[kyleb]

It's really tough to tell whether or not something is a rotator cuff injury without looking at it, and even then, it often requires an MRI. Simple things like poor posture or weak stabilization muscles (scapula, lower back, lats, core strength) can cause pain in the shoulder area. Even referral pain from the upper arm or extremities can be the source of the damage.

However, pain under the shoulder seam of the T-shirt could either be rotator cuff or labrum-related. You want the former to be the case - definitely NOT the latter.