Platelet-rich Plasma –
a biotechnology of the future being practiced today
(Written by Dr. Julien Frietag)
For over 20 years platelet-rich plasma (PRP) has been safely used in various fields of medicine without knowledge of its true mechanism of action. As our understanding of cellular mechanisms in tissue healing and regeneration has improved there has been a recent renewed focus (particularly within Europe and the United States) on the use of autologous blood products such as PRP in musculoskeletal medicine. Unfortunately whilst it theoretically provides a useful adjunctive therapy to traditional rehabilitation and perhaps is a potential alternative to more invasive surgical options there remains a paucity of clear evidence to support its use.
A sleeping medical community in Australia was perhaps woken from its slumber in 2007 when a desperate AFL team, only weeks from the Grand Final, flew a star midfielder to Europe for treatment on a chronic and recurring hamstring injury. The treatment - a product known as Actovegin. A deproteinised haemodialysate extract from calf blood, Actovegin has been used by doctors across Europe, China and Russia for over 60years.
Actovegan has been shown across several therapeutic trials to influence oxygen absorption and utilization and to exert insulin like activity. It has shown promising benefit in the treatment of dementia, diabetic neuropathy and musculoskeletal injury. It has also anecdotally been used as a performance enhancing substance. Despite the length of time it has been used, there remains a lack of data on its biochemical mechanism of action. This, along with case reports of anaphylaxis and secondary multi-organ failure has meant that its use has not been universally accepted (it is not approved for medical use in many countries including Australia and the US).
Based on our growing awareness of cellular healing mechanisms and the autologous nature of platelet-rich plasma (PRP), one would expect that PRP would displace therapies such as actovegan and have a real place in the treatment algorithm of musculoskeletal injuries. Unfortunately, lack of data, compounded by differences in `recipe’ have meant that PRP is still viewed within an evidence based medical community with deserved skepticism.
What is Platelet-rich Plasma ?
Our understanding of the healing mechanism and of tissue regeneration has seen medical treatments shift towards the area of biotechnologies - with a more focused effort on developing ways in which we can assist the body to heal. Autologous platelet-rich plasma is one such medium that has become both widely used and studied as a medium to accelerate tissue healing over a broad area of applications.
Autologous PRP is defined as a volume of the plasma fraction of blood having a platelet concentration above that of baseline. The importance of platelets is due to the growth factors which they actively secrete. Whereby once we only understood platelets as being involved in the coagulation cascade we now appreciate their wider effect on tissue healing.
Several anabolic and trophic factors have now been identified within PRP preparations. Growth factors expressed by platelets include transforming growth factor beta, vascular endothelial growth factor, platelet derived growth factor, and epithelial growth factor. Growth factors expressed by platelets have the ability to influence and direct tissue regeneration through angiogeneis, chemotaxis and cell proliferation and also effect the synthesis and of extracellular matrix proteins. Platelets also release cell adhesion molecules such as fibronectin, fibrobrinogen and vitronectin which influence extracellular matrix synthesis and thus connective tissue development/regeneration.
The ability to influence such powerful pathways of healing has seen PRP explored as a therapeutic option in applications such as orthopaedics, sports medicine, maxillo-facial surgery and plastics.
Unfortunately despite its suggested theoretical benefits, platelet-rich plasma has inconclusive evidence to support its use, with some studies indicating significant benefits whilst others showing no change. The problem lies partially in the ‘recipe’.
The PRP Recipe
Given the correct equipment a clinician can develop PRP within their own clinic. But not all PRP is created equal and depending upon the chosen `recipe’ will have a different cellular and biochemical make-up - and hence a different effect. Unfortunately it is not as simple as choosing a technique that yields the greatest platelets. In this case ‘more is not better’.
Research has indicated that the optimal platelet concentration for healing is ~1million cells per μl. Lower counts may lead to sub-optimal tissue stimulation and higher amounts may in fact have an inhibitory effect. Remember also that within PRP you do not just have platelets. You have an autologous medium that also contains both inflammatory cells and inflammatory mediators/cytokines that play an important role in healing. Roles which may be counter productive or stimulatory to the healing process depending upon what you are using if for and how you direct it.
As a practitioner who uses PRP for treatment of various musculoskeletal conditions the PRP preparation remains a very `fluid’ process. The recipe chosen depends upon what structure I am treating and what I hope to achieve. Platelet count, white cell count, anti-inflammatory and pro-inflammatory cytokine content are all variables that can be specifically manipulated to achieve a chosen response.
With such discrepancy in PRP preparation how then can you use current literature to assess the efficacy of PRP? The answer is you can’t. Papers with poor outcomes lead not to the conclusion that PRP does not work but to the conclusion that the specific chosen PRP recipe and its protocol for use does not work in the studied situation. Another recipe may lead to completely different results. Similarly, if a study shows a positive outcome for the use of PRP, unless you are using the same recipe and protocols you are not guaranteed the same outcome. ‘Oils aint oils’.
Areas of use within Sports Medicine
Tendon injuries account for between 30% - 50% of all musculoskeletal injuries. They cause significant morbidity and activity restriction in not just the elite athletic population but also the recreational athlete and even the more sedentary patient in regards to activities of daily living. As past modalities such as intra-tendinous cortisone injection have now been shown to result in poor long term outcome, PRP has become a new therapeutic option in the treatment of tendon injuries that fail to respond to more conventional rehabilitation therapies.
