@SpeedDemon
Read the article earlier.
IMO velo is the common denominator.
I sat in a grand rounds lecture that was given by a team of UAB Sports Orthopedist about two months ago. James Andrews along with several other sports med researchers were there, and their conclusions were that Velocity equals elbow issues. Repetition equals shoulder issues. Spin rates and breaking balls probably also contribute to elbow injuries, but that correlation is less predictable (mainly because you can't definitively verify when kids are starting to use breaking pitches and so far Spin rate numbers are routinely being recorded like velocity).
Their data showed that there is without a doubt a significant direct correlation with fastball velocity and UCL injury and those associations were more significant as you move to younger age ranges. In other words, the sooner a kid is hitting 90 mph, the greater likelihood of UCL damage. A couple of things that these researchers pointed out was that velocity over 80 MPH is where UCL strain starts to appears. So, you can imagine what a young person at age 16 throwing 90 mph is doing, and you compound that with the fact that kids are constantly straining the arm with a goal of getting more velocity for 6 months or more out of the year, and you wonder why so many D1 schools are seeing so many arm injuries. Another thing that Andrews pointed out in the conference was that in the early 2000's they were doing TJ surgery on mostly MLB guys, with only single digit high school pitchers having TJ surgery. He said now the overwhelming number of surgeries for UCL injuries that his group are performing are on high school pitchers. He said, "It's all about the drive for more velocity."
Elbow (UCL) damage happens with the constant drive for higher velocity and younger and younger ages. If you have a kid that is in the 10th grade throwing 90 plus then there is a high probability that some UCL damage has occurred. Shoulder injuries such as SLAP tears of the labrum and rotator cuff happen with overuse and excess repetition. My son had an MRI of his arm last fall. It revealed a SLAP tear, but the UCL was in perfect condition. His velocity was just reaching 90 MPH in May of last year. (let it be known that he pitched 97 innings for his high school team that spring. Much of that was due to the fact that they went all the way to the state championship series). He had shoulder surgery in the fall when he started noticing pain when long tossing to get ready for the WWBA Jupiter tournament.