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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.
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.
Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the brachialis muscle. At the junction of this surface with the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the brachialis; to the lateral border of this tuberosity the oblique cord is attached.
The olecranon is situated at the proximal end of the ulna, one of the two bones in the forearm. [1] When the hand faces forward the olecranon faces towards the back (posteriorly). It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus during extension of the forearm. [2] [3]
The ulnar collateral ligament (UCL) or internal lateral ligament is a thick triangular ligament at the medial aspect of the elbow uniting the distal aspect of the humerus to the proximal aspect of the ulna.
The major exception is when the joint between these bones, the distal radioulnar joint (or DRUJ), is unstable. When the DRUJ is unstable, the ulnar styloid may require independent treatment. An excessively long styloid process of the ulna can cause painful contact with the triquetral bone in the wrist, known as ulnar styloid impaction syndrome. [1]
The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the trochlear notch of the ulna, prevents any lateral movement. Flexion in the humeroulnar joint is produced by the action of the biceps brachii and brachialis , [ 3 ] assisted by the brachioradialis , with a tiny contribution from the muscles ...
The dorsal surface is rough for the attachment of ligaments. The volar surface presents, on its medial part, an oval facet, for articulation with the pisiform; its lateral part is rough for ligamentous attachment. The lateral surface, the base of the pyramid, is marked by a flat, quadrilateral facet, for articulation with the lunate.