If I were you (and had a little time to blow on a lawsuit), I'd get my doc to prescribe a Segway. Then I'd go buy one and roll all over SF sidewalks, daring the city to write me a ticket for using my medical device.
Disclaimer from Segway site:
Important notice: Purchaser (or the person to whom the Segway HT is to be shipped) must attend Segway provided training and completely and carefully review all user materials provided by Segway before using the Segway HT. The Segway HT has not been designed, tested, or approved as a medical device. Riders must be able to step on and off the Segway HT, requiring physical abilities similar to climbing and descending stairs.