AC Joint: Understanding Tests, Common Pathologies, and Diagnosis

What is the Name of the Test for the AC Joint?

While there isn't one single definitive test, several orthopedic special tests are commonly employed to assess the integrity and pathology of the acromioclavicular (AC) joint. The Cross-Body Adduction Test (also known as the Horizontal Adduction Test) is one of the most frequently cited and utilized tests for suspected AC joint pathology, though it is often used in conjunction with other assessments like the AC Shear Test and Paxinos' Test.

Understanding the Acromioclavicular (AC) Joint

The acromioclavicular (AC) joint is a crucial articulation in the shoulder complex, connecting the acromion process of the scapula (shoulder blade) to the distal end of the clavicle (collarbone). This relatively small joint plays a vital role in the overall mobility and stability of the shoulder girdle, facilitating the transmission of forces from the arm to the axial skeleton.

Its stability is primarily maintained by two sets of ligaments:

• Acromioclavicular (AC) ligaments: These surround the joint capsule itself, providing direct support.
• Coracoclavicular (CC) ligaments: Comprising the conoid and trapezoid ligaments, these are stronger and located inferior to the joint, connecting the clavicle to the coracoid process of the scapula. They are critical for preventing superior displacement of the clavicle relative to the acromion.

Common AC Joint Pathologies

Due to its exposed position and role in force transmission, the AC joint is susceptible to various injuries and conditions, particularly from direct trauma (e.g., falls onto the shoulder or outstretched arm). Common pathologies include:

• AC Joint Separations (Sprains): Graded I through VI based on the degree of ligamentous damage (AC and CC ligaments) and displacement. Grade I is a mild sprain, while Grade VI involves severe displacement.
• AC Joint Osteoarthritis: Degenerative changes within the joint, often seen in older adults or those with a history of previous injury.
• Distal Clavicle Osteolysis: A condition characterized by bone resorption at the end of the clavicle, often seen in athletes involved in repetitive overhead activities or weightlifting.

Key Orthopedic Special Tests for AC Joint Assessment

Healthcare professionals utilize a battery of orthopedic special tests to help diagnose AC joint pathology. These tests aim to selectively stress the AC joint and its surrounding structures to reproduce pain or identify instability.

• Cross-Body Adduction Test (Horizontal Adduction Test):

  • Procedure: The examiner passively or actively adducts the patient's arm horizontally across the body, bringing the arm towards the opposite shoulder.
  • Positive Sign: Pain localized to the AC joint, especially at the end range of motion, suggests AC joint pathology (e.g., sprain, arthritis).
  • Mechanism: This movement compresses the AC joint surfaces, potentially irritating damaged cartilage or ligaments.

• AC Shear Test (Compression Test):

  • Procedure: The patient is typically seated. The examiner places one hand on the spine of the scapula and the other hand over the distal clavicle. The hands are then squeezed together, compressing the AC joint.
  • Positive Sign: Pain, crepitus (grinding sensation), or excessive movement at the AC joint indicates potential AC joint sprain or instability.
  • Mechanism: Directly applies a shearing or compressive force to the AC joint.

• Paxinos' Test:

  • Procedure: The patient is seated. The examiner places the thumb of one hand under the acromion and the fingers of the same hand over the distal clavicle. The index finger of the other hand is placed on the middle of the clavicle. Downward pressure is applied through the thumb on the acromion while upward pressure is applied through the index finger on the mid-clavicle.
  • Positive Sign: Pain localized to the AC joint.
  • Mechanism: Creates a shearing force across the AC joint, similar to the AC Shear Test but with a slightly different vector.

• O'Brien's Test (Active Compression Test):

  • Procedure: While primarily known for detecting superior labral anterior-posterior (SLAP) lesions, O'Brien's test can also provoke AC joint pain. The patient flexes the shoulder to 90 degrees, adducts it 10-15 degrees, and internally rotates the arm so the thumb points down. The examiner applies downward resistance. The test is then repeated with the arm externally rotated (palm up).
  • Positive Sign for AC Joint: Pain at the AC joint during the internally rotated (thumb down) position that is reduced or eliminated when the test is repeated with external rotation (palm up).
  • Mechanism: The internal rotation and adduction component can compress the AC joint.

Interpreting Test Results and Clinical Significance

It is crucial to understand that no single orthopedic special test is 100% accurate in diagnosing AC joint pathology. These tests are tools that provide valuable information when combined with a thorough clinical examination, including:

• Patient History: Mechanism of injury, location of pain, aggravating and relieving factors.
• Palpation: Tenderness directly over the AC joint.
• Range of Motion Assessment: Pain with specific movements.
• Imaging Studies: X-rays (especially stress views), MRI, or CT scans are often used to confirm the diagnosis and assess the extent of injury, particularly for AC joint separations.

The results of these special tests help guide the clinician's suspicion and inform the need for further diagnostic imaging or consultation.

The Importance of Professional Diagnosis

While understanding these tests can be beneficial for fitness enthusiasts and students of kinesiology, it is paramount to emphasize that these assessments should only be performed and interpreted by trained healthcare professionals, such as physicians, physical therapists, or orthopedic specialists. Self-diagnosis based solely on these tests is unreliable and can lead to inappropriate management or delayed effective treatment. A proper diagnosis ensures the correct course of action, whether it involves conservative management (rest, ice, physical therapy) or surgical intervention.

Conclusion

When asking "What is the name of the test for the AC joint?", it's important to recognize that there isn't just one. Instead, a suite of specific orthopedic tests, including the Cross-Body Adduction Test, AC Shear Test, and Paxinos' Test, are utilized to evaluate the integrity and pathology of the acromioclavicular joint. These tests, combined with a comprehensive clinical examination and diagnostic imaging, form the cornerstone of accurately diagnosing AC joint injuries and conditions, paving the way for effective treatment and rehabilitation strategies.