Acromioclavicular Pain: Understanding Causes, Symptoms, and Treatment

What is Acromioclavicular Pain?

Acromioclavicular (AC) pain refers to discomfort and functional limitation stemming from issues within or around the acromioclavicular joint, the articulation between the collarbone (clavicle) and the highest part of the shoulder blade (acromion).

Understanding the Acromioclavicular (AC) Joint

The AC joint is a crucial component of the shoulder girdle, playing a vital role in shoulder movement and stability. It's classified as a gliding synovial joint, allowing for slight but essential movements during shoulder elevation and rotation.

• Anatomy: The AC joint is formed by the distal end of the clavicle (collarbone) and the acromion process, which is a bony projection extending from the scapula (shoulder blade).
  • Stabilizing Ligaments: The joint's stability is primarily provided by two sets of strong ligaments:
    • Acromioclavicular Ligaments: These surround the joint capsule, reinforcing it and resisting anterior-posterior displacement of the clavicle.
    • Coracoclavicular Ligaments: Comprising the trapezoid and conoid ligaments, these are located slightly medial to the AC joint, connecting the clavicle to the coracoid process of the scapula. They are critical for preventing superior displacement of the clavicle and transferring forces from the arm to the axial skeleton.
• Function: The AC joint allows the scapula to rotate and glide, facilitating the full range of motion of the arm, especially during overhead activities. It also acts as a strut, transmitting forces from the arm through the clavicle to the sternum.

What Causes AC Joint Pain?

AC joint pain can arise from a variety of sources, broadly categorized into traumatic injuries, degenerative conditions, and overuse syndromes.

• Traumatic Injuries (AC Joint Separations/Sprains):
  • These are the most common cause of acute AC joint pain, often resulting from a direct fall onto the tip of the shoulder or a fall onto an outstretched arm (FOOSH).
  • The severity is graded based on the extent of ligamentous damage and displacement:
    • Grade I: Mild sprain of the AC ligaments; no significant displacement.
    • Grade II: Partial tear of AC ligaments; mild superior displacement of the clavicle.
    • Grade III: Complete tear of AC and coracoclavicular ligaments; significant superior displacement.
    • Grades IV-VI: More severe injuries involving greater displacement and often associated muscle tears or clavicle displacement into surrounding tissues, which are less common.
• Degenerative Conditions (Osteoarthritis):
  • Similar to other joints, the AC joint can develop osteoarthritis due to wear and tear of the articular cartilage. This is common in older adults, but can also occur in younger individuals with a history of AC joint injury or repetitive overhead activities.
  • Bone spurs (osteophytes) may form, leading to impingement and pain.
• Overuse/Repetitive Strain Syndromes:
  • Distal Clavicular Osteolysis (Weightlifter's Shoulder): This condition involves the erosion or breakdown of the bone at the end of the clavicle. It is frequently seen in individuals who engage in repetitive heavy overhead lifting (e.g., bench press, overhead press), where compressive and shear forces are repeatedly applied to the AC joint.
  • Repetitive Overhead Activities: Sports like swimming, throwing, volleyball, and occupations requiring frequent arm elevation can lead to chronic inflammation and irritation of the AC joint.
• Inflammation:
  • While less common as a primary cause, inflammation of the joint capsule (capsulitis) or surrounding soft tissues can contribute to AC joint pain.

Common Symptoms of AC Joint Pain

The symptoms of AC joint pain vary depending on the underlying cause and severity, but typically include:

• Localized Pain: Sharp or aching pain directly on top of the shoulder, precisely over the AC joint.
• Tenderness to Touch: The joint is often very tender when pressed.
• Pain with Movement: Pain is typically exacerbated by:
  • Reaching overhead.
  • Reaching across the body (horizontal adduction).
  • Lifting heavy objects.
  • Sleeping on the affected side.
• Swelling and Bruising: Common with acute injuries (AC joint separations).
• Clicking, Grinding, or Popping: May be felt or heard with movement, especially in cases of osteoarthritis or chronic instability.
• Reduced Range of Motion: Difficulty or pain when moving the arm through its full range.
• Visible Deformity: In higher-grade AC joint separations, a noticeable "bump" or prominence may be visible on top of the shoulder due to the clavicle displacing superiorly.

Diagnosis of AC Joint Pain

Accurate diagnosis of AC joint pain involves a thorough clinical evaluation and often imaging studies.

