Joost Peerbooms

128 Chapter 8 PRP Preparation There are a number of standard steps for preparing PRP. The key steps in the preparation process are collecting peripheral blood from the patients by vena puncture, conducting blood centrifugation to retrieve platelet-enriched fraction and activating platelets to release growth factors. 40,41 In each of these phases, there is variability based on the volume of blood collected, the type of anticoagulant, centrifugation protocols and the type of platelet activators. 36,42 The concentration of leukocytes also differed extensively between the systems studied ( Chapter 2 ). PRP separation systems are typically divided into systems producing high and low concentrations of leukocytes. 44,45 Plasma-based methods minimise leukocyte fractions. Buffy coat-based methods actively concentrate leukocytes. 42,46,47 This type of PRP preparation is generally referred to as leukocyte-rich PR P (LR-PRP). Currently, the presence of leukocytes in PRP is under debate, as both beneficial and adverse effects of leukocytes have been suggested. 48 Potential benefits of the presence of leukocytes include their role in tissue remodelling and increased antibacterial and immunological resistance. 50,51 Furthermore, the presence of leukocytes in PRP is associated with an increased concentration of growth factors, especially VEGF. 41,51,52 On the other hand, leukocytes may have catabolic and inflammatory effects due to their release of pro-inflammatory cytokines, which is associated with decreased proliferation and increased apoptosis. 53-58 In the studies we performed, LR-PRP was used. ( Chapter 3, 5, 6, 7 ). This leukocyte- rich type of PRP is also most commonly used for treatment of tendinopathy in other studies. Hardly any study, however, provides a detailed characterisation of the compositions of the PRP used, which makes comparing different studies a challenge. 59 The characterisation of the cell types in PRP used is important, but many other parameters need to be considered (e.g., the activation of the growth factors, the presence of red blood cells). 60-62 All of these factors make it intrinsically difficult to compare the effectiveness of PRP in different studies. Furthermore, there is no proof or consensus on the optimal preparation method and composition of PRP for different musculoskeletal conditions. 63 STRENGTHS and LIMITATIONS All of our RCTs ( Chapter 3, 5, 6, 7 ) were double blind multicentre RCTs. They all provide a thorough description of the preparation of the PRP and the system used. Both of our RCTs on tendinopathy ( Chapter 5, 6, 7 ) involved an above average enrolment of patients. On the other hand, in the plantar fasciitis study, the number of patients with which we were unable to follow up after a year was quite high ( Chapter 7 ). 27% (17 out of 63) of the patients in the PRP group and 31% (16 out of 52) in the control group