Shoulder anatomy is complex and susceptible to a variety of problems. In fact, sometimes two or more painful conditions occur together. For example, acromioclavicular osteoarthritis can be seen alongside shoulder impingement syndrome or glenohumeral osteoarthritis.
No single test can definitively diagnose acromioclavicular osteoarthritis, so physicians use a comprehensive approach to rule out other potential sources of pain, including rotator cuff problems or cervical degenerative disc disease, which can cause referred pain.
Most individuals over age 50 will have signs of osteoarthritis in their major joints that can be seen on an x-ray, even though many have no pain or other symptoms. Therefore, an x-ray, MRI, or other diagnostic study should not be used alone to provide a diagnosis. Rather, diagnostic imaging is best used to verify a clinical diagnosis.
To make an accurate diagnosis, a number of investigative tools are employed:
A doctor will ask about the patient’s work, lifestyle, activities, and previous shoulder injuries. The doctor will also ask about family history and the onset of shoulder symptoms, the pattern of pain, limitations to range of motion, as well as what makes the symptoms better or worse. The patient’s answers to these questions are important for diagnosis and treatment.
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The patient’s painful joint will be examined for signs of previous injury, tenderness and pain points, and muscle weakness. The doctor will observe differences between the affected shoulder and the unaffected shoulder.
One common assessment tool is called the cross-body adduction test. During this test, the doctor supports and moves the patient’s extended arm across the body (towards the other shoulder). If the patient feels pain in the top part of the shoulder then AC joint arthritis is the likely cause.
A clinician may press the skin over the AC joint to see if it generates pain. He or she may also look for problems in other joints, as these may indicate an inflammatory condition such as rheumatoid arthritis or pseudogout.
Medical Testing and Imaging
Follow-up tests may be included as part of the diagnostic process, both to gain further information about the extent of the acromioclavicular arthritis and/or to rule out other possible problems.
- Injection of a local anesthetic. One way to test for arthritis is by injecting a local anesthetic, such as lidocaine, directly into the painful joint.1 If the patient’s pain is relieved temporarily, then a diagnosis of arthritis is confirmed. If the pain persists, another shoulder problem, such as a rotator cuff injury, is most likely the source of the pain.
X-rays. If an x-ray shows the acromioclavicular joint’s bones are closer together than normal, it indicates possible loss of cartilage (osteoarthritis). The x-ray may also show changes in the bone, such as the growth of bone spurs.
It is important to note that some people may have x-rays that show significant signs of acromioclavicular osteoarthritis and experience no pain, while others may have x-rays that show few signs of acromioclavicular osteoarthritis and have significant pain. In fact, one study comparing the x-rays of AC joints of people with and without osteoarthritis symptoms found no significant difference between the two groups.
MRI. Magnetic Resonance Imaging (MRI) provides images of the soft tissue (such as ligaments, tendons, and muscle) as well as bone. This more detailed image of the shoulder joints can be helpful if x-rays are inconclusive or if the doctor suspects symptoms are due to something other than osteoarthritis, such as damage to the rotator cuff. When an acromioclavicular joint is inflamed, the MRI usually shows the presence of excess fluids and abnormal swelling at and around the joint.
An MRI is more expensive than an x-ray, as well as more time-consuming, requiring the patient to remain perfectly still for about 30 minutes.
- Lab tests. While lab tests cannot identify the presence of AC joint osteoarthritis, they can be used to rule out other problems that can cause shoulder pain, such as rheumatoid arthritis. Lab tests may require a blood draw or an aspiration of the shoulder joint.
Medical imaging and testing alone does not provide a diagnosis; rather, they are tools to be used along with the patient interview and physical exam.