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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 radius is a long bone, prism-shaped and slightly curved longitudinally. The radius is part of two joints: the elbow and the wrist. At the elbow, it joins with the capitulum of the humerus, and in a separate region, with the ulna at the radial notch. At the wrist, the radius forms a joint with the ulna bone.
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 radial head subluxation, there is little complaint of pain, and the person generally reports pain in the proximal forearm. The mechanism is slippage of the head of the radius under the annular ligament. The distal attachment of the annular ligament covering the radial head is weaker in children than in adults, allowing it to be more easily torn.
In human anatomy of the arm, the capitulum of the humerus is a smooth, rounded eminence on the lateral portion of the distal articular surface of the humerus.It articulates with the cup-shaped depression on the head of the radius, and is limited to the front and lower part of the bone.
The radial notch of the ulna (lesser sigmoid cavity) is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before backward, and its prominent extremities serve for the attachment of the annular ligament.
the annular ligament (AL), from the posterior to the anterior margins of radial notch on the ulna, encircles the head of radius and holds it against the radial notch of ulna. [5] the accessory lateral collateral ligament (ALCL), from the inferior margin of the annular ligament to the supinator crest.
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