If you search for "dermatome map," you will see that specific spinal nerves innervate specific pathways in the limbs. It sounds like you are suffering from some nerve compression. This could be from the spondylolisthesis, if that's what you were referring to. Or, I imagine there is a lot of inflammation from the tissues surrounding the fractures which could be pressing on a nerve.

If you should develop any problems with the control of your bowel or bladder, call your doctor immediately. This is a symptom of Cauda Equina Syndrome. If it should develop into CES, you need to act fast so that you do not have permanent nerve damage. If curious, you can read about it here:

http://www.caudaequina.org/definition.html

I TAKE IT YOU ARE YOUNG. BE PATIENT. THE BRACE AND REST WILL HELP HEAL THE INFLAMATION AND SWELLING. A GOOD 70% OF THESE INJURIES HEAL WITHOT FURTHER INTERVENTION.

You said you have fractures, and I am assuming that was diagnosed with x-ray. This is probably a silly question, but did they do an MRI on you? The pain going down your leg is a symptom of something being compressed, and I think it is important that your doctor knows how extreme your pain is right now. Give him a call Monday. A round of steroids may help to reduce inflammation, which could relieve some of the pain, or there are other things the doctor could do for you. Be sure to alternate ice and heat while you are in this early stage. Oh, and don't go riding a horse for a few weeks, ha ha. (just kidding you) I'm sure that would hurt to go trotting along with a fractured back!