AC Joint Dislocation (Shoulder Separation): Causes, Symptoms, and Treatment

What is an AC Joint Dislocation?

An AC joint dislocation, often referred to as a shoulder separation, occurs when the ligaments supporting the acromioclavicular joint are stretched or torn, causing the collarbone (clavicle) to separate from the shoulder blade (scapula).

Understanding the Acromioclavicular (AC) Joint

The acromioclavicular (AC) joint is a critical articulation at the top of the shoulder, connecting the acromion (a bony projection of the shoulder blade, or scapula) to the lateral end of the collarbone (clavicle). Unlike the more commonly dislocated glenohumeral (shoulder) joint, which involves the humerus and scapula, an AC joint dislocation specifically refers to the separation at this clavicle-scapula junction.

This joint is stabilized by two primary sets of ligaments:

• Acromioclavicular (AC) Ligaments: These surround the joint capsule, providing horizontal stability and preventing the clavicle from separating from the acromion.
• Coracoclavicular (CC) Ligaments: Comprising the conoid and trapezoid ligaments, these are stronger and provide crucial vertical stability, connecting the clavicle to the coracoid process (another part of the scapula).

The AC joint plays a vital role in shoulder motion, allowing for slight gliding movements that facilitate a full range of arm elevation and rotation, particularly when the arm is raised overhead.

What is an AC Joint Dislocation?

An AC joint dislocation is an injury to the ligaments that stabilize the acromioclavicular joint. When these ligaments are sprained or torn, the integrity of the joint is compromised, leading to a separation of the clavicle from the acromion. The severity of the injury depends on which ligaments are damaged and the extent of the damage. It's important to distinguish this from a "shoulder dislocation," which typically refers to the much larger glenohumeral joint where the ball of the upper arm bone (humerus) comes out of its socket. An AC joint dislocation is more accurately termed a "shoulder separation."

Causes of AC Joint Dislocation

AC joint dislocations are predominantly caused by direct trauma to the shoulder. The most common mechanisms include:

• Direct Fall onto the Shoulder: This is the leading cause, often occurring during sports activities (e.g., football tackles, hockey checks, cycling accidents, skiing falls) or from a fall directly onto the point of the shoulder. The force drives the acromion downwards, while the clavicle remains relatively fixed, leading to ligamentous tears.
• Direct Blow to the Shoulder: A forceful impact to the top or side of the shoulder, common in contact sports, can also cause the injury.
• Fall onto an Outstretched Arm (less common): While more typical for other shoulder injuries, a fall onto an outstretched arm can sometimes transmit force up to the AC joint, leading to a dislocation.

These injuries are particularly prevalent in athletes involved in contact sports, but can also affect anyone who experiences a significant fall or impact to the shoulder.

Recognizing the Symptoms

The symptoms of an AC joint dislocation can vary based on the severity of the injury but typically include:

• Pain: Localized pain at the very top of the shoulder, often worsening with arm movement, especially across the body or overhead.
• Deformity: A visible bump or prominence on top of the shoulder, caused by the clavicle being displaced upwards. This is more pronounced in higher-grade injuries.
• Swelling and Bruising: Inflammation and discoloration around the AC joint.
• Tenderness: The area around the AC joint will be tender to touch.
• Limited Range of Motion: Difficulty moving the arm, particularly lifting it overhead, reaching across the body, or carrying objects.
• Popping Sensation: A distinct pop or tearing sensation may be felt at the time of injury.

Diagnosing an AC Joint Dislocation

Diagnosis typically involves a combination of a thorough physical examination and imaging studies:

• Physical Examination: An orthopedic specialist or physician will assess the shoulder for tenderness, swelling, and deformity. They will also perform specific stress tests, such as the cross-body adduction test, to evaluate the stability of the AC joint and reproduce pain.
• X-rays: Standard X-rays (AP view, Zanca view) are crucial to visualize the bony alignment of the clavicle and acromion and rule out fractures. Sometimes, "weighted" X-rays are taken (with the patient holding weights in each hand) to exaggerate any separation and better assess the degree of instability.
• MRI (Magnetic Resonance Imaging): While not always necessary for diagnosis, an MRI may be used to assess the extent of soft tissue damage, particularly to the AC and CC ligaments, and to rule out other associated injuries.

