Effect of Intramuscular and Intratendinous Platelet-Rich Plasma Injections on Systemic Concentrations of Performance-Enhancing Growth Factors

To understand the short-term systemic effects of local PRP injections, we will measure the serum concentrations of six growth factors before and during the four days following PRP injection: human growth hormone (hGH), IGF-1, basic FGF, PDGF-BB, VEGF, and IGFBP-3. These molecules are of particular interest because they may have stimulatory effects that enhance athletic performance, and because they have been banned in competitive athletes by the World Anti-Doping Agency (WADA).

We aim to recruit 40 patients who are receiving ultrasound-guided intratendinous (IT) or intramuscular (IM) PRP injections. Blood will be drawn immediately before (baseline); 15 minutes after; and 3, 24, 48, 72 and 96 hours after receiving PRP therapy. A fraction of the therapeutic PRP preparation will be isolated for growth factor analysis. Serum concentrations of growth factors will be quantified by ELISA. Statistical analyses will be conducted to assess the change in each growth factor following PRP injection. To understand the impact of injection site on systemic growth factors, changes in concentration will also be compared between the intratendinous and intramuscular groups.

Study subjects will participate in the following steps: (1) Initial diagnostic visit with Orthopaedic Surgeon, (2) Blood collection as part of PRP therapy, (3) Ultrasound-guided PRP therapy administered by Stanford radiologist, and (4) Blood collection for the study. Steps (1) through (3) are all part of the standard of care, which the patient will have chosen independently of the study. In step (4), blood samples will be collected by venipuncture at various time points and assayed for growth factor concentrations. Less than 10 mL (2 teaspoons) of blood will be collected at each of seven time points over five consecutive days. In order to minimize inconvenience to the patient we will meet patients at a location of their choosing, such as the patient's home or office, for blood collection on days 2-5. Participants will be compensated after all seven blood samples have been donated.