PST (pulsed signal therapy) is a unique form of pulsed electromagnetic field therapy (PEMF) for stimulating healing of damaged structures such as cartilage, bones and soft tissues. The physical effect of the pulsed electromagnetic field (PEMF) has been focus of research in various studies, with cartilage being the most studied, and which has demonstrated an increase in the synthesis of proteoglican and collagen in vitro. This is an randomized, controlled and double blind clinical trial. The main objective is to evaluate clinical improvement regarding anterior knee pain after PST intervention in patients with patellar condropathy.