AUTHOR AND EDITOR INFORMATION

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INTRODUCTION

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Injuries in and around the shoulder are common in today's athletic society. Proper knowledge of the different problems and treatment options is necessary to get patients back to their preinjury state.

Background

Acromioclavicular (AC) joint injuries are common and often seen after bicycle wrecks, contact sports, and car accidents. The AC joint is located at the top of the shoulder where the acromion process and the clavicle meet to form a joint. Several ligaments surround this joint and depending on the severity of the injury, a person may tear one or all of the ligaments. Torn ligaments lead to AC joint sprains and separations. The distal clavicle and acromion process can also be fractured. Injury to the AC joint may injure the cartilage within the joint and can later cause arthritis of the AC joint. This article discusses the anatomy of the joint, the diagnosis of this condition, and the different treatment options.

Frequency

United States

Injuries to the AC joint are the most common reason that athletes seek medical attention following an acute shoulder injury. Glenohumeral dislocations (see Shoulder Dislocation) are the second most common injuries seen. Men in their second through fourth decades of life have the greatest frequency of AC joint injuries. These injuries are most often incomplete tears of the ligaments.

Functional Anatomy

The AC joint is made up of 2 bones (the clavicle and the acromion), 4 ligaments, and a meniscus inside the joint.

• The AC joint is surrounded by a thin joint capsule and 4 small ligaments. These ligaments mostly give joint stability to anterior and posterior translation. They provide the horizontal stability to the joint.



• Another set of ligaments also provides vertical stability to the AC joint. These ligaments are called the coracoclavicular (CC) ligaments. The CC ligaments are found medial to the AC joint and go from the coracoid process on the scapula to the clavicle.



• Different injuries result in different tears of the 2 CC ligaments (the conoid and the trapezoid). Torn AC joint ligaments and/or torn CC ligaments are seen in AC joint sprains. The meniscus that lies in the joint may also be injured during sprains or fractures around the AC joint.

Sport Specific Biomechanics

When a person falls onto their shoulder, the force pushes the tip of the shoulder down. The clavicle is usually kept in its anatomic position while the shoulder is driven down, which injures the different ligaments or causes a fracture. When the ligaments are injured they are either sprained or, in more severe cases, torn.

AC joint sprains have been classified according to their severity. In a type I sprain, a mild force applied to these ligaments does not tear them. The injury simply results in a sprain, which hurts, but the shoulder does not show any gross evidence of an AC joint dislocation. Type II sprains are seen when a heavier force is applied to the shoulder, disrupting the AC ligaments but leaving the CC ligaments intact. When these injuries occur, the lateral clavicle becomes a little more prominent. In type III sprains, the force completely disrupts the AC and CC ligaments. This leads to complete separation of the clavicle and obvious changes in appearance. The lateral clavicle is very prominent. A few more types of AC joint sprains have been classified, but types I - III are the most common.

Classification of acromioclavicular (AC) joint injuries.

An AC joint sprain is more common than a fracture after an injury. However, fractures of the distal clavicle and the acromion process may occur, so the health care provider must be aware of such injuries and ready to diagnose and treat them as well (see Clavicular Injuries).

CLINICAL

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History

Acromioclavicular (AC) joint injury should be considered in any patient complaining of pain over the superior part of the shoulder. Injuries to this part of the body are painful.

• The most common mechanism for an AC joint injury is a fall directly onto the acromion with the arm adducted up against the body. Multiple indirect forces can result in an AC joint injury. A fall onto an outstretched hand and a downward force on the upper extremity have been implicated in AC joint injuries.



• In the immediate setting, the patient may initially experience generalized shoulder tenderness and swelling; however, as the diffuse pain resolves, specific point tenderness over the AC joint is usually noted. The athlete may note a significant abrasion or prominence of the distal clavicle.



• Athletes involved in weight training typically experience pain with specific exercises such as bench press and dips.



