Four joints comprise the shoulder complex:
Glenohumeral joint
The glenohumeral joint is the articulation between the head of the humerus and the glenoid cavity of the scapula. It is a ball-and-socket type of synovial joint. The glenohumeral joint allows for adduction, abduction, medial and lateral rotation, flexion, and extension of the arm.
Acromioclavicular joint
The acromioclavicular joint is the articulation between the acromion process of the scapula and the lateral end of the clavicle. It is a plane type of synovial joint. The acromion of the scapula rotates on the acromial end of the clavicle.
Sternoclavicular joint
The sternoclavicular joint is the articulation of the manubrium of the sternum and the first costal cartilage with the medial end of the clavicle. It is a saddle type of synovial joint but functions as a plane joint. The sternoclavicular joint accommodates a wide range of scapula movements and can be raised to a 60-degree angle during elevation of the scapula.
Scapulocostal joint
The scapulocostal joint (also known as the scapulothoracic joint) is a physiological joint formed by an articulation of the anterior scapula and the posterior thoracic rib cage. It is musculotendinous in nature and is formed predominantly by the trapezius, rhomboids, and serratus anterior muscles. The pectoralis minor also plays a role in its movements. The gliding movements at the scapulocostal joint are elevation, depression, retraction, protraction, and superior and inferior rotation of the scapula.
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