Does Concentrated PRP Hurt or Help Tendon Healing?
If you inject PRP into tendons that is just 3-5 times concentrated (which most systems produce), at least according to one study, you may be poisoning rather than helping tendon cells. Is this true? How is it possible that you get great results injecting tendons with PRP and the in-vitro research says that you shouldn’t be seeing these results?
Well, first, there are two research camps with two diametrically opposed conclusions. Researchers in camp one suggest that platelet rich plasma (PRP) at even moderate concentrations can hurt tendon cells. While researchers in camp two suggest the opposite: that higher concentrations of PRP can help tendon cells. So which research camp should you believe? The Interventional Orthopedics Foundation (IOF) performed its own research to answer the question because it’s critical for everyone that uses PRP.
The video above describes the two research camps and their results as well as the results of the IOF research. It is a variation of a talk that was given at the 2017 IOF Conference in Denver, and a summary of the video follows (please refer to the video for further detail and images referenced).
Why Would We Use Concentrated PRP?
There are a couple of different concepts underlying why we would want to use concentrated PRP. First, with older patients, our internal data has shown that with mesenchymal stem cells (MSC) in culture, if you go higher on the concentrations of platelets, you get much better proliferation and growth in the cells. The second concept is that higher concentrations of PRP may allow for fewer treatments in patients.
But the concern at hand here, and the question several research groups have investigated is, does this concentrated prp hurt or help tendon healing? What does each research camp say?
- Camp 1: Increasing platelet concentration in PRP inhibits tendon cell proliferation and migration (i.e., hurts tendons).
- Camp 2: Increasing platelet concentration in PRP does NOT inhibit tendon cell proliferation and migration (i.e., doesn’t seem to hurt tendons at all).
Obviously, all things being equal, both sides can’t be correct. So which one is? Let’s first look at each camp and some of their studies more in depth. References cited can be found at the bottom of this post.
Leading the charge in camp 1, one study (Giusti) seemed to show that as you go higher in platelet concentration, really anything above 1–2X, the amount of tenocyte, or tendon cell growth, goes down. Think about that for a second and let it swirl around in your head. This means that pretty much every commercially available machine on the market that makes PRP is creating a product that harms tendon cells?
The conclusions from this study were as follows:
- “Excessively high platelet concentrations (above 1X!) have an inhibitory effect on proliferation (and massive cell death occurs at the highest concentration that was tested (3-5X!).”
- “In light of this, it is obvious that the ‘more is better theory’ is not valid in this case.”
I have to note here, most commercial platelet systems concentrate to about 3-5X, and we and others have not observed this study’s conclusions clinically. We aren’t seeing tendons being destroyed by PRP—quite the opposite; we’ve actually seen that 5X PRP and higher works in tendons.
The same study used what’s called a scratch model. A scratch model creates a kind of gap within the growing cells (see video for clear images of this model). The purpose is to wait for the cells to fill in the gap. Healthy cells fill the gap quickly. The scratch model in this study seemed to show, again, as they went higher in the platelet concentration, the tendon cells didn’t fill the gap very well.
Another study (Russell) falling under camp 1 showed the same thing: the higher the platelet concentrations the poorer the health of the tendon cells (see video for images).
The camp 2 research provides the opposite conclusions, showing not only does increasing the platelet concentration in PRP NOT inhibit tendon-cell proliferation and migration, but, in fact, it helps.
One study (Jo) found that as platelet concentration went up, lots of different cell types, including tendon cells, did better by growing faster. Their conclusion: “PRP was found to have no inhibitory effect on cell proliferation at levels of more than 50-fold over the physiological level.” And they went all the way up to 50X PRP. So this is diametrically opposed to what we just saw in camp 1.
Another study (Anitua) showed the same thing.
So why the different conclusions between camp 1 and camp 2, and which is right?
Camp 1 or Camp 2? The Answer Can be Found in Poor Study Design
The camp-1 studies utilized problematic in vitro (meaning in the lab) study designs; the camp-2 studies utilized more appropriate study designs. So, based on the IOF research (see below), we believe the camp-2 research is correct.
