In previous studies, it has been showed its potential to reduce pain and improve functional status in patients treated by simple intra-articular injections. However, there are several PRP formulation currently available in clinical use, and therefore it is very difficult to compare data coming from trials using different products. The most debated aspect concerning PRP formulation is the role of leukocytes, which might stimulate an early inflammatory response in the joint due to the release of metalloproteases and other pro-inflammatory cytokines.