Í've been experiencing the same problem so I've tried many different things to alleviate my pain.
First of all, of course, not landing backseated, and also, surprisingly, , wearing my boots looser.
I only buckle the lower 2 real hard and keep the upper part just nearly tight. It helps to make the backseated landing smoother. If I fall leanin back just once then im screwed for the rest of the day.