AC joint arthrosis is a common degenerative condition affecting the shoulder. It impacts the acromioclavicular (AC) joint, located at the top of the shoulder, connecting the collarbone (clavicle) to the acromion, a part of the shoulder blade. This condition involves the deterioration of the joint’s protective cartilage, leading to pain and limitations in shoulder movement.
Understanding AC Joint Arthrosis
The AC joint allows for a range of arm movements, including raising the arm overhead and moving it across the body. In a healthy AC joint, the ends of these bones are covered by smooth, flexible articular cartilage, which ensures frictionless motion.
Arthrosis refers to the degenerative wear and tear of this cartilage. Over time, the cartilage in the AC joint can thin, become rough, and eventually wear away. This loss of cartilage means the bones can begin to rub directly against each other, causing pain, inflammation, and stiffness. As the condition progresses, the body may attempt to repair the damage by forming abnormal bony growths, known as bone spurs or osteophytes, around the joint. These bone spurs can further restrict movement and potentially irritate surrounding tissues, contributing to discomfort.
Causes and Symptoms
AC joint arthrosis often develops from a combination of factors, with wear and tear being a primary cause. Repetitive overhead activities, such as those performed by weightlifters or construction workers, can place continuous stress on the joint, accelerating cartilage degeneration. Past shoulder injuries, including AC joint separations from falls or accidents, also increase the likelihood of developing arthrosis later in life. Aging is another significant factor, as joints naturally wear down over time, making this condition more common in middle-aged individuals and older adults.
Individuals with AC joint arthrosis experience pain and tenderness at the top of the shoulder. This pain worsens with specific movements, such as reaching the arm across the chest, lifting it overhead, or performing push-ups or bench presses. Sleeping on the affected side often increases discomfort. Accompanying symptoms can include a clicking, popping, or grinding sensation (crepitus) when the shoulder moves. There may also be swelling around the joint and a noticeable decrease in shoulder movement or stiffness.
Diagnosis and Management
Diagnosing AC joint arthrosis begins with a thorough physical examination. The healthcare provider assesses the shoulder for tenderness directly over the AC joint and observes how pain responds to specific movements, such as bringing the arm across the chest. Imaging studies are also an important part of the diagnostic process. X-rays can reveal signs of degeneration, such as narrowing of the joint space and the presence of bone spurs. In some cases, an injection of a local anesthetic into the joint may be used to confirm the diagnosis, as temporary pain relief after the injection indicates the AC joint as the source of discomfort.
Management of AC joint arthrosis starts with conservative approaches. Rest and modifying activities that aggravate the pain, particularly avoiding repetitive overhead motions, can help reduce symptoms. Over-the-counter pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs), are recommended to manage pain and inflammation. Physical therapy improves shoulder strength, flexibility, and range of motion, which can help alleviate symptoms and enhance overall function. If conservative measures are insufficient, corticosteroid injections directly into the AC joint can provide temporary pain relief and reduce inflammation.
For individuals whose symptoms do not improve with conservative treatments, surgical options may be considered. The most common surgical procedure for AC joint arthrosis is distal clavicle excision, also known as the Mumford procedure. This procedure involves removing a small portion (about 5-10mm) of the end of the collarbone where it meets the acromion, creating a space between the bones to prevent rubbing and reduce pain. The surgery can be performed using either an open technique or a minimally invasive arthroscopic (keyhole) approach, with the latter often preferred for faster recovery. After surgery, scar tissue forms in the created space, allowing for continued movement without bone-on-bone friction.