This article mentions the problems that occur because of ligament disease and collagen loss. I know a long list of former athletes who have no collagen or virtually no collagen in their knees now. When you play certain sports for a long period of time, the knees take a heavy beating.
When the collagen is worn away, you have bone on bone and as you can imagine that can be very painful. I am fortunate because I still have collagen. However, I have had some ligament damage in my ankles and knees and these areas swell when I exercise too heavily.
At some point in the future, I may need surgery. How well the surgery works depends on who you ask. Some people say the surgery made a world of difference, and other people say they are still in pain and wouldn't recommend going under the knife.