Acromioclavicular joint

The joint connecting the collarbone to the highest point of the shoulder blade.

The acromioclavicular (AC) joint is a synovial joint formed by the acromion process of the scapula and the lateral end of the clavicle. This joint plays a crucial role in allowing a wide range of motions of the shoulder and provides stability to the upper limb during various activities such as reaching and lifting. The joint is surrounded by a capsule that contains synovial fluid, allowing for smooth movement.

Terminologia Anatomica

articulatio acromioclavicularis

System

Skeletal system

Function

The acromioclavicular joint plays a pivotal role in shoulder mobility and stability. It allows for a range of movements, including elevation, depression, rotation, and horizontal adduction of the shoulder. This joint enables activities such as raising the arm overhead, which is essential for actions like throwing, swimming, or lifting objects. In addition to facilitating movement, the AC joint acts as a critical support structure, absorbing forces and ensuring the proper alignment of the shoulder girdle during dynamic activities. By maintaining its stability, it protects the shoulder complex from injuries and contributes to the overall function of the upper extremity.

Location

Located at the top of the shoulder, the acromioclavicular joint is positioned where the acromion, an extension of the scapula, meets the clavicle, or collarbone. It lies just above the shoulder joint, approximately 2 to 3 centimeters from the midline of the body. The joint is easily palpable at the highest point of the shoulder and can be identified as a slight bump when feeling the area of the shoulder girdle. It is surrounded by muscles and ligaments, providing connection and support to the upper limb while allowing for a significant range of motion.

Did You Know?

The acromioclavicular joint can undergo injury from falls, especially in contact sports, often resulting in a condition known as an AC joint separation.
The joint's stability is largely maintained by ligaments, including the acromioclavicular ligament and the coracoclavicular ligaments.
In some cases, a degenerative condition known as osteoarthritis can affect the acromioclavicular joint, leading to pain and reduced range of motion.