ACGelenk

The acromioclavicular joint (AC joint), referred to in German as ACGelenk, is a small synovial diarthrosis at the top of the shoulder that connects the lateral end of the clavicle to the acromion of the scapula. It is part of the shoulder girdle and contributes to the full range of shoulder motion.

Anatomy and ligaments: The joint surfaces are the lateral end of the clavicle and the acromion. The joint capsule is reinforced by the acromioclavicular ligaments (superior and inferior) and the coracoclavicular ligaments (conoid and trapezoid), which suspend the scapula from the clavicle and provide stability. An articular disc is variably present in some individuals. The arrangement allows small gliding movements between the bones.

Function and biomechanics: The AC joint permits slight translational gliding that accompanies elevation and rotation of the scapula, aiding shoulder motion. The coracoclavicular ligaments mainly prevent excessive vertical and horizontal displacement of the clavicle relative to the scapula, helping to maintain joint stability during arm movements and weight bearing.

Clinical relevance: The joint is susceptible to injuries, particularly from direct trauma or falls onto the shoulder, leading to acromioclavicular joint separation. Classification systems (for example, Rockwood grades I–VI) describe the extent of ligament injury and clavicular displacement. Osteoarthritis of the AC joint can occur with aging or overuse. Treatment ranges from rest and physical therapy for minor injuries or degenerative changes to immobilization and analgesia for moderate injuries, with surgical reconstruction or distal clavicle resection considered in selected high-grade or persistent cases.

Diagnosis and imaging: Diagnosis is clinical, supported by radiographs in multiple views to assess alignment and ligament disruption. MRI can evaluate associated injuries or concurrent pathology.