ACROMIOCLAVICULAR JOINT SPRAIN
Acromioclavicular joint (ACJ) sprains are common among young adults who engage in sporting activities, and usually result from falling directly on the acromion or onto an outstretched hand. The forces involved in such a fall drive the acromion inferiorly and superiorly, respectively.
The ACJ is a synovial joint located between the distal clavicle and the acromion. The posterolaterally facing medial facet of the distal clavicle articulates with the anteromedially facing acromion. Static stabilizers of the ACJ are the acromioclavicular (AC) and coracoclavicular (CC) ligaments. The superior, inferior, anterior, and posterior AC ligaments become part of the AC joint capsule. The CC ligaments, trapezoid and conoid, extend from the coracoid process to the inferior surface of the clavicle. The trapezoid is lateral and has a wide insertion on the clavicle, whereas the conoid is medial and has a thin insertion on the posterior tubercle of the clavicle. Dynamic stabilizers of the ACJ are the deltoid and trapezius, also known as the deltotrapezial complex. The deltoid prevents superior and posterior migration of the clavicle. Contraction of the trapezius compresses the ACJ.
Five to 8 degrees of motion at the ACJ facilitates clavicular rotation along the long axis and elevation and retraction of the distal clavicle. This motion aids in maintaining the subacromial space during terminal arm elevation.
ACJ sprain or separation can be diagnosed clinically by localized pain and deformity. The horizontal adduction test compresses the ACJ and causes pain in the presence of injury. The Zanca view radiograph allows for optimal visualization of the joint. ACJ sprains and separations are graded on a scale from I to VI, using the Rockwood classification.
Type I injury results in a sprain of the capsule and AC ligaments, but the AC and CC ligaments remain intact. No clavicular instability can be detected on examination, and radiographs are normal.
Type II injury results in rupture of the capsule and AC ligaments, but the CC ligaments remain intact. The clavicle is unstable under direct stress. Stress radiographic views are negative; however, the lateral clavicle can be slightly elevated.
Type III injury results in complete rupture of the AC and CC ligaments without disruption of the deltotrapezial fascia. On examination, the lateral clavicle appears elevated, with the acromion depressed. The clavicle is unstable vertically and horizontally. ACJ separation is evident on stress radiographs.
Type IV injury results in rupture of the AC and CC ligaments, with posterior displacement of the clavicle into the trapezius. This is evident both clinically and radiographically on axillary view.
Type V injury results in a type III injury with disruption of the deltotrapezial fascia. The lateral clavicle is elevated and the scapula is downwardly displaced. Radiographs demonstrate a 100–300% increase in the clavicle-to-acromion distance (CC distance)....