The swivel joint is equivalent to a wheel or pivot joint. A pivot rests in a groove in these joints, where it allows for movements such as rotation. The ulna-spoke joint in particular is prone to injury and disease.
What is the rotational joint?
Bones meet in the human body in articulated joints called joints, which are subdivided into unreal and real joints. The true joints have a joint space and have different shape variations. One form variant of the genuine joints is the so-called swivel joint. They are made up of a pin and a groove. The pin-shaped joint surface engages in the channel-shaped joint socket according to the hand-in-glove or key-in-lock principle. Pivot joints play an essential role in the mobility of the arm bones. For example, the radioulnar joint is a rotational joint in the distal and proximal planes. All rotational joints are so-called plane joints, which in themselves do not have a geometric center of motion. In addition to the typical rotational joints at the ulna and radius, the vertebral or intervertebral joints, for example, are also plane joints. Swivel joints are either pivot joints or wheel joints. The degree of freedom of rotary joints in terms of movement is translational, i.e. their movements are rectilinear. Compared to other joints, swivel joints are rigid, rather than dynamic joints.
Anatomy and structure
The anatomy of any true joint makes, that is, any diarthrosis, is characterized by a gap between the two bones. This gap corresponds to the joint space. Healthy joint surfaces are always covered by cartilage and lie within a joint capsule composed of an outer membrana fibrosa of tight connective tissue and an inner membrana synovialis of epithelium-like connective tissue tissues. Capsular or articular ligaments reinforce the outer articular membrane. On top of stabilizing ligaments in the joint cavity lies a layer of membrana synovialis, which has a connection to the joint capsule. The joint cavity is enclosed without gaps by the joint capsule, which lies flaccidly against the joint body and contains the viscous synovial fluid. This is a fluid that is also called synovia. As a true joint, the rotational joint is also characterized by the properties described. The further anatomy of the swivel joints depends on whether they are the subform of the wheel joint or the pivot joint. In a wheel joint, the socket moves around a fixed pivot. In the trunnion joint, the trunnion is the rod end and moves in the associated socket. Normally, the pivot of the swivel joint rests in the short and channel-like socket and is stabilized in this position by taut, circularly running ligaments.
Function and tasks
Joints have several tasks at once: they connect bones together, stabilize the bone joint, and at the same time allow the bones involved a certain degree of motion. How large this degree of motion is and how many axes it includes depends on the localization and shape of the joint. Compared with other types of joint, rotary joints tend to be static and usually have a single axis of motion that allows translational and thus straight-line movements. For example, rotational movements such as internal rotation and the corresponding external rotation are realized in swivel joints. In addition, rotary joints are generally capable of pronation and supination. Supination and opposing pronation are particularly relevant with regard to the radioulnar joint. It is a wheel joint with a single axis of motion: rotation. The proximal radioulnar joint is also known as the proximal ulna-spoke joint and connects the inside of the ulna to the head of the radius. This is where the rotational movements of the forearm take place. The distal ulna-spoke joint is close to the wrist and provides the rotational movements of the hand. This is especially true for the inward rotation of the forearm, in which the thumb side of the associated hand rotates medially and the back of the hand rotates toward the front. This pronation of the forearm is made possible by muscles such as the pronator quadratus muscle, the pronator teres muscle, and the brachioradialis muscle in response to a nerve-mediated command from the central nervous system.Supination is the opposing movement that returns the forearm to its original position. In internal rotation in the rotational joint, an extremity rotates about its own longitudinal axis and points inward in its direction of rotation when viewed from the front. External rotation is the opposite process. The more degrees of freedom a rotational joint has, and thus the higher the degree of motion, the more likely it is that pathological incidents such as joint rotations will occur.
Diseases
Pathological phenomena frequently take place especially in the proximal and distal ulna-spoke joints. These pivotal joints of the body are highly complex constructions. The guidance of the distal ulna-spoke joint depends on two lateral ligaments and a so-called annular ligament. Together with the joint, these ligaments form a functional unit, which lies enclosed by the joint capsule. The advantage of the elbow construction is its tripartite nature. Three partial joints meet in the elbow and allow a high range of motion. In addition, the ligaments of the elbow are strong enough to give the construction the stability it needs. Because of the stable flexibility in the elbow, a person can perform relatively nimble movements with the forearm while carrying heavy objects without harming the joint. When loaded incorrectly, it is the pivot joint between the ulna and radius and the hand and forearm that are susceptible to injury. In turn, after monotonous load, the wheel joints are accessible to overuse diseases. Injuries usually affect the ligaments of the joints. Overstretching or torn ligaments are not uncommon at these structures. In addition, the joint can also suffer from inflammation as a result of incorrect loading or overloading. In this case, the swivel joint fills up with synovial fluid, causing severe pain. Also due to accidents, the swivel joints in the base of the elbow are susceptible to pathological phenomena, since the elbow is relatively exposed. For example, the joints can fill with blood as a result of an accident and cause hemarthrosis, which in the course of time damages the joint cartilage. In addition, there are age-related signs of wear and tear. When the age-related wear and tear on the joint exceeds a certain level, we speak of osteoarthritis. In addition to overload, bone fracture-related misalignments and incorrect stresses can be to blame for this painful disease.
