Acromioclavicular Joint

articulatio acromioclavicularis

The acromioclavicular joint is a small but critical joint at the top of the shoulder that allows the scapula to rotate relative to the clavicle during arm elevation. Its stability depends on the AC ligaments for horizontal control and the coracoclavicular ligaments for vertical control. AC joint injuries are extremely common in contact sports, particularly rugby and cycling, and range from mild sprains to complete dislocations requiring surgical reconstruction.

Region: Shoulder

Clinical Relevance

Clinical Notes

AC joint injuries are classified by the Rockwood system from grade I (sprain, no displacement) to grade VI (inferior dislocation). The step deformity at the AC joint and the piano key sign of reduced superior clavicular displacement with direct pressure are classic findings. Stress radiographs with weights held in each hand assess the degree of coracoclavicular ligament disruption by measuring the CC distance increase compared to the normal side. Grades I through III are managed conservatively and grades IV through VI require surgical intervention.

Pathology

Common Injuries & Conditions

AC Joint Separation

Graded I through VI injury to the acromioclavicular and coracoclavicular ligaments from a fall on the shoulder or outstretched arm, presenting with a step deformity and graded by the degree of clavicular displacement.