Acromioclavicular injuries -Daniel M. Veltri MD

Acromioclavicular injuries (AC separations) are common shoulder injuries in contact sports.  The mechanism of injury is a fall onto the point of the shoulder or a fall onto an outstretched hand. The majority of these athletic injuries can be treated conservatively. We will outline the diagnosis and treatment of acromioclavicular injuries


The clavicle connects the upper extremity to the apppendicular skeleton through its connection to the scapula. This includes both the acromioclavicular  joint and its capsule and accompanying ligaments and the coracoclavicular ligaments.  Pure acromioclavicular separations involve ligament injuries of varying degrees of the acromioclavicular (AC) ,and coracoclavicular(CC) ligaments.  Fractures of the coracoid and clavicle also can mimic acromioclavicular joint separations since they also disrupt the connection between the scapula and axial skeleton. The distal clavicle physis does not close until 18-22 years of age, so physeal fractures of this area may clinically and radiographically appear as AC separations.

The acromioclavicular capsule and ligaments provide the primary restraint to horizontal translation of the clavicle. The posterior superior acromioclavicular ligaments   prevent posterior translation of the clavicle relative to the acromion. The conoid and trapezoid ligaments are the primary restraint to vertical displacement of the clavicle relative to the scapula. (1) The deltoid and trapezius, through their attachments to the clavicle, provide dynamic stability to the ac joint.

Mechanism of Injury

The most common mechanism of AC joint separation is a direct impact on the shoulder with the shoulder adducted with the arm at the side. The force directly drives the acromion inferiorly relative to the clavicle. The sequence of injury is first to the acromioclavicular ligaments and capsule followed by the coracoclavicular ligaments and then the deltotrapezial fascia. This mechanism is exemplified by the football player being tackled to the ground while holding the ball at his side or the hockey player being checked into the boards with initial impact to the shoulder.   Similar injury can occur by indirect force with a fall on an outstretched hand or elbow. In an adolescent with an open distal clavicular physis the same type of injury can result in failure of the physis and result in an accompanying fracture prior to ligament failure. Finally the coracoid can fracture prior to failure of the coracoclavicicular ligaments mimicking an AC separation.


AC joint injuries are most commonly classified by the Rockwood classification Type I through VI.(2) Type I represents injury to the AC ligaments alone without instability. Type II is an injury to both AC and CC ligaments with horizontal and some vertical instability. Type III represents injury to the AC and CC ligaments with 100% displacement of the clavicle relative to the acromion. Type IV injuries involve posterior displacement of the clavicle through the trapezial fascia and cannot be reduced with physical exam. Type V injury involves complete injury to the AC and CC ligaments with disruption of the deltotrapezial fascia. There is 300% displacement or greater of the clavicle relative to the acromion. Type VI is a rare injury with distal displacement of the clavicle in a subcoracoid position. In this classification Type IV through VI are generally treated with surgery, and Types I and II are treated with rehabilitation. The majority of Type III injuries are treated with rehabilitation.


The patient initially presents with a history of a traumatic fall either to the shoulder or to the elbow and hand. The patient complains of pain localized to the AC joint. Inspection of the shoulder  reveal swelling over the AC joint, ecchymosis , possible abrasions in the impact area, and some degree of drooping of the shoulder relative to the clavicle.(Figure 1)  Tenderness is present over the AC and CC ligaments.  Palpation reveals horizontal and vertical instability of the distal clavicle of varying degrees. Manual reducibility of the AC joint is tested by stabilizing the distal clavicle with one hand and lifting the elbow and accompanying acromion upward.  O’Brien and crossed body adduction stress tests are used to assess stability of the AC joint. If the clavicle crosses over the acromion with shoulder adduction, the injury is more likely to require surgery.  Standard neurovascular exam should be performed to rule out any associated injuries especially in Type IV through V injuries. Also standard tests for labral injuries should be performed due to the recent findings of labral tears associated with higher types of AC separations.(3,4)

Radiographic evaluation

Standard AP and 10-15 degree Cephalic tilt views are useful in assessing the Type of AC injury. (Figure 2) Weighted AC views are not useful in the acute setting due to the patients guarding with pain, Scapular Y views may show the clavicle overriding the acromion.  Axillary views are helpful for determining posterior displacement of the clavicle and possible coracoid fracture.


Type I and II injuries are treated with a sling for 1-2 weeks for comfort followed by rehabilitation to regain full strength and range of motion. Contact sports are avoided until the AC and CC ligament injuries are healed to avoid potential  additional injury, There are no studies that determine a safe return to sport but in general  most surgeons recommend 2-3 months prior to returning to full contact sport.

Traditionally Type IV through VI  have been treated with surgery. Initial attempts at reconstruction involved transfer of the coracoacromial ligament with AC or CC stabilization with k-wires , screws or sutures.(5)  Dynamic transfers of the conjoint tendon to the distal clavicle have also been used.

More recently, anatomic coracoclaviclular reconstructions have been popularized . These reconstructions use allograft or autograft tissue through or around the coracoid to reconstruct the CC ligaments while fixing the clavicle to the coracoid with temporary additional fixation with sutures or screws. (6) (Figure 3)

Finally newer arthroscopic techniques for AC separations have been developed to reduce the clavicle to the coracoid using metal buttons and high strength suture with or without allograft support.(7-10) There are no Level I studies supporting one specific technique, but open  anatomic coracoclavicular techniques are gaining popularity due to early high success rates in maintaining stability and reduction(6) but they are not free of complications.(11-12) Most athletes can return to sports 6 months following surgical reconstruction.

There is some persistent controversy in the management of Type III AC separations, Traditionally h these were treated with rehabilitation except for laborers and high demand athletes. With the proliferation of new arthroscopic techniques, there has been a new enthusiasm for surgically treating more Type III separations. However there is no data to support routine surgical treatment of Type III AC separations.(13-15)A recent Level I Canadian Study did not support improved outcomes for surgical management of Type III AC separations using a temporary hook plate.  While other techniques of fixation may result in better outcomes, current data suggest the majority of Type III injuries should be treated with rehabilitation.

AC separations are common sports injuries to the shoulder. They can occur with direct or indirect trauma to the shoulder. With appropriate history, physical exam, and radiographs one can determine the extent of the injury. Classification helps determine management. Types IV through VI are treated with surgery and Types I and II are treated with rehabilitation. While treatment of Type III injuries remains controversial, the majority are treated with rehabilitation.  The majority of AC separations can be treated to allow the athlete a full return to sports.


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