• Many individuals experience nocturnal pain and awakening when rolling onto the involved shoulder. Rolling onto the shoulder puts pressure on the AC joint.



• Rarely, the patient may report popping or catching in the region of the AC joint.

Physical

• Patients have pain over the AC joint. Swelling, bruising, and a prominent clavicle may be evident, depending on the type of sprain that the patient has sustained. In types I and II, deformity is usually minimal. In type III, the distal clavicle is abnormally prominent. Of note, clavicle fractures, without AC joint sprains, can also cause the clavicle to be prominent.



• The patient has poor shoulder range of motion and moderate pain when trying to raise up the arm.



• In the acute situation, the examiner may have difficulty ruling out a concomitant rotator cuff tear as active and passive shoulder abduction maneuvers are difficult to perform in the face of an AC joint separation.



• The most reliable physical examination test for AC joint pathology is the cross-body adduction test. The test is performed by elevating the arm on the affected side 90º while the examiner grasps the elbow and adducts the involved arm across the body. Although reproduction of pain with this maneuver may occur in patients with posterior capsule tightness or subacromial impingement, pain is suggestive of AC joint pathology. Restriction of range of motion, which is rarely associated with AC joint pathology, more likely suggests adhesive capsulitis or glenohumeral arthritis.

Causes

See History.

DIFFERENTIALS

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Other Problems to be Considered

Glenoid labrum tear

WORKUP

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Imaging Studies

• Radiographs
  
  
  • As with all skeletal injuries, a minimum of 2 views is necessary to evaluate the individual injury.
    
    
    • Anteroposterior (AP) and lateral views are the minimum needed to evaluate an acromioclavicular (AC) joint injury. The AP view should be taken with the arms at the side, and both AC joints should be imaged for comparison. If a true AP view is obtained, the AC joint can be seen superimposed on the spine of the scapula; hence, some authorities have recommended the Zanca view, in which 10-15° of cephalic tilt of the radiographic beam provides a clearer image of the AC joint.
    
    
    
    • An axillary lateral view is also needed in suspected AC joint injuries to account for any anterior or posterior displacement of the distal clavicle.
      
      
      Type III AC joint separation.
  
  
  
  • If an unstable AC joint injury is suspected, yet not confirmed on routine AP and lateral views, stress views may be indicated.
    
    
    • Ten to 15 lb of weight should be attached to the wrist of the affected side, and an AP view can be taken. This stress tests the integrity of the coracoclavicular (CC) ligament, and, if the ligament has been disrupted completely, the test will demonstrate the complete dislocation.
    
    
    
    • Routine use of stress radiographs is not recommended in the emergency department setting because of the painful nature of the test. Weighted stress tests may be valuable in follow-up care if the clinician has any doubt about the instability of the AC joint. Even with conservative care of types III-VI AC disruptions, this test may be helpful for determining a timetable for return to conditioning and sporting activities.
       
  • Athletes with a prior history of AC injury or a history of heavy weight lifting may present with relatively acute shoulder pain over the distal clavicle and may have classic radiographic findings of distal clavicle osteolysis or AC osteoarthritis (ie, joint narrowing, distal clavicle or acromial spurring). When these radiographic findings are present, the clinician may expect that seemingly little trauma may result in significant pain.
• MRI
  
  
  • MRI is not ordered routinely in the management of straightforward AC disruptions. Detailed knowledge of AC and CC ligamentous injury is not needed for conservative or, in rare cases, surgical care.
  
  
  
  • In middle-aged and older patients who continue to have disabling shoulder pain after the acute pain of an AC disruption abates, one may consider an MRI to evaluate for a possible rotator cuff tear.
  
  
  
  • Very rarely, athletes with persistent pain over the AC joint merit an MRI to determine whether or not the cartilaginous disk has been damaged irreversibly and determine whether or not the process of distal clavicle osteolysis or early osteoarthritis has begun.

