If you break cartilage in your knee, avoid sports that cause further damage such as those requiring running and jumping. You can help to prevent more cartilage loss with an exercise program that strengthens the muscles that control your knee. Bones are soft. To keep them from wearing down at joints, their ends are covered with a thick white gristle called cartilage. Broken cartilage never heals. Removing broken cartilage may increase a person's chances of needing a knee replacement in the future, particularly if the exerciser continues to run and jump.
Former world-class athletes are supposed to have tough, strong bodies, but they suffer high risk for permanent knee damage, while non-competitive exercisers are at very low risk. Repeated cortisone-type injections can weaken cartilage and cause further damage. Nonsteroidal pain medications do not prevent further damage. Weak thigh muscles increase chances for further knee damage, so all people with knee damage should strengthen the muscles that control their knees using a special knee weight machine, and start a supervised program of cycling or swimming, provided that it does not hurt.