Joost Peerbooms

94 Chapter 6 injection or surgery was also larger in the corticosteroid group than in the PRP group. Actually, of the 11% getting worse after the injection, the vast majority was found in the corticosteroid group. Smidt et al. 26 showed in a meta-analysis that the effects of steroid injections compared with placebo injection, injection with local anaesthetics, injection with another steroid, or another non-operative treatment are not significantly different in the intermediate and long term. However, the studies acknowledging the relatively good results of a wait-and-see policy, physiotherapy, and even corticosteroid injections are studies that included patients who all had nonchronic lateral epicondylitis (i.e., patients with complaints of less than 6 months’ duration). The current study included patients with a duration of symptoms of > 6 months. Smidt et al. 27 showed most patients recover from lateral epicondylitis within 1 year but that beyond 6 months, not much natural recovery is seen. Our original power analysis in the 1-year follow-up paper 20 with an alpha of .05 and a beta of .9 was based on the 93% success in the Mishra and Pavelko 15 study for PRP and the 65% success in the Hay et al. 10 study for corticosteroid injection, both obtained after 6 months. Our study presents the results after 2 years so possibly the power at 6 months is correct, but the power after 2 years of follow-up does not need to be, rendering this study underpowered at the 2-year follow-up. However, a beta of .9 is higher than in most studies. More important, there is no additional improvement in symptoms from a wait-and-see policy or a steroid injection beyond 1 year (actually, there seems to be no additional gain in recovery percentages in waiting beyond 6 months). 27 Although we do not know what the success percentages will be at 2 years of natural history or after 1 steroid injection, there is no evidence to suggest it would be very different from what we used for the 6-month power analysis. For those who do not recover, there are various types of surgical procedures for patients with chronic lateral epicondylitis. Verhaar et al. 33 noted an improvement in 60% to 70% of the patients after surgical treatment, although more recently higher success rates (80%-90%) have been reported. 31 Patients remain, however, interested in an alternative to surgical intervention. Platelet-rich plasma is promoted as an ideal biologic autologous blood-derived product. It can be exogenously applied to various tissues, where after platelet activation, high concentrations of platelet-derived growth factors that enhance tissue healing are released. 8,36 Utilizing the Recover system, the patient’s own platelets can be collected into a highly concentrated formula. No activation agent was used during our procedure. The activation of the platelets will occur through the exposure of platelets to the thrombin. The thrombin is produced as a reaction to the injection of the platelets into the tendon tissue using a peppering technique. The exposed collagen may also serve as an activator. Several negative side effects are known when using bovine thrombin as an exogenous activator, limiting its clinical use: undesirable immune responses in humans, 13