Assessment and diagnostic classification¶
The evaluation of Acromioclavicular (AC) joint injuries relies fundamentally on a comprehensive history and physical examination. Expert consensus supports the use of detailed patient history and specific physical manoeuvres, although single tests often possess limited diagnostic utility alone.
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1. Evidence Base for Patient History
A thorough and comprehensive history is crucial for AC joint evaluation and should cover several specific areas.
Knowledge Check
An acute AC joint injury is defined as less than 2 weeks, while a subacute injury is 2 to 6 weeks. This timeline is important for determining appropriate treatment approaches and prognosis.
History Component Key Details/Relevance
Injury Include the degree of **pain, weakness, and Characteristics instability** in the AC joint area. Identifying what motions cause the pain is relevant.
Acuity and The acuity of the injury should be documented. Timing An acute injury is defined as less than 2 weeks, while a subacute injury is 2 to 6 weeks. Consensus was not reached on the precise timeline defining a chronic AC joint injury.
Patient Factors & History should include the patient's **functional Goals demands and goals** regarding their arm/shoulder. Relevant factors include occupation, recreational activities/hobbies, hand dominance, and smoking status.
Mechanism The mechanism of injury is essential. AC injuries often result from a direct fall onto the outer aspect of the shoulder, forcing the acromion inferiorly.
Pain Location Pain reported at the AC joint is an important consideration. Pain reported at the posterior shoulder or scapula is also a relevant element when determining treatment options.
Aesthetic History should include the patient\'s perception of Concerns the importance of cosmesis.
2. Components of the Physical Examination¶
You can conduct the physical with the patient standing or sitting so that the weight of the arm pulling downward stresses the AC joint, making any deformity more visible
A. Inspection and Palpation¶
• Observation/Deformity: Patients with acute AC joint injury typically present holding their arm adducted to relieve pain. The primary visual clue is the prominence of the distal clavicle in relation to the acromion. This prominence is sometimes described as a "pseudo-elevation" of the clavicle caused by the depression of the scapula after the loss of its bony bridge to the thorax. The "piano key sign" may be present in higher-grade injuries, where the elevated clavicle rebounds after inferior compression. Swelling, hematoma, or altered scapular posture may also be noted.
• Palpation: Palpation should assess for tenderness localized specifically to the distal clavicle or the AC joint itself, rather than surrounding bone. Point tenderness along the bone suggests a bony injury.
• Neurovascular Status: A complete neurovascular examination of the affected extremity is vital, as neurological injury (e.g., to the brachial plexus) can be associated with traumatic AC injuries as this typically involves marked scapular depression, hence traction of the brachial plexus.
B. Assessment of Instability and Movement¶
Knowledge Check
In low-grade AC separations (Types 1, 2, 3A), laxity is mainly in the horizontal direction, while high-grade separations (Type 3B, 4, 5) exhibit both vertical and horizontal laxity. This distinction helps guide treatment decisions.
A Delphi Consensus of orthopaedic surgeons was conducted and they agreed on some aspects of physical examination including assessment of vertical and horizontal instability reached on several key dynamic aspects of the physical exam:
• Vertical Instability and Horizontal Instability: (Acromioclavicular anterior to posterior compression -- clasping your hands over the lateral clavicle and spine of scapula and squeezing these together -- note you shouldn't be actually touching the AC-joint on this, and as always, first do this on the uninvolved side you you and the patient can appreciate what "normal" is for them). Horizontal instability should be assessed using either the cross-arm test (also called the Scarf Test). In low-grade AC separations (Rockwood/ISAKOS 1, 2, 3A), laxity is mainly in the horizontal direction, while high-grade separations (Type 3B, 4, 5) exhibit both vertical and horizontal laxity.
• Range of Motion (ROM) and Weakness**:** Assessing shoulder weakness and range of motion are considered important aspects of the physical examination. Limitation of motion is painful, particularly with flexion and abduction beyond 90°. Note that especially in long-standing, "overuse" type AC joint injury, resisted internal rotation will be painfully weak due to compression of the AC joint by contraction of the internal rotators. You should retain a high index of suspicion of osteolysis of the distal end of the clavicle in these cases.
C. AC Joint Provocative Tests¶
No single test has been found to be 100% sensitive or specific for diagnosing AC joint dislocation. However, specific tests are valuable for identifying AC joint pathology, especially when combined:
1. AC Joint Tenderness¶
◦ This test is highly sensitive (96%) for AC joint pain, but often has low specificity.
◦ It is a component of the most diagnostically accurate test clusters.
Knowledge Check
AC joint tenderness is highly sensitive (96%) for AC joint pain, though it has low specificity. It's most useful when combined with other tests in a diagnostic cluster.
2. Paxinos Sign¶
◦ Performed by applying squeezing pressure across the AC joint (thumb on posterior lateral acromion, fingers superior to clavicle); positive if pain is elicited.
3. Active Compression Test / O'Brien test¶
◦ The test is positive if pain is elicited when the arm is flexed to 90°, adducted to 15°, and internally rotated (thumb down), and this pain is reported to be "on top" of the shoulder (note that this is primarily considered to be a diagnostic test for the superior labrum, where the test is repeated with the arm supinated and the shoulder externally rotated when the pain is reported as "inside" the shoulder).
4. Cross-Arm Adduction Test (Cross-body test/Horizontal Adduction Test, Scarf Test)¶
◦ This manoeuvre involves passively moving the arm across the patient's chest, causing compression at the AC joint that elicits pain.
◦ For isolated chronic AC lesions, it showed a sensitivity of 77% and a specificity of 79%.
5. Test Clustering:
◦ While single tests are limited, combining AC joint tenderness, , AC joint tenderness, and Paxinos sign in a cluster greatly increases the likelihood of AC joint injury being the primary diagnosis.
D. Scapular Evaluation¶
Evaluating the function of the associated scapulothoracic joint is essential, as injury to the AC joint can negatively affect scapulothoracic function and scapulohumeral rhythm.
• Scapular Dyskinesis: AC joint instability may result in scapular dyskinesis (abnormal motion, position, or rhythm of the scapula). This is due to the clavicle acting as the anterior strut supporting the scapula, and proper function relying on intact AC and coracoclavicular ligaments.
• Timing of Evaluation: Scapular malfunction should be assessed at a minimum of 10 days to 3 weeks following acute injury, as severe pain can lead to false-negative results.
• Assessment Tools: Scapular evaluation should include the Scapular Assistance Test (SAT) and Scapular Retraction Test (SRT).
Knowledge Check
Scapular malfunction should be assessed at minimum 10 days to 3 weeks following acute injury because severe pain can lead to false-negative results if assessed too early.
• Clinical Significance: The presence of therapy-resistant scapular malfunction, particularly in Rockwood type III injuries, may indicate the need for surgical stabilization. Scapular dyskinesis is common in chronic type III AC joint injuries, reported in 70% of cases.