I am from the "old school" and I still believe JWB broke his fibula at Ford's. This may be a minority view nowadays. I am not sure.
Lincoln assassination researcher and author Mike Kauffman has written the arguments for JWB breaking his leg when his horse took a fall. Hopefully this (scanned from Blue & Gray magazine, June 1990) can be read, but it's possible you might have to enlarge it depending on your monitor's settings: