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The word radius is Latin for "ray". In the context of the radius bone, a ray can be thought of rotating around an axis line extending diagonally [clarification needed] from center of capitulum to the center of distal ulna. While the ulna is the major contributor to the elbow joint, the radius primarily contributes to the wrist joint. [5]
The head of the radius has a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation with the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna , narrow in the rest of its extent, which is embraced by the annular ligament .
The annular ligament binds the head of the radius to the radial notch of the ulna, preventing any separation of the two bones laterally.Therefore, the humeroradial joint is not functionally a ball and socket joint, although the joint surface in itself allows movement in all directions.
The head of the radius is wider than the bone's neck, and, because the annular ligament embraces both, the radial head is "trapped" inside the ligament which thus acts to prevent distal displacement of the radius. [4] It helps to stabilise the proximal radial head, [6] and the radioulnar joint. [7]
In the forearm, the interosseous membrane is flexible enough to allow for rotation of the radius bone during forearm movements. Thus in contrast to the stability provided by the tibiofibular syndesmosis, the flexibility of the antebrachial interosseous membrane allows for the much greater mobility of the forearm.
Pronation of the foot is a compound movement that combines abduction, eversion, and dorsiflexion. Regarding posture, a pronated foot is one in which the heel bone angles inward and the arch tends to collapse. Pronation is the motion of the inner and outer ball of the foot with the heel bone. [13]
To cover the ulna head by extending the articular surface of the distal radius. Load transmission across the ulnocarpal joint and partially load absorbing; Allows forearm rotation by giving a strong but flexible connection between the distal radius and ulna. It also supports the ulnar portion of the carpus.
Pivot joints allow for rotation, which can be external (for example when rotating an arm outward), or internal (as in rotating an arm inward).When rotating the forearm, these movements are typically called pronation and supination.