The shoulder is comprised of three bones: 1) the humerus (arm), 2) the scapula (shoulder blade) and, 3) the clavicle (collarbone). These bones form two joints: the shoulder joint (glenohumeral) and the AC (acromialclavicular) joint.
An AC joint shoulder separation occurs when the clavicle becomes dislocated from the roof of the shoulder (acromion). This results in severe pain, especially when attempting overhead movements or when swinging the arm across the body. Shoulder separations are usually caused by contact sports such as football. Injuries can vary from minor, as when only the acromioclavicular ligament is torn, to major, as when the coraclavicular ligaments are ruptured, affecting the entire shoulder.
There are three common types of separation injury (although there are more severe grades usually caused by major or life-threatening accidents). The typical sports injuries include:
- Type I: stretching or slight tearing of the acromioclavicular
- Type II: complete tearing of the acromioclavicular ligament
- Type III: complete joint separation involving the tearing of the acromioclavicular ligament and the coraclavicular ligaments, causing the clavicle to push up so that the damage is visible on the shoulder