Our hypothesis of what happened in the camp-1 study designs boils down to the fact that all cells in culture need certain components to survive and grow: food and fertilizer.
Cell food consists of minimal essential medium (MEM) components, which follow:
- Inorganic salts (Na+, K+, Ca2+)
- Carbohydrates (glucose)
- Amino acids (essential and nonessential)
- Vitamins (B-group vitamins)
- pH buffering system (bicarbonate & CO2)
Cell fertilizer consists of platelet-derived medium supplement components (PRP lysates, activated PRP releasates, or FBS), which follow:
- Growth factors (FGF, PDGF, TGFB, VEGF)
- Attachment and spreading factors (fibronectin)
- Carrier proteins (albumin) in the serum
The camp-1 design flaw was in the ratio of fertilizer to food. Every time researchers in the camp-1 studies increased the volumes of PRP fertilizer, they decreased the volume of food, starving—and killing—the cells in the process. So while they may have attributed the cell death to the increase in platelets, the more likely conclusion is the death occurred due to the decrease of food.
This also explains the drastic difference in the camp-2 conclusions. The researchers in the camp-2 studies maintained the volume of fertilizer to food—they kept it all constant. Specifically, they maintained nutrient supply and pH buffering capacity while increasing growth factor content. So consequently, they didn’t see those same effects camp 1 saw.
The IOF Research
Of course, we tested our hypothesis in our IOF lab because it would be important for doctors to know if Guisti and the other camp-1 researchers were correct. Nobody would want to continue using PRP to inject tendons if it in fact, was killing cells.
The IOF research results showed that as the platelet concentrations increased, there was better tendon cell growth. There are some great graphs and images on the video that support and explain this in detail. This includes a scratch test, which showed that as the PRP concentration went from 1X to 3.5X and all the way up to 14X, the ability of the cells to close the scratch, or fill in that gap, got better and better. As mentioned before, this is what we would expect to see if the platelets were helping the tendon cells as they go into higher concentrations.
The upshot? Does concentrated PRP hurt or help tendon healing? The IOF research supports that more concentrated PRP, even as high as 14X, is better for cells, including tendon cells. So, certainly, this research supports that using 3X or 5X PRP, which the Guisti study would say is a bad idea, is just fine. Sorry, Camp 1—Camp 2 has this one!
Anitua, E., et al. “Fibroblastic response to treatment with different preparations rich in growth factors.” Cell Prolif 42, 162–170 (2009).
Choi, B.H., et al. “Effect of platelet-rich plasma (PRP) concentration on the viability and proliferation of alveolar bone cells: an in vitro study.” Int J Oral Maxillofac Surg 34, 420–424 (2005).
Fliefel, R., et al. “Mesenchymal stem cell proliferation and mineralization but not osteogenic differentiation are strongly affected by extracellular pH.” J Croniomaxillofac Surg 44, 715–724 (2016).
Giusti, I., et al. “Platelet Concentration in Platelet-Rich Plasma Affects Tenocyte Behavior In Vitro.” BioMed Research International (2014).
Jo, C.H., Kim, J.E., Yoon, K.S. & Shin, S. “Platelet-rich plasma stimulates cell proliferation and enhances matrix gene expression and synthesis in tenocytes from human rotator cuff tendons with degenerative tears.” Am J Sports Med 40, 1035–1045 (2012).
Mishra, A., et al. “Buffered platelet-rich plasma enhances mesenchymal stem cell proliferation and chondrogenic differentiation.” Tissue Engineering Part C: Methods 15, 431–435 (2009).
Russell, K.A. & Koch, T.G. “Equine platelet lysate as an alternative to fetal bovine serum in equine mesenchymal stromal cell culture—too much of a good thing?” Equine Vet J 48, 261–264 (2015).
Wuertz, K., Godburn, K. & Iatridis, J.C. “MSC response to pH levels found in degenerating intervertebral discs.” Biochem Biophys Res Commun 379, 824–829 (2009).