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.

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To make an accurate diagnosis, a number of investigative tools are employed:

Patient interview. 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.

Physical exam. 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 with the unaffected shoulder (i.e., left vs. right AC joint). In addition, the doctor will test the shoulder’s passive (assisted) and active range of motion.

One common assessment tool is called the cross-body adduction test; if a patient feels pain in the top part of the shoulder when an extended arm is passively moved across the body (towards the other shoulder) then the acromioclavicular joint is the likely culprit.

Direct palpation of the AC joint can also generate immediate pain. A doctor may also look for problems in other joints, as these may indicate an inflammatory condition such as rheumatoid arthritis or pseudogout.

Testing. The patient interview and physical exam provides the doctor with enough information to rule out certain causes of the patient’s pain. 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 effective way to test for arthritis is by injecting a local anesthetic, such as lidocaine, directly into the painful joint.4 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.5

    Pain can be substantial if minor cartilage damage or bone spurs are in a sensitive spot. Therefore, an x-ray does not in and of itself provide a diagnosis; rather, it is one tool to be used along with the patient interview and physical exam.

  • MRI. Magnetic Resonance Imaging (MRI) provides images of the soft tissue (e.g., 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. Lab tests cannot identify the presence of AC joint osteoarthritis, but they can be used to rule out other problems, such as infection or gout, which can also cause shoulder pain. Lab tests may require a blood draw or an aspiration of the shoulder joint.
  • References

    1. Docimo et al, “Surgical Treatment for acromioclavicular joint osteoarthritis” Curr Rev Musculoskelet Med (2008) 1:154-160. PMID: 19468890 [PubMed]
    2. Pennington et al. Radiological features of osteoarthritis of the acromioclavicular joint….” J Orthop Surg (Hong Kong). 2008 Dec;16(3):300-2. PubMed PMID: 19126894.
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