AC Joint Separation
Anatomy of the Shoulder
The shoulder is made up of two joints, the acromioclavicular (AC) joint and the glenohumeral joint. The AC joint is located at the tip of the shoulder, where the collarbone (clavicle) meets the highest point of the shoulder blade (acromion). The acromion is part of the shoulder blade (scapula).
The glenohumeral joint is where the ball (humeral head) and the socket (the glenoid) meet.
As with other joints in the body, there is a strong, flexible tissue (cartilage) between the two bones. Cartilage reduces friction and prevents the bones from rubbing together. Ligaments are fibrous connective tissues that attach bone to bone. Ligaments found in the AC joint are the AC ligaments and the coracoclavicular (CC) ligament, which serves to connect the clavicle and the coracoid process of the scapula.
What Is AC Joint Separation?
While often referred to as a shoulder separation, this type of injury actually involves the AC joint. An injury to the ligaments that surround and stabilize the AC joint can cause a dislocation of the clavicle from the acromion. An AC joint separation can range from a mild sprain to a severe shoulder separation.
There are 6 types of AC joint separation, and they are classified by the severity of the injury and which ligaments are torn.
- Type 1: A mild injury involving a sprain of the AC ligaments that does not cause the bones to shift out of place.
- Type 2: A more serious injury where the AC ligaments are torn, and the CC ligament is sprained or slightly torn. This puts the clavicle out of alignment with the acromion and results in a bump at the AC joint.
- Type 3: Both the AC ligaments and the CC ligaments are completely torn, and the clavicle is no longer tethered to the acromion. The AC joint is noticeably out of position, with a larger bump, and other associated tissues may be damaged.
- Type 4: Clavicle is posterior to acromion
- Type 5: Wide separation, skin tented, and severe deformity
- Type 6: Very rare
Causes of AC Joint Separation
The most common cause of AC joint separation is a direct hit to the shoulder, potentially from a motor vehicle accident, sports collision, or a fall. The injury can happen when a fall causes you to land directly on top of your shoulder, with your arm pinned to your body. It can also happen when you fall onto an outstretched hand, where the AC joint absorbs the force of the fall.
Symptoms of AC Joint Separation
General symptoms of an AC tear include pain at the top of your shoulder, tenderness at the AC joint, and limited range of motion in the shoulder. However, the symptoms vary depending on the grade of tear.
A grade 1 injury could mean mild swelling, slight pain, and a normal appearance to the shoulder and arms. A grade 2 injury could cause greater pain and swelling, with a minimal change in the appearance of the shoulder. In still more severe injuries, the shoulder may move downward from the weight of the arm. The pain and swelling may be intense, and there is a possibility of bruising or even the collarbone protruding from the skin.
Diagnosis of AC Joint Separation
If you have symptoms of an AC joint separation, your doctor will discuss your medical history with you and give you a physical examination. They will examine your shoulder, arm, and AC joint for tenderness and swelling.
Severe injuries may be diagnosed with just a physical exam, as the separation of the shoulder is obvious, but your healthcare provider will likely order x-rays. This can help them classify the injury by grade. During the x-ray, you may be asked to hold a weight on the injured side, to more clearly see the separation.
Treatment of AC Joint Separation
Most people, including professional athletes, can return to normal function without surgery. In most patients, nonsurgical treatments such as wearing a sling, applying a cold pack to the affected area, and taking over the counter (OTC) medication works to decrease pain until they regain full motion and function.
For type 5 AC separation, surgery may be recommended to restore the function and stability of the impacted acromioclavicular joint.
At a Glance
Dr. Jeffrey Harrison
- Board-Certified, Fellowship-Trained Orthopedic Surgeon
- Head Team Physician US Women's Alpine Team and Weber State University
- Performs over 800 surgeries per year
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