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8054 Yonge St. Thornhill. Just south of the intersection of Yonge and HWY 7/407

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Anatomy of the Acromioclavicular Joint

The acromioclavicular joint, commonly referred to as the AC joint, is formed by the union of the lateral end of the clavicle (the end of the collarbone closest to the shoulder) and the acromion process of the scapula (otherwise known as the shoulder blade).

It is one of four joints that form the complex structure of the shoulder. This joint is lined by a synovial capsule, which provides protection and some stability; the joint is further stabilized by two ligaments: the superior and inferior capsular ligaments.

The AC joint is also supported by the conoid ligament, the trapezoid ligament, and the acromioclavicular ligament. The AC joint serves as an attachment point for four muscles, the pectoralis major, the sternocleidomastoid, the deltoid, and the trapezius.

Studies have demonstrated that facet joint injury is responsible for the chronic neck pain of whiplash in 60% of those with persisting pain, and for chronic low back pain in 5 to 40% (depending on the study) of those with post-injury low back pain.

How does osteoarthritis develop in the acromioclavicular joint?

Osteoarthritis in the AC joint typically develops due to day-to-day wear and tear; those who regularly perform repetitive or strenuous upper limb movements, such as manual labor or weightlifting, are more susceptible to AC joint degenerative changes as a result.

As the protective membrane surrounding the joint begins to wear down, movement in the joint causes friction, which then results in pain, inflammation, and further degenerative changes to the joint.

Trauma to the AC joint is also associated with a higher risk of developing osteoarthritis.

What are the symptoms?

Some symptoms of AC joint arthritis include:

  • Tenderness to touch at the top of the shoulder where the AC joint is located

  • Discomfort in the shoulder when sleeping on the side

  • Discomfort with certain shoulder/arm movements

  • Decreased range of motion in the shoulder joint

  • Localized swelling or visible changes to the joint area

  • Popping or crunching noises associated with shoulder movement

How common is osteoarthritis of the acromioclavicular joint?

The AC joint helps to facilitate the unique range of motion of the shoulder joint; however, due to its complex structure and the heavy and repetitive demand often placed on it, the AC joint is very susceptible to injury and degenerative change.

Let’s look at what some studies have shown

According to an article published in 2013 in the Emergency Medicine International journal, “acromioclavicular (AC) joint dislocation is one of the most common shoulder problems accounting for 9% of all shoulder injuries, in particular during sports activities which involve contact” (Chillemiet al. 2013).

A more recent article, titled Acromioclavicular joint injury, which was published on September 24, 2022, noted that it was estimated that “acromioclavicular joint injuries account for more than forty percent of all shoulder injuries” (Kiel et al. 2022).

An article in Healthline noted that “as many as 67 percent of people will experience shoulder pain in their life and up to 26 percent experience it at any given time” (

What are the risk factors associated with osteoarthritis of the acromioclavicular joint?

Common risk factors for AC joint osteoarthritis include:

  • Age

  • Heavy/repetitive arm and shoulder use, such as that seen in construction workers and weight lifters

  • Athletes participating in contact sports

  • Trauma to the shoulder joint —The most common AC joint injury is caused by a fall where one catches oneself with arms outstretched; other common causes of AC joint trauma include MVAs or falls off a bicycle

  • Inflammatory or autoimmune conditions, such as rheumatoid arthritis or psoriatic arthritis

  • Joint infection

How is the condition diagnosed?

Diagnosis of AC joint osteoarthritis requires a doctor’s appointment. During this appointment, a detailed medical history will be taken, including information such as the type of symptoms experienced, when and how the symptoms were first presented, what movements or positions provoke pain, and any other relevant medical conditions, injuries, and medications.

A physical examination will assess for tenderness in the AC joint or pain with certain movements. Your physician may request that diagnostic imaging, such as an X-ray, be performed to determine if the AC joint is narrowed or if bone spurs are present.

Another diagnostic tool that may be utilized is the injection of a numbing agent into the affected area to determine if the pain temporarily resolves.

How is the condition treated?

After a diagnosis of acromioclavicular joint osteoarthritis, the approach that is best for you will be dependent on several factors, including your age, the severity of your pain and physical limitation, and your overall state of health.

While arthritic changes are irreversible, there are numerous options available to manage pain and slow or even prevent the progression of degenerative changes.

Some of the options to manage pain include:

  • Acetaminophen to reduce pain

  • NSAIDs (non-steroidal anti-inflammatory drugs) to reduce pain and inflammation

  • Other oral medications specific to treating arthritis and inflammation

  • Topical creams, such as Lidocaine, Menthol, Traumeel, and Tiger Balm

  • Physiotherapy

  • Aquatics or pool therapy program

  • Hot/cold therapy, using heat and ice to reduce pain and swelling

  • Acupuncture and Acupressure

  • Massage therapy

  • Occupational therapy (including improving the ergonomics of your workstation, if applicable)

  • Exercise to improve body mechanics or exercise modification if your workout routine is a source of aggravation to the AC joint

  • Dietary changes to reduce inflammation

  • Smoking cessation

What do we do at WMC?

At the Wilderman Medical Clinic, we offer a variety of interventional and non-interventional treatment options, including:

Interventional pain management for osteoarthritis of the AC joint:

  • cortisone injections

  • Dextrose (prolotherapy) injections for AC joint osteoarthritis

  • PRP (plasma-rich protein) injections for AC joint osteoarthritis

  • nStride injections for AC joint osteoarthritis

Non-interventional pain management for osteoarthritis of the AC joint:

  • Psychotherapy

  • Kinesiology education sessions

When is surgery required?

If conservative options, such as those listed above, fail to provide adequate pain relief, surgery may be recommended as an alternative.

For AC joint osteoarthritis, a procedure called a distal clavicular excision (or DCE) is performed; this procedure involves removing a small portion of bone from the end of the clavicle, or collarbone, to increase the space in the joint where the clavicle and scapula meet.

This procedure has been performed since the mid-1900s, and can now be performed arthroscopically, making it less invasive and, therefore, speeding the recovery time.

Works Cited

Chillemi C, Franceschini V, Dei Giudici L, Alibardi A, SalateSantone F, Ramos Alday LJ, Osimani M. Epidemiology of isolated acromioclavicular joint dislocation. Emerg Med Int. 2013;2013:171609. doi: 10.1155/2013/171609. Epub 2013 Jan 28. PMID: 23431452; PMCID: PMC3568861.

Kiel J, Taqi M, Kaiser K. Acromioclavicular Joint Injury. [Updated 2022 Sep 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from:

Role of the AC joint. Healthline. Retrieved from


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