Your doc probably told you being confined to a cast can be dangerous to your cartlidge.  When I broke my wrist it turned into a 4 yr ordeal.  The end result,  my wrist was fused.  I am hoping and praying for you that you don't go through anything like that!  Best Wishes....  Do the therapy! 

Hey,

so for all that care, i did break my arm, it looks like its broken in a couple different spots.  They can't tell exactly how many times it is broken yet, but they know it is. They casted me for a week and told me to come back and have x-rays and get recasted for some number of weeks. The purpose is to let the swelling go down some before we get new x-rays, so that we can decide how long I need  to be in the cast. It is looking to be somewhere around a month or more. I slipped walking to class on some ice.... when I fell I heard it crack and knew it had broke.

Brianna