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Blood therapy, anyone? Platelet-rich plasma (PRP) injections bathe troubled cells in a concentrated mixture made from your own blood. Hopefully this stimulates healing where it is otherwise failing — especially stubborn, slow-motion injuries like tendinitis — but no one really knows for sure yet.
Despite all the not-knowing, it’s easy to pay someone to do this for you these days: extract some of your blood, spin it in a centrifuge to get the platelets, and then pump them back into you. It’s not cheap, but PRP injections have become super popular, particularly with elite athletes (ever the guinea pigs for unproven, expensive new treatments for musculoskeletal injuries). It sounds perfect for injuries like patellofemoral pain, an extremely common pseudo-arthritis of the knee in runners,1 or IT band syndrome, another kind of common runner’s knee — a huge potential market, in other words. In the fall of 2009, ScienceBasedMedicine.org scathingly criticized the marketing of PRP:2
Without any clear evidence of benefit beyond placebo, PRP is now being marketed aggressively as a cure-all for sports injuries. And at about $300 per injection (the NYT reports $2000/treatment), there’s plenty of money to be made. … a nation-wide marketing initiative has begun, using sports celebrities as guinea pigs.
A Case Study In Aggressive Quackery Marketing, Jones (ScienceBasedMedicine.org)
At that time, the problem was that the marketing was irresponsible in light of the lack of evidence. It was a short wait for more. Today, the marketing is irresponsible in light of the evidence we now have …
Cynics can stop reading here. You know this doesn’t end well.
Meet the Clotters! Platelets are the major clotting tool in your blood, and they are curious critters, neither cells nor molecules, but a strange hybrid often called “cell fragments”: platelets are to blood cells what wood chips are to a log … if the chips were extremely clever. Platelets have a bunch of interesting biological features, but they are best known for their work in clotting — and that’s mainly what gives them that healing mystique.
There are countless biochemical factors that regulate healing — it’s complex, to say the least. Platelets are part of that equation, playing “a critical role in tissue repair and regeneration”; specifically they “regulate fundamental mechanisms involved in the healing process including cellular migration, proliferation, and angiogenesis.”3 Since they are involved in healing, so more of them must be good, right? This is the basic rationale for PRP.
In fact, PRP is often called “regenerative medicine,” because the idea of genuinely accelerated heating is so tantalizing, like science fiction (or salamanders). But it’s more marketing than biology, surprise surprise.4 You could probably talk people into drinking a platelet smoothie if you told them it would “regenerate” them. It is not safe to assume a soup of platelets is regenerative.
In fact, it’s not even safe to assume it’s safe …
Injecting medications into muscles might not be harmless. (No one’s surprised by that, right? Good!) Anaesthetics and NSAIDs probably are a little myotoxic — poisonous to muscles — and there’s “conflicting evidence” about PRP. It might be fine, but it’s important to bear in mind that faddish new injection treatments are never risk free.
Who says more platelets stimulates healing? Is that in the Platelet User Guide? “For extra healing, generously apply platelets to wound.” Dosage is critical with many medicines. More is not only not always better, it’s routinely worse. Do other cells like being bathed in ten times the normal number of platelets? Or is it a suffocating mess that throws everything off kilter?
Or is it just kind of ho hum?
In PRP marketing and hype, it’s common to see claims that it’s a “natural” treatment — because it’s your own blood being returned to you, see? — and what could be safer and healthier than you-stuff? But this is bio-illogical: there’s lots of stuff inside of me that I do not want to be extracted, concentrated, and returned! Pick any hormone, for instance: many of those are just as involved in healing as platelets, but too much of most of them is just a disaster. In general, what you want in biology is just-right amounts of everything, not lots of extra anything. For an example close to platelets conceptually, there is a disease of excessive iron, hemochromatosis — a major component of red blood cells, essential to life, something you could easily think you want a lot of for vitality and healing. And indeed you do, if you’re anemic. But chronically absorb too much, and it’s a disease.
It’s really quite odd to assume that a platelet-rich sauce o’ blood is natural and safe and helpful just because the stuff came from you. Which is why this treatment needs to be tested, not assumed — like every treatment.
