Hello i went to a surgery orsomething like it around my area and yes she told me there was an excercise and i belive it has worked for me beacause my legs ar straighter but you need to do it constantly
i will try to describe it to you.
1. lean the inside of your knee against a flat surface e.g a wall.
2. use your opposite leg to push your knee against the wall (in a kind of ice skating position)
<---- its a long link sorry but his is the kind of position you should be in
3. swap legs and o the same
4. whilst doing this push your knee slightly more and more against the wall
hope it works for you
try not to hurt yourselfs, it may hurt slightly