My GP thought I might have a torn rotator cuff because I had sharp pain and severely limited range of movement. He sent me to an orthopedist, who diagnosed it as frozen shoulder, or adhesive capsulitis. He spotted it with an X-ray (no MRI needed) and relieved about 75% of the stiffness and pain with a cortisone shot. Eight or nine rounds of physical therapy loosened it up further to the point where I had about 85% of use ... now, a couple years later, it's pretty much back to normal. Happily, no surgery required.

Here's a link to a page about the condition: Frozen Shoulder (Adhesive Capsulitis) Symptoms, Causes, Treatment – MedicineNet.com