Classifying AC Joint Dislocation Grades

AC joint dislocations are commonly classified using the Rockwood Classification system, which categorizes the injury into six types based on the degree of ligamentous damage and the displacement of the clavicle relative to the acromion:

• Type I: A sprain of the AC ligaments with no significant tearing or displacement of the joint. The joint appears normal on X-ray. Pain is mild to moderate.
• Type II: A complete tear of the AC ligaments, but the stronger coracoclavicular (CC) ligaments are only stretched or partially torn. There is a noticeable but slight superior displacement of the clavicle, often visible as a small bump.
• Type III: Complete tears of both the AC and CC ligaments. The clavicle is significantly displaced superiorly, creating a prominent bump at the top of the shoulder. While functionally debilitating, many Type III injuries can be managed non-surgically.
• Type IV: Complete tears of both AC and CC ligaments, with the clavicle displaced posteriorly (backwards) into or through the trapezius muscle. This is a rare and severe injury.
• Type V: Complete tears of both AC and CC ligaments, with severe superior displacement of the clavicle (often 100% or more). There is also detachment of the deltoid and trapezius muscles from the clavicle, leading to a very large and obvious bump.
• Type VI: A very rare and severe injury where the clavicle is displaced inferiorly (downwards) and lodges beneath the coracoid process or behind the acromion.

Treatment Approaches

Treatment for an AC joint dislocation depends heavily on the grade of the injury, the patient's activity level, and their specific symptoms.

Conservative (Non-Surgical) Treatment: This is the preferred approach for most Type I, II, and many Type III injuries.

• RICE Protocol: Rest, Ice, Compression, and Elevation immediately after the injury to reduce pain and swelling.
• Sling Immobilization: A sling may be used for 1 to 3 weeks to provide support and rest the joint, allowing initial healing.
• Pain Management: Over-the-counter or prescription non-steroidal anti-inflammatory drugs (NSAIDs) for pain and inflammation.
• Physical Therapy: Once initial pain subsides, a progressive rehabilitation program is crucial to restore range of motion, strength, and stability.

Surgical Treatment: Surgery is generally considered for Type IV, V, and VI injuries, and sometimes for Type III injuries in high-demand athletes, manual laborers, or individuals experiencing persistent pain and instability after a trial of conservative management.

• Goals: Restore the anatomical alignment of the joint, stabilize the clavicle, and facilitate ligament healing or reconstruction.
• Techniques: Various surgical techniques exist, including:
  • Direct Repair: Reattaching torn ligaments.
  • Ligament Reconstruction: Using a graft (from the patient or a donor) to reconstruct the torn CC ligaments.
  • Coracoclavicular Fixation: Using screws, plates, or strong sutures to temporarily stabilize the clavicle to the coracoid process while the ligaments heal.
  • Arthroscopic vs. Open Surgery: Procedures can be performed minimally invasively (arthroscopically) or through a larger incision (open surgery).

Rehabilitation and Recovery

Regardless of whether the treatment is conservative or surgical, rehabilitation is a critical component of recovery. The process is typically phased:

• Phase 1 (Acute/Protection Phase): Focus on pain and inflammation control, gentle range of motion exercises (pendulum swings), and isometric strengthening, typically while wearing a sling.
• Phase 2 (Mobility & Early Strengthening Phase): As pain decreases, emphasis shifts to restoring full range of motion and initiating light strengthening exercises for the rotator cuff and scapular stabilizers.
• Phase 3 (Progressive Strengthening & Return to Activity): Advanced strengthening exercises, proprioceptive drills, and sport-specific training are introduced. A gradual return to full activity, including contact sports, is permitted once strength, stability, and pain-free range of motion are fully restored.

Recovery time varies significantly by the grade of injury and treatment approach. Type I and II injuries may recover in a few weeks to 2-3 months, while Type III and surgically treated higher-grade injuries can take 4-6 months or longer for full recovery.

Prevention Strategies

While not all AC joint dislocations are preventable, certain measures can reduce the risk:

• Proper Falling Techniques: Learning how to fall safely, especially in sports or activities with a high risk of falls (e.g., cycling, skiing), can help distribute impact away from the direct point of the shoulder.
• Shoulder Girdle Strength and Stability: Regular strength training that targets the muscles surrounding the shoulder (rotator cuff, scapular stabilizers, deltoids, pectorals) can enhance joint stability.
• Protective Gear: Athletes in contact sports should always wear appropriate shoulder pads and protective gear.
• Awareness: Being mindful of your surroundings and avoiding unnecessary risks can also play a role.

When to Seek Medical Attention

If you experience a fall or direct blow to your shoulder and observe any of the following, it is crucial to seek prompt medical attention:

• Severe pain at the top of your shoulder.
• A visible bump or deformity on your shoulder.
• Significant swelling or bruising.
• Inability to move your arm or shoulder through its full range of motion.
• Numbness or tingling in your arm or hand.

Early diagnosis and appropriate management are key to optimizing recovery and preventing long-term complications such as chronic pain, weakness, or arthritis in the AC joint.