Pretty yucky stuff, fatboy. But as you rightly said, it's pretty uncommon to see injuries like that at an MX event.
The only 2 bad ones I've personally had to deal with were both in desert racing where the speeds are generally much higher.
One guy very sadly died on the spot and the other "just" had his femur poking out through his pants with red sand stuck to the end of it.
In both cases I dealt with it at the time, but definitely rode even slower than normal for the rest of the day...............
Best wishes to those injured for a quick and full recovery.
Hoony and MX?: when you get a sniff of the guy in front of you next race day, I'm sure the last thing you'll be thinking of is this thread!