The ulna is one of the two long bones located in the forearm, extending from the elbow to the wrist. It runs parallel to the radius, the other forearm bone, and is situated on the pinky finger side of the arm when in the anatomical position. The ulna plays a significant role in providing structure to the forearm and facilitating various movements of the arm, wrist, and hand.
Identifying the Ulna’s Head
The head of the ulna is located at the distal, or wrist, end of the bone. You can easily feel this part of the ulna as a distinct, rounded bony prominence on the back of your wrist, specifically on the side closer to your pinky finger.
To locate it, gently run your fingers along the pinky finger side of your forearm, moving towards your wrist. Just above your wrist joint, you will encounter a small, rounded knob of bone. Below and slightly behind it, you might also feel a smaller, more pointed projection called the ulnar styloid process, which extends from the head of the ulna.
Observing your wrist as you rotate your forearm can further help identify this structure. As you turn your palm up and down, you may notice the head of the ulna appearing more prominent or receding slightly. This movement highlights its articulation with the radius and its role in forearm rotation.
The Ulna’s Role in Wrist and Forearm Function
The head of the ulna is key to wrist and forearm mechanics. It articulates primarily with the distal radius, forming the distal radioulnar joint (DRUJ). This joint is fundamental for the rotational movements of the forearm, known as pronation (turning the palm downwards) and supination (turning the palm upwards).
While the ulna provides stability, the radius pivots around it at the DRUJ during these rotations. The head of the ulna also interacts with a specialized structure called the triangular fibrocartilage complex (TFCC). This complex acts as a cushion and helps stabilize the wrist joint, preventing the ulna’s head from directly articulating with the carpal bones of the wrist.
Through these articulations, the ulna contributes to arm mobility and stability, enabling a wide range of hand and wrist positions. The coordinated movement between the ulna and radius, facilitated by the ulna’s head, is essential for functional upper limb use.
Understanding the Ulna’s Structure
In anatomical terminology, the “head” of a bone typically refers to a rounded, articular (joint-forming) end. For many bones, such as the humerus (upper arm bone), the head is located at the proximal end, closer to the body’s core. However, the ulna is an exception, as its “head” is located at its distal end, near the wrist.
The other end of the ulna, at the elbow, is larger and features a prominent bony projection called the olecranon process. This process forms the point of your elbow and articulates with the humerus to create the elbow joint, allowing for bending and straightening of the arm. While substantial, this proximal end is not referred to as the “head” of the ulna.
Therefore, the term “head of the ulna” specifically designates the rounded, articulating surface found at the wrist end of the bone. The ulna’s shape, with its larger proximal end and smaller distal head, contrasts with the radius, which has a smaller proximal head and a larger distal end.