Acromioclavicular (AC) Joint Dislocation

The acromioclavicular (AC) joint is a small but important synovial joint located at the top of the shoulder. It is formed by the articulation between the acromion (the top part of the shoulder blade) and the distal (lateral) end of the clavicle. Like most joints in the human body, the AC joint is enclosed by a thin fibrous joint capsule. This capsule helps contain the synovial fluid, which lubricates the joint and facilitates smooth movement. Several ligaments stabilize the AC joint and help prevent dislocation:

• Acromioclavicular ligament: Connects the acromion and clavicle directly and provides horizontal stability.
• Coracoclavicular ligaments(further divided into the conoid and trapezoid ligaments): These ligaments connect the coracoid process of the scapula to the clavicle and are crucial for vertical stability of the AC joint.

Within the joint space lies a fibrocartilaginous disc, also referred to as the articular meniscus.

This disc varies in size and shape among individuals and acts as a shock absorber between the two bones, enhancing joint congruency and aiding in force transmission across the joint.

The acromioclavicular (AC) joint plays a crucial role in shoulder movement and stability, especially when lifting the arm or reaching overhead.

The most common cause of injury to the AC joint is a direct impact to the top of the shoulder, often due to a fall. This typically occurs when someone falls with the arm at their side, causing the force to travel through the shoulder and impact the joint directly. Sports like football, hockey, cycling, and skiing often see a higher incidence of AC joint injuries due to the nature of collisions or falls involved.

Mechanism of AC joint injury

This typically occurs when someone falls with the arm at their side, causing the force to travel through the shoulder and impact the joint directly. Sports like football, hockey, cycling, and skiing often see a higher incidence of AC joint injuries due to the nature of collisions or falls involved.

The severity of an AC joint injury depends on the extent of damage to the ligaments that stabilize the joint:

1. Ligament Sprain or Strain (Mild)

• Involves partial tearing or stretching of the AC ligament.
• May present with pain, swelling, and minor joint tenderness, but the joint remains in place.
• Commonly referred to as a Type I injury.

2. Partial Ligament Tear (Moderate)

• May involve a complete tear of the AC ligamentbut an intact coracoclavicular (CC) ligament.
• Results in some elevation of the clavicle, often categorized as a Type II injury.

3. Complete Ligament Rupture (Severe)

• Both the AC and CC ligaments are torn, leading to a dislocation of the AC joint.
• The clavicle is no longer anchored and typically appears to be protruding or elevated, a condition known as a “step-off” deformity.
• This is usually a Type III or higher injury (Types IV-VI involve more severe displacement and soft tissue damage).

According to Rockwood’s Classification, there are six types of AC joint dislocations.

• Type I: A sprain of the AC ligament, with no significant displacement. The CC ligaments are intact.
• Type II: A partial dislocation where the AC ligament is torn, and the CC ligaments are sprained. There is minimal displacement.
• Type III: A complete dislocation with tears in both the AC and CC ligaments, resulting in significant displacement of the clavicle.
• Type IV: Complete tears of both AC and CC ligaments, with posterior displacement of the clavicle into or through the trapezius muscle.
• Type V: Complete tears of both AC and CC ligaments, with severe displacement and significant disruption of the shoulder girdle.
• Type VI: Severe dislocation where the clavicle is displaced inferiorly, often beneath the coracoid process.

Your doctor will review your symptoms and medical history and perform a thorough physical examination to check for range of motion, stability, and strength of the joint. Initially, during examination, the characteristic prominence of the clavicle beneath the skin is often observed.

Palpation of the area is particularly painful. If necessary, your doctor will order certain imaging tests such as X-ray, MRI, CT scan, or ultrasound for a detailed evaluation of the joint and surrounding soft tissue structures to confirm the diagnosis. A radiograph of the contralateral (uninjured) shoulder is often taken for comparison.

The treatment of Acromioclavicular (AC) Joint Dislocation depends on the severity of the injury:

• Mild shoulder injuries (Types I & II) are treated conservatively. This typically includes painkillers and anti-inflammatory drugs. It is placed a sling to support the arm, mainly to reduce pain. Once the intense pain subsides (in about 5–7 days), patients can gradually resume daily activities and sports activities after about 3 weeks.
• Severe shoulder injuries (Types IV to VI) require surgical treatment using shoulder arthroscopy with AC TightRope technique that is a minimally invasive surgery that stabilizes the clavicle and acromion using a strong suture device.
• Moderate shoulder injuries (Type III) may be treated either conservatively or surgically. Surgery tends to offer faster pain relief, better cosmetic outcome (less deformity) and improved joint stability.

Physical therapy is important after immobilization or surgery to restore strength and range of motion. Most mild injuries heal well without surgery. Surgery in severe cases helps prevent chronic pain, weakness, and deformity. If untreated or improperly managed, chronic pain, arthritis, or shoulder dysfunction may develop.

After surgery, the arm is immobilized in a sling. This helps reduce pain, supports the joint, and protects the surgical repair by preventing movement that could disrupt healing.

From the second day, rehabilitation begins with physiotherapy and passive mobilization. This helps maintain joint flexibility and prevents stiffness without stressing the repaired tissues.

From the 2^nd week, active strengthening exercises begin to rebuild the muscles around the shoulder and support joint stability. These exercises focus on the deltoid, trapezius, and rotator cuff muscles, which are critical for shoulder function.

Lifting light objects is usually allowed from the third week post-surgery, depending on healing progress. This gradual reintroduction helps the patient regain functional use without risking damage.

Full return to sports or high-demand activities generally happens after 6 to 8 weeks, when the joint is considered sufficiently healed and muscles are stronger.