The US ADA provides a requirement that an employer provide reasonable accomodations to allow you to do youe job. There are a lot of things you could do in the medical field, in a wheelchair. Some would be more difficult than others. The easiest that comes to mind right now would be to work in a lab, path asst, med tech, etc. If you want to take care of patients, office or hospital based PA/NP/MD practice are all possible. I think you would have trouble assisting in surgery, but that's really it as I see it. Pick something and go for it.
Pat