The radius is the larger and shorter of the two bones of the forearm.
It is a long bone placed obliquely downward between the elbow joint above and the carpal joint below.
It consists of a shaft and two extremities.
Shaft
It is flattened from before backwards.
It has two surfaces and two borders.
The dorsal face is convex in its length, smooth and covered by the extensors of the carpus and digits.
The volar face is concave in its length. It presents along its lateral border a narrow rough area where it is attached with the ulna by interosseous ligament. This rough area is interrupted above and below by two smooth areas which forms the proximal and distal radio-ulnar arches or interosseous space. These two arches are connected laterally by the radio-ulnar groove which is for the passage of the interosseous vessels.
The medial border is for the most part subcutaneous presents proximally, a rough area for the brachialis and the medial ligament of the elbow.
The lateral border is rounded in its proximal third, wide and flat below and is limited by the radio-ulnar groove. This border gives attachment to the lateral digital extensor and the extensor carpi obliquus.
Proximal extremity
It presents an articular area, which is divided by a sagittal groove into two divisions, the medial being the larger.
It articulates with the distal extremity of the humerus and is surrounded by a rim, which carries the coronoid process about the middle of the anterior surface. The coronoid process is received into the coronoid fossa of the humerus during the extreme flexion of the elbow.
Posteriorly just below the articular surface are two facets for articulation with the like facets of the ulna and between these and the proximal interosseous space is a quadrilateral rough area to which the ulna is attached.
The medial aspect of the anterior face presents a radial tuberosity into which the biceps brachii is inserted. The lateral tuberosity is more prominent and gives attachment to the lateral extensor of the digit.
Distal extremity
It is wide.
It presents three oblique facets for the carpal bones viz., radial, intermediate and ulnar carpals from within outward.
The facet for the ulnar carpal is partly furnished by the ulna.
On the medial and lateral aspects are rough elevations for the collateral ligaments of the carpus.
The radius and ulna are relatively long and articulate with each other at their extremities enclosing a narrow interosseous space and permit a certain degree of movement.
The proximal extremity of radius is small and bears a concave surface for articulation with the humerus above and a convex marginal area posteriorly for the ulna.
The distal extremity is wide and its medial border projects downward forming the styloid process of radius. Laterally there is a concave facet for the ulna.
The bones of forearm are nearly parallel to humerus.
Of the two bones the radius is slender while the ulna is thicker and longer.
They articulate at their ends and enclose a wide interosseous space.
The proximal extremity of the radius presents a concave articular area while the distal extremity is flattened from side to side and articulates with the radial carpal.
