When you have damaged knee or joint cartilage the only way to get the damaged joint or knee cartilage repaired is to have medical treatment done to repair the knee cartilage.
Some other tissues in the body can repair themselves but knee and joint cartilage cannot repair itself like the other bodies tissues.
If you leave your damaged knee cartilage untreated then the knee cartilage can deteriorate even more into debilitating osteoarthritis and chronic pain, ultimately necessitating a joint replacement surgery.
So if you damaged your knee cartilage you need to go to urgent care or the emergency room and have the knee cartilage repaired.
Some people who have damaged knee cartilage can have their knee cartilage repaired without the use of surgery and they usually respond well to conservative treatment, which can include special exercises, NSAIDs (non-steroidal anti-inflammatory drugs), and sometimes steroid injections.
Surgery for the damaged knee cartilage is usually used as a last resort to repair the damaged knee cartilage but without any medical treatment the damaged knee cartilage cannot repair itself.