The forearm contains two bones namely; radius and ulna. Radius is shorter in size and lateral in position. Proximally it articulates with the humerus, and distally it supports the carpus. It consists of a proximal end, a body, and an expanded distal end. The body is narrow proximally, but increases in all its diameters distally.
Proximal End of Radius:
Proximal end of radius consists of head, neck and tuberosity. The head of radius is disc-shaped and provided with a shallow concave surface proximally for articulation with the capitulum of the humerus. The circumference of the head is smooth and is embraced by the annular ligament. The neck is the constricted part of the body which supports the head. Distal to the neck, on the medial side, there is an outstanding oval prominence, the radial tuberosity.
Body of Radius:
The body is narrow proximally and broad distally. It has a lateral curve and is wedge-shaped in cross section. The edge of the wedge forms the sharp medial interosseous border of the bone while its base corresponds to the thick and rounded lateral border over which the anterior surface becomes confluent with the posterior surface.
The interosseous border is faint proximally where it lies in line with the dorsal margin of the tuberosity. It becomes sharp and prominent in the middle third of the bone. Distal to this it splits into two faint lines, which lead to either side of the ulnar notch on the distal end of the bone, thus including between them a narrow triangular area. To this crest, as well as to the dorsal of the two divergent lines, the interosseous membrane is attached.
The lateral surface is thick and rounded proximally, but becomes thinner and more prominent distally, where it merges with the base of the styloid process.
The anterior surface is crossed obliquely by a line which runs from the tuberosity distally and laterally towards the middle of the lateral surface of the body. This is often called the anterior oblique line.
The posterior surface is also crossed by an oblique line, less distinct than the anterior.
Distal end of Radius:
The distal end, which tends to be turned slightly forwards, has a somewhat triangular form. Its distal carpal articular surface, concave from before backwards, and slightly so from side to side, is divided into two facets by a slight antero- posterior ridge.
The anterior border, prominent and turned forwards, is rough at its edge, where it serves for the attachment of the anterior part of the capsule of the wrist-joint.
The posterior border is rough, rounded, and tubercular, and is grooved by many tendons.
The styloid process lies to the lateral side of the distal end; broad at its base, it becomes narrow and pointed distally where by its medial cartilage-covered surface it forms the summit of the distal triangular articular area
On the medial side of the distal extremity is placed the ulnar notch for the reception of the head of the ulna. It is concave from before backwards, and plane proximo-distally. It forms a rectangular edge, by its inferior margins, which separates it from the distal carpal surface.
Nutrient Foramina of Radius:
The openings of several small nutrient canals may be seen in the region of the neck. That for the body, which has a proximal direction, is usually placed on the anterior surface of the bone, medial to the anterior oblique line, and about two inches distal to the tuberosity. The dorsal surface of the distal extremity of the bone is pierced by many small vascular foramina.
Ossification of Radius:
The center for the body makes its appearance early in the second month of intra-uterine life. A secondary center appears in the cartilage of the distal extremity about the second or third year. This does not unite with the body until the twentieth or twenty-fifth years, somewhat earlier in the female. From this the carpal and ulnar articular surfaces are formed. The center for the head appears from the fifth to the seventh year, and fuses with the neck about the age of eighteen or twenty. It forms the capitular articular surface and combines with the neck to form the area for articulation with the radial notch of the ulna. A scale-like epiphysis capping the summit of the tuberosity has been described; this appears about the fourteenth or fifteenth year, and rapidly fuses with that process.