Per the Arizona Republic:
Cardinals running back Ryan Williams underwent a platelet-rich plasma injection in his ailing right knee about 10 days ago. Williams is just one of many athletes to receive such injections, which are designed to send highly-concentrated platelets, the part of blood that helps us heal, to the injured area.
It works like this: The patient’s blood is drawn and then put through a centrifuge. That concentrates it down to 7-10 times the normal amount of platelets. The substance is then injected into the injured area. “It tricks the body into regenerating,” said Dr. Luga Podesta, an orthopedic surgeon at Kerlan-Jobe Orthopaedic Clinic in Los Angeles.
Williams is currently listed behind Rashard Mendenhall on the Cardinal’s depth chart and will need to see steady improvement in the knee to keep that spot.