TRIP

Acromioclavicular Articulation

Gray, Henry Anatomy of the Human Body , 2000

(Articulatio Acromioclavicularis; Scapuloclavicular Articulation) The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula.
—The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments.
—This ligament is a quadrilateral band, covering the superior part of the articulation, and extending between the upper part of the acromial 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 is somewhat thinner than the preceding; it covers the under part of the articulation, and is attached to the adjoining surfaces of the two bones.
It is in relation, above, in rare cases with the articular disk; below, with the tendon of the Supraspinatus.
When present, it generally only partially separates the articular surfaces, and occupies the upper part of the articulation.
—There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two.
It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion.
   The Trapezoid Ligament ( ligamentum trapezoideum ), the anterior and lateral fasciculus, is broad, thin, and quadrilateral: it is placed obliquely between the coracoid process and the clavicle.
It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle.