Platelet-rich plasma therapy can have a positive affect on a tendon’s composition and structure, but each treatment plan has many variables.
First, not all tendons are exactly the same, and their composition and structure can vary depending on:
- Where in the body the tendon or ligament is located
- The function of the tendon or ligament
- The nature of the injury
- The person’s biochemistry and age
Because of these variations, certain tendons may be more likely to respond to PRP treatments. For example, it may be that PRP therapy successfully treats most cases of tennis elbow but is less likely to successfully treat rotator cuff tendonitis.
Variations in PRP
Just as there are differences in tendon composition, there can be differences in the precise make-up of platelet-rich plasma. These differences are described below.
Blood composition (e.g. number of platelets) can differ between patients.
Concentration of platelets
PRP has 2.5 to 9 times the concentration of platelets found in normal blood (150,000 to 450,000 platelets per microliter [μL]).1 This concentration of platelets depends on the individual’s blood, how much blood was drawn, the centrifuge process (e.g., rotation speed and duration), and other clinical preparation methods.
While it may seem logical that plasma with the highest possible platelet concentration will get better results than plasma with a lower platelet concentration, that is not necessarily the case. If plasma concentration is too high it may inhibit cell growth.2 More research is needed in this area.
White blood cell count
A healthy immune system depends on white blood cells, but the cells’ role in PRP therapy is unclear. Researchers have a few theories:
- White blood cells inhibit a tissues’ ability to heal.3
- White blood cells have no negative affects, or may even have beneficial effects.
- White blood cells may help tendons but not joints.
As with the concentration of platelets, the concentration of white blood cells is determined by an individual’s blood sample as well as clinical preparation methods.
Certain substances may be added to the PRP. These additives, called thrombin and calcium chloride, artificially activate the platelets. This activation results in platelet clotting and platelet growth factor release. Some researchers hypothesize the additives enhance platelet-rich plasma’s regenerative properties.
Collagen contained within tendons and thrombin released from bleeding caused by the needling injection may result in platelet activation without the additional additives. How these factors affect PRP therapy’s effectiveness is not well understood.
Classifying PRP Formulas
Because the preparation and ingredients of PRP injections can vary widely, it is difficult to determine if PRP therapy is effective when comparing different research studies. Some scientists recommend a classification system to distinguish between various formulations of platelet-rich plasma.4 Such a system could help researchers figure out whether these differences matter and, if so, what preparation methods and formulas works best (if at all) for specific conditions.
Determining the optimal combination of white blood cells and platelets is challenging, and may differ depending on the condition. Future research may show that the preparation and composition of platelet-rich plasma should be tailored for specific medical conditions. For example, one “recipe” may be best suited for treating tendinosis while another is optimal for treating osteoarthritis.