The rotator cuff is a group of muscles in the shoulder that work together and is composed of the supraspinatus, infraspinatus, teres minor and subscapularis. The shoulder is a ball and socket joint and depends on the rotator cuff to stabilize the ball of the upper arm bone, the humerus, in the socket, or glenoid cavity. The muscles also work to abduct the arm and to perform internal and external rotation. Disease of the rotator cuff is the leading cause of shoulder pain in adults, according to O. Opsha, A. Malik, R. Baltazar, et al. in MRI of the Rotator Cuff and Internal Derangement. Injury can be caused by a sudden trauma to the shoulder, by repetitive use in sports, such as pitching in baseball or in job-related activities such as assembly line work. Physicians identify a rotator cuff tear by using various diagnostic imaging techniques.
Featuers of the Diagnostic Techniques
The "gold standard" for identifying a rotator cuff tear is the arthrogram. Under a local anesthetic, an injection of special dye is placed in the shoulder joint and x-rays are taken to determine if the joint capsule and supporting musculature are intact. The MRI, or magnetic resonance imaging, test is a more recently developed technique that uses radio frequency waves in a magnetic field to alter the alignment of nuclei in the cells. Different body tissues resonate at different frequencies. A computer processes the information and creates a digital picture of the joint.
Arthrogram Considerations
The arthrogram uses x-rays, which are a form of ionizing radiation. Too much radiation may be harmful to the body's tissues. While there is very little risk in damage from one set of x-rays, the effects are cumulative over a lifetime and should be discussed by the patient and physician prior to testing. Another potential risk is developing an allergic reaction to the dye. Some patients are unable to undergo arthrograms for this reason and different testing procedures must be used.
MRI Considerations
Instead of ionizing radiation, the MRI uses a powerful magnetic field. This makes it unsuitable for patients with implants that contain iron such as pacemakers, insulin pumps, or older types of prosthetic joints. In a typical MRI, the patient is placed inside the machine in its central tunnel, which is often quite narrow. Patients with claustrophobia or who cannot remain still for the duration of the test are inappropriate candidates. Some of the newer models, called open MRIs, resolve the claustrophobia issue but may not be able to produce images of the same quality as the closed version.
Availability
Because x-ray technology is readily available in hospitals and even many surgeons' offices, the arthrogram is relatively easy to schedule and perform. Not all hospitals have MRI capability and for those that do, scheduling is often more challenging, as preference is given to stroke, brain injury, and cancer patients. Many patients and physicians do not wish to wait days or even weeks to get a conclusive diagnosis.
Insurance Involvement
The test that is ultimately chosen for identification of a rotator cuff tear may not be the first choice of either the patient or physician. Some insurance companies mandate which test to perform first. Only if the first test is inconclusive will they authorize a second type of examination. The arthrogram is less expensive overall than the MRI.
Expert Insight
The American College of Radiology provides guidance about the type of test that is most appropriate for shoulder injuries. For a shoulder with acute trauma and normal x-rays showing intact bone structure, the recommendation is for an MRI. If a patient is not a candidate for this test for any reason, the ACR advises performing an arthrogram. An MRI is also the first recommendation for a shoulder without acute trauma but with chronic pain symptoms.
References
- "European Journal of Radiology"; MRI of the Rotator Cuff and Internal Derangement; O. Opsha, A. Malik, R. Baltazar et al.; 2008
- Fundamentals of Musculoskeletal Imaging, 2nd Edition; L.N. McKinnis; 2005.
- ACR Appropriateness Criteria
