A rotator cuff injury usually is diagnosed by physical examination. Your doctor will rotate your arm at the shoulder and then will raise your arm. If this type of motion causes pain, the rotator cuff may be inflamed.
If you have noticeable weakness, you will need further testing to check for a rotator cuff tear. Your doctor may inject a numbing medicine into your shoulder to help distinguish actual weakness of the tendon from your muscle "giving way" because of pain.
If a tear is suspected, a magnetic resonance imaging (MRI) scan can confirm the diagnosis. An alternative diagnostic test is a shoulder arthrogram. An arthrogram is an X-ray of a joint following injection of dye into the joint. Because MRIs provide excellent pictures without putting a needle into a joint, arthrograms are done less frequently today.
Shoulder X-rays are not always needed, but may be helpful if you have had trauma to the shoulder or if your doctor cannot move your shoulder through its full range of motion. Another reason to do a shoulder X-ray is too look for calcium deposits in or around the shoulder. Calcium deposits form on a persistently inflamed tendon, causing a condition called calcific tendonitis.