AC Joint Arthritis: Understanding Causes, Symptoms, Diagnosis, and Treatment

What is AC joint arthritis?

AC joint arthritis is a degenerative condition affecting the acromioclavicular joint, where the collarbone meets the shoulder blade, characterized by the breakdown of articular cartilage leading to pain, stiffness, and reduced shoulder function.

Understanding the Acromioclavicular (AC) Joint

The acromioclavicular (AC) joint is a small, yet crucial, articulation located at the top of the shoulder. It is formed by the distal end of the clavicle (collarbone) and the acromion, a bony projection of the scapula (shoulder blade). This joint is stabilized by several ligaments, including the strong coracoclavicular ligaments (conoid and trapezoid) and the acromioclavicular ligaments, which collectively provide stability while allowing for a small degree of motion essential for full shoulder range of motion. The AC joint plays a vital role in transmitting forces from the upper extremity to the axial skeleton and facilitating the complex movements of the shoulder girdle.

What is AC Joint Arthritis?

AC joint arthritis refers to the inflammation and degeneration of the articular cartilage within the acromioclavicular joint. Most commonly, it manifests as osteoarthritis, a "wear-and-tear" condition where the smooth cartilage that cushions the ends of the bones gradually breaks down. This breakdown leads to bone-on-bone friction, causing pain, inflammation, and reduced mobility. Less commonly, AC joint arthritis can be a result of post-traumatic arthritis (following an injury like an AC joint separation) or inflammatory arthritis (such as rheumatoid arthritis).

Causes and Risk Factors

The development of AC joint arthritis is often multifactorial, stemming from a combination of mechanical stress, previous injury, and natural aging processes.

• Repetitive Overhead Activities: Sports like weightlifting (especially bench press, overhead press, and dips), swimming, tennis, and volleyball, as well as occupations involving frequent overhead work, place significant stress on the AC joint, accelerating cartilage wear.
• Previous AC Joint Trauma: A history of AC joint sprains or separations (e.g., from falls directly onto the shoulder) can disrupt the joint's mechanics and lead to premature degenerative changes.
• Age: As a primary form of osteoarthritis, the incidence of AC joint arthritis increases with age due to natural wear and tear on the cartilage over decades of use.
• Genetics: A family history of osteoarthritis may indicate a genetic predisposition to developing the condition.
• Anatomical Variations: Subtle differences in joint alignment or bone structure can sometimes contribute to uneven load distribution and increased wear.

Common Symptoms

The symptoms of AC joint arthritis typically develop gradually and can range from mild discomfort to debilitating pain.

• Localized Pain: The most common symptom is pain directly over the top of the shoulder, specifically at the AC joint. This pain may radiate into the neck, trapezius muscle, or deltoid muscle.
• Pain with Specific Movements: Activities that compress or shear the AC joint often exacerbate pain. These include:
  • Overhead reaching or lifting.
  • Cross-body adduction (bringing the arm across the chest, as if reaching for the opposite shoulder).
  • Push-ups, bench presses, or dips.
  • Sleeping on the affected side.
• Tenderness to Palpation: The AC joint itself will often be tender when pressed.
• Clicking, Popping, or Grinding (Crepitus): A sensation or audible sound of grinding within the joint during movement, indicating cartilage degradation and bone-on-bone friction.
• Stiffness: Especially noticeable after periods of inactivity, such as first thing in the morning.
• Decreased Range of Motion: While the glenohumeral joint (main shoulder joint) might have full range, pain in the AC joint can limit terminal shoulder elevation or cross-body movements.

Diagnosis

Diagnosing AC joint arthritis typically involves a thorough clinical assessment combined with imaging studies.

• Physical Examination: A healthcare professional will examine the shoulder, palpating the AC joint for tenderness, assessing range of motion, and performing specific provocative tests. The cross-body adduction test (also known as the scarf test) and O'Brien's test are common maneuvers that can elicit pain in an arthritic AC joint.
• Imaging Studies:
  • X-rays: Standard plain X-rays, particularly an AP (Anteroposterior) view and a Zanca view (which angles the X-ray beam to better visualize the joint space), can reveal narrowing of the joint space, osteophytes (bone spurs), and subchondral sclerosis (increased bone density beneath the cartilage) characteristic of arthritis.
  • MRI (Magnetic Resonance Imaging): While not always necessary for diagnosis, MRI can provide more detailed images of the cartilage, ligaments, and surrounding soft tissues, helping to rule out other shoulder pathologies.
• Diagnostic Injection: In some cases, a corticosteroid injection directly into the AC joint can be performed. If the injection provides significant temporary pain relief, it strongly supports the diagnosis of AC joint arthritis.

