The coracoid process, a small, hook-like bony projection, is located on the anterior aspect of the scapula, or shoulder blade, superior to the glenoid cavity. This projection, often described as resembling a raven’s beak, serves as a significant anatomical landmark in the shoulder region. It plays a role in stabilizing the shoulder joint and provides numerous attachment points for muscles and ligaments, facilitating the complex movements and stability of the upper limb.
Structures Attaching to the Coracoid Process
The coracoid process is a hub for the attachment of several important muscles and ligaments that contribute to the function of the shoulder and arm. Three muscles—the pectoralis minor, coracobrachialis, and the short head of the biceps brachii—originate or insert on this bony projection.
The pectoralis minor muscle inserts onto the coracoid process, specifically on its medial border and superior surface. This muscle originates from the anterior surfaces of the 3rd, 4th, and 5th ribs. The coracobrachialis muscle originates from the tip of the coracoid process. Its insertion is on the medial surface of the humerus shaft. The short head of the biceps brachii also originates from the apex of the coracoid process.
Several ligaments also find their attachment on the coracoid process, forming crucial connections within the shoulder girdle. The coracoacromial ligament connects the coracoid process to the acromion, forming a protective arch over the shoulder joint. This ligament typically attaches to the lateral border of the coracoid process.
The coracoclavicular ligaments consist of two distinct parts: the conoid and trapezoid ligaments. The conoid ligament, which is more medial and cone-shaped, attaches from a rough impression at the base of the coracoid process to the conoid tubercle on the inferior surface of the clavicle. The trapezoid ligament, positioned anterolateral to the conoid, is broad and quadrilateral, connecting the upper surface of the coracoid process to the trapezoid line on the clavicle. These two ligaments merge at their attachment on the coracoid process. Another ligament, the coracohumeral ligament, originates from the coracoid process and blends with the joint capsule, extending to the greater and lesser tubercles of the humerus.
Role of Coracoid Process Attachments
The attachments to the coracoid process are integral to the stability and extensive range of motion of the shoulder. The coracoclavicular ligaments are particularly important for suspending the scapula and the entire upper limb from the clavicle. These ligaments prevent excessive vertical displacement of the clavicle relative to the scapula, maintaining the integrity of the acromioclavicular joint. They also limit excessive rotation of the clavicle and scapula.
The coracoacromial ligament forms part of the coracoacromial arch, which acts as a protective roof over the head of the humerus. This arch shields the underlying rotator cuff tendons and the subacromial bursa from direct trauma and prevents superior dislocation of the glenohumeral joint. The coracohumeral ligament reinforces the upper part of the shoulder joint capsule and helps stabilize the glenohumeral joint.
The muscles attaching to the coracoid process facilitate a variety of arm and scapular movements. The pectoralis minor, by inserting on the coracoid process, helps to depress and protract the scapula, moving it forward and downward. The coracobrachialis muscle, originating from the coracoid, contributes to the flexion and adduction of the arm at the shoulder joint. The short head of the biceps brachii, also originating from the coracoid, assists in flexing the elbow, supinating the forearm, and weakly flexing the shoulder.