Humeroulnar joint

The humeroulnar joint, is part of the elbow-joint, between the ulna and humerus bones and is a simple hinge-joint, which allows of movements of flexion and extension only.

Owing to the obliquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus.

When the forearm is extended and supinated, the axes of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm (the carrying angle). During flexion, however, the forearm and the hand tend to approach the middle line of the body, and thus enable the hand to be easily carried to the face.

The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement.

Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the Brachioradialis, with a tiny contribution from the muscles arising from the medial epicondyle of the humerus.

Extension is produced by the Triceps brachii and Anconæus, with a tiny contribution from the muscles arising from the lateral epicondyle of the humerus, such as the Extensor digitorum communis.