Egg joints are also known as elipsoid joints and are one of several types of joints in the human body. A concave articular surface with an oval end engages a larger socket in these joints. Osteoarthritis is one of the most important joint diseases.
What is an egg yolk joint?
Bones come together in joints to form movable joints. The human body contains 143 joints. Among them are unreal and real joints. Real joints carry a gap between the ends of bones, which is also called a joint space. The real joints of the human body have different shapes depending on their location and the associated functional requirements. One type of joint is the egg yolk joint. This form variant of real joints owes its name to its egg-like anatomy. Like many other types of joints, the egg-yolk joint is based on the so-called key-lock or hand-in-glove principle. The two bones that meet in it are accordingly designed according to the form-counterform principle and in this way loosely interlock. This interlocking makes different levels of movement possible in the joint, each of which has a certain degree of mobility. For example, the biaxial egg yolk joint is characterized by adduction, abduction, flexion and extension. Egg joints are sometimes called elipsoid joints. A characteristic example of this type of joint is the wrist. The first head joint also corresponds to an egg joint.
Anatomy and structure
Egg joints consist of two differently shaped articular surfaces. These surfaces engage with each other like a key in a lock. The egg-like structure consists of a convex articular surface and its counterpart: the socket. The convex articular surface has an oval cross-section that fits snugly into the slightly larger socket. Because ovoid joints are true joints, the ovoid joint has a different anatomy than the so-called false joints. As a true joint, the elipsoid joint belongs to the diarthroses, which carry a gap in the form of the joint space between their bone ends. All joint surfaces involved are covered with articular cartilage. A joint capsule lies around the egg yolk joint and thus stabilizes it. This joint capsule consists of an outer membrana fibrosa in the form of tight connective tissue and an inner membrana synovialis in the form of epithelium-like connective tissue dressings. The articular or capsular ligaments reinforce the stabilizing outer membrane. Articular ligaments in the joint capsule of true joints support a layer of membrana synovialis and are thus connected to the capsule. The joint capsule of the egg joint encloses its joint cavity without gaps and is attached to the joint bodies. Joint capsules contain a viscous fluid called synovium or synovial fluid.
Function and tasks
All joints in the body connect two or more bones together, act as stabilizers, and also give the bones some degree of mobility. The ability of joints to move depends on their location and is ideally matched to the functional requirements that arise for individual bones and limbs. Joints are capable of uniaxial or multiaxial motion depending on their type. Ovoid joints move biaxially. They are capable of four movements on their two axes of motion. The first movement is the sideways movement in right or left direction. This movement is also called adduction. The opposite movement and thus the backward movement from the sideways movement corresponds to abduction. In addition to these two movements, elipsoid joints realize forward and backward movement. Forward motion in this context is known as flexion. The backward movement is extension. In general, these two forms of movement are extensions and flexions to realize minimal rotational movements in the position. Egg joints are found in the human body mainly in the form of the upper cervical joint between the atlas and the skull and in the form of the upper wrist again. The upper upper cervical joint between the atlas and the skull is involved with its flexion and extension movements, for example, in everyday processes such as nodding. Like the wrist, the upper cervical joint is significantly limited in its range of motion compared to other types of joints. The stabilizing character comes into play at this point.Consequently, egg joints inherently already possess protection against twisting, which is intended to prevent damage to the joint and hold the joint surfaces together.
Diseases
Probably the best known disease of the joints is osteoarthritis. This is an excessive wear and tear of the joints or rather their protective cartilage layer. According to the narrower definition, arthrosis is only present when the wear and tear exceeds the normal level for the age of the joint. Excessive stress due to increased body weight or traumatically caused malpositions can promote the painful joint disease. Congenital causes are also possible risk factors, for example, a congenital malposition of the joints or deformities due to hereditary bone diseases. In individual cases, arthrosis also occurs as a result of joint inflammation and is referred to in this case as secondary arthrosis. In the case of effusion formation due to overload in the joint, a resulting arthrosis is counted among the secondary inflammatory reactions and is called activated arthrosis. In principle, not only the egg yolk joint but any type of joint can be affected by arthritic changes. Worldwide, osteoarthritis is therefore one of the bone diseases with the widest distribution. The most important symptoms include load-dependent pain, which, depending on the stage of the arthrosis, eventually also extends to resting phases. In the course of the disease, the protective cartilage over the joint surfaces wears away more and more. Dislocations are much less common in egg joints such as the wrist than arthritic processes because of their hand-in-glove anatomy.
