Multiple PRP injections are more effective than single injections and hyaluronic acid in knees with early osteoarthritis: a randomized, double-blind, placebo-controlled trial - Görmeli, G; Görmeli, C A; Ataoglu, B; Çolak, C; Aslantürk, O; Ertem, K (Knee Surg Sports Traumatol Arthrosc, 2017)