While the exact cause of acromioclavicular osteoarthritis is unclear, people who develop the disease tend to exhibit one or more of the traits below.

Joint trauma. Serious injury or surgery can cause damage to the AC joint and eventually lead to acromioclavicular osteoarthritis, although symptoms may not appear for months or even many years later. For example, a previous shoulder separation, in which the ligaments that hold the bones of the acromioclavicular joint together are sprained or torn, increases the likelihood of developing acromioclavicular osteoarthritis.

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Joint stress and chronic injury. People who spend a lot of time lifting objects overhead can experience “mini-traumas” in their shoulder joints and are more likely to develop acromioclavicular osteoarthritis. People who have spent years weightlifting or participating in high-impact sports, such as football and rugby, also can be particularly prone to acromioclavicular osteoarthritis.1

Congenital defect or illness. Poor bone alignment can increase the risk of shoulder separations, thereby increasing the likelihood of developing osteoarthritis of the shoulder. Other congenital conditions, metabolic disorders, and episodes of gout or septic arthritis can also increase risk.

Advanced age. The prevalence of symptomatic acromioclavicular osteoarthritis increases with age. In fact, almost everyone develops this type of arthritis by age 40 or 50, even if they do not have painful symptoms.2 This is because, over time, the shoulder joints experience wear and tear—cartilage thins and becomes less flexible. The degeneration of the joints that is characteristic of osteoarthritis is why the condition is also called “degenerative joint disease.”

Family history. Similar to height and hair color, the risk of developing painful osteoarthritis is influenced by genetics.3 The exact extent of genetic factors is not known.

The risks factors listed above predispose certain individuals to osteoarthritis, but they are not causative. Some people without any of the above risk factors may develop AC joint arthritis, and people with all of the above characteristics may never develop it.

A sudden onset of pain is more likely to be caused by trauma or another condition, not by osteoarthritis. Likewise, if the acromioclavicular joint feels hot or the skin around the joint turns red, then osteoarthritis is probably not the culprit. An infection (if it is only one side) or rheumatoid arthritis may be the cause.

References

  1. Docimo S., Kornitsky, D., Futterman B., Elkowitz DE, “Surgical Treatment for acromioclavicular joint osteoarthritis: patient selection, surgical options, complications and outcome” Curr Rev Musculoskelet Med (2008) 1:154-160. Accessed September 12, 2011, http://www.ncbi.nlm.nih.gov
  2. Pennington RG, Bottomley NJ, Neen D, Brownlow HC. Radiological features of osteoarthritis of the acromioclavicular joint and its association with clinical symptoms. J Orthop Surg (Hong Kong). 2008 Dec;16(3):300-2. PubMed PMID: 19126894.
  3. Arthritis Foundation. What is Osteoarthritis? Accessed March 31, 2012. http://www.arthritistoday.org
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