If you are in a leg cast, what are you likely using to help yourself walk? What kind of shoes do doctors recommend for you to wear if you are using #1? Do sandals fit the requirements of #2?
Sandal
If you are using crutches, it is advised to have non-slip shoes with a closed toe. Most sandals do not have non-slip traction and, by definition, don't have closed toes.  If you are in a leg cast you are likely to be using crutches.
Type of footwear with an open upper
If one of your feet is in a leg cast, should the other be in a sandal?