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The acromioclavicular (AC) joint is the articulation between the two bones of pectoral girdle; the clavicle and scapula. It is a plane synovial joint, with flat articular surfaces which are approximately the same in size. Since there are no muscles that act directly on this joint, the movements within it are entirely passive. It is a multiaxial joint, allowing the movements in the three degrees of freedom; protraction-retraction, elevation-depression, and axial rotation.
The function of this joint is to enable the pectoral girdle to follow the movements of the shoulder joint, particularly after the sternoclavicular joint has reached its maximal range of motion. In addition, the AC joint also allows for transmission of forces from the upper limb to the clavicle.
This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the lateral end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibers, which interlace with the aponeuroses of the trapezius and deltoideus; below, it is in contact with the articular disk when this is present. This ligament provides horizontal stability to the acromioclavicular joint
The treatment of this pathology is performed by arthroscopy, where, under direct visualization, an acromioclavicular resection is carried out, that is to say a filing of the bone peaks that rub together, leaving a free space of 8 mm in width to remove the pain.
With an AC joint injury, you may experience: