Anatomical observations on the acromioclavicular joint and supporting ligaments.

An anatomical study of the acromioclavicular (AC) joint and its supporting ligaments was performed using both macroscopic and microscopic methods. The project used 63 cadaver shoulders of unknown ages. Fifty-three joints were used for macroscopic and 10 for microscopic study. The data consisted of micrometer measurements of the dimensions of the extrinsic and intrinsic ligaments of the AC joint; measurement and description of the intraarticular meniscus and the superior and inferior capsular ligaments of the AC joint; and the anatomical course and relationship of the coracoacromial (CA) ligament to the supporting ligaments of the AC joint and a description of its insertion on the acromion process. The following observations were made: The coracoclavicular ligament, especially the trapezoid ligament, provides significant soft tissue restraints to upward displacement of the clavicle. A complete AC joint disc was found in only one, meniscoid discs in 25, remnants of discs in 16, and no discs in 11 of the 53 joints studied macroscopically. (No age correlation was made since the ages of the cadavers were unknown). The CA ligament interconnects with the inferior capsular ligament of the AC joint as well as with the coracoclavicular and coracohumeral ligaments. It also has a broad area of insertion on the inferior acromial surface. The CA ligament appears to function as a buffer between the acromion and the rotator cuff, and to provide support for the AC joint. Transection of the CA ligament may result in loss of this buffering function.