Joost Peerbooms

130 Chapter 8 proved to have a positive effect on pain relief and function in patients with lateral epicondylitis either due to their mechanical effect or because of a placebo effect. 19,21 Outcome bias PRP may have all the requirements of an ideal placebo. Filardo and Kon demonstrated that apart from expectations about outcome, marketing, a new sort of treatment and the way PRP is given to the patient are all parts of the placebo effect when patients receive PRP injections. 71 Needling in itself is a powerful tool, especially when patients are allocated for repeated injections. 72 It is important to remember that the psychological effects of this innovative treatment may be in the financial interests of physicians in some countries and may bias the outcome of studies. Additionally, industry-sponsored studies may bias final outcomes. Nessello et al. noted that industry-sponsored studies were more likely to show positive results, as did articles with a lower quality of evidence. 73 In addition to the influences of the industry, another possible influence is that both the physician and the patient might be aware of emerging technologies, such as PRP. 74 The PRP products are often linked with keywords such as orthobiologics, growth factors, regenerative medicine, stem cells and others, which may be attractive to patients. In short, PRP is popular among physicians and patients for reasons beyond scientific evidence, such as competition and anecdotal evidence of efficacy. 1 Regarding scientific evidence several systematic reviews and meta-analysis have been published in the last decade. It is important to keep in mind that a majority of studies regarding PRP and tendinopathy use a control group with active clinical treatments (i.e., corticosteroids, autologous blood injections). 75 This may also influence the final conclusions found in systematic reviews because of the (negative) effect of the treatments in the control groups. Rehabilitation Many studies do not provide sufficient information about PRP products, but many studies also fail in describing the rehabilitation protocols used after PRP treatment for tendinopathies. This makes it also difficult to determine which part of the treatment is effective. It is not clear whether the PRP injection, the exercise program after the injection or a combination of the two causes the outcome. It may also be possible that no treatment might enhance the self-limiting nature of these conditions. The effect of rehabilitation itself is a compelling topic on its own, but this goes beyond of the scope of this thesis.