The glenoid cavity is one of two surfaces of a joint. It is used to hold the articular head and allows the range of motion of a joint. When dislocation occurs, the condyle slides out of its associated socket.
What is the glenoid cavity?
The human body is equipped with 143 joints that significantly determine flexibility and motor function. Each joint in the human body has essentially the same structure. In addition to articular cartilage, a joint space with synovial fluid, a joint capsule and a ligamentous apparatus to strengthen the joint, each joint contains a condyle and a glenoid cavity. The glenoid cavity corresponds to the concave section of the joint and serves to accommodate the convex articular head. Once two bones meet in the human body, they form a joint with each other. The end of one bone acts as a socket and thus as a receptacle for the condyle formed by the other end of the bone. The shape of a socket thus depends on the condyle that it is to receive. Accordingly, the socket of a ball and socket joint such as the hip or shoulder looks different from the socket used to receive a hinge joint, saddle joint, pivot joint, egg joint, or plane joint.
Anatomy and structure
Articular sockets usually have a more or less concave shape, especially the ball and socket joints of the body. The shape of a socket is relatively variable and depends on the type of joint. For example, the hip du shoulder joint are ball and socket joints. The glenoid cavity of the shoulder joint is comparatively small in relation to the joint head and appears rather flat at first glance. The hip joint is also a ball and socket joint. The socket of the hip joint is also called the acetabulum and corresponds to a relatively deep and pit-shaped socket that encompasses the joint head in large parts. These relationships show how different even the sockets of the same type of joint can be. In hinge joints such as the humeroular joint, a hollow-cylindrical socket receives a cylindrical condyle. Saddle joints such as the thumb saddle joint, on the other hand, consist of two concave articular surfaces, with the upper part of the joint resting on a saddle-shaped socket similar to a rider. Swivel joints such as the radioulnar joint have a peg-like head that sits in a channel-shaped short socket. The socket of egg joints is larger than the articular head, and plane joints such as the vertebral arch joint do not have a socket in the strict sense, but consist of two planar surfaces that slide freely against each other.
Function and tasks
Articular sockets are cup-shaped formation for receiving the joint head. They are one of two articular surfaces. As a rule, the rod end of a particular joint moves in the associated socket similar to a mortar in the shell. Exactly how a socket works depends on the type of joint. When bones meet in a joint, the shape of the bone surfaces, and therefore the shape of the socket, dictates the movements that become possible in the joint. In ball and socket joints such as the hip and shoulder, a spherical condyle in the oppositely shaped socket allows movement in all directions. In a hinged joint such as the upper ankle joint, on the other hand, the combination of head and socket allows movement exclusively about a single axis. In this case, the channel-like reception of the cylindrical joint head prevents other types of movement. Compared to this, saddle joints such as the thumb saddle joint allow somewhat more movement. In these joints, the movements take place in two directions perpendicular to each other. In pivot joints, only rotational movement is possible due to the socket and the associated head. Sockets and rod ends thus have two main functions. On the one hand, they connect bones or bone ends to each other, and on the other hand, they enable their flexible connections to move the bones. This means that the glenoid cavity has a function within the motor system that is about as important as the head of the joint. Without the unity of head and socket, neither extensions, nor flexions, abductions, approaching movements or external and internal rotations would be possible. Accordingly, the mobility of the person would be restricted to a similar extent as by paralysis of the muscles involved in the movement.
Diseases
Joints can be affected by injuries under certain circumstances that cause the two joint surfaces to lose contact with each other. Usually, such phenomena are caused by external force. When the head of a joint no longer lies in the socket, the medical profession refers to this as a dislocation. In most cases, luxation is accompanied by a tear in the associated joint capsule, which causes the two joint surfaces to shift or slide apart. Luxation can also be incomplete and is then called subluxation. In direct dislocation, an external force acts directly on the affected joint, causing a tear in the ligament and capsule that causes the condyle to slide out of the socket. Indirect dislocation is different. In this type of dislocation, the natural motor inhibition of a joint is overcome by the long lever arms. Thus, a bone leverages the condyle out on the socket in this type of dislocation. In addition to dislocation, the glenoid cavity can also acquire pathologic value in conditions such as the rare Legg-Calvé-Perthes disease. In this disease, the femoral head is unilaterally or bilaterally affected by avascular necrosis. Although the necrosis is compensated by processes of osteogenesis, the resulting bone is often deformed. As a consequence, the femoral head often no longer fits into the acetabulum.
