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The annular ligament (orbicular ligament) is a strong band of fibers that encircles the head of the radius, and retains it in contact with the radial notch of the ulna. [1] Per Terminologia Anatomica 1998, the spelling is "anular", [2] but the spelling "annular" is frequently encountered.
In this movement the ulna, which is connected to the humerus by a simple hinge-joint, remains stationary, while the radius rotates, carrying the wrist and hand with it. To allow this rotation, the proximal (elbow) end of the radius is held in proximity to the ulna by a ligament known as the annular ligament.
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 radial collateral ligament is attached to the lateral epicondyle below the common extensor tendon. Less distinct than the ulnar collateral ligament, this ligament blends with the annular ligament of the radius and its margins are attached near the radial notch of the ulna. [8]
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 ulna or ulnar bone (pl.: ulnae or ulnas) [3] is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the radius, the forearm's other long bone. Longer and thinner than the radius, the ulna is considered to be the smaller long bone of the lower arm.
It occurs between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament. [2] The interosseous membrane of the forearm and the annular ligament stabilise the joint. [2] A number of nerves run close to the proximal radioulnar joint, including: median nerve; musculocutaneous nerve ...
the radial collateral ligament [proper] (RCL), from the lateral epicondyle to the annular ligament deep to the common extensor tendon [1] the lateral ulnar collateral ligament (LUCL), from the lateral epicondyle [3] to the supinator crest on the ulna. Near the attachment on the humerus this ligament is normally indistinguishable from the RCL ...