The elbow joint is a hinge-like complex connecting the humerus (upper arm bone) with the radius and ulna (forearm bones). While the joint allows for bending and straightening, it is defined by distinct bony projections. The structure most people recognize as the “point” of the elbow, especially when the arm is bent, is a prominent, rounded piece of bone at the very back of the joint, easily felt just beneath the skin.
The Specific Anatomical Name
The prominent bony tip at the back of the elbow is formally known as the olecranon. This anatomical name is derived from the Greek words olene (elbow) and kranon (head). The olecranon is not a separate bone but is the large, curved projection found at the proximal, or upper, end of the ulna bone.
The olecranon is thick and curved, forming a distinctive lip-like process integral to the elbow’s function. When the arm is straightened, this bony tip fits securely into a corresponding depression on the humerus called the olecranon fossa. This mechanism helps stabilize the joint and prevents hyperextension.
Structural Role and Muscle Attachment
The olecranon acts as a powerful lever arm within the elbow joint. This projection is the main insertion point for the triceps brachii muscle, the large muscle on the back of the upper arm. The triceps tendon attaches directly to the superior surface of the olecranon process.
The triceps muscle is responsible for extending the forearm, or straightening the arm. When the triceps contracts, it pulls on the olecranon, using the projection’s length to gain a mechanical advantage. This leverage allows for powerful pushing and throwing movements. The olecranon also works with the humerus to form a stable hinge joint, providing structural stability during movement.
Vulnerability and Superficial Structures
The olecranon’s location just beneath the skin makes it vulnerable to injury or irritation of superficial structures. One structure is the olecranon bursa, a small, fluid-filled sac situated between the bone and the skin. The bursa reduces friction, allowing the skin to glide smoothly over the bony prominence during movement.
The bursa is susceptible to inflammation from direct impact or prolonged pressure, a condition known as olecranon bursitis. This is sometimes called “student’s elbow” and causes the bursa to swell noticeably. Another structure in the area is the ulnar nerve, which passes closely around the medial side of the olecranon. When the back of the elbow is struck, the nerve is temporarily compressed against the bone, causing the sharp, tingling sensation known as hitting the “funny bone.”