TREATMENT

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Acute Phase

Rehabilitation Program

Physical Therapy

Acromioclavicular (AC) joint injuries are painful and the patient often lacks full range of motion after the injury. Physical therapy plays a role in the treatment of these patients. The author routinely starts therapy within the first couple of weeks in AC joint sprains. For fractures, wait until evidence of healing is apparent either clinically or on radiograph before starting formal therapy. Therapy for degenerative joint disease of the AC joint has not been proven successful.

Surgical Intervention

AC joint sprains do well with conservative management. Type I and II injuries never necessitate surgical care to reconstruct the injured ligaments. These injuries may need further care if the AC joint gets arthritic from the injury (see image). Surgical intervention may be an option in type III AC joint sprains, but only after the patient has failed a good trial of conservative treatment with physical therapy and medication. The procedure for these patients is reconstruction of the torn coracoclavicular (CC) ligaments with either local tissue or an allograft. In the past, surgeons have used screws, sutures, suture-tape, synthetic grafts, and K-wires to try to repair the defect. These have all fallen out of favor and the criterion standard is to reconstruct the torn ligaments as mentioned above. 

Postoperative CC ligament reconstruction. The clavicle is back to its normal position. The anchor in the clavicle keeps the allograft tendon from coming off of the clavicle. Also note the distal clavicle has been excised because it had traumatic arthritis from the injury.

Fractures in and around the AC joint are mostly treated conservatively in a sling. The few times surgery needs to be considered is for a moderate amount of displacement of the fracture fragments. Surgery is indicated for open fractures, neurovascular injury, and for those in which the skin is compromised and may rupture from the pressure of the prominent bone.

Injuries that lead to arthritis of the AC joint are also treated with conservative measures first. Anti-inflammatory medication and intra-articular steroid injections work well for degenerative changes in the AC joint. In patients who failed conservative therapy, excision of the distal clavicle can be performed with a minimally invasive arthroscopic procedure.

Consultations

If the athlete has sustained concomitant rib fractures with shortness of breath, good quality chest radiographs are indicated. A consult from a pulmonary physician or cardiovascular chest surgeon may be necessary.

MEDICATION

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Initial treatment of degenerative arthritis of the acromioclavicular (AC) joint may include the use of nonsteroidal anti-inflammatory drugs (NSAIDs) along with occasional corticosteroid injections.

Drug Category: NSAIDs

Have analgesic, anti-inflammatory, and antipyretic activities. Their mechanism of action is not known, but they may inhibit cyclo-oxygenase activity and prostaglandin synthesis. Other mechanisms may exist as well, such as inhibition of leukotriene synthesis, lysosomal enzyme release, lipoxygenase activity, neutrophil aggregation, and various cell membrane functions.

Drug Category: Corticosteroids

Have anti-inflammatory properties and cause profound and varied metabolic effects. Corticosteroids modify the body's immune response to diverse stimuli.

FOLLOW-UP

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Return to Play

The author has the following strict return to sports criteria that he addresses with the patients and physical therapists.

• No swelling/pain with functional activity



• Isokinetic strength 80% of opposite rotator cuff



• Full active and passive range of motion



• Scapula stable through full range of motion and has normal scapulohumeral rhythm



• Pain-free activities of daily living (ADL)

Complications

Just like any other joint in the body, once the acromioclavicular (AC) joint has been injured it has a tendency for arthritis and pain. The most common problem after these injuries is pain in the AC joint. In type III sprains, the most common setback is also instability in the clavicle from the torn ligaments. 

Postoperative complications may also arise. The most common complication is mild residual instability after ligament reconstruction. This was more common when screws, sutures, suture-tape, and K-wires were being used to repair the coracoclavicular (CC) ligament tears. Infections may also occur, but are rare, occurring less than 1% of the time. 

When a patient is dealing with an arthritic AC joint, the most common problem is inadequate resection of the clavicle during surgery. This causes continued AC joint pain in these patients, but is easily fixed with proper arthroscopic resection of this fragment.