• Clinical Examination:
  • Palpation: The clinician will carefully feel for tenderness and swelling directly over the AC joint.
  • Range of Motion Assessment: Evaluating active and passive movements of the shoulder, particularly those that stress the AC joint (e.g., cross-body adduction).
  • Specific Orthopedic Tests: Various tests are used to provoke pain and assess joint integrity, such as the cross-body adduction test (also known as the horizontal adduction test) and the O'Brien's test (active compression test).
• Imaging:
  • X-rays: Standard X-rays can reveal AC joint separation (especially with stress views where weights are held to accentuate displacement), bone spurs, or degenerative changes.
  • Magnetic Resonance Imaging (MRI): Provides detailed images of soft tissues, useful for assessing ligamentous damage (AC and coracoclavicular), cartilage integrity, and bone edema.
  • Ultrasound: Can be used for dynamic assessment of the joint and to guide injections.

Management and Treatment Strategies

Treatment for AC joint pain depends on the cause and severity, ranging from conservative measures to surgical intervention.

• Conservative Management (Most Common):
  • Rest and Activity Modification: Avoiding activities that aggravate the pain is crucial.
  • Ice Application: For acute injuries and inflammation, applying ice packs can help reduce swelling and pain.
  • Non-Steroidal Anti-Inflammatory Drugs (NSAIDs): Over-the-counter or prescription NSAIDs can help manage pain and inflammation.
  • Physical Therapy: A cornerstone of recovery. A physical therapist will guide you through:
    • Pain Management Techniques: Modalities like ultrasound or electrical stimulation.
    • Restoring Range of Motion: Gentle exercises to regain shoulder mobility without stressing the AC joint.
    • Strengthening Exercises: Focusing on the rotator cuff muscles, scapular stabilizers, and deltoid to improve overall shoulder stability and mechanics.
    • Proprioception and Neuromuscular Control: Exercises to improve joint awareness and coordinated movement.
    • Ergonomic and Postural Correction: Addressing contributing factors in daily activities.
  • Corticosteroid Injections: For chronic inflammation or osteoarthritis, an injection of corticosteroids directly into the AC joint can provide temporary pain relief.
• Surgical Intervention:
  • Surgery is typically reserved for high-grade AC joint separations (Grade III and above, especially Grades IV-VI) that cause significant deformity or functional limitation, or for chronic pain not resolved by conservative treatment (e.g., persistent distal clavicular osteolysis).
  • Surgical procedures may involve:
    • Ligament Reconstruction: Using grafts to reconstruct the torn AC or coracoclavicular ligaments.
    • Distal Clavicle Excision (Mumford Procedure): Removing a small portion of the end of the clavicle to create more space and prevent bone-on-bone impingement, often performed for osteoarthritis or osteolysis.

Rehabilitation and Prevention

Effective rehabilitation is key to full recovery and preventing recurrence of AC joint pain.

• Rehabilitation Principles:
  • Progressive Loading: Gradually increasing the demands on the joint and surrounding muscles.
  • Functional Movement Integration: Incorporating exercises that mimic daily activities and sport-specific movements.
  • Return-to-Sport/Activity Training: A structured progression to safely resume desired physical activities.
• Prevention Strategies:
  • Proper Lifting Mechanics: Use correct form during weightlifting, especially for overhead and pressing movements, to minimize stress on the AC joint.
  • Gradual Progression: Avoid sudden increases in training volume or intensity, allowing the body to adapt.
  • Strength and Stability: Regularly strengthen the rotator cuff and scapular stabilizer muscles to ensure optimal shoulder mechanics.
  • Maintain Good Posture: Slumped posture can alter shoulder alignment and increase AC joint stress.
  • Awareness of Risk Factors: Recognize activities or sports that place the AC joint at risk and take appropriate precautions (e.g., protective gear, technique review).

When to Seek Professional Help

It is advisable to consult a healthcare professional, such as an orthopedic specialist, physical therapist, or sports medicine physician, if you experience:

• Sudden, severe pain after a fall or direct blow to the shoulder.
• Significant swelling or bruising around the AC joint.
• A visible deformity or "bump" on top of your shoulder.
• Inability to move your arm or bear weight on it.
• Persistent pain that doesn't improve with rest and basic pain relief measures.
• Pain that interferes with daily activities or sleep.