Acromioclavicular osteoarthritis (AO) is a common type of arthritis that affects the shoulder. It happens when the cartilage wears down between the collarbone and the acromion, the bony tip of the shoulder blade.

Although AO is not as common as osteoarthritis of the knee or hip, it does affect a significant number of older adults. Experts estimate that 1 in 3 people over the age of 60 years have some degree of AO.

As with other types of osteoarthritis, AO results from wear and tear on the cartilage that covers the bones in the shoulder joint.

Usually, this cartilage allows the bones to glide smoothly over each other. When the cartilage becomes thin or damaged, this smooth gliding is no longer possible, and a person may experience stiffness, pain, or swelling. These symptoms may make it difficult to move the arm.

There is no cure for AO, but treatment via medications, physical therapy, exercise, and surgery can improve the symptoms.

This article explores AO in more detail, including its symptoms, diagnosis, and treatment.

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AO is a type of osteoarthritis that affects the shoulder. It specifically affects the acromioclavicular joint, which is situated where the collarbone meets the bony tip of the shoulder blade, known as the acromion.

Articular cartilage covers the ends of the bones. This type of cartilage is a smooth tissue that allows the bones to move easily over each other. AO develops when this cartilage breaks down, and the bones begin to rub against one another in an irregular motion.

As the bones scrape against each other, bone spurs can form as the bone attempts to heal itself. The irregular motion, bone spurs, and inflammation can cause significant pain and loss of motion.

AO is not as common as other types of osteoarthritis, but it is more common than the other form of shoulder arthritis, which affects the glenohumeral shoulder joint.

The most common symptom of shoulder arthritis is pain. In AO, the pain tends to be at the top of the shoulder and may radiate up the side of the neck.

When an individual is physically active, the pain may worsen. As the condition progresses, a person may experience pain while at rest, and it may begin to interfere with their sleep.

Other common symptoms include limited motion and stiffness. These symptoms may make it challenging to perform everyday movements that require the arm, such as taking a drink or reaching for an item on a high shelf.

People may also notice grinding and clicking noises as they move the shoulder, which doctors call crepitus.

AO can be primary or secondary. Primary AO has no specific cause, but it occurs more often in people over the age of 50 years. It is also more common among females than males.

Secondary AO occurs when the condition develops entirely or partially as a result of an underlying problem. Examples of these problems include:

  • injury
  • history of shoulder dislocation
  • rotator cuff tears
  • infection

In addition, individuals who work in physically active jobs, including heavy construction, and those who partake in certain sports may have an increased risk of developing shoulder osteoarthritis.

As part of the diagnostic process for AO, a doctor will ask a person about their symptoms and medical history. They will then carry out a physical exam.

During the exam, the doctor will assess and check for various factors, including:

  • muscle strength
  • mobility
  • tenderness or pain
  • swelling or enlargement

They may also look for and ask about previous injuries or listen for noises as the joint moves.

Depending on their findings, the doctor may then order X-rays. Narrowing of the joint space, changes in the shape of the bones, and the formation of bone spurs can show on the images, indicating AO.

In some cases, a doctor may use ultrasound imaging to help them distinguish between AO and other conditions that can look similar on scans, such as problems with the rotator cuff.

Doctors consider AO a chronic degenerative condition, meaning that it worsens over time. However, treating and managing the condition helps preserve mobility, ease pain, and improve quality of life.

A doctor may recommend the following treatments:

  • Medications: Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most effective oral medications for OA. These include ibuprofen (Advil), naproxen (Aleve), and diclofenac (Voltaren). They work by blocking enzymes that trigger pain and swelling. Doctors may also recommend acetaminophen or corticosteroids.
  • Hyaluronic acid: Hyaluronic acid injections deliver lubrication directly into the joint. Currently, the Food and Drug Administration (FDA) has only approved this treatment for knee arthritis, but doctors can prescribe it off-label for shoulder arthritis, too.
  • Physical therapy: Physical therapy, strength training, and flexibility exercises may help reduce pain and maintain mobility in the joint.
  • Self-care: Therapies such as massage, acupuncture, and heat or cold therapy may help alleviate pain and reduce inflammation.
  • Surgery: If other treatments have not worked, a doctor may recommend joint surgery. One option is to resect the AC joint, removing the ends of each bone. Another option is AC joint fusion, in which a surgeon fuses the ends of the bones to fix them in place.

Without treatment, AO can get worse and cause significant pain or disability. For this reason, it is important for anyone experiencing symptoms to speak with a doctor as early as possible to get a diagnosis.

A diagnosis allows someone to access treatment and support to improve the condition and minimize the effect it has on their life. This may require an ongoing commitment to taking medications regularly, getting injections, or participating in physical therapy to manage the symptoms.

Acromioclavicular osteoarthritis is a common type of arthritis that affects the shoulder. It develops when the cartilage between the acromion and the collarbone wears down.

Injuries, previous dislocations, or rotator cuff tears can increase the risk of AO. However, the condition often occurs with no specific cause, especially in older adults.

AO has no cure, but treatments are available to manage the symptoms and improve quality of life. These include medication, physical therapy, and surgery. Anyone experiencing shoulder pain should speak with a doctor to get a diagnosis and discuss their options.