Hope you heal up fast. If you need to panic stop, slide your ass off your saddle all the way back as far as it will go then squeeze the front brake. You can use the rear brake as well but you need to know you can't apply as much braking power as the front brake. Your rear wheel will start to skid if you use the rear brake too much. Here's a web site which sums it up:
http://www.seattlebicycleclub.org/me...anic_stop.html