Pain and tenderness at the top of the shoulder and difficulty reaching the arm across the body—to swing a golf club or put on a seat belt, for example—may be a sign of acromioclavicular arthritis.

The acromioclavicular (ah-kro-mee-o-klah-vik-u-ler) joint, sometimes called the AC joint, is located at the top of the shoulder where the clavicle (collarbone) and highest part of the scapula (shoulder blade) meet. Most people are not familiar with this joint in the body, but arthritis in the AC joint is actually more common than arthritis in the glenohumeral joint, the shoulder’s large ball-and-socket joint.

Typically, arthritis is indicated by a gradual onset of pain, tenderness and limited range of motion. Acromioclavicular arthritis comes in many forms, most commonly osteoarthritis, followed by forms of inflammatory arthritis, such as rheumatoid arthritis.

Osteoarthritis is a degenerative joint disease that involves two primary processes:

  • The cartilage in the joints breaks down.
  • Abnormal bony growths, called osteophytes or bone spurs, develop in the joint.

While factors such as genetics also play a part, acromioclavicular cartilage degeneration is often preceded by an injury—sometimes years earlier—or by chronic mini-traumas from overuse. The degeneration eventually leads to abnormal joint function, pain and inflexibility.

The osteoarthritic process is gradual, with symptoms that may come and go and eventually worsen over time. The primary symptom of acromioclavicular osteoarthritis is pain in one or both shoulders, such as in the examples below:

  • Localized tenderness and pain at the top, front of the shoulder that comes and goes, possibly with a chronic low level of pain punctuated by intermittent flare-ups of more intense pain
  • Pain with certain activities, such as reaching the arm across the body to make a backhanded tennis shot, reaching behind the back to zip a dress, or lifting an item from an overhead cabinet.

Moderate-to-severe AC joint osteoarthritis can be painful, affecting even everyday habits like putting on a seat belt. Moreover, the bone spurs caused by this type of osteoarthritis can pinch and irritate the shoulder’s tendons and rotator cuff muscles, called shoulder impingement syndrome, resulting in even more pain.

  • Understand why the complex shoulder joint is prone to injury in Shoulder Anatomy

While there are many similarities in the symptoms and treatments of acromioclavicular pain from various types of arthritis, this article focuses on acromioclavicular (AC joint) osteoarthritis.

This article provides an in-depth review of the symptoms, causes and risk factors, diagnostic process, non-surgical and surgical treatments for acromioclavicular osteoarthritis.

Osteoarthritis of the AC joint is less common than osteoarthritis of weight-bearing joints such as knees and hips. For those who do have it, however, AC joint arthritis can be painful. Chronic discomfort or minor pain in the shoulder should not be ignored.

Understanding the symptoms and causes of acromioclavicular osteoarthritis, getting an accurate diagnosis and following an appropriate treatment program can encourage healthy joint function and may minimize or halt the progression of symptoms.

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