When ever you injure yourself the neural paths that allow us to do things without tobbling over is damaged. The greater the injury the more damage occurs so a Grade 3 injury can destroy the muscle memory.

So if you have been injured you need to do some basic balance exercises. If you have had a severe injury many of the neural paths would have been wiped out so start off at the first level and build up. The more you do the stronger the neural links become. For less serious injuries you should manage the first few exercises quite comfortably but if you can not that is also a possible reason for the injury in the first place.