How can I gain calf muscles if I can't move my ankles?

I'm an 18 year old girl. My ankles were fused at birth. Therefor, my calves are very skinny and have pretty much nonexistent muscle. I can't wear shorts or skirts or dresses because they're too skinny. I would like to gain muscle there but I don't know how I can because I cannot move my ankles. Any exercises I can do? Please help......