Rockwood Classification of AC Joint Injuries

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The patient typically presents after a direct fall onto the point of the shoulder — common in cycling, rugby, skiing, and contact sports. Pain is localised to the AC joint; the arm is held adducted close to the body to relieve strain on the injured ligaments.

Examination sequence:

• Look: Inspect both shoulders from behind. Compare the clavicle contour — a type III or V injury shows a prominent superior step at the AC joint. Type IV may show a posterior bulge. Type VI shows the shoulder sitting inferiorly with a shortened clavicular profile. Check for skin tenting, abrasions, and swelling over the AC joint.
• Feel: Palpate directly over the AC joint — point tenderness is present in all types. Palpate along the clavicle for tenderness extending to the CC ligament interval. In type IV, the posterior edge of the clavicle may be palpable behind the acromion.
• Move: Active forward flexion and abduction are painful, particularly in the mid-range. Cross-body adduction compresses the AC joint and reproduces pain in all types. Assess scapular dyskinesis — early fatigue and abnormal scapulohumeral rhythm may indicate trapezius dysfunction in higher-grade injuries.
• Special tests: Cross-body adduction test — forward flex the arm to 90 degrees then forcibly adduct across the chest. Pain over the AC joint is positive and highly sensitive for AC joint pathology. AC joint compression (Paxinos) test — downward force on the proximal humerus with the arm adducted. Active compression (O'Brien) test — sensitive but less specific for AC joint disorders.

The classification describes six grades of acromioclavicular separation based on the structures disrupted and the magnitude and direction of clavicular displacement.

• The type III debate is the single biggest exam topic. The evidence does not support routine operative fixation for acute type III injuries. Multiple level-1 and level-2 trials and systematic reviews show that non-operative treatment produces comparable functional outcome scores, return-to-work rates, and patient satisfaction at two to five years. Surgery offers better cosmetic appearance and marginally stronger isometric strength, but carries a complication rate of 20 to 40 per cent including hardware failure, wound infection, loss of reduction, and the need for re-operation. Most guidelines recommend non-operative treatment as first line with surgery reserved for specific patient factors (overhead athletes, manual labourers, dominant arm, acute injury less than three weeks, high cosmetic demands).
• Inter-observer reliability is only moderate. Studies using both plain radiographs and CT show fair to moderate agreement between surgeons when classifying the same injury, particularly distinguishing between type III and V injuries and between III and IV when the axillary view is suboptimal. The CC distance measurement threshold between types varies between institutions.
• Weighted stress views are debated. Some centres use bilateral weighted views (5 to 10 kg per hand) to demonstrate dynamic CC instability and help differentiate type II from III. Critics argue that the test is painful, non-standardised, and that all patients with complete CC disruption show widening under stress regardless of treatment implications.
• The classification does not capture chronicity. A type III injury treated non-operatively that remains painful and unstable at six months is a chronic type III — this is functionally a different clinical entity from an acute type III, and the treatment algorithm shifts toward late reconstruction.
• Rockwood type VI is rare and poorly studied. Most published series have fewer than five cases. The classification was described before widespread adoption of CT, and the true incidence and optimal surgical technique are not well established.
• Imaging limitations. Plain radiographs underestimate CC distance compared with CT or MRI. The Zanca view is technically dependent on beam angulation (10 to 15 degree cephalic tilt). MRI can directly visualise the ligaments but is not routine in acute injury management. Normal CC distance is 1.1 to 1.3 cm; a difference greater than 50 per cent compared with the contralateral side suggests complete CC disruption.
• The classification does not account for associated injuries. Concomitant rotator cuff tears, superior labral anterior-posterior (SLAP) lesions, and coracoid fractures can occur with any type and change the treatment plan independently of the Rockwood grade.