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.

Dr. Podesta isn’t treating Williams but performs PRP regularly and has had success using it in athletes with elbow ligament tears Achilles injuries and patellar tendon tears.

Williams suffered a patellar tendon tear nearly two years ago and his current knee problem is believed to be related.

“We’ve had great success with throwing athletes” Dr. Podesta said. “With high-grade partial tears we’ve been able to get 80 percent of them back in 12 weeks.”

So what’s the normal recovery time for patients who have undergone a PRP injection?

“Initially you want to limit the activity because you want the cells to grow” Dr. Podesta said. “In my experience for the first two weeks I let them do a minimal amount just range of motion and strengthening exercises using only their own weight.”