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Introduction Chronic Achilles tendinopathy occurs frequently and is very hard to treat. The disease involves local degeneration of tendon tissue, of which regeneration may be improved by injecting platelet-rich plasma (PRP), an increasingly used therapy for releasing growth factors into degenerative tendon. However, high-quality randomised clinical trials on this topic are lacking. The aim of this study was to evaluate the effect of a PRP injection in patients with chronic Achilles tendinopathy. Methods In this stratified, block randomised, double-blind, placebo-controlled trial at single center 54 patients aged 18–70 years were randomised in two treatment groups. Next to an eccentric training program the patients received a blinded injection containing either PRP group or saline (placebo group). Primary outcome, the objective and validated Victorian Institute of Sports Assessment-Achilles (VISA-A) score, was assessed and ultrasound examination was performed at baseline and all follow-up appointments. Results After randomisation into the PRP group (n=27) and the placebo group (n=27) there was a complete follow-up. After one year, the mean VISA-A score improved in both the PRP-group and the placebo group. There was no significant difference in increase between both groups (adjusted between-group difference, 5.5; 95% CI, −4.9 to 15.8, p=0.292). Ultrasonographic tendon structure improved significantly in both groups, but not significant different between both groups (adjusted between-group difference, 1.2 %, 95% CI, −4.1 to 6.6, p=0.647) Conclusion One-year follow-up analysis of the world’s first randomised controlled trial showed no evidence for the use of platelet-rich plasma injection in chronic Achilles tendinopathy. These findings are in line with our 6 months results (De Vos et al JAMA 2010).

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We present Monte Carlo (MC) simulations of the structure factors of polydisperse hard-sphere fluids. The simulations were carried out for 108 particles and packing fractions up to φ=0.5. The size distribution of the particles was chosen randomly from a log-normal distribution. The MC results are compared with predictions obtained using Percus–Yevick approximation. It is found that for all but the highest densities and the highest polydispersities studied, the Percus–Yevick approximation provides a satisfactory description of the MC data.