Elbow

The elbow is the joint region between upper arm and forearm, involving the humerus, radius and ulna. Its geometry supports flexion and extension while interacting with forearm rotation. A named joint region can therefore contain more than one articular relation.

The olecranon is the proximal projection of the ulna forming the point of the elbow. Attachment of the triceps brachii connects contraction to elbow extension, illustrating how a bony projection supplies a mechanical lever.

Elbow extension increases the angle between upper arm and forearm at the elbow. The triceps brachii is its principal muscular contributor. The resulting movement depends on joint position, external load and the line of pull.

Elbow flexion decreases the angle between upper arm and forearm at the elbow. Contributors include the brachialis and biceps brachii. Their mechanical contributions change with joint position and, for the latter, forearm orientation.