The glenoid cavity, also known as the glenoid fossa of the scapula, is the depression in the shoulder blade bone, or scapula, in which the ball-shaped top of the upper arm bone, or humerus, is set. The shoulder has three joints. One of those joints, called the glenohumeral joint, is a ball in socket joint and the glenoid cavity is the socket portion of this joint. Its function is to allow the head of the humerus to rotate broadly around the point of the shoulder. The bones, tendons and muscles, in combination with the joint, also allow the upper body to pull, push and lift objects and without this socket the shoulder would have limited mobility.
While ball and socket joints, such as the hip joint, can bear and sustain substantial weight, the joint of the shoulder sacrifices some of its stability for greater range of motion. The increased flexibility of the shoulder joint is due to more delicate tendons and ligaments in this area. In addition, the head of the humerus is proportionally much larger than the glenoid cavity, making it prone to pop out.
Both the glenoid cavity and the humerus are covered in cartilage to allow virtually frictionless movement within the joint. The cartilage also helps to make the shallow hollow of the glenoid cavity somewhat stronger. In the glenohumeral joint, the cartilage surrounding the head of the humerus is thick at the point where it hits the center of the cavity. By contrast, the glenoid cavity has a collar of cartilage surrounding it called the labrum. The labrum wraps around the thickened portion of cartilage on the head of the humerus making this cursory socket moderately stronger.
The most common injuries involving this cavity are a fracture, damage to the labrum or a dislocation of the joint. A glenoid fracture is a break of the glenoid socket resulting in pain and swelling that prevents the injured person from lifting the arm or extending it across the body. This type of fracture is treated by mobilization during healing or surgically with bone screws.
Damage or tear of the labrum will produce a decreased range of motion in the shoulder, intense pain and even a clicking sound during shoulder rotation. To repair the cartilage, rest and anti-inflammatory medication is used to reduce the swelling, followed by physical therapy. When the damage is severe, arthroscopic surgery may be necessary to repair the tears.
The pain and often uselessness of the shoulder following a dislocation often makes this injury fairly obvious. A dislocated shoulder needs to be relocated by a medical professional and the shoulder should be kept as immobile as possible until a doctor can be reached. Once the joint has been popped back in, the shoulder is immobilized while the tendons and muscles heal.