Radius and Ulna Bones of the Forearm

The long bones constituting the region between the wrist and the elbow of our forearm are called radius and ulna. The radius is the lateral one whereas the ulna is the medial part among the two bones present in this antebrachial region.

These bones have evolved physiologically to support the unique movements that our forearms can make using the adjacent muscles in this region and other parts of the musculoskeletal system. There are 20 muscles supporting these two bones resulting in a coordinated movement and assisting to perform the essential functions of the forearm.

Radius and Ulna Structure and Features

The two prime bones present in the upper part of our arms in between the wrist and elbow are called radius and ulna. These two bones constitute the upper part of the arm that helps us to work and use our hands. If we look closely then the radius bone supports the thumb or lateral region of our forearm whereas the ulna supports the medial side of the forearm. In this article, we will discuss the physiology, features, and functions of these two bones.

Radius and Ulna Bones Anatomy

Let us check the key factors of the ulna and radius bone anatomy to understand the configuration of these two bones with the adjacent muscles in the forearm.

1.Radius Bone

• Proximal End

Radius is the smaller one among the two bones. It also runs parallel to the ulna and is the thicker one. It has a slight longitudinal curve. There are two joints formed by this bone. At the elbow, it forms a joint with the capitulum of the humerus and with ulna in the radial notch in another section. In the wrist, both these bones form a joint that supports the wrist bones.

There are two extremities in this bone. The head is proximally located and is called caput radii. The proximal end of this bone forms a part of the upper surface of the joint to fit the capitulum of the humerus and a radial notch for the accommodation of one end of the ulna. It is a prism-shaped long bone present at the lateral side of the forearm between the wrist and the elbow.

• Neck

The neck region of this bone is where it narrows down till the bicipital tuberosity. The radial tuberosity can be located between the neck and head of this bone. It is an oval-shaped structure where the biceps brachii muscles fit or insert.

• Radial Shaft

The radius bone shaft is long with a convex shape at the lateral side but shows enlargement when we move in the direction of the wrist. There are three borders called the interosseous anterior, and posterior along with lateral, anterior, and posterior surfaces. The anatomical structure of these surfaces and borders will show several junctions where the tendons insert and join with this bone.

Two muscles are attached to this bone. They are supinator muscles in the radial head region and the pronator teres muscle that adheres to the radial shaft. The latter muscle attaches to the pronator tuberosity.

There are two other muscles attached to this bone are flexor digitorium superficialis and flexor pollicis longus. The distal end of this shaft is covered by the pronator quadratus muscle. To its opposite side, we find the insertion region for the brachioradialis muscle. It is located just above the styloid process.

• Distal Radius

In this region, it has bony developments. The dorsal tubercle is located in the posterior aspect of the radius bone anatomy lying between the grooves of muscle tendons of brevus and extensor carpi radialis longus. It also homes the notch for the tendons of extensor pollicis longus.

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2. Ulna Bone

• Proximal End

This part of the ulna bone consists of the olecranon, the trochlear notch, the coronoid process, and the radial notch. The coronoid process of ulna is the triangular eminence that projects forward from the front upper part of this bone.

• Ulnar shaft

The anatomy of the shaft part shows tapering in the distal region and increased thickness in the neck region. The lateral part is sharper and has the interosseous membrane, also called the interosseous border.

Below the coronoid process, the brachialis muscle attachment region or the ulnar tuberosity is found. The supinator fossa is the concave region that holds the supinator muscle. Another crest is found right beneath this muscle that holds the flexor pollicis longus muscle.

• Distal Ulna

In this part, the articular circumference connects with the wrist bones. Any projection is present at the posterior part called the styloid process. The medial aspect of this bone homes the attachment of the pronator quadratus, the muscle that runs amidst the radius and ulna.

• Interosseous Membrane

It is a membrane made of dense and fibrous connective tissue spanning between the ulna and radius. It forms a syndesmosis joint.

This is the anatomy of the two bones' radius and ulna forming the integral part of the forearm between the elbow and the wrist along with 20 different muscles. Study the different parts of these bones and refer to a proper radius and ulna diagram to understand how these bones attach to the muscles and function.