The hinge joint is a form of the true joint that allows uniaxial motion. A cylindrical joint head engages a socket that is shaped similar to a hollow cylinder segment. Diseases of hinge joints may correspond to osteoarthritis, among other conditions.
What is the hinge joint?
Where bones meet in the body, they often form a joint. These jointed connections between two or more bones create ability to move along at least one axis of motion, allowing at least two different types of movement. The human body has true and false joints. The true joints have a joint space between the bones that meet. The so-called hinge joint is a form variant of real joints, which is characterized by a roller-like joint head and the associated socket. Hinge joints, like most other types of joints, function according to the hand-in-glove or key-in-lock principle. This means that the cylindrical rod end rests in the socket as precisely as if it were a key in a lock or a hand in a glove. For this purpose, the joint socket has the shape of a hollow cylinder segment. Hinge joints belong to the uniaxial joints and thus realize two movements. The best-known examples of hinge joints are the interfinger joints and the elbow joint.
Anatomy and structure
Anatomically, a true joint has a different structure than a false joint. It carries a gap between the bones that meet, called the joint space. The joint surfaces are covered with cartilage and rest in what is called the joint capsule, which lies slack against its elements. The joint capsule consists of an inner portion of epithelial connective tissue dressings and an outer portion of taut connective tissue. To support the outer capsular membrane, real joints are equipped with capsular and articular ligaments. The joint capsule also contains the viscous synovial fluid, also known as synovium. The joint cavity is enclosed by the joint capsule without any gaps. Hinged joints differ anatomically from other form variants of the true joint. They consist of a cylindrical condyle and a complementary socket in which the condyle fits snugly. For the sake of accuracy of fit, the socket acts like the segment of a hollow cylinder. The hinge joint is also usually stabilized by tightly tensioned collateral ligaments. In addition, many hinge joints carry additional guide ridges and guide grooves in their articular cartilage.
Function and tasks
The functions of joints in the human body are many and varied. Joints connect bones together and thus have a stabilizing function. In addition, they are also irreplaceable for the ability to move. In hinge joints, the stabilizing segment corresponds primarily to the taut collateral ligaments. The stabilizing function exceeds the movement function in hinge joints. This means that this type of joint is a joint with a highly restricted movement potential that can only move along a single axis. This distinguishes them, for example, from ball joints, which are said to have unrestricted movement potential in space. Hinged joints have only two forms of motion on their one axis. These forms of movement are flexion and extension. In medicine, this refers to the flexion and extension of limbs or finger joints. Together with the roll, wheel or pivot joint, the hinge joint is also counted among the cylindrical joints, whose common characteristic is the uniaxial ability to move. All hinge joints cannot be moved to the side. They also do not allow rotational movements, but can only be stretched or bent linearly. This applies to the finger joints, with the exception of the base joints, just as it does to the elbow joint. Despite this restriction in freedom of movement, hinged joints meet the functional requirements in the human body.
Diseases
Hinge joints can be affected by various diseases that impair their function. The elbow joint, for example, often becomes diseased as a result of incorrect stresses and overloads, and in this context causes more or less severe pain.When the joint is incorrectly stressed, conditions such as tennis elbow, ulnar groove syndrome or golfer’s elbow develop. Ulnar groove syndrome corresponds to pressure damage to the ulnar nerve, which runs close to the elbow joint. Sensory disturbances of the arm are symptomatic of the syndrome. Epicondylitis or tennis elbow, on the other hand, corresponds to an irritation condition of tendons involved in the joint, which is usually the result of unilateral stress. Elbow dysplasia can also cause hinge joint disorders. In dysplasias, the bones are deformed. As a result, the bones of a hinge joint that meet no longer fit into each other with a perfect fit. Dysplasia of the bones involved in the elbow hinge joint is a relatively common phenomenon that corresponds to a developmental disorder of the elbow joint. In the human species, the disorder is less common than among other mammals, such as tall dog breeds. Elbow dislocations are much more common among humans. After dislocations of the shoulder, dislocated elbows are even the most common dislocation of the large joints. In most cases, the phenomenon is associated with tears of the collateral ligaments or is accompanied by fractures such as the radial head fracture or an epicondyle tear. Because the elbow is extremely exposed, it is frequently affected by fractures in the course of falls. During a fall, large forces act on the elbow joint, causing not only the bones but also the joint itself to fracture as part of a comminuted fracture. At the hinge joints of the fingers, osteoarthritis is one of the most important diseases. This degenerative disease is often related to misalignment and overload, and bit by bit it breaks down the cartilage of the joint surfaces. This results in pain that is initially concentrated in weight-bearing situations and later spreads to periods when the joint is at rest.
