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3 Common AC Joint Injuries

What is AC Joint Dislocation/Acromioclavicular Joint Dislocation?

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 stabilized 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.

Causes of AC Joint/Acromioclavicular Joint Dislocation

The most common cause of AC joint dislocation is a fall onto the shoulder which injures the surrounding ligaments that stabilize the joint. If the force of the fall is severe, the ligaments attached to the underside of the collarbone are ruptured, causing dislocation of the shoulder blade and the collarbone. Some of the causes of AC joint dislocation include:

  • A direct blow to the joint
  • Heavy fall onto the tip of the shoulder or top of the shoulder
  • Fall on an outstretched hand
  • Arthritis of the joint
  • Lifting heavy objects, such as weightlifting
  • Repetitive overhead activity
  • Sports injury, such as contact sports
  • Fractures

Signs and Symptoms of AC Joint/Acromioclavicular Joint Dislocation

Some of the signs and symptoms of AC joint dislocation include:

  • Pain
  • Joint instability
  • Restricted range of motion
  • Swelling
  • Bruising
  • Tenderness
  • 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. 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, surgery is required. The treatment methods include:

Conservative Method

  • Medications: You will be provided with anti-inflammatory pain medications like ibuprofen or naproxen to reduce swelling and pain.
  • Rest: You will be instructed to avoid activities that provoke pain and to use a sling to immobilize your shoulder and arm.
  • Ice: An ice pack can be applied for 15-20 minutes at a time to reduce swelling and pain.
  • Physical therapy: Specific exercises will be recommended to help strengthen the shoulder muscles.

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.

Surgical Method

Surgery is considered when the deformity is severe and pain continues to persist. 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 stabilize the bones with or without the help of fixation devices, such as plates.

Surgery is followed by rehabilitation to restore motion, flexibility, and strength.