AC Joint Osteoarthritis

AC joint arthritis occurs when the cartilage that cushions the ends of the clavicle and acromion wears down over time. As the cartilage deteriorates, the bones begin to rub against each other, leading to pain, inflammation, and the formation of bone spurs. Several factors contribute to the development of AC joint arthritis, including:

1. Age-Related Wear and Tear – The AC joint is frequently used in daily activities, making it susceptible to degeneration with age. It is one of the most common sites for osteoarthritis in the shoulder, particularly in individuals over 40.
2. Repetitive Shoulder Use – Athletes, weightlifters, and manual laborers who frequently engage in overhead or cross-body motions place excessive stress on the AC joint, accelerating cartilage breakdown.
3. Previous Shoulder Injuries – Trauma, such as an AC joint separation or fractures involving the clavicle, can increase the risk of arthritis by altering joint mechanics and leading to premature cartilage wear.
4. Genetics and Joint Structure – Some individuals may have a genetic predisposition to developing arthritis or variations in joint anatomy that increase stress on the AC joint.
5. Inflammatory Conditions – Rheumatoid arthritis, gout, and other autoimmune conditions can cause chronic inflammation and joint damage, affecting the AC joint.

AC joint arthritis often develops gradually, with symptoms ranging from mild discomfort to significant pain and functional limitations. Common symptoms include:

• Pain at the Top of the Shoulder – Discomfort is typically localized at the AC joint and may extend to the side of the neck or upper arm.
• Pain with Overhead and Cross-Body Movements – Activities such as reaching above the head, throwing, lifting, or moving the arm across the chest can aggravate pain.
• Swelling and Tenderness – The AC joint may become swollen and tender to touch, particularly after physical activity.
• Clicking or Grinding Sensation – As the cartilage wears down, patients may feel a clicking or grinding (crepitus) sensation when moving the shoulder.
• Decreased Shoulder Function – Stiffness and discomfort can make it difficult to perform daily activities, including dressing, lifting objects, and sleeping on the affected side.

Symptoms often worsen over time, with flare-ups occurring after periods of increased activity or strain on the shoulder.

A thorough evaluation is essential for diagnosing AC joint arthritis. The diagnostic process typically involves:

Medical History and Physical Examination

• Dr. Boden will review the patient’s symptoms, activity level, and history of shoulder injuries.
• A physical exam will assess pain levels, tenderness at the AC joint, and range of motion.
• The cross-body adduction test, where the patient moves their arm across the chest, is commonly used to reproduce AC joint pain.

Imaging Studies

• X-rays – These are the primary imaging tool used to assess joint degeneration, bone spurs, and joint space narrowing.
• MRI – If additional shoulder conditions, such as rotator cuff injuries, are suspected, an MRI may provide more detailed images of soft tissues and cartilage damage.
• Ultrasound – This imaging method can assess inflammation and detect fluid buildup around the AC joint.

Diagnostic Injections

• To confirm that the AC joint is the source of pain, Dr. Boden may perform an injection of a local anesthetic and corticosteroid into the joint. Dr. Boden does these injections using an ultrasound to ensure proper placement of the medication into the joint. If the pain temporarily subsides, it suggests the AC joint is the primary cause of discomfort.

AC joint arthritis is a degenerative condition that can lead to chronic shoulder pain and functional limitations. It is commonly caused by age-related wear and tear, repetitive motion, or previous injuries. Symptoms often include pain at the top of the shoulder, discomfort with overhead and cross-body movements, swelling, and joint stiffness. Diagnosis involves a combination of medical history, physical examination, imaging studies, and sometimes diagnostic injections.