AC Joint Injury Overview
The AC (acromioclavicular) joint is located in the shoulder where the collarbone (clavicle) meets the acromion process of the shoulder blade (scapula). This joint is reinforced by ligaments which provide stability while allowing for some motion to occur between the collar bone and acromion. The ends of the bones are covered by cartilage within the joint. Most people can identify their AC joint by simply feeling it on the top of their shoulder – it is the bony bump that is felt on top.
The most common cause of an acromioclavicular joint injury is a fall directly onto the shoulder. This can lead to a shoulder sprain in mild cases or to a separated shoulder in extreme cases. A separated shoulder is associated with injures to the ligaments that surround and stabilize the AC joint. If the trauma is severe enough, the ligaments attaching to the underside of the clavicle can tear, creating a complete separation of the collarbone and acromion process (termed an “AC Separation”). Dr. Jeff Padalecki, Austin, Texas orthopedic shoulder specialist, specializes in treating acromioclavicular joint pain caused by an AC joint injury.
There are varying grades of an AC joint injury ranging from a Grade 1 injury which causes mild acromioclavicular joint pain and no deformity to a Grade 6 injury which is a complete disruption of the ligaments.
AC Joint Injury Symptoms
Symptoms of an acromioclavicular joint injury can range from tenderness and minor swelling to intense acromioclavicular joint pain that may signify a complete shoulder separation. In more severe cases, the separation could be visible to the naked eye creating a disfigured bony appearance from under the skin and bruising on top of the skin. A pop or snap is also often heard during more severe cases.
AC Joint Injury Diagnostic Testing
A thorough physical exam and X-ray can often lead to a concrete diagnosis of an acromioclavicular joint injury. An MRI can sometimes be helpful to determine the grade of injury and assess which ligaments have been damaged. It is important to rule out any additional injury associated with the bone such as a fracture.