If the torn cartilage in the knee is not very severe then you can usually go to the doctor and they can repair the torn cartilage in the knee through physical therapy with muscle strengthening to stabilize the the knee joint.
When that doesn't work then you will usually require surgery of the knee to repair the more severely damaged torn cartilage in your knee.
Though knee surgery is usually the last resort when it comes to repairing torn cartilage in a persons knee.
When you have knee surgery for the torn cartilage the surgeon will try to repair the torn cartilage in your knee or if that is not effective they will remove the torn cartilage.
But the doctor will usually suggest and use the physical therapy to hopefully repair the torn cartilage in your knee unless they decide that the knee surgery is required instead.