Prevention

Prevention of significant AC joint degenerative pathology simply consists of early diagnosis of the problem and avoidance of causative maneuvers, if possible.

Prognosis

Although the literature does not contain studies investigating the natural history of AC joint degenerative disease, some studies report that athletes with distal clavicle osteolysis often experience resolution of symptoms with avoidance of provocative activities.

Published studies of patients undergoing both arthroscopic and open resection have reported good or excellent results in approximately 60-100% of cases. No prospective comparisons of open versus arthroscopic treatment have been published; however, retrospective studies have shown similar long-term results. Patients undergoing arthroscopic treatment are likely to return to activity more quickly than other patients.

MISCELLANEOUS

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Medical/Legal Pitfalls

• Failure to diagnose and treat a concomitant pathologic condition

MULTIMEDIA

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Media file 1:  Classification of acromioclavicular (AC) joint injuries.
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Media type:  Illustration

Media file 2:  Postoperative CC ligament reconstruction. The clavicle is back to its normal position. The anchor in the clavicle keeps the allograft tendon from coming off of the clavicle. Also note the distal clavicle has been excised because it had traumatic arthritis from the injury.
	View Full Size Image
Media type:  Radiograph

Media file 3:  Type III AC joint separation.
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Media type:  Radiograph

Media file 4:  Type III AC joint separation.
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Media type:  Radiograph

Media file 5:  Postoperative rehabilitation.
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Media type:  Photo

REFERENCES

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• Authors and Editors
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• Allman FL Jr. Fractures and ligamentous injuries of the clavicle and its articulation. J Bone Joint Surg Am. Jun 1967;49(4):774-84. [Medline].
• Cahill BR. Osteolysis of the distal part of the clavicle in male athletes. J Bone Joint Surg Am. Sep 1982;64(7):1053-8. [Medline].
• Flatow EL, Duralde XA, Nicholson GP, et al. Arthroscopic resection of the distal clavicle with a superior approach. J Shoulder Elbow Surg. Jan-Feb 1995;4(1 Pt 1):41-50. [Medline].
• Fukuda K, Craig EV, An KN, et al. Biomechanical study of the ligamentous system of the acromioclavicular joint. J Bone Joint Surg Am. Mar 1986;68(3):434-40. [Medline].
• Murphy OB, Bellamy R, Wheeler W, Brower TD. Post-traumatic osteolysis of the distal clavicle. Clin Orthop Relat Res. 1975;(109):108-14. [Medline].
• Rockwood CA, Green DP. Fractures in Adults. In: Injuries to the Acromioclavicular Joint. Volume 1. Philadelphia. J.B. Lippincott; 1984:pp. 860-910.
• Seade LE. Coracoclavicular Ligament Reconstruction with Semitendinosus Allograft for AC Joint Separations. Austin, Texas: Texas Orthopaedic Association Annual Meeting; May 14, 2004.
• Seade LE. Coracoclavicular Ligament Reconstruction with Semitendinosus Allograft for AC Joint Separations, 2-5 year Follow-Up. Santa Fe, New Mexico: Western Orthopaedic Association; October 13, 2006.
• Shaffer BS. Painful conditions of the acromioclavicular joint. J Am Acad Orthop Surg. May-Jun 1999;7(3):176-88. [Medline].
• Slawski DP, Cahill BR. Atraumatic osteolysis of the distal clavicle. Results of open surgical excision. Am J Sports Med. Mar-Apr 1994;22(2):267-71. [Medline].
• Urist MR. Complete dislocation of the acromioclavicular joint: The nature of the traumatic lesion and effective methods of treatment with analysis of 41 cases. J Bone Joint Surg Am. 1946;28A:813-837.
• Zanca P. Shoulder pain: involvement of the acromioclavicular joint. (Analysis of 1,000 cases). Am J Roentgenol Radium Ther Nucl Med. Jul 1971;112(3):493-506. [Medline].

Article Last Updated: Oct 26, 2006