OPTIMUM PLATELET CONCENTRATION LEVEL FOR PRP Outpatient PRP preparation systems exist with the ability to concentrate platelets from two to eight times. There is some controversy about what the optimum platelet concentration should be, but a level of at least 1 million platelets per L appears to be the magic number. Since the average patients platelet count is 200,000 +/- 75, a four to five times concentration appears to be the desired level. When levels are in the 5x range, the influx of adult stem cells has been noted to increase by over 200%. In 2008, Kajikawa et al concluded that PRP enhances the initial mobilization of circulation-derived cells in the early stage of tendon healing. Circulation-derived cells are defined as mesenchymal stem cells that have the potential to differentiate into reparative fibroblasts or tenocytes as well as macrophages. Under normal circumstances, circulation-derived cells last only a short time after tendon injury. The authors suggest this as one of the main reasons for the known low healing ability of injured tendons. If the circulation derived cells could be activated and their time-dependant decrease stalled with PRP, then the wounded tendon could more fully heal. One study found an increase in the circulation-derived cells with the PRP group, as well as increased production of types I and III collagen in the PRP group versus control. This finding of additional fibroblast proliferation and type I collagen production enhanced by increasing platelet concentrations concur with an earlier study by Lui et al. This provides evidence that PRP stimulates the chemotactic migration of human mesenchymal stem cells to the injury site in a dose-dependent manner - i.e., the more concentrated the platelets, the more stimulation.

PROLOTHERAPY VERSUS PRP The use of hyperosmolar dextrose (Prolotherapy) has been shown to increase platelet-derived growth factor expression and upregulate multiple mitogenic factors that may act as signaling mechanisms in tendon repair. Saline Prolotherapy can have a similar effect. An interesting study published in the January 2010 JAMA compared PRP versus saline injection (basically saline Prolotherapy) for chronic Achilles tendinopathy. Both groups improved significantly by Yellonel et al and the authors conclude there was no statistical difference between the improvement of both groups. Therefore, both PRP and Prolotherapy have been shown to stimulate natural healing and both can be effective and both should be considered in the treatment plan for connective tissue repair. However, PRP may be more appropriate in some cases. When PRP is used as a Prolotherapy formula for chronic or longstanding injuries, the PRP increases the initial healing factors and thereby the rate of healing. The Prolotherapy itself (irritation, needle microtrauma) is what is tricking the body into initiating repair at these long forgotten sites as well as the PRP, itself, which also acts as an irritating solution. This is especially important with chronic injuries, degeneration and severe tendonosis, where the body has stopped recognizing that area as something to repair. In these cases, PRP may be more appropriate, however this determination should be made by the physician on an individual basis. PRP can also be used preferentially over dextrose Prolotherapy in the case of a tendon sheath or muscle injury- areas occasionally but not typically treated with dextrose Prolotherapy where the focus is the fibroosseous junction (enthesis). It can also be used preferentially over dextrose Prolotherapy because of patient preference.

WHOLE BLOOD INJECTIONS VERSUS PRP Even before PRP, it was not unheard of to use whole blood as a Prolotherapy solution, especially where the patient was hypersensitive to other formulas. A 2006 study in the British Journal of Sports Medicine studied the use of whole blood with needling(irritation such as with Prolotherapy) and concluded that the use of autologous blood injection, combined with dry needling, appears to be an effective treatment for medial epicondylitis. Another study in that same journal in 2009 compared injections using whole blood, dextrose Prolotherapy, platelet rich plasma and polidocanol (a sclerosing agent), and concluded that there is evidence to support the use of each of these agents in the treatment of connective tissue damage. However, there are only three known studies using whole blood, all of which were prospective case series without controls and small patient numbers. PRP studies, on the other hand, are growing not only in number, but also in quality. When examining the physiology of how activated platelets signal repair cells, it seems logical that using PRP (with higher levels of platelets per unit volume) would be more effective than autologous blood although no study has yet directly compared the two.

CORTISONE VERSUS PRP The use of cortisone in musculoskeletal injuries is controversial and the subject of various studies over the years. In February 2010, researchers in the Netherlands published the results of a well designed, two year randomized controlled blinded trial with a significant test group of 100 patients, comparing corticosteroid use to an injection of concentrated platelet rich plasma without ultrasound guidance. The PRP injection was given to the lateral epicondyle area of maximum tenderness, and a peppering technique was used in order to activate the thrombin release from the tendon- in this case endogenous thrombin is the activator for the injected platelet growth factors. The researchers indicate the importance of the inflammation phase the first two days post treatment) during which there is a migration of macrophages to the injured tissue site. Macrophages release additional growth factors, and there is increased collagen synthesis on days three to five. The conclusion of the Netherlands study was that PRP reduces pain and significantly increases function, exceeding the effect of the corticosteroid injection.

SAFETY ISSUES Like Prolotherapy, PRP therapy has low risk and few side effects. Concerns such as hyperplasia have been raised regarding the use of growth factors, however there have been no documented cases of carcinogenesis, hyperplasia, or tumor growth associated with the use of autologous PRP. PRP growth factors never enter the cell or its nucleus and act through the stimulation of external cell membrane receptors of adult mesenchymal stem cells, fibroblasts, endothelial cells, osteoblasts, and epidermal cells. This binding stimulates expression of a normal gene repair sequence, causing normal healing - only much faster. Therefore PRP has no ability to induce tumor formation. Also, because it is an autologous sample, the risk of allergy or infectious disease is considered negligible. Evidence also exists in studies that PRP may have an antibacterial effect.

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