After the physical examination, the third step in diagnosing shoulder pain is obtaining appropriate diagnostic tests. Too often, this is viewed as the first step. Most people assume that an MRI is the best way to determine what is causing a shoulder to be painful. This assumption may lead to unnecessary surgeries. In an excellent article in the New York Times on the overuse of MRIs, renowned orthopaedic surgeon, Dr. James Andrews, was quoted, "If you want an excuse to operate on a pitcher's throwing shoulder, just get an MRI". He found in his research that close to 90% of professional baseball pitchers without shoulder pain had damage to their cartilage or rotator cuff. They continued to pitch in the big leagues despite having MRI evidence of shoulder pathology that could have resulted in surgery.
Usually, after the history and physical exam, I have narrowed the possible diagnoses to just a few. The radiologic tests are ordered to verify the most likely diagnosis or exclude some of the other possibilities.
X-Rays - The first test usually ordered is an X-Ray. Many patients don't want an X-Ray and wish to go immediately for an MRI. X-Rays, however, are useful for looking at the bones and joints which MRIs do not visualize as well. It is often the best exam for arthritis. It can easily visualize a bone spur that may be impinging on the rotator cuff. It can also exclude a fracture, bone lesion, or calcium deposit such as calcific tendinitis.
X-Ray image of calcific deposit in the rotator cuff tendon
Ultrasound - Another, more recent advancement for diagnosing shoulder pathology is the ultrasound. Many shoulder surgeons have ultrasound available in their office. It allows a quick evaluation of the rotator cuff and biceps tendons. Ultrasound is high frequency sound waves directed into your body. They are completely harmless. These sound waves pass through soft tissue structures such as muscle and skin but bounce off harder structures such as bone. The sound wave reflections come back as echoes. The computer analyzes the echoes and produces an image. Structures without any substance, such as a pocket of fluid, are completely black (no echo). Hard structures, such as bone, are white. Tendons with intermediate density are a grayish color. Tendon tears with surrounding fluid can often be seen. While the accuracy of the ultrasound is very dependent on the experience of the user, it can be a useful tool for diagnosis. Some studies have shown close to a 90% accuracy for diagnosing rotator cuff tears. It is especially helpful when there has been previous surgery on the shoulder. Post-surgical changes can make MRIs more difficult to read. Ultrasound is painless, non-invasive, not claustrophobic and cheaper than MRIs.
Ultrasound image of a rotator cuff tear (arrow).
Black area under the arrow is fluid filling the gap in the tear
MRI - The MRI has been available for evaluating shoulder pathology for almost 30 years. MRI stands for magnetic resonance imaging. A patient's body is placed inside a large magnet and the magnetic force causes a change in the position of the hydrogen atoms. A radiofrequency pulse is applied which can change the alignment of some of the atoms. When the pulse is stopped, the atoms return to their original alignment and produce energy. This energy is measured by a computer and an image is produced. Since most of the human body is made of water, and hydrogen is the primary component of water (H2O), the MRI is very good at looking at fluid or tissue that contains fluid such as fat or cartilage. The MRI is not as accurate for structures that do not have much water content such as the harder rim of bone. The images produced can be as thin as a few millimeters and when stacked together like a loaf of bread will allow a detailed evaluation of the inside of the shoulder.
However, MRIs are not perfect. The quality of the MRI image depends on the strength of the magnet. Open MRIs usually have a lower strength (lower magnetic field). This means the image quality will not be as good as with a stronger magnet. This is especially important for smaller structures that are deeper in the shoulder and not surrounded by much fluid. Tears of the labrum are difficult to see on an MRI. A high field magnet (3 Tesla) or the use of a contrast dye injected into the joint are helpful to evaluate it completely.
The MRI diagnosis alone should not be the reason to operate on a shoulder. Many older patients will have a torn rotator cuff and will be completely asymptomatic. A partial tear in the rotator cuff may be seen on an MRI when in fact it is just fluid from inflammation that would respond to medication. It is very important that the MRI is only used to confirm a suspected diagnosis, evaluate the severity of the diagnosis or exclude other possibilities. An MRI should not be obtained simply for a painful shoulder without having conducted a thorough history and physical examination.
MRI of a left shoulder demonstrating a complete tear
in the rotator cuff. The white gap is fluid in the tendon