semsox said:
I sort of wondered about this too, but I think it's illustrative to try it out yourself. Hold up your arm, and put your index and middle finger up as if you were holding a fastball. Now spread those fingers as far apart as possible (the splitter grip), and think about where you are feeling the difference. Certainly near your fingers, but there's definitely additional strain all the way through the forearm in this configuration.
Well sure, but that additional strain may be coming because you are stretching the fingers, which causes the forearm muscle to twist further when the hand is pronated, which increases pressure on nerves leading through one's shoulder. In other words, the additional strain may not be a muscular strain, and it may not add to strain put on the UCL. Just because something is hard to do, doesn't mean there's an increased risk of injury.
That being said, the effort required to maintain such a grip, could interfere with a smooth pitching motion, which would definitely increase the risk of injury. So I could see it going both ways.
I don't really know the literature on this topic, as I'm not an orthopedist (DRS? I've got 10 bucks here if you can address what is known about this). However, from the little that I've read (here's one citation, there are others that seem to echo the same thing in college/major league pitchers
http://www.researchgate.net/publication/231215830_Prevention_of_elbow_injuries_in_youth_baseball_pitchers), it seems that overhand pitching, overuse, fatigue, and breaking balls are potential risk factors for a UCL injury. However, splitters are not.
Then again, the splitter is so rare, I don't know if it was even studied in any epidemiological paper.