I Will tell you this from experience: When your doc tells you to start p.t. ankle exercises, DO IT. I put it off, and put it off, and eventually 6 years had passed and I developed back pain from uneven strength and I have weird pain and weakness in my ankle. I'm working on it now but DAMN I wish I had listened. Good luck! :-)
You could do arm circles forward and backwards
whether you're able-bodied or not, losing weight is best accomplished with a plan that has its foundations in good eating habits.
You could theoretically not exercise at all and still lose weight easily by carefully tracking calories and avoiding certain problem foods.
Working your core is great for health though, so, regardless of calories burned, you should at least be doing those kinds of exercises.