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Really, chief? It has very little to do with a pitcher's mechanics, as others have pointed out. The simple act of pitching puts more stress on the elbow.
I'd argue the major reason for the increase in the number of TJ surgeries is twofold. First and foremost, I think the early specialization of kids in a sport is wearing out their arms faster. Kids are playing baseball and pitching year-round now from the time they're like 10. It's ridiculous. Until the last 10 years or so, kids played the Big 3 sports as the season dictated. They took a break from stressing their arms and played other sports, allowing the body to heal over the course of several months. But now they're being told you have to "focus" on one sport to be elite at it and parents trying to live vicariously through their kids' athletic achievements are pushing them to play the sport year-round. Throw in a coach who doesn't know what he's doing or rides a kid too hard, and you get what we're seeing with the increase in TJ surgeries.
I'd say the second reason for the increase in TJ surgeries is better medical awareness and diagnosis. In the old days if a pitcher suddenly lost velocity, he'd just "lost it" as far as baseball and medicine were concerned. You couldn't get an MRI and see that he'd torn up his elbow. And even when you could get an MRI, the procedure itself was highly experimental and a monumental risk. Now it's been done so much that the vast majority of guys are coming back better than they were before the TJ surgery. Look at ACL tears as an example. In 1992, Sleepy tearing an ACL was a career ender. Now we see guys tearing ACLs and coming back in 8 months better than before because of how routine the procedure is. Same thing is happening with TJ surgery.