Why is my front knee getting torqued on my snowboard?

I am riding a burton king snow board with burton custom bindings. I ride regular footed. My angles are set at just past +15 on the front and +7.5 on the back. I am riding in the alps, and there are a lot of left running trails and I find myself riding on my back edge a lot. After a day of snowboarding the out side of my front foot is really painful and my knee feels like it is about to be torqued out of the socket. I kind of feel like I am standing on the outside of my foot. Are there any changes that I can make to the adjustments to get rid of this.