Radius and Ulna Bones
Anatomy Quizzes
Table of Contents
Background
Introduction
The radius and ulna are two long bones that provide structural support for the forearm, the area between the elbow and the wrist. The radius is located on the forearm’s lateral side (thumb side), while the ulna is on the medial side (little finger side).
The radius is shorter and sturdier than the ulna and bears most of the load when moving the hand. The longer ulna, with its prominent olecranon process at the elbow, provides a surface for muscle attachment and acts as a stabilizer during forearm movements.
Proximal End Anatomy
Radius Landmarks
A disc-shaped radial head forms the superior end of the bone. On the upper surface of the head is a shallow depression that articulates with the rounded capitulum of the humerus. The outer edge of the head (circumference) is smooth and articulates with the radial notch of the ulna at the proximal radioulnar joint.
The bone narrows beneath the head, forming the neck of the radius. On the lower medial side of the neck is an oval-shaped bump called the radial tuberosity. This bump serves as a distal attachment point for the biceps brachii muscle.
Ulna Landmarks
The trochlear notch is a prominent C-shaped bony projection located at the proximal end of the ulna. It curves around the humerus’s trochlea to form the elbow joint. When extending the forearm, the upper posterior part of the trochlear notch, known as the olecranon process, fits behind the humerus’s trochlea to form the elbow’s bony tip.
The lower anterior edge of the trochlear notch extends forward to create a noticeable bony lip-like protrusion called the coronoid process.
Inferior to the coronoid process is a roughened elevation called the ulnar tuberosity, which serves as the distal attachment point for the brachialis muscle.
Lateral and inferior to the trochlear notch is a slight depression called the radial notch of the ulna. The head of the radius fits into this depression to form the proximal radioulnar joint, the proximal pivot joint between the radius and ulna.
Radius Proximal End
Ulna Proximal End
Mid-Portion Anatomy
Radius Landmarks
The radius’s shaft is triangular along most of its length, with its narrow medial margin forming a ridge called the interosseous border. This ridge provides attachment for the interosseous membrane that binds the radius and ulna bones.
This thin sheet of connective tissue attaches the two bones and helps transfer weight-bearing loads from the proximal radius to the distal ulna. Additionally, several muscles that move the hand attach to this membrane.
The long radial shaft extends downwards from the radial tuberosity and provides much of the forearm’s support. It is relatively narrow at its top end but widens near the wrist joint..
Ulna Landmarks
Inferior to the ulna’s radial notch and tuberosity, the ulna narrows to form the shaft, the extended middle portion of the bone. The shaft is triangular along most of its length but becomes rounded at its distal end.
The interosseous border is along the lateral edge of the shaft. This sharp margin is the attachment point for the forearm’s interosseous membrane.
Radius Mid-Portion
Ulna Mid-Portion
Distal End Anatomy
Radius Landmarks
The distal end of the radius is the widest near the wrist, giving it a triangular appearance. Its smooth, concave inferior surface articulates with the wrist’s rounded carpal bones to form the radiocarpal joint.
A shallow depression, the ulnar notch, appears on the medial side of the distal radius. The head of the ulna articulates with the ulnar notch of the radius to form the distal radioulnar joint. The ulnar notch of the radius pivots around the ulnar head, allowing the radius to cross over the ulna while turning the wrist.
The styloid process of the radius is located on the lateral side of the bone. This downward, cone-shaped projection is the attachment point for the brachioradialis muscle, a flexor of the forearm. It also serves as the attachment site for a wrist tendon that restricts sideways hand movements.
Ulan Landmarks
The head of the ulna extends inferiorly from the distal or lower end of the bone. This small, knob-like protuberance fits into the ulnar notch of the radius to form the distal radioulnar joint. Movement at the distal radioulnar joint allows the distal end of the radius to rotate or pivot around the ulna while rotating the wrist and hand (supination and pronation).
The styloid process is posterior and medial to the ulnar head. This short downward projection is an attachment point for ligaments that help stabilize the distal radioulnar and radiocarpal joints.
Radius Distal End
Ulna Distal End
Quizzes
Ulna Matching Quiz
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Radius Matching Quiz
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References and Attributions
NIH: National Library of Medicine – “Anatomy, Shoulder and Upper Limb, Forearm Radius.”
NIH: National Library of Medicine – “Increased Carrying Angle is a Risk Factor for Nontraumatic Ulnar Neuropathy at the Elbow.”
Openstax – “Bones of the Upper Limb.”
Radiopaedia – “Radius.”
Radiopaedia – “Ulna.”
Wikipedia – “Radius (bone).”
Wikipedia – “Ulna.”