Hey Allen,
Sorry to hear about the accident.. Stuck Throttle Condition is serious on any bike, but a 500 twosmoke can be deadly...
There may be several scenario's that lead to this. If the little clip on the top of the carb came loose the sheath on the cable can get hung up on the slack adjuster on the top of the carb.
A frayed throttle cable may hang in the sheath, a cable may have picked up some sand or dirt, the slide may have picked up sand or dirt, and the throttle housing itself may have been the culprit.
When you are back on your feet all you can do is take your time and watch each part of the system for any suspicious characters.
Remove your carb and look for signs of scrathing, peeling of the chrome off the aluminum slide, and or dirt / sand on the slide or in the carb body.
If the throttle hosing, throttle tube, cable and carb check out. You may have had and air leak and leaned out the engine to a point of auto ignition. It's not too far fetched to get the piston, plug or piece of carbon to the point of igniting off the fuel air mixture when the conditions are right.
I'll put a good word in for you to have a speedy and complete recovery !
Tuck\o/