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The trochlear notch (/ ˈ t r ɒ k l ɪər /), [1] also known as semilunar notch and greater sigmoid cavity, is a large depression in the upper extremity of the ulna that fits the trochlea of the humerus (the bone directly above the ulna in the arm) as part of the elbow joint. It is formed by the olecranon and the coronoid process.
While the trochlea together with its associated fossae almost covers a 360° angle, the trochlear notch on the ulna forms a 190° arc and the gap in between allows flexion and extension at the elbow. Maximum elbow flexion and extension is made possible because the two fossae accommodates to coronoid and olecranon processes. [4]
The olecranon (/ oʊ ˈ l ɛ k r ə n ɒ n /, from Greek olene 'elbow' and kranon 'head'), is a large, thick, curved bony process on the proximal, posterior end of the ulna. It forms the protruding part of the elbow and is opposite to the cubital fossa or elbow pit ( trochlear notch ).
The olecranon fossa is a deep triangular depression on the posterior side of the humerus, superior to the trochlea. It provides space for the olecranon of the ulna during extension of the forearm .
The coronoid fossa is smaller than the olecranon fossa and receives the coronoid process of the ulna during maximum flexion of the elbow. Coronoid fossa of the humerus Above the front part of the capitulum is a slight depression, the radial fossa , which receives the anterior border of the head of the radius, when the forearm is flexed.
The semilunar notch is a large depression, formed by the olecranon and the coronoid process, and serving as articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and indicates the junction of the olecranon and the coronoid process.
The humeroulnar joint (ulnohumeral or trochlear joint [1]) is part of the elbow-joint. It is composed of two bones, the humerus and ulna, and is the junction between the trochlear notch of ulna and the trochlea of humerus. [1] It is classified as a simple hinge-joint, which allows for movements of flexion, extension and circumduction.
The structure to resist these forces is a pronounced keel on the trochlear notch on the ulna, which is more flattened in, for example, humans and gorillas. In knuckle-walkers , on the other hand, the elbow has to deal with large vertical loads passing through extended forearms and the joint is therefore more expanded to provide larger articular ...