Acromioclavicular (AC) Joint Arthritis

Acromioclavicular (AC) joint arthritis, a type of osteoarthritis, can arise from either injury leading to instability due to ligament rupture or from chronic stress and degeneration of the joint (articular) surfaces. In the vast majority of cases, the exact cause of the disorder cannot be determined.
The AC joint is formed by the articulation of the lateral end of the clavicle (collarbone) and the acromion, a bony projection off the scapula (shoulder blade). These bony surfaces are lined with articular cartilage, a smooth, firm, and resilient material that allows low-friction movement within the joint. Over time, or following trauma, this cartilage can break down, leading to thinning, softening, or complete erosion of the cartilage layers. This results in bone-on-bone contact, osteophyte (bone spur) formation, and narrowing of the joint space between the clavicle and the acromion.
In addition, the ligaments supporting the AC joint, particularly the acromioclavicular and coracoclavicular ligaments, may weaken or rupture, either from acute trauma or cumulative microtrauma, exacerbating joint instability and accelerating degenerative changes.
As the joint deteriorates, the surrounding synovial membrane—a soft tissue lining that secretes lubricating synovial fluid—may become inflamed, contributing to pain and swelling. These changes often lead to disturbances in the underlying subacromial space, which lies beneath the acromion and above the humeral head. The rotator cuff tendons, particularly the supraspinatus tendon, pass through this narrow corridor and are especially vulnerable to impingement.
Degenerative changes in the AC joint can result in the downward protrusion of osteophytes or joint swelling into this subacromial space, causing mechanical compression of the tendons and subacromial bursa. This increased pressure can lead to the development of subacromial impingement syndrome (SAIS), a painful condition that further disrupts shoulder mechanics and can lead to rotator cuff tendinopathy or tears if left untreated.

Symptoms:

The most common symptom of AC joint arthritis is localized pain at the top of the shoulder, particularly when raising the upper limb forward and across the body toward the opposite side (adduction). This movement compresses the AC joint, often eliciting sharp discomfort. The pain may also radiate into the neck or down the shoulder, mimicking other shoulder pathologies such as rotator cuff disorders or cervical radiculopathy.

Patients frequently report tenderness when pressure is applied directly over the joint (on palpation), and pain during rest, especially when lying on the affected shoulder, which can disrupt sleep. Overhead activities, lifting, or carrying objects—especially across the chest—can aggravate the symptoms.

As the arthritis progresses, some individuals may experience joint stiffness, a clicking or popping sensation during shoulder motion, and reduced range of motion due to pain and mechanical restriction.

During the clinical examination, specific orthopedic tests help reproduce the symptoms and confirm AC joint involvement. The most reliable is the Cross-Body Adduction Test (also known as the Cross-Arm Test), where the patient is asked to elevate the arm anteriorly and then adduct it across the body. This movement compresses the AC joint, and pain during this test is considered a positive sign of pathology.

Joint swelling or prominence over the AC joint may be visible, especially in cases with chronic degeneration or previous ligament injuries. In such cases, there may be increased anterior-posterior mobility of the distal clavicle, indicative of joint instability or subluxation.

Imaging & Diagnosis:

X-rays (Radiographic Evaluation):
Radiographs are the first-line imaging tool. They may show:

• Narrowing of the joint space,
• Sclerosis(hardening of the subchondral bone),
• Osteophyte formation(bone spurs),
• Cystic changes, and
• Enlargement or irregularity of the distal clavicle.

In cases with chronic ligament instability (especially coracoclavicular ligament involvement), an elevation or superior displacement of the distal clavicle may also be observed, particularly on stress or weight-bearing views.

MRI (Magnetic Resonance Imaging):
MRI provides a more detailed assessment of soft tissues. It may reveal:

• Synovial inflammationor synovitis,
• Joint effusion(fluid accumulation),
• Thickening of the joint capsule,
• Bone marrow edema, and
• Associated pathologiessuch as rotator cuff tendinopathy, tears, or subacromial bursitis.

MRI is particularly useful when AC joint arthritis is suspected to be contributing to subacromial impingement syndrome (SAIS) or when surgical planning is being considered.

Conservative (Non-Surgical) Management:

The initial approach to treating AC joint arthritis is conservative, focusing on symptom relief and functional improvement. This typically includes:

• Analgesic and anti-inflammatory medication(e.g. NSAIDs) to reduce pain and inflammation.
• Activity modification, avoiding movements that exacerbate symptoms—especially overhead activities and cross-body motions.

Physical therapy is aimed at:

• Improving shoulder mechanics
• Strengthening the rotator cuff and scapular stabilizers
• Enhancing flexibility and range of motion
• Reducing compensatory muscle tension

In some cases, corticosteroid injections directly into the AC joint may provide temporary but significant pain relief by reducing inflammation. This can help confirm the diagnosis as well as delay or potentially avoid surgery.

However, due to the progressive degenerative nature of arthritis, many patients may experience persistent or worsening symptoms that limit daily function and quality of life despite conservative care.

Surgical Treatment:

If conservative treatments fail, surgical correction may be considered. The procedure of choice is called distal clavicle resection, also known as the Mumford procedure.

The operation is performed exclusively via shoulder arthroscopy, a minimally invasive technique that allows for faster recovery, less postoperative pain, and minimal scarring.

The surgeon removes approximately 5 mm of the distal (lateral) end of the clavicle, creating a small gap between the clavicle and acromion.

Osteophytes (bone spurs) are also removed during the procedure to relieve mechanical impingement and restore smoother shoulder motion.

Care is taken to preserve the acromioclavicular ligaments, which are critical for maintaining joint stability and shoulder biomechanics.

This procedure reduces bone-on-bone contact, thereby relieving pain, inflammation, and impingement symptoms.

Postoperative Care and Rehabilitation:

Immediately after surgery, the upper limb is placed in a sling for comfort and protection, typically for 1 week.

Starting from the 2nd postoperative day, a structured physical therapy program is initiated. Key goals include:

• Restoring range of motion
• Preventing stiffness
• Rebuilding shoulder strength
• Improving scapular stabilityand overall shoulder function

Isometric exercises and active-assisted motion are introduced early, progressing to resistance and strengthening exercises by the 2^nd week.

Most patients can return to light activities within 2–3 weeks, with full return to sports or manual labor typically expected around 6–8 weeks, depending on individual recovery and demands.

Prognosis and Outcomes:

Surgical outcomes for isolated AC joint arthritis treated with arthroscopic distal clavicle resection are generally very favorable, with:

• High patient satisfaction
• Significant pain reduction
• Improved shoulder function
• Low complication and recurrence rates

Success largely depends on accurate diagnosis, appropriate patient selection, and adherence to a structured rehabilitation protocol.