Structure & Components of Glenohumeral Joint
The Bony Design Allows for the Large Range of Motion
Oct 9, 2009
The glenohumeral joint is at risk for all types of acute and chronic injuries. The structures around the joint are susceptible to injury because of the joint’s design, function, and location.
Bony Structures of the Glenohumeral Joint
The glenohumeral joint is made up of the head of the humerus on one side and the glenoid fossa of the scapula on the other side. Although the head of the humerus is a somewhat round shape, the glenoid fossa is an extremely shallow structure with which the humerus articulates. It is this design that enables the large range of motion of the shoulder, but places this specific joint at risk for all types of injuries (Foundations of Athletic Training: Prevention, Assessment, and Management, 4th Ed., 2009).
Together the head of the humerus and glenoid fossa of the scapula form a “ball and socket” joint. The shape of the head of the humerus (ball) allows the humerus to roll and glide in multiple directions within the glenoid fossa (socket) thus enabling the shoulder to have a large range of motion in multiple planes.
Because the amount of bony surface that is in contact between the head of the humerus and the glenoid fossa is small, there are several additional soft tissue structures specifically designed to enhance the stability of the joint without compromising the mobility of the joint.
Soft Tissue Structures of the Glenohumeral Joint
The deepest connective tissue designed to assist in the stability of the head of the humerus within the glenoid fossa is the labrum. The labrum is a dense tissue that surrounds the glenoid fossa for the sole purpose of increasing the depth of the fossa. Because the head of the humerus can slide within the glenoid fossa, the labrum is susceptible to tears as it is the first soft tissue structure that resists the head of the humerus from slipping out of the glenoid fossa.
The next line of soft tissue defense to enhance the stability of the glenohumeral joint is the strong anterior and posterior ligaments. Ligaments are dense connective tissues that connect bone to bone. The glenohumeral joint has a strong arrangement of three anterior (located in the front of the joint) ligaments that withstand the force of the head of the humerus when the humerus is abducted and externally rotated (overhead throwing position). These ligaments restrict the movement of the head of the humerus and help maintain the humerus within the glenoid fossa.
One or more of these ligaments can be torn if the anterior force of the humerus is stronger than the tensile strength of the ligaments. When this occurs, the humerus can either sublux or dislocate from its original position within the glenoid fossa and end up positioned in front of and below the acromion process. This is the most common type of glenohumeral dislocation.
The next layer of connective tissue is the joint capsule. The joint capsule surrounds the glenohumeral joint with its fibers specifically arranged to provide multi-directional stability. The fibers of the joint capsule are arranged in all different directions to withstand tensile forces from all directions. Some of the glenohumeral ligaments may actually blend into the joint capsule creating a strong stabilizing structure.
Role of the Rotator Cuff in Stabilizing the Glenohumeral Joint
The last stabilizing structures lie in the deep muscles of the rotator cuff. The rotator cuff includes four specific muscles whose primary purpose is to assist the head of the humerus in maintaining its position safely within the glenoid fossa. These muscles include the:
- Teres Minor (posterior)
- Infraspinatus (posterior)
- Supraspinatus (superior)
- Subscapularis (anterior)
Keeping the muscles of the rotator cuff strong can help in stabilizing the head of the humerus within the glenoid fossa. It is important to know that these individual muscles are small and need to be strengthened with light weights and more repetitions. They can be isolated by performing exercises for internal rotation, external rotation, and abduction.
Understanding how the bony structures of the glenohumeral joint work together to enhance mobility can help people better understand the importance of the soft tissue structures to stabilize the joint. If any of the soft tissue structures are damaged in or around the joint, the stability of the joint will be compromised.
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