In the human arm, the

humeral The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a rou ...

trochlea is the medial portion of the articular surface of the

elbow The elbow is the region between the arm and the forearm that surrounds the elbow joint. The elbow includes prominent landmarks such as the olecranon, the cubital fossa (also called the chelidon, or the elbow pit), and the lateral and the me ...

joint which articulates with the trochlear notch on the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

in the forearm.

Structure

In humans and

ape Apes (collectively Hominoidea ) are a clade of Old World simians native to sub-Saharan Africa and Southeast Asia (though they were more widespread in Africa, most of Asia, and as well as Europe in prehistory), which together with its sister g ...

s it is trochleariform (or trochleiform), as opposed to cylindrical in most monkeys and conical in some

prosimian Prosimians are a group of primates that includes all living and extinct strepsirrhines ( lemurs, lorisoids, and adapiforms), as well as the haplorhine tarsiers and their extinct relatives, the omomyiforms, i.e. all primates excluding the si ...

s. It presents a deep depression between two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity.

The trochlea has the

capitulum capitulum (plural capitula) may refer to: *the Latin word for chapter ** an index or list of chapters at the head of a gospel manuscript ** a short reading in the Liturgy of the Hours *** derived from which, it is the Latin for the assembly known ...

located on its lateral side and the medial epicondyle on its medial. It is directly inferior to the

coronoid fossa Superior to the anterior portion of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. It is directly adjacent to the radial fossa The radial fossa is a slight d ...

anteriorly and to the

olecranon fossa 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. Structure The olecranon fossa is located on ...

posteriorly. In humans, these two fossae, the most prominent in the humerus, are occasionally transformed into a hole, the supratrochlear foramen, which is regularly present in, for example, dogs.

Carrying angle

When viewed from in front or behind, the trochlea looks roughly cylindrical, but when viewed from below its true oblique shape and the spiralling nature of its groove become apparent. The spiralling nature of the trochlear groove results in the varying transverse axes of the elbow joint. Most frequently, the groove is vertical on the anterior side but runs down laterally on the posterior side. During elbow flexion, the vertical anterior part of the trochlea keeps the upper arm and forearm aligned (when viewed in front). During elbow extension, however, the oblique posterior part makes contact with the trochlear notch on the ulna so that this obliquity forces the main axis of the forearm to form a small angle with that of the upper arm. This angle is known as the ''carrying angle'' and is more prominent in women than in men. Less frequently, the anterior part is oblique too, but in the opposite direction of the posterior side. Consequently, during full elbow flexion, the hand tends to rest outside the shoulder. Very rarely, the anterior part is oblique in the opposite direction, resulting in the hand's resting on the chest during flexion.

Function

The elbow is a hinge joint with a rotatory component where the trochlea forms the convex, proximal surface which articulates with the concave, distal surface on the ulna, the trochlear notch. 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.

Ossification

While the ossification of the capitulum has started a year after birth, the ossification of the trochlea begins at 8–9 years of age; that of the

head of radius 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 ra ...

and the medial epicondyle at 4–5 years and that of the lateral condyle at 10 years.

Additional images

File:Elbow joint - deep dissection (anterior view, human cadaver).jpg, Elbow joint. Deep dissection. Anterior view. File:Slide2xzxzxz.JPG, Elbow joint. Deep dissection. Anterior view.

References

External links

* {{Authority control Bones of the upper limb Humerus