A dislocation occurs when the ends of your bones are partially or completely moved out of their normal position in a joint. A partial dislocation is referred to as a subluxation, whereas a complete separation is referred to as a dislocation.
AC joint dislocation is the separation of the collar bone or clavicle from the acromion (the top portion of the shoulder blade or scapula at the outer edge of the shoulder) due to severe trauma or injury. AC joint dislocation usually occurs as a result of a direct fall on to the top of the shoulder which causes the shoulder blade to be forced downwards and the collarbone to pop up. It is most commonly seen in individuals involved in sports such as mountain biking, rugby, football, snowboarding, motocross, and horse riding.
Acromioclavicular (AC) joint dislocation is also referred to as acromioclavicular joint separation, subluxation, or disruption.
Anatomy of the AC Joint/Acromioclavicular Joint
The AC joint is located at the highest point of the shoulder. It acts as a junction between the acromion of the shoulder blade (scapula) and the collarbone (clavicle). The section of the scapula that connects to the clavicle is known as the acromion. The joint is easily identified as a slight bump that you feel when you move your hands over the top of your shoulder. The AC joint is supported and stabilised by the capsule of the joint and two ligaments known as the coracoclavicular ligaments that attach the collarbone with the front portion of the shoulder blade (coracoid process). The joint enables you to lift your arm overhead and is used to transmit forces from your arm to the skeleton.
Types of AC Joint/Acromioclavicular Joint Dislocation
The type of AC joint dislocation depends upon the extent of the tear of the acromioclavicular or coracoclavicular ligaments that secure the AC joint in place. The common types of AC joint dislocation include:
Type 1: The acromioclavicular ligament is slightly torn, but there is no damage to the coracoclavicular ligament.
Type 2: The acromioclavicular ligament is totally torn, but there is a slight or no tear to the coracoclavicular ligament.
Type 3: Both the acromioclavicular and coracoclavicular ligaments are totally torn. In this scenario, the clavicle separates from the end of the scapula.
Signs and Symptoms of AC Joint/Acromioclavicular Joint Dislocation
Some of the signs and symptoms of AC joint dislocation include:
- Joint instability
- Restricted range of motion
- Weakness in the arm or shoulder
Diagnosis of AC Joint/Acromioclavicular Joint Dislocation
Your doctor will review your symptoms and medical history and perform a thorough physical examination to check for range of motion, stability, and strength of the joint. Usually with a Type 3 dislocation it is very obvious due to the prominence of the outer end of the clavicle. If necessary, your doctor will order certain imaging tests such as X-ray, MRI, CT scan, or ultrasound for a detailed evaluation of the joint and surrounding soft tissue structures to confirm the diagnosis.
Treatment for AC Joint/Acromioclavicular Joint Dislocation
Conservative treatment is usually effective, but in cases of a severely unstable joint and or ongoing symptoms then surgery may be required.
Most people are able to return to their normal function and contact sports after conservative treatment within 3 months with either few or no symptoms.
Surgery is considered when the deformity is severe, and pain and shoulder dysfunction continue to persist. If the problem is primarily pain and there is minimal or no deformity, then your surgeon may recommend trimming the end of the clavicle in order to prevent it from rubbing against the acromion.
If there is significant deformity noted, then your surgeon may recommend reconstructing the ligaments that attach to the underside of the clavicle. The reconstructive surgery can be performed either arthroscopically or as an open surgery to repair and reattach torn ligaments and stabilise the bones with or without the help of fixation devices, such as plates.
Surgery is followed by rehabilitation to restore motion, flexibility, and strength.