless, always crippled by “garbage in, garbage out.” These two studies are the cream of the crop.

Which ain’t saying much, unfortunately.

• One of them is a weirdo, with baffling flaws and too-good-to-be-true results I just don’t believe.
• The other is more believable, but still flawed, and there is less to believe: mediocre results even if true.

Study #1: Mahindra et al

This 2016 trial seems like a big win for PRP from the right kind of science: a double-blind, randomized, and placebo-controlled design. But it is too seriously flawed to take seriously. Indeed, I was seriously irritated by the time I was done with it.

Mahindra et al sloppily tested PRP, corticosteroids, and placebo injections for seventy-five chronic plantar fasciitis patients. The authors present their work as a landmark study proving that PRP works much better than placebo, with mighty effect sizes that beat even steroids. They did design a great looking trial, but, alas, they did not conduct one. Bizarrely, they did not (statistically) test PRP versus placebo! This is such a major malfunction that it casts doubt on the whole thing. Maybe the paper should even have been retracted (although that normally takes more than methodological bloopers, no matter how big). Regardless, the peer reviewers sure seemed to be asleep on the job.

Ironically, if they had done the right stats, it likely would have made PRP look great. But they didn’t, and it truly is a deal-breaker, a textbook example of the “within-group significance fallacy.”

Without replication, this trial is best viewed as an outlier. It’s the worst kind of science in my opinion: the kind that looks way better than it actually is. Shiny junk. And I bet it has been extensively cited by people selling PRP.

The details (800 more words on PainScience.com, and the details are also included in the members-only audio version of this post). Now, let's look at literally the only other placebo-controlled trial published since then …

Study #2: Shetty et al

In 2019, Shetty et al. compared platelet-rich plasma (PRP), corticosteroid, and placebo injections for 90 patients with chronic plantar fasciitis — one of the few three-arm RCTs of its kind, and with unusually long follow-up (18 months). On paper, that makes it a more ambitious and credible effort than most studies of PRP (or much of anything else in this business) — better in both principle and execution than Mahindra et al, which was aiming almost as high but missed by a lot more.

And yet this superior study still has three real strikes against it:

• At least one non-trivial statistical flaw.
• A high risk of bias.
• Results that — although undeniably good news — don’t exactly thrill even if they can be believed.

So this is quite a bit more credible than Mahindra et al., but still has one clear blooper, and its results are less promising! It’s a study that puts a skeptic in an awkward position: reluctant to blow off a perfectly good positive result, but still thinking, “So … meh?” This is hardly the validation PRP fans want to see.

The details (500 words).

And so that’s the “cream of the crop”? Yikes! Two of the best studies you can cite to support “PRP is good for plantar fasciitis,” and they are a mixture of unbelievable and/or unimpressive.

Citation still needed.

Since there is no more compelling evidence to cite, they cannot change my general impression that PRP is a great example of a modern snake oil. Regenerative medicine may be a real thing someday. But I doubt PRP is it.

I have not yet finished updating my plantar fasciitis book or PRP article with these key citations, but I will soon, along with other details.