Many non-quadsters were facing injuries in the past and are facing injuries now, which is what happens in sport. Just take Loena Hendrickx, we are cheering for her curent results and that can be an inspiration for all the injured skaters who can see that they can always get back and still improving, but I'm mentioning her also because she was dealing with her troubles for years. She withdrew from competitions, then started competing again, then withdrew from other ones, there and back again and again. It's not like a skater, a coach or a doctor have a crystal ball and not always the diagnosis or the prognosis can be set. And of course if any athlete would cease competing/training after every trouble there would be only empty stadiums or arenas. It's simply impossible to forecast everything even if there are "troubles".
Like an athlete starts to feel something. OK, we will go to the doctor, the coach probably says, the doctor does some examination. Either he finds soemthing disturbing, then the cure is set, or he finds it's something minor that can be treated soon, then the training is stopped or reduced according to seriousness. Or possibly nothing specific is found, then perhaps some options are proposed and according to possible danger/not danger the further steps are considered. Of course it mostly workds but no doctor is House M.D., to whom screenplay allows to always find the right cause of the problem.
And of course plenty of top skaters are injured currently who have nothing to do with TT. Injuries mostly happen in training, because like 95 % of time and load the skater spends and gets in the training, but there are still those 5 %.