Balance board and balance mat
You can exercise and prevent damages or rehabilitate your knees and ankles just by using a balance board or a relief mat. Try for example Steppie balance board, Back App 360 balance board or Active Stand board.
The products are very different to each other, because humans and our needs are too. Even to all of them is that they strengthen your balance, joints and muscles in the back, knees and ankles when you stand on them. Some models are more adjustable and challenging than others, so you have a good chance of finding a board or a mat that suits your needs perfectly.