that little bump on top of the shoulder joint (if i read you right) is the acromium, small bone that extends from the clavicle to form sort of the top of the 'socket' (its not really a socket). thats where 'separations' occur-the union of the acromium and the clavicle. if the pain is closer down towards the tip of the shoulder (the top of the humorus)...it could be a lot of things.
I partially tore my rotator cuff and completely torn my labrum in april playing ice hockey. cortisone injection and 6 weeks of pt help me avoid surgery. but the tear in the labrum never heals (its cartiladge with very little blood flow), but the PT helps to strengthen the muscles around the joint to keep everything in line.
the funniest thing about the whole injury was..it wasn't the first time! one ortho took one look at my naked shoulders and pointed at the acromium and said you've separated your shoulders before, right? duh, I dunno...XRAYS and MRIs later...yup, arthritis forming in my clavical-acromium region. oh and by the way, you've got a torn rotator cuff, and and SLAP tear....sent me to a surgeon.
the surgeon took about a 20 second look at my MRI..."well the labral tear has been there for years, the rotator cuff looks new." huh? what happend was my shoulder subluxed (partial dislocation...which torn the rotator cuff) because the labrum wasn't there to hold it in place, when it subluxed a flap from the tear went down inside the joint not allowing it to pop back into place. (it popped back in 2 days later when I rolled over in bed....man did that feel good). then he smiled and said, "you finished the game, didn't you?" ah....yup, it was the playoffs
"hockey players!"
said since the tear in the labrum had been there for years and I'd been getting along normally all that time...no need to repair it surgically. just gotta get the shoulder strengthened back to where it was.
long story short...GO SEE A DOCTOR!....you never really know what it is until the poke around.
I took about a month off from shooting, but when I started back up again in June, I found absolutely no pain/stiffness etc. seems that most of my shoulder strength was in that lateral pulling direction anyway...gee, I wonder why?