AC joint Osteology the AC joint is a diarthrodial joint fibrocartilaginous intraarticular disc is located between the osseous segments Motion majority of motion is from the bones, not through the joint clavicle rotates 40-50° posteriorly with shoulder elevation 8° of rotation through AC joint remainder from scapular rotation and sternoclavicular motion joint itself is limited to gliding motions only Stability acromioclavicular ligament provides horizontal stability has superior, inferior, anterior, and posterior components superior ligament is strongest, followed by posterior coracoclavicular ligaments (trapezoid and conoid) provides vertical stability trapezoid inserts 3 cm from end of clavicle stabilizer against horizontal and vertical loads conoid inserts 4.5 cm from end of clavicle in the posterior border more important ligament vertical stabilizer of AC joint normal CC distance (superior coracoid to inferior clavicle) is 11-13mm deltotrapezial fascia, capsule, deltoid and trapezius act as additional stabilizers