Looking at the trophic effects of platelet-rich plasma we can hypothesize that it has relevance to tendon healing through growth factor modulated pathways. VEGF may be relevant in regards to stimulating appropriate angiogenesis. PDGF and TFGβ1 along with cell adhesion molecules have relevance in regards to stimulation of tenocytes and production of a collagen network. Interestingly the potential fibrotic scarring response that may be associated with TGFβ1 seems perhaps counter balanced by the expression of hepatocyte growth factor that has a strong anti-fibrotic stimulus.
But does the theoretical science match the clinical outcome? This is perhaps the greatest weakness in the argument for use of biotechnologies such as PRP where the theoretical and in vitro evidence has not been supported by clear controlled clinical research. Numerous case series suggest a therapeutic benefit of PRP in the treatment of common tendon injuries though unfortunately without appropriate control and/or placebo groups their remains a question of what is producing the improvement in outcome measures. Is it the PRP or just the technique of dry/wet needling that is the stimulus for improvement? Is it just that the patients perceive an active management of their condition and the result is best explained by a `placebo effect’?
The strongest scientific study – and first randomised controlled trial - on use of PRP in the treatment of achilles tendinopathy showed no significant difference between PRP and placebo (saline injection) groups. Whilst a scientifically well designed study and the first level one research to be published on the use of PRP in tendinopathy it is arguably not as robust when assessing its clinical strength. Patients were excluded if they had done an eccentric program in the past. All patients underwent PRP or placebo (saline) injection in conjunction with commencing an eccentric loading program. An interesting study design when it is accepted that up to 80% of patients with achilles tendinopathy will respond to an eccentric loading program within 12 weeks (and this intervention was used on both the PRP and placebo groups). Further, only a single injection of PRP was used. Those using PRP in a clinical setting would likely agree that its value is best seen in patients who have failed traditional eccentric loading and that multiple injections are often required to achieve improved long term outcome. Also, tendinopathy was diagnosed on clinical evaluation rather that ultrasound examination which can assist in determining a patients suitability for PRP therapy (ie. intrasubstance tears). Finally, a commercial PRP preparation technique was used, platelet counts were not recorded and no attempt was made to modify white cell or cytokine levels. Hence the importance of the `recipe’.
Osteoarthritis (OA) is a major cause of disability and chronic pain in Australia. It is estimated that at least 3.85 million people are affected across the Australian community, at a cost to our economy of greater than $23.9 billion each year.
Current medical treatment strategies for OA are aimed at pain reduction/symptom control rather than disease modification. These pharmacological treatments are limited and can have unwanted side effects. Viscosupplement/Hyaluronic acid intra-articular injections can be used to treat symptoms of mild to moderate knee OA, however, their mechanism of action is uncertain, with some studies suggesting little improvement beyond that achieved with placebo injections.
Recent research on the mechanisms of OA have focussed on the catabolic cytokines involved in destruction of hyaline cartilage and joint degeneration. Interleukin-1 (IL-1) has been identified as a potent mediator of cartilage loss and reciprocally Interleukin-1 Receptor Antagonist (IL-1RA) has been shown to limit the intra-articular actions of IL-1.
Autologous conditioned serum (ASC) is an injectable peripheral blood derived IL-1RA medium that has been used within Europe for the treatment of osteoarthritis. Research has indicated significant improvement in symptoms of OA post ACS therapy though no research has been undertaken to determine whether ACS is disease modifying. The use of ACS is limited due to cost and need for autologous blood to be incubated overnight prior to re-injection.
Like ACS, PRP has also shown promise in the treatment of OA. In vitro studies have shown PRP to stimulate increased cartilage matrix expression indicating potential disease modifying properties. Further research has demonstrated that PRP stimulates the natural synthesis of hyaluronic acid from joint synovium. An initial retrospective case series indicated significant pain reduction post intra-articular injection of PRP compared with commercial hyaluronic acid supplements in knee OA and more recently a prospective case cohort series has shown significant pain and functionality improvement with use of intra-articular PRP injections.
Clinician, mad scientist or witch doctor?
Our improved understanding of musculoskeletal injury has led to the advent of biotechnologies and a focus on `assisted’ healing. Platelet-rich plasma shows considerable theoretical promise but what we have learnt from the paucity of research available is that theoretical benefit has not always correlated with observed outcomes. And yet despite some studies that question the efficacy of PRP others indicate significant benefits.
Whilst the research is incomplete, the use of PRP within clinical practice (in particularly the US) has outpaced the evidence. Sadly it is a real possibility that a promising therapeutic modality may be discredited undeservedly due to inappropriate use.
What has become apparent to me is that if we are to use PRP in the treatment of our patients then we need to be able to show clinical justification. Appropriate follow up of our patients with use of validated outcome scores shows that we are interested in the results and not just blindly playing the role of ‘witch doctor’.
Despite my misgivings about the accelerated development of therapies such as PRP, I do in fact use PRP regularly in my own clinical practice. My `recipe‘ is different to that used in published studies and I will often alter the recipe depending upon the condition I am treating. I may choose to use a white cell rich PRP preparation on one patient and a white cell poor PRP preparation for another patient. I may choose to expose the PRP to UV light activation to enhance its anti-inflammatory properties. Importantly all my patients are followed up routinely to assess outcome and I am also actively involved in numerous PRP related studies. I may be a clinician but born out of a necessity to practice evidence based medicine I have also become the scientist.
Dr Julien Freitag a registered physician of the Australasian College of Sports Physicians. He has a keen interest in the areas of tendinopathy and osteoarthritis and is directly involved in research into next-generation treatment of these conditions.