J Mejia diagnosed with a "Posterior Cuff Strain"

1. What exactly is a posterior cuff strain?
1. The rotator cuff is made up of four muscles, and the two muscles that are referred to the "posterior cuff" are the teres minor and infraspinatus. Specifically, they are the two main muscles that allow the arm to externally rotate (allow the pitcher to get into a "90/90 position", also referred to as the cocked position).
2. How does someone strain their posterior cuff?
1. That's where it gets complicated. The posterior cuff strain, or rotator cuff tendonitis is a result of 'something', but it's not 100% clear what that 'something' is.
1. Is the something the result of putting a 20-year old who has never pitched in the bullpen and having him warm up multiple times a week?
2. Is it the result of conditioning the body for the above bullpen work and the body wasn't able to adjust to throwing 40+ pitches when he went down to the minors?
3. Is there something in his delivery that is causing the tendonitis, or was it the above work-load changes that caused the strain?
2. The main role of the external rotators in pitching is to decelerate the arm while following through.
1. There is a tremendous amount of stress during that part of the pitching motion
3. What is the prognosis?
1. First the Mets will make sure if he pain-free before having him resume throwing of any type (playing catch). No one can guess when this will occur (can be two days to two months, but I'll guess short-term).
2. He will also undergo a formal rehab program to strengthen his rotator cuff, specially the external rotators.
3. Long-term he should be fine and this may turn into a case where the Mets are just being overly cautious with their young star, and this is the correct thing to do.