The diaphysis (shaft or body) of the radius is the long and thin middle part of the bone. It is convex on the lateral side and widens towards the wrist.

The radial shaft has three borders and three surfaces:

Anterior (volar) border - a well-pronounced border on the anterior aspect of the bone; it separates the anterior and posterior surfaces;
Posterior (dorsal) border - a rounded border on the posterior side of the bone;
Interosseous (internal) border - the sharp medial border that faces the ulna; it begins below the radial tuberosity and goes down towards the ulnar notch; it gives attachment to the interosseous membrane of the forearm;
Anterior (volar) surface - an area that is found between the anterior and interosseous borders; it serves as an attachment site for the supinator, pronator quadratus, flexor digitorum superficialis, and flexor pollicis longus;
- Oblique line - an oblique line that begins at the base of the radial tuberosity and spirals inferolateral; it continues as the anterior border in the inferior direction;
- Nutrient foramen - a small opening in the anterior surface of the body; usually, it is found more or less at the proximal aspect of the surface; it transmits vessels that supply the bone and are found within its medullary cavity;
Posterior (dorsal) surface - positioned between the posterior and interosseous borders; it provides the attachment site to the abductor pollicis longus, extensor pollicis brevis, and supinator;
Lateral surface - located between the anterior and posterior borders; it gives attachment to the brachioradialis, supinator, and pronator teres;
- Pronator tuberosity - a distinct rough area in the middle of the lateral surface.

Just below the neck of the radius on the anteromedial aspect of the bone is the radial or bicipital tuberosity. It is an oval-shaped and slightly convex blunt bony prominence that serves as an attachment site for the biceps brachii muscle.

On the distal anterolateral aspect of the radial shaft, there is another landmark - the suprastyloid crest. It is a relatively sharp ridge that continues in the distal direction and leads to the styloid process.

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Radius (diaphysis)