Ultimate Fighting and Knee Injuries

In recent years ultimate fighting has gained much popularity in North America. Ultimate fighting brings together representatives of various martial arts, for instance boxing, wrestling, Jiu-Jitsu, and many others, who then compete for money, fame, and acknowledgment that their martial art is the most effective.
Somehow ultimate fighting has become the sport for many couch potatoes like me. First it was boxing, then wrestling, and now ultimate fighting. Having a round cage vs. a square ring boosts the excitement of the audience - and maybe even our animal instincts of survival of the fittest.
I wonder whether with every new "trend" in this category of sport are there also more potential risk factors for mental and physical health. Or how long does a fighter usually last in ultimate, boxing, and wrestling? Several months? Does anybody have any insights on knee injuries in this new full contact sport? Remembering the many Taekwondo friends I have ACL injuries are a given. But they do not even practice full contact.
For more general info on ultimate fighting visit http://www.ufc.com/index.cfm?fanews.UfcInTheNewsh