DAMAGE TO THE ACROMIOCLAVICULAR JOINT (AC)
A shoulder dislocation is a fairly common injury, especially in certain sports. Most of the injuries are damage to the acromioclavicular joint (AC). The AC joint connects the shoulder blade and the collarbone. Shoulder dislocation and damage (dislocation) of the acromioclavicular joint are often confused with each other. These are completely different injuries. This guide will help you understand: what is the acromioclavicular joint (AC)? What happens when the joint is damaged (dislocated)? How is the AC joint damage treated?
How is the AC joint built and what is its function? The shoulder joint consists of three bones: scapula, humerus and collarbone. The part of the shoulder blade that forms the vault of the joint is called the acromion. The AC joint is the junction between the acromion and collarbone. The ligaments stabilize the connection. The ligaments are bands of the soft tissue that connect the bones. The acromioclavicular ligaments surround and stabilize the AC joint, forming the articular capsule. It is a waterproof bag that surrounds the joint, it is filled with joint fluid. Two other ligaments, the coracoclavicular ligaments, stabilize the collarbone by attaching to the coracoid process of the scapula. Damage to the AC joint can be mild to severe, depending on which ligaments have been stretched or torn. The mildest type of an injury is a minor damage (strain) of the acromioclavicular ligaments. It is the first degree injury, while the second degree injury is damage to the AC ligaments and the coracoclavicular ligaments. Complete rupture of the AC ligaments and the coracoclavicular ligaments is the third degree injury with a positive “piano key sign”.
How does the AC joint damage occur?
The most common cause of AC joint damage is a fall on the shoulder. When the limb hits the ground, the force of the impact moves the blade downwards. Because the collarbone is attached to the chest, it cannot move enough to follow the movement of the shoulder blade. As a result – the ligaments stabilizing the AC joint are damaged, displacing the collarbone.
The symptoms range from mild to severe pain of the AC joint in the event of complete dislocation. The second and third degree injury may cause swelling and bruising. In the third degree injury, the patient can experience the feeling of loose collarbone displacement (‘piano key sign’) and deformation of the AC joint.
What examinations will be performed?
Your doctor will need to obtain the information about an injury and take detailed medical history. You will be asked questions about recent shoulder injuries. You will have to assess pain on a scale from one to ten. Diagnosis is usually preceded by a physical examination. The doctor can move the shoulder. It can be painful, but it is very important that your doctor finds the exact location of pain and identifies movements triggering pain. The doctor may order an X-ray to visualize damage to the joint and exclude collarbone fracture. Occasionally, an X-ray with loading of both hands is performed in order to confirm instability.
Treatment (What are treatment options?)
Treatment of the first and second degree injury is usually analgesic with a short period of rest using a sling. The rehabilitation program is prepared by a physiotherapist. Treatment of the third degree AC injury is somewhat controversial. Many studies have shown no difference between surgical and conservative treatment. Even with surgery, there is a possibility of persistent deformity of the area of an injury. A large proportion of patients after operation need another, additional surgery.
Research has revealed the condition of the AC joint after an injury. Many patients, regardless of whether they have undergone surgery or non-surgical treatment, will require surgery in the future. This is due to the fact that a damaged joint degenerates faster than an intact joint. It becomes deformed and painful over time. The process may take several years, but sometimes even one to two years.
Some surgeons prefer to operate third degree AC joint injuries, especially in competitive hammer/discus/javelin athletes. Surgery is usually done through an incision over the AC joint. A surgeon sets the articular structures in the correct position (reposition). A screw or other type of fixation is used to stabilize the collarbone during the process of biological healing of the ligaments. Stabilization of the AC joint with a screw is based on joining the shoulder end of the collarbone with the coracoid process of the scapula. Some operators use tape to fix the clavicle with the coracoid process. Small holes are made in the collarbone and the coracoid process, tape is threaded through the structures and fixed, in some cases, ligaments are also repaired. If a screw is used, it is usually removed six to eight weeks after surgery.
In the Szpital Zakonu Bonifratrów, arthroscopy of the shoulder is performed by a team of specialists in orthopedics and traumatology:
Stanisław Szymanik, MD – Head of the Diagnostic and Treatment Department
Michał Latos, MD
Michał Starmach, MD