What is platelet rich plasma (PRP)?
Platelet rich plasma is a portion of the blood that has been processed, usually by centrifuge, to contain a higher concentration of platelets than in the whole blood. The PRP contains platelets and varying numbers of white blood cells (WBCs) and red blood cells (RBCs), depending on the method of preparation. In addition to cells, PRP contains other growth factors and substances that are normally in the plasma, such as insulin-like growth factor 1 (IGF-1). Platelet rich plasma can be injected at a site of injury, or it can be made into a platelet-rich fibrin clot (PFRC) to use as a scaffold and source for sustained release of growth factors.
Why use PRP?
The rationale for using PRP is that platelets contain many growth factors and signaling molecules in their granules. The most important of these are transforming growth factor beta (TGF-β1) and platelet derived growth factor (PDGF). These growth factors reduce the expression of inflammatory cytokines, such as IL-1 and TNF-a, which dampens the neutrophil response and the production of destructive matrix metalloproteinases (MMPs). Additionally, they encourage proliferation and differentiation of resident cells. The goal is that the body’s natural healing response is enhanced by delivering a high concentration of growth factors directly to the site of injury.
How is PRP prepared?
The most common way to prepare PRP is to draw the patient’s blood and then separate the blood using one or two spins in a centrifuge, but there are other methods, such as filtration. When the whole blood (WB) is spun in the centrifuge, it separates out into a layer of red cells, a buffy coat layer that contains the platelets and WBCs, and platelet poor plasma.
There is tremendous variability in the final platelet, WBC, and RBC concentrations between commercial PRP preparation, between patients and between species. Such variability makes it difficult to evaluate the evidence and compare studies, as all PRP preparations are not equal. It is important to understand the make-up of the particular PRP preparation being used. The higher the platelet concentration, the more growth factors are available.More studies are needed to determine the ideal platelet and WBC concentrations for each application.
How successful is PRP in treating orthopaedic injuries?
Platelet rich plasma has been used in humans for a variety of orthopaedic conditions, including tendon/ligament injuries, osteoarthritis, muscle injuries, meniscal tears, cartilage defects, fractures, total joint arthroplasties, and others. Overall, the success of PRP treatment is highly variable, likely due in part to the variability in the PRP preparations used. In veterinary medicine, PRP has most often been reported for tendon/ligament injuries and osteoarthritis. Most of the veterinary literature reporting on PRP involves its use in equine patients, and evidence in canine patients is lacking. In a study of eight dogs with experimentally created patellar tendon lesions, use of a PRFC did not enhance healing.
However, in a study of 12 dogs with experimentally created Achilles tendon tears, use of PRFC resulted in decreased lameness and improved histologic scores. In a blinded, controlled clinical study of canine patients with elbow osteoarthritis, intra-articular injection with a PRP-related product, called autologous conditioned plasma (ACP), resulted in similar improvement as dogs receiving intra-articular injection of a corticosteroid and hyaluronic acid. Additional prospective, controlled clinical trials are needed to understand the role for PRP in treating canine orthopaedic injuries and diseases.
In summary, PRP appears to be safe and potentially useful in treating several orthopaedic conditions – in vitro data and clinical results in other species are encouraging. However, the significant variability in PRP preparations and lack of consistent results make it difficult to assess the utility of PRP therapy. The ideal concentrations of platelets and WBCs are unknown, and likely depend on the type and chronicity of the injury. High level evidence for their use is severely lacking for canine patients, and the decision to use PRP should be made with the knowledge of the composition of the PRP and after discussion between the veterinarian and client about the costs, risks, limited evidence, and other traditional treatments.