AJCC 2002

January 2002

AC Seperation

by Gregg J. Carb, D.C. and Al Ueda, D.C.

Shoulder pain is a common problem in the adult population, and in many cases is the result of some type of injury. Certainly, shoulder pain can arise gradually from an underlying joint or soft-tissue degenerative process. Postural deformities that alter the resting position of the scapulae and the dynamic tension of the scapular stabilizer muscles, such as thoracic hyperkyphosis and forward-rounded shoulders, are possible contributory factors for a progressive pathological course. When the onset of shoulder pain is acute, however, the need for proper assessment and swift action is often more imperative as patients often view new injuries as a threat of unknown proportion to their daily lives.

One common shoulder injury is the acromioclavicular (A/C) joint separation. Because the A/C joint lies at the top of the shoulder under a thin layer of skin, the region is susceptible to trauma and separations between the acromion process of the scapulae and the distal clavicle are easily recognized. The lump that may be observed when the A/C joint separates is referred to as the horizon sign (see figure one). Although it appears as if the distal end of the clavicle has risen, it is usually the scapulae that has dropped, due to the downward sagging of the unsupported upper extremity.1 It should be appreciated that the clavicle is the only bony attachment of the upper extremity to the rest of the skeletal frame.

Ligamentous support of the acromioclavicular (A/C) joint is provided by a relatively thin capsule with some reinforcement from the acromioclavicular ligaments. True support is provided by the coracoclavicular ligaments, which prevent excessive movements of the clavicle on the acromion. There are two components: the more medial conoid ligament and the more lateral trapezoid ligament. Both arise from the coracoid process and insert on the undersurface of the clavicle. The two divisions of the coracoclavicular ligaments function to prevent vertical movement.2 The nearby coracoacromial ligament does not perform any stabilizing function for the acromioclavicular joint, but rather acts as an extended roof for the rotator cuff between the coracoid and acromion processes. (see figure two)

The coracoclavicular ligaments are at risk for injury due to sudden tension (stretch) rather than compression. Falling forward on the tip of the shoulder while running is an example of an injury that would drive the scapulae (acromion) inferior relative to the clavicle. Taking an upward blow to the bottom of the clavicle is an example of an injury that would drive the clavicle superior relative to the acromion. Falling back onto an outstretched and extended arm is an example of an injury that would drive the acromion medial and anterior relative to the clavicle.

Shoulder injury sufficient to cause an A/C joint separation may also irritate the underlying subacromial bursa. Even when subacromial bursitis is present, the irritated sub-deltoid (subacromial) bursa is not usually considered a primary pathology. Most patients will have primary involvement of the rotator cuff, the articular capsule, the biceps tendon sheath and/or the A/C joint by way of an acute traumatic or chronic degenerative process that only secondarily involves the bursa.3

A/C joint separations have been classified by type to describe the sequence of ligamentous tearing that occurs in A/C joint injuries. A type I separation involves some disruption of the acromioclavicular ligament only. A type II separation involves complete disruption of the acromioclavicular ligament and some disruption of the coracoclavicular ligaments with accompanying upward movement of the clavicle. A type III separation involves complete disruption of the all three ligaments: aromioclavicular and coracoclavicular (conoid and trapezoid) with significant relative upward displacement of the clavicle.2

Testing for A/C Joint Separation / Bursitis.

Cross Over Maneuver

The cross over maneuver involves taking the arm on the injured side and crossing it over the body to place the hand on the opposite shoulder top. This maneuver compresses the A/C joint and causes local pain when pathology is present.1

Dawbarn’s Sign

The patient’s arm should rest at their side. The examiner palpates the subacromial region just lateral and anterior to the A/C joint deeply with one finger. Usually a specific, localized pinprick-tender spot can be found when subacromial bursitis is present. The examiner holds his finger on the painful spot and abducts the patient’s arm passively to shoulder level. If the spot becomes nontender upon abduction of the shoulder, the test indicates subacromial bursitis.2

Muscle Test

The coracobrachialis test uses the mechanoreceptors at the proximal end of the coracobrachialis muscle where its tendon ends at the coracoid process but is continuous with fibers of the conoid and trapezoid (A/C) ligaments extending up to attach onto the clavicle itself. The patient lies supine and flexes the shoulder joint and the elbow joint each about 40 degrees. The patient’s arm may be slightly externally rotated. The examiner stands at the head of the patient facing footward, contacts the patient’s arm just above the elbow (lower biceps) with both hands, and attempts to push the patient’s elbow down to the table. Significant weakness compared to the opposite side indicates an A/C separation, especially if the test is repeated while the patient presses down and holds on the involved A/C joint with their opposite-side hand and then tests much stronger.1

X-Ray

An A/C joint separation can be appreciated on x-ray with an A-P view aimed at the coracoid process. Weigh the involved arm down with a ten-pound bag. Typically, a grade one sprain of the A/C ligaments will not show any separation of the clavicle in relation to the coracoid process on x-ray. A grade two or three sprain will usually demonstrate a relative superior displacement of the clavicle at the acromion process. When separated, the distance between the clavicle and acromion will measure greater than 1.1-1.3cm. Image both extremities to compare the anatomy of each side, and always rule-out fractures. (see figures 3-6)

Treatment

A/C joint separations, besides being classified by type, are also ligamentous injuries that can be graded according to the degree of ligamentous fiber disruption. The degree of ligamentous sprain and type of separation determines the treatment approach. Grade one sprains describe a condition in which the ligament remains largely intact with only minor disruption. Grade two describes a more serious injury in which there is significant internal fiber disruption but the ligament maintains its attachments. Grade three is a complete rupture of the ligamentous fibers.

Type I separations involve grade one and two sprains to the acromioclavicular ligament that can be treated by instructing the patient to avoid lifting their elbow above shoulder level or lying on the injured side. Ice should be applied at regular brief intervals (the thin skin over the A/C joint is easily burned with a prolonged single icing application). Patients should perform a pain-free ROM in all three plane of motion: sagittal (flexion/ extension), frontal (adduction/abduction), and horizontal (internal/external rotation) multiple times daily below shoulder level for four weeks, thereafter working gradually up to full motion within six weeks. If the coracobrachialis test is weak, an A/C joint adjustment is usually indicated.

Type II separations involve a grade three sprain of the acromioclavicular ligament and a grade one or two sprain of the coracoclavicular ligaments. These injuries require taping or bracing for four to six weeks time to allow the ligamentous A/C fibers to reattach themselves. After two weeks of taping or bracing support, active ROM and isometric exercises should begin within a range allowed while wearing the support. At the conclusion of taping or bracing, full ROM and strengthening exercises should be incorporated. Exercises should concentrate on strengthening the deltoid and the trapezius muscles. Within this timeframe the coracobrachialis test should strengthen, and if not, manipulation of the A/C joint may be considered.

Type III separations involve a grade three sprain of the acromioclavicular and the coracoclavicular ligaments. These injuries require constant taping or bracing for at least six weeks. The muscles of the shoulder joint may be lightly contracted in an isometric fashion during the last few weeks of the immobilization period to facilitate healing. After the six weeks of taping or bracing , active ROM and isometric exercises should begin with a very gradual and progressive return to full motion over the course of several additional weeks. If the taping/bracing and post-immobilization rehabilitation fails to stabilize the joint, surgical pinning or acromioplasty is always an option — so the conservative approach is worth a try.