Acromioclavicular Joint Sprain

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Acromioclavicular Joint Sprain

The acromioclavicular (AC) joint is a plane diarthrodial articulation often accompanied by an intra-articular fibrocartilaginous disc. It is reinforced by its fibrous capsule and by the acromioclavicular and coracoclavicular ligaments. The AC joint is poorly supported by muscles with only the attachments and fascia of the deltoid and trapezius crossing the joint. These structures provide some stability when the ligaments have been damaged.

The joint has limited motion but is capable of a few degrees of axial rotation and some translation and joint angulation. The clavicle acts as a strut that maintains the position of the scapula and the shoulder to the side of the body, contributing to a greater range of motion for the shoulder.

Injuries to the AC joint account for nearly 10% of all injuries in contact sports. Injuries to the AC joint are graded according to the severity of the injury ranging from a mild sprain of the acromioclavicular joint ligaments to complete disruption and dislocation of the distal clavicle.

Type I: Acromioclavicular ligament sprained. Acromioclavicular joint, coracoclavicular ligament, deltoid, and trapezius muscles are intact.

Type II: Acromioclavicular ligament completely torn, acromioclavicular joint disrupted with joint widening, coracoclavicular ligament sprained. May have a partial detachment of the deltoid or trapezius from the distal clavicle.

Type III: Dislocation of the acromioclavicular joint with superior displacement of the distal clavicle, partial or complete disruption to the coracoclavicular ligament, high probability of detachment of the deltoid or trapezius from the distal clavicle.

Types IV, V, and VI are variations of the Type III injury (dislocation):

Type IV: Dislocation of the acromioclavicular joint with the distal clavicle displaced posteriorly into or through the trapezius, partial or complete disruption to the coracoclavicular ligament, high probability of detachment of the deltoid or trapezius from the distal clavicle.

Type V: Dislocation of the acromioclavicular joint with marked elevation of the distal clavicle, complete disruption to the coracoclavicular ligament with at least doubled the normal coracoclavicular interval, high probability of detachment of the deltoid or trapezius from the distal clavicle.

Type VI: Dislocation of the acromioclavicular joint with a displacement of the distal clavicle inferior to the acromion, complete disruption to the coracoclavicular ligament with loss of the coracoclavicular interval, detachment of the deltoid or trapezius from the distal clavicle.

• Anterosuperior shoulder pain with the individual often pointing directly to the AC joint
• History of direct trauma to the lateral shoulder while the arm is adducted against the body, or of falling onto the hand or elbow with the arm adducted
• Pain aggravated by sleeping on the affected side, on elevating the arm well above shoulder level, or by reaching across the front of the body
• May have pain spreading into the anterolateral neck or over the anterolateral deltoid

Clinical findings will depend on the severity of the injury:

• Inspection may reveal deformity (e.g., elevation of the distal clavicle), swelling, or ecchymosis
• Tenderness directly over the AC joint and in the coracoclavicular space
• The “Piano Key Sign” may be present (pressure applied to the distal clavicle causing it to depress and then rebound when the pressure is removed)
• Aggravation of pain in the final stages of shoulder abduction
• Positive Acromioclavicular Crossover test and Acromioclavicular Shear test
• Pain produced at the top of the shoulder when O’Brien’s test is performed

Plain radiography is generally sufficient. It may be necessary to include weight-bearing stress views when an acromioclavicular joint injury is suspected, but initial radiographs appear normal. Radiographs should reveal the presence of soft tissue swelling, widening of the acromioclavicular joint, increased coracoclavicular distance, and displacement of the distal end of the clavicle.

MRI or CT may be required if plain radiography appears to underrepresent the degree of injury.

The following are examples of red flags for patients presenting with shoulder pain:

• History of a significant injury
• Severe pain
• Unrelenting pain
• Nocturnal pain or pain at rest
• Fever
• Deformity
• Large joint swelling
• Significant loss of range of motion
• Significant neurological impairment (suggestive of a space-occupying lesion)
• Severe tenderness on palpation or severe pain with any examination procedure

If any red flags are identified during history taking and clinical examination, referral for urgent medical evaluation and further investigation is warranted.

Sleeping Posture

Patients with acromioclavicular joint injury may experience shoulder discomfort during sleep. Sleeping with the involved arm supported on a pillow may help to reduce that discomfort.

Anterosuperior Shoulder Pain

In the adult age group, in addition to acromioclavicular joint injury, the differential diagnosis of anterosuperior shoulder pain should include several other conditions such as:

• Myofascial Pain Syndromes of pectoralis minor, anterior deltoid and biceps muscles
• Bicep Tendinopathy
• Anterior Deltoid Strain