Bony landmark · Elbow

Olecranon

Olecranon

The olecranon is the point of the elbow — the hook of the ulna that wraps up behind the end of the arm bone. The triceps inserts on its upper surface, so it is the lever the entire back of the arm pulls on to straighten the elbow. As the elbow reaches full extension the olecranon drops into a matching notch on the humerus, and that bone-on-bone catch is what gives a straight elbow its solid end-stop. A bursa sits between the bone and the skin, which is why leaning on the elbow is uncomfortable.