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Acromioclavicular Joint Sprain

What is an Acromioclavicular Sprain?

(also known as AC Joint Sprain)

An acromioclavicular (AC) joint injury is commonly referred to as "shoulder separation" and should not be confused with a shoulder dislocation.

What is the Acromioclavicular (AC) Joint?

The shoulder joint is formed at the junction of three bones: the collarbone (clavicle), the shoulder blade (scapula), and the arm bone (humerus). The scapula and clavicle form the socket of the joint, and the humerus has a round head that fits within this socket. The end of the scapula is called the acromion, and the joint between this part of the scapula and clavicle is called the acromioclavicular joint.

When the acromioclavicular joint is disrupted, it is called a shoulder separation and can form a "step" if displaced. Another name for this injury is an acromioclavicular joint separation, or AC separation or an AC joint sprain.

The ligaments that hold the joints together are the acromioclavicular, coracoacromial and coracoclavicular (trapezoid and conoid) ligaments.

How is the Acromioclavicular (AC) Joint Injured?

Direct forces can injure it when a person collides with a solid object or surface such as a fall from a bicycle or during a football tackle where the shoulder hits the ground. It may also be injured indirectly when a person falls on an outstretched arm. The contact force is transmitted up through the arm, which forces a separation of the acromion and clavicle. The ligaments are stretched and damaged in the process.

What are the Symptoms of an AC Joint Sprain?

Pain is the most common symptom of a separated shoulder, and is usually severe at the time of injury. Evidence of traumatic injury to the shoulder, such as swelling and bruising, are also commonly found.

The injury is graded by severity from Grade I (minimal joint disruption) to Grade III (severe injury). If the injury is more severe, Grade III, a bump caused by the separated joint may be seen or felt at the tip of the shoulder bones. The diagnosis of shoulder separation is often quite apparent from hearing a story that is typical of this injury, and a simple physical examination.

An x-ray should be performed to ensure there is no fracture of these bones. If the diagnosis is unclear, an x-ray while holding a weight in your hand may be helpful. When this type of x-ray is performed, the force of the weight will accentuate any shoulder joint instability and better show the effects of the separated shoulder.