What are the important structures of the glenohumeral joint?
The glenohumeral joint is formed by the articulation of the “ball” or head of the humerus (upper arm bone) into the glenoid socket of the scapula (shoulder blade). This ball-and-socket joint arrangement enables movement in several directions making it the most mobile joint in the body.
The labrum is a thick and fibrous ring of cartilage attached circumferentially around the glenoid socket. This cartilaginous ring provides an attachment site for several shoulder ligaments and the biceps tendon (top portion or superior). The labrum is primarily responsible for joint stabilization by deepening the glenoid socket of the scapula.
- Glenohumeral Ligaments: The inferior, middle, and superior glenohumeral ligaments connect the glenoid socket of the scapula and the head of the humerus. Together, these three ligaments reinforce the glenohumeral joint capsule with various upper limb movements.
- Transverse Humeral Ligament: This broad ligament band originates from the greater tubercle of the humerus and attaches to the lesser tubercle of the humerus. The main responsibility of this ligament is to retain the long head of the biceps tendon within the bicipital groove on the humerus.
- Coracohumeral Ligament: The coracoid process of the scapula and the head of the humerus are connected by the coracohumeral ligament. This ligament functions to strengthen the shoulder joint capsule.
The rotator cuff is a group of four muscles and tendons found covering the humerus (upper arm bone) at the humeral head (“ball”). There are two rotator cuff tendons on the upper (superior) portion, one on the front (anterior), and one in the back (posterior). This muscle and tendon group stabilizes the humeral head within the glenoid socket while also contributing to the shoulder’s incredible range of motion.
Surrounding the glenohumeral joint capsule are a number of small, fluid-filled sacs that produce a viscous fluid to reduce friction with joint movement.