Having had an impact fracture of one knee and a torn cartilage in the other I know what its like. For me most rides over 3hrs are a problem. Go to the quack, explain exactly what has happened and most likely they will tell you that you should stop cycling, walking, running, movement of any kind. Then once you have left feeling slightly pi$$ed off find a good sports physio (yes it’ll cost) and they should be able to sort it out. Things you can do are excersizes to strengthen the muscles round the knee, I think there was something in a recent issue of ST. Plus the usual rest, ice etc…. hope this helps a little