What to Know About the Acromioclavicular Joint (AC Joint)
The acromioclavicular joint, otherwise known as the AC joint, is the junction between the acromion (highest point of the shoulder) and the clavicle (collarbone). The AC joint is a main connection between the arm and skeleton, therefore, it is a critical structure to the shoulder. The acromioclavicular joint is quite small and has a limited range of motion, allowing the ability to raise the arm above the head. Dr. Jeff Padalecki, orthopedic shoulder specialist serving the greater Austin, Texas area, is well versed at treating orthopedic injuries associated with the shoulder AC joint.
AC Joint Anatomy
Stabilized by three ligaments and two sets of muscles, the AC joint is relatively strong. The acromioclavicular ligament runs horizontally from the acromion to the clavicle. The two coracoclavicular (CC) ligaments connect the coracoid process, a portion of the scapula, to the clavicle. The deltoid muscle and trapezius muscle are the two sets of muscles responsible for assisting with support of the shoulder AC joint.
The AC joint capsule is composed of a loose fibrous layer which encloses the two articular surfaces. As a plane type synovial joint, the joint capsule is lined by a synovial membrane that releases synovial fluid into the joint cavity.
Much like those of the sternoclavicular joint, the articular surfaces of the shoulder AC joint are lined with fibrocartilage. The cavity of the acromioclavicular joint is partially divided by an articular disc, a wedge of fibrocartilage suspended from the upper portion of the capsule.
AC Joint Function
The acromioclavicular joint is classified as a synovial joint. Located where the collarbone meets the shoulder blade, the AC joint allows the ability to raise the arm above the head. It also allows the transmission of forces from the upper arm to the rest of the skeleton. No muscles act directly on the joint so all movement is initiated by movement at other joints, and is considered passive movement.
AC Joint Injuries
Shoulder AC joint injuries are quite common and often result from a hard fall, direct hit or other trauma, such as an automobile accident. Some examples of these injuries include:
In order to diagnosis and treat an injury to the shoulder AC joint, Dr. Padalecki will perform a thorough physical examination to assess the joint, and then prescribe an appropriate treatment, either surgical or non-surgical depending on the severity.
For additional resources on the shoulder AC joint, please contact the Austin, Texas orthopedic practice of Dr. Jeff Padalecki, shoulder specialist.