First get the studies, X-Ray, CT, MRI... Just do it and remember you have to ask for it. Then its build it up or repair it. Either way you end up building it up but building it up without knowing the extent of damage can make it worse. Also remember that there are not that many exercises for building up a rotator cuff. They need to be prescribed by someone who knows the exact mechanism of injury or things will get worse again.
A rotator injury can be severe even without any major force or impact. My wife tore hers swinging a fly swatter... dam fly!
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No matter where you're at... There you are... Δf:=f(1/2)-f(-1/2)