The radius (Latin radius) is the name given to a bone of the forearm. The radius is located on the thumb side and is stronger than the opposite ulna in mammals. The radius is a tubular bone.
What is a radius?
Anatomical diagram showing outward rotation and inward rotation of the forearm. Click to enlarge. The radius is a tubular bone in the forearm that is often titled the radius in German-speaking countries. It is assumed that this name is based on the similarity of the radius to the spoke of a wagon wheel. The tubular bone is connected to the upper arm and extends to the bones of the carpus (lat. Ossa carpalia). The radius, like almost every other human long bone, is divided into three sections: the head of the radius, which joins the humerus (caput radii), the neck of the radius (collum radii) that follows it, and the shaft or body of the radius (corpus radii).
Anatomy and structure
The radius is divided into three sections in anatomy. It consists of the radial head, the radial neck, and the radial body or shaft. The upper end of the radius is directed toward the center of the body and thus represents the proximal (near-body) end of the radius (called the epiphysis proximalis radii). The head of the radius is covered by cartilage and acts here like a wheel resting on the neck of the radius. On the articular surface of the radius neck, at the junction with the humerus, there is an indentation (called fovea capitis radii) intended for the humerus head (lat. capitulum humeri). Above this indentation is a partial joint (the articulatio humeroradialis), which belongs to the elbow joint (articulatio cubiti). However, the head of the radius is also encompassed by a coronary articular surface (circumferentia articularis), which provides a mobile connection to the ulna. The middle part of the radius is called the spoke shaft or spoke body. Together with the ulna, this part forms a unit that influences the function of the forearm. This is also evident from the fact that these two bones are coupled and thus connected in different ways. They have a proximal, but also a distal movable connection to each other. Furthermore, a stable ligament spans between the two bones (the membrana interossea antebrachii), which extends almost through the entire forearm. This ligament is also known as the ligamentous bond and provides a tight traction throughout the arm, originating at the radius and forming a kind of rim (margo interosseus) toward the ulna. This rim can even be felt through the skin. Two other edges are found on the front (margo anterior) and on the back (margo posterior) of the radius. The posterior margin, however, is not as sharp-edged and therefore not as palpable, since there is less traction on it. The radius widens steadily from the middle of the body, so that the lower end has an articular surface for the carpal bones (ossa carpi). Here, a bony protrusion for the carpus also protrudes laterally. This protrusion is known in medicine as the styloid process (lat. Processus styloideus radii). This is where the muscle of the radius of the upper arm (the brachioradialis muscle) attaches. The distal end of the radius (called the epiphysis distalis radii) also has an indentation (lat. incisura ulnaris), which together with the ulna forms the distal radius-ulna joint.
Function and tasks
The radius has two important functions and thus tasks: First, it represents a part of the wrist joint. Thus, it also influences the musculoskeletal system of the latter. On the other hand, the radius belongs to the elbow joint and also ensures here proportionally that this can be moved within the known framework. Overarching, however, the spoke represents rather a connection of the upper arm to the wrist and supports the wrist and the elbow joint only in their tasks.
Diseases and complaints
The most common types of injury and disease that can affect the radius are a fracture. Both usually occur as a result of trauma caused by an accident or other external impact. However, in older people or people with a disease of the bone substance, a fracture of the radius can also be caused by wear and tear. In addition, the radius is usually also affected when the opposite ulna suffers a fracture or break.This is because both bones partially stabilize each other and can only fulfill their full function together. A fracture or break of the radius is usually stabilized by a cast or splint for several weeks so that the bone can heal. Also, the radius can also be affected by an Essex-Lopresti injury or by a radial head subluxation. A radial head subluxation is a joint blockage, but it usually affects children. An Essex-Lopresti injury is an extremely rare combination of injuries to the arm that usually also affects the ulna and the radial head. Again, severe trauma is often the cause. However, the healing process is more complicated and prolonged. Often, parts of the head must be restored by surgery to restore function to the radius and the affected joint.
