Shoulder Separation
Injury of the Acromioclavicular Joint of the Shoulder
A common, but misunderstood sports injury, shoulder separation involves sprain or tear of two strong ligaments in the shoulder.
The term shoulder separation describes an injury of the acromioclavicular (AC) joint, which forms the bony “roof” of the shoulder. The rotator cuff of the shoulder passes under the AC joint, and is protected by it. Shoulder separation involves injury to the supporting ligaments of the AC joint, which may result in widening or deformity of the joint. This in turn causes pain, and may affect proper functioning of the rotator cuff. Shoulder separation should not be confused with shoulder dislocation – the latter involves the “ball and socket” of the shoulder (glenohumeral joint), rather than the AC joint.
Shoulder separation is usually caused by a direct fall on the shoulder. The blow to the shoulder results in either sprain or tear of one or both of the ligaments that support the AC joint.
AC Joint Anatomy
The acromioclavicular joint is formed by the articulation of the end of the collar bone (clavicle) and the acromion process, a bony protuberance that arises from the top of the shoulder blade (scapula). The bones are held in place by two strong ligaments. One ligament extends directly across the acromioclavicular joint, and is known as the AC ligament. The second ligament extends from a second bony prominence of the shoulder blade, called the coracoid process, to the clavicle. This is the coracoclavicular, or CC, ligament.
Types of Shoulder Separation
Shoulder separations are described by severity. The three types of separations are:
- Grade I
- Grade II
- Grade III
Grade I shoulder separation involves sprain of the AC ligament only. A patient with a Grade I separation is tender over the AC joint, but there is no deformity of the joint. Routine x-rays of the AC joint are normal in Grade I shoulder separation.
Grade II shoulder separation involves a tear of the AC ligament, and a sprain of the CC ligament. The patient is tender over the injured joint, and there may be a slight visible deformity. The Grade II separation is also visible on “weight bearing” x-rays of both shoulders. The patient is x-rayed while holding a light weight in each hand. The weight bearing images will reveal slight widening of the injured joint, versus a normal joint on the uninjured side.
Grade III shoulder separation occurs when the AC and CC ligaments are both torn. The AC joint will be tender, and have an easily visible deformity as the clavicle “flys” away from its normal articulation with the acromion. Grade III separation may be obvious on physical exam, but x-rays are usually taken anyway, to exclude a concomitant fracture of the clavicle.
Treatment of Shoulder Separation
Most shoulder separations, even those associated with significant deformity of the AC joint, are treated conservatively with rest (arm in a sling), icing, and pain medication. Most patients with shoulder separation will regain full function with this regimen. However, some patients may experience persistent pain due to arthritis or compromised function after conservative therapy. These individuals may require surgical reconstruction of the AC joint to alleviate the pain and restore normal function.
Resource: American Academy of Orthopaedic Surgeons
