The anterior shoulder refers to the structures forming the front portion of the shoulder joint as well as the muscles acting on this joint. Also known as the glenohumeral joint, the shoulder is found where the ball-shaped head of the humerus bone in the upper arm meets the glenoid fossa, a socket-like cavity in the upper outer portion of the scapula or shoulder blade. Another bone that is significant to the anterior shoulder is the clavicle or collarbone, which crosses the upper chest laterally to meet the acromion process, one of two projections of the top of the scapula, just adjacent to the glenohumeral joint. Several major ligaments of the anterior shoulder hold these bones together, including those linking the clavicle to the two processes of the scapula, those linking the scapular processes to each other, and those linking the scapula to the humerus. Muscles of the anterior shoulder include the anterior deltoid and pectoralis major, which are the muscles that move the shoulder joint to bring the arm in front of the body.
Though the bulk of each scapula bone is found in the upper back behind the ribcage, the top outer portion of the shoulder blade projects outward and forward to form a part of the anterior shoulder. It does this by way of two irregularly shaped projections: the acromion and coracoid processes. The acromion process forms the apex of the shoulder joint, and the coracoid process is found medial or to the inside of the shoulder joint, just below the clavicle on the front of the shoulder. Together with the lateral end of the clavicle, the two processes and the ligaments between them form a triangle found just medial to the glenohumeral joint on the anterior shoulder.
The glenohumeral joint itself is a ball-and-socket joint located where the arm meets the torso. It comprises the humeral head and the glenoid fossa, which is situated on the upper outer aspect of either shoulder blade, with the head inserting into the fossa like a ball in a cup. Structures covering the anterior aspect of this joint are the capsular ligaments enclosing the joint capsule. these extend laterally from the neck of the scapula on its anterior side to the neck of the humerus bone on the same side.
Above or superior to the capsular ligaments are the coracohumeral ligaments, which run parallel to the capsular ligaments and link the coracoid process of the scapula to the top of the humerus bone. Spanning the space above the coracohumeral ligaments are coraco-acromial ligaments, which run upward and outward from the coracoid process to the acromion process. Similar ligaments link the acromion to the lateral end of the clavicle and the coracoid to the outer third of the clavicle directly above it.
Superficial to this triangle of shoulder ligaments are the major muscles of the anterior shoulder, which enable forward shoulder movement by attaching to the clavicle and pulling anteriorly on the humerus. The anterior deltoid is the front portion of the deltoid muscle, which extends from the outer third of the clavicle to the lateral aspect of the humerus bone about midway down the upper arm. Alongside the anterior deltoid in the chest is the pectoralis major, which runs from the inside half of the collarbone across the anterior shoulder to a niche on the front of the humerus bone called the intertubercular groove.
