Acromioclavicular (AC) Joint Separation

An acromioclavicular joint separation, or AC separation, is a frequent injury among accident victims. In an AC separation, the clavicle (collar bone) separates from the scapula (shoulder blade). In most cases, AC injuries respond well to conservative management, such as physical therapy; but sometimes, the separation causes such extensive structural damage that surgical correction is required.

How do AC Separations Occur?

AC separations occur when downward force is applied to the shoulder blade. Even though the shoulder blade pulls on the clavicle during an impact, the clavicle generally remains in a fixed position, anchored by joint ligaments known as sternoclavicular. The trauma that results from this pulling force disrupts the ligaments connecting the two bones: the scapula and clavicle.  AC joint separations do not always—but can—result in fractures.

Six Degrees of Separation

AC separations are classified based on the degree of displacement and the location of the distal clavicle into six types. These are summarized below:

Type I: Ligamentous Sprain. Pain may be experienced when the shoulder joint is touched or moved. There is no pain in the area of the coracoclavicular ligaments (see diagram). Bruising and slight swelling may occur around the joint.

Type II: AC joint disruption with intact coracoclavicular ligaments (fibrous, stretchy tissue connecting the scapula to the clavicle). Pain at the joint may be moderate to severe, and arm movement hurts. There may be a small bump on the top of the shoulder where the shoulder blade ends. The clavicle may move when it is pushed. The area around the coracoclavicular ligaments may be painful when touched.

Type III: Both acromioclavicular and coracoclavicular ligaments are torn, but the protective layer or fascia of important shoulder musculature—deltoid or trapezial muscles—is not significantly damaged. A large bump, created by the clavicle’s dislocation, can be easily seen near the end of the clavicle. This bump is permanent, and the pain associated with this type of injury is severe.

Type IV: This is like a Type III injury with the separation of the coracoclavicular ligament from the clavicle. The end of the clavicle is displaced and may poke (but typically not break) the skin. This is a very serious injury and generally requires surgical correction to resolve the resulting pain, disability and deformity.

Type V: Type V AC joint separation presents much like a Type III except that the trapezial and deltoid fascia is stripped from the acromion (bony outgrowth at the end of the shoulder blade) and clavicle. The pain is excruciating. The shoulder permanently droops due to the downward displacement and functional loss of the scapula and humerus. This injury requires surgery.

Type VI: This is considered an extremely serious injury. Type VI AC joint separation is usually the result of severe trauma, such as a vehicular accident, and frequently presents with multiple other injuries. The injury is believed to be caused by dramatic forces pulling and externally rotating the arm. The entire shoulder unit is decimated, with disruption of ligaments and clavicle. Type VI injuries typically cause loss of sensation/numbness which resolves after surgery. Pain and disability is significant. Surgery is required and involves the removal and reattachment of damaged tissue.


Diagnosis of AC joint separation is based on a physical examination of the shoulder and X-rays. Special tests involving various arm movements, such as flexing the elbow and crossing the arms over the chest, can also help confirm the diagnosis.


Treatment of AC joint separation depends on the severity of the injury. Type I and II injuries are typically addressed through resting (immobilizing with a sling) and icing the joint. Physical therapy may also be recommended for restoring range of movement and restoring muscle strength.

Type IV, V and VI AC separations require surgery followed by physical therapy to restore full range of motion, muscle strength and shoulder stability. (Some surgeons also believe that surgery is the best option for a Type III injury as well.)

Consult with a Top Trial Attorney

As personal injury lawyers, we have represented numerous cases involving all types of AC joint separation. The best course of treatment is not always clear-cut, but we can help guide you to top orthopedic specialists who can provide recommendations as to the most appropriate course for your injury. Our goal is to help you regain full and productive function of your life, the way it was before the trauma that upended it. If you or a loved one has suffered an AC joint separation due to the negligent or purposeful actions of another, call one of our top trial lawyers to discuss your legal options at 314-409-7060 or 855-40-CRASH (toll free).

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