Final answer:
The glenohumeral joint is stabilized by the glenoid labrum, intrinsic ligaments, and the rotator cuff muscles.
Step-by-step explanation:
The structures that help stabilize the glenohumeral joint and keep the humeral head in the glenoid fossa include the glenoid labrum and the intrinsic ligaments of the articular capsule. The glenoid labrum is a small lip of fibrocartilage that deepens the glenoid cavity. The intrinsic ligaments, such as the coracohumeral ligament and the glenohumeral ligaments, provide additional support to strengthen the superior and anterior capsule walls.
However, the primary support for the glenohumeral joint comes from the muscles crossing the joint, particularly the four rotator cuff muscles. These muscles (supraspinatus, infraspinatus, teres minor, and subscapularis) form tendons that encircle the head of the humerus and become fused to the walls of the articular capsule. The fusion of these muscle tendons forms the rotator cuff, which serves as the main structural support for the joint.