of two ligaments, the conoid and the trapezoid ligaments. The Coracoclavicular Ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to the acromioclavicular joint articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the trapezoid ligament and conoid ligament. These ligaments are in relation, in front, with the Subclavius and Deltoideus; behind, with the Trapezius. Variation An X-ray study of 100 shoulders in US soldiers found considerable variation in the size and shape of the joint. The articular surfaces were notably different in size and form. On some they are separated by a meniscus attached to the superior acromioclavicular ligament. This meniscus may be a blade of fibrocartilage that extends nearly halfway into the joint or it may form a complete disc that divides the joint into two parts. In other joints no synovial joint is present with the joint being made by a pad of fibrous tissue attached to the outer end of the clavicle, and no articular cavity. Function The acromioclavicular joint provides the ability to raise the arm above the head. This joint functions as a pivot point (although technically it is a gliding synovial joint), acting like a strut to help with movement of the scapula resulting in a greater degree of arm rotation. Clinical significance Injury A common injury to the AC joint is dislocation, often called AC separation or shoulder separation. This is not the same as a "shoulder dislocation," which refers to dislocation of the glenohumeral joint. Acromioclavicular joint dislocation is particularly common in collision sports such as ice hockey, football, Judo, rugby and Aussie rules, and is also a problem for those who participate in swimming, horseback riding, mountain biking, biking, snow skiing and skateboarding. The most common mechanism of injury is a fall on the tip of the shoulder or FOOSH (Fall On OutStretched Hand). Acromioclavicular joint dislocations are graded from I to VI. Grading is based upon the degree of separation of the acromion from the clavicle with weight applied to the arm. Grade I is slight displacement of the joint, and a badly stretched or partially torn AC ligament. It has the normal separation of <4 mm. Grade II is a partial dislocation of the AC joint with a complete