PRP fans and purveyors will tell you there is good evidence that PRP works, but they are cherry picking from a few studies that worked out in their favour one way or another. A few positive studies never not mean much; indeed, most “positive” study results are actually just bogus.5
Taken as a whole, the evidence is somewhere between inconclusive and discouraging. Although more research is needed (of course!) enough decent studies have now been done that the evidence reviews have started to come out. They all warn that most of the evidence is poor quality, and they are all basing their conclusions on just barely enough good data. They all emphasize that PRP methods are not standardized — there are many versions of PRP, all based on speculation, not data.
The bad news got rolling in 2010. The New York Times reported6 (very) bad science news:
Now, though, the first rigorous study asking whether the platelet injections actually work finds they are no more effective than saltwater.
Nothing has improved since. Three noteworthy reviews were published in 2014. Sandrey found “strong evidence” that PRP does not improve plantar fasciitis when combined with several other therapies, and limited evidence that it might be beneficial on its own.7 Moraes et al found “insufficient evidence to support the use of PRT for treating musculoskeletal soft tissue injuries.”8 And de Vos et al was extremely negative:9
Three high-quality studies (75%) and two low-quality studies showed no significant benefit at the final follow-up measurement or predefined primary outcome score when compared with a control group. One high-quality study (25%) showed a beneficial effect of a PRP injection when compared with a corticosteroid injection (corticosteroid injections are harmful in tendinopathy). Based on the best evidence synthesis, there is strong evidence that PRP injections are not efficacious in chronic lateral epicondylar tendinopathy.
The only good news is coming from isolated or fatally flawed studies. Isolated positive evidence about over-hyped treatments is a huge red flag, which usually means “researchers made errors in their favour.” It’s the pattern of evidence that counts, and so far the pattern is distinctly bad.
Any hope? Maybe a little. There are different ways of doing PRP, and there different conditions in different stages may respond better or worse. It’s biologically plausible that PRP could fail with chronic tendinitis but still succeed with a acute muscle strains, for instance, or even fail with one kind of muscle strain and succeed with another. Hammond et al, an experiment on rats — rats were harmed and treated for our edification — reported a difference between two kinds of muscle strain. Initially promising in principle, I predict that PRP will now be mired in trumped-up controversy for years.It worked better on a more serious injury, where regeneration of muscle tissue was part of the healing process. PRP might assist with that regenerative process, but have no effect on a less serious strain where no regeneration is occurring.10
But these are faint hopes. In general, one would hope that the methods and conditions tested so far are at least in shouting distance of being the right formula — close enough to be at least a little more encouraging.
Initially promising in principle, I predict that PRP will now be mired in trumped-up controversy for years. It will die a slow death, only beaten into submission over many years by a growing pile of underwhelming evidence, while its proponents continue to overconfidently sell the service and defend it from detractors, mainly by betting — with dwindling odds — that just the right formula can still be proven effective for just the right kind of patient. If so, great: I will be pleased to admit that my prediction was wrong! But I’m betting against them for now.
My final word on this topic has to be “placebo” — PRP is a perfect storm for it. It’s got everything! Bearing in mind that it’s been thoroughly demonstrated that people get stronger placebo effects from treatment features trivial as a more potent pill colour…
I can hardly imagine a better formula for a powerful expectation effect or “relief from belief.” Unfortunately, despite placebo’s weirdly good reputation, its powers are quite limited.11 The next time you hear a positive anecdote about PRP, remember: it’s probably the placebo talking.
The bar for “worth a try” is fairly high. No invasive treatment can qualify for it without being proven at least safe. And you really need clear, consistent evidence of non-trivial benefit across several good trials before anything injected is “worth a try.” Before that it’s more like “hey, it’s your knee, don’t stab it”!
I am a science writer, former massage therapist, and I was the assistant editor at ScienceBasedMedicine.org for several years. I have had my share of injuries and pain challenges as a runner and ultimate player. My wife and I live in downtown Vancouver, Canada. See my full bio and qualifications, or my blog, Writerly. You might run into me on Facebook or Twitter.