Is a cast appropriate treatment for bone bruise of the metatarsals?

No Bones About It: Them metatarsals is way down there where all that body weight ends up.That can hurt and walking on them unprotected could delay healing.Fractures definitely need a cast,but as far as you,the doctor must have seen that your injury was pretty serious, fracture or no fracture.And maybe was taking care in case there was a tiny one not picked up yet on x-ray. Anyways,there's a lot in there besides bone

Yes: ultimately anything that minimizes the stress in the bones will help give it time to heal (6-8 weeks)