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Injuries to the acromioclavicular joint are also known as shoulder separation injuries. They are distinct from shoulder dislocations which take place at the shoulder joint itself, the gleno-humeral joint. Shoulder separations occur at at the small joint at the top of the shoulder where the outer end of the clavicle ( collar bone ) meets the acromion, the superior outermost portion of the scapula

Injury to the acromioclavicular joint (AC joint) usually occurs from a fall on to the outer portion of the shoulder and usually with the arm at the side. It is characterized by varying degrees of pain and swelling dependent upon the extent of the injury to the supporting ligaments. The patient will point directly to the top of the shoulder as the painful injured area.

The AC joint is held together and stabilized by the acromioclavicular ligaments that surround the joint and by the very strong coracoclavicular ligaments that hold the clavicle at its mid portion to the coracoid, another adjacent part of the scapula.

The extent of injury to the AC joint is determined by the degree of trauma sustained and is measured by the extent of injury to both the AC (acromio-clavicular ) and CC ( coraco-clavicular ) ligaments.

Injuries to the acromioclavicular joint may be classified into three major groups.

Grade 1 injuries are a sprain or partial tearing of the AC ligaments and capsule that surround the AC joint and do not give rise to any clavicular instability.The coracoclavicular ligaments remain intact.

Grade 2 injuries involve a complete rupture of the AC ligaments and capsule and allow some displacement ( subluxation ) of the clavicle from its normal relationship to the acromion. The patient presents with pain and swelling about the AC joint and possibly some limited prominence of the distal end of the clavicle.

In both Grade1 and Grade 2 injuries the coracoclavicular ligaments remain intact.

Grade 3 injuries involve complete tearing of both the AC and CC ligaments and those injuries allow significant upward and posterior dislocation of the clavicle in relation to the acromion. The patient presents with considerable pain and swelling and obvious upward displacement of the clavicle.

Treatment of these injuries varies, of course, with the extent of injury.
Grade 1 injuries are treated with ice for swelling, possibly anti-inflamatories and analgesics as needed and a sling for support. As the acute symptoms subside a self-administered or formal therapy program is used to help regain motion and function and when appropriate the shoulder is guided back to a full activity schedule. The results are almost always good.

Grade 2 injuries are treated in a similar conservative manner. They take longer to resolve but results are usually good as is the return of function of the A-C joint. On occassion Grade 2 injuries may result in late symptoms related to the AC joint Attention to the joint at a later date will usually yield good results.

Grade 3 injuries are also mostly treated conservativly and on occassion with support to bring the clavicle down to more normal position. There are further subclassifications of the Grade 3 injury depending on the degree of soft tissue damage. Grade 3 injuries are frequently considered for surgical repair. Surgical repair involves operative fixation and repair of both the CC ligaments and the AC joint and the other injured soft tissue structures. Results are usually good but both the extent of injury and surgery lead to a more prolonged recovery and rehabilitation period.

Rehabilitation is an important part of the recovery process and becomes more important and prolonged with the more severe Grade 2 and 3 injuries. The patient must be guided through a program designed to recover range of motion, strength and neuromuscular control of the shoulder.

Results of treatment for AC injuries are generally quite good for the less extensive injuries but results may be compromised to some degree in the more extensive injury. Patient perception of outcomes will vary with age and functional demands of the shoulder.

In summary – Acromioclavicular separation is usually caused by a fall on the outer aspect of the shoulder. The degree of injury is related to the extent of injury to the acromioclavicular and coracoclavicular ligaments and varies from the more simple sprain to complete rupture of all noted ligaments and dislocation of the clavicle. Treatment is usually conservative but the more extensive injuries may require a more aggresive surgical approach.