Management and Treatment Strategies

Treatment for AC joint arthritis typically begins with conservative approaches, aiming to reduce pain and improve function. Surgical intervention is considered if conservative measures fail to provide adequate relief.

Conservative Management

• Activity Modification: Avoiding or modifying activities that aggravate the joint is crucial. This might involve adjusting exercise techniques, reducing load, or temporarily refraining from certain movements.
• Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Over-the-counter or prescription NSAIDs can help manage pain and inflammation.
• Physical Therapy: A cornerstone of conservative management. A physical therapist will design a program focused on:
  • Pain management techniques (e.g., ice, heat, modalities).
  • Improving shoulder girdle mechanics and posture.
  • Strengthening the rotator cuff muscles and scapular stabilizers (e.g., serratus anterior, lower trapezius) to enhance dynamic stability and reduce stress on the AC joint.
  • Restoring pain-free range of motion.
• Corticosteroid Injections: Injections of corticosteroids directly into the AC joint can provide temporary relief from pain and inflammation, allowing for more effective participation in physical therapy.
• Manual Therapy: Techniques such as joint mobilizations or soft tissue release may be used to address compensatory tightness or dysfunction in surrounding musculature.

Surgical Intervention

When conservative treatments fail to provide sufficient pain relief and functional improvement, surgery may be considered.

• Distal Clavicle Excision (DCE) / Mumford Procedure: This is the most common surgical procedure for AC joint arthritis. It involves removing a small portion (typically 5-10 mm) of the distal end of the clavicle. This creates a space between the clavicle and the acromion, preventing bone-on-bone friction and alleviating pain. The procedure can be performed open or arthroscopically (minimally invasive).
• Post-Surgical Rehabilitation: Following surgery, a structured rehabilitation program is essential for restoring strength, range of motion, and function. This typically progresses from passive range of motion to active exercises, strengthening, and eventually sport-specific or activity-specific drills.

Rehabilitation and Exercise Considerations

For individuals with AC joint arthritis, whether managing it conservatively or post-surgery, a targeted exercise program is vital. The focus is on optimizing shoulder mechanics and strengthening supporting musculature to offload the symptomatic joint.

• Pain-Free Movement: All exercises should be performed within a pain-free range. Pushing through pain can exacerbate inflammation and further damage the joint.
• Scapular Stability: Strengthening the muscles that control the scapula (shoulder blade) is paramount. Exercises targeting the serratus anterior (e.g., push-up plus, wall slides) and lower trapezius (e.g., prone Ys, I's, and Ts) help to ensure proper scapular upward rotation and posterior tilt, which can reduce impingement and stress on the AC joint.
• Rotator Cuff Strengthening: A strong and balanced rotator cuff (supraspinatus, infraspinatus, teres minor, subscapularis) is essential for glenohumeral joint stability and efficient shoulder movement, indirectly reducing compensatory stress on the AC joint. Exercises like external rotations and internal rotations (with bands or light weights) are beneficial.
• Posture Correction: Addressing forward head posture and rounded shoulders can significantly improve shoulder girdle mechanics and reduce anterior shoulder stress. Exercises promoting thoracic extension and awareness of neutral spine alignment are important.
• Modifying Pressing Movements: For weightlifters, modifying exercises like bench press and overhead press is crucial. This might involve using a neutral grip, reducing the range of motion (e.g., board presses), or finding alternative exercises (e.g., dumbbell presses with external rotation emphasis). Dips are often particularly problematic and may need to be avoided.
• Gradual Progression: Exercise intensity and volume should be increased slowly and progressively, always guided by pain response.

Prevention and Long-Term Outlook

While not always entirely preventable, certain strategies can help minimize the risk or slow the progression of AC joint arthritis.

• Proper Exercise Technique: Learning and consistently applying correct form for all exercises, especially those involving the shoulders (e.g., pressing, overhead movements, dips), is critical. Avoid excessive loads or ranges of motion that put undue stress on the AC joint.
• Balanced Training: Ensure a balanced strength training program that doesn't over-emphasize anterior shoulder muscles (e.g., pectoralis major, anterior deltoid) at the expense of posterior shoulder and scapular stabilizers.
• Warm-up and Cool-down: Always perform a thorough warm-up before activity and a cool-down afterward to prepare muscles and joints.
• Listen to Your Body: Pay attention to early signs of discomfort. Persistent pain in the AC joint area warrants evaluation by a healthcare professional. Early intervention can often prevent the condition from worsening.

The long-term outlook for AC joint arthritis is generally good. Most individuals can effectively manage their symptoms with conservative treatments and activity modifications. For those who require surgery, the Mumford procedure typically offers significant pain relief and allows for a return to most activities, though some limitations may persist depending on the individual and their activity level. Regular adherence to rehabilitation principles and a commitment to maintaining proper shoulder mechanics are key to successful long-term management.