The radius is the lateral bone of the forearm, and is homologous with the tibia of the lower limb. Radius along with ulna connects elbow to forearm.It has an upper end, a lower end and a shaft.
The Upper End
1. The head is disc shaped and is covered with hyaline cartilage. It has s uperior concave surface which articulates with the capitulum of the humerus at the elbow joint. The circumference of the head is also articular. It fits into a socket formed by the radial notch of the ulna and the annular ligament, thus forming the superior radioulnar joint
2. The neck is enclosed by the narrow lower margin of the annular ligament. The head and neck are free from capsular attachment and can rotate freely within the socket.
3. The tuberosity lies just below the medial part of the neck. It has a rough posterior part and a smooth anterior part.
It has three borders and three surfaces.
1. The anterior border extends from the anterior margin of the radial tuebrosity to the styloid process. It is oblique in the upper half of the shaft, and vertical in the lower half. The oblique part is called the anterior oblique line. The lower vertical part is crest like.
2. The posterior border is the mirror image of the anterior border, but is clearly defined only in its middle one third. The upper oblique part is known as the posterior oblique line
3. The medial (or interosseus) border is the sharpest of the three borders. It extends from the radial tuberosity (above) to the posterior margin of the ulnar notch (below). The interosseus membrane is attached to its lower three fourths. In its lower part it forms the posterior margin of an elongated triangular area.
4. The anterior surface lies between the anterior and interosseus borders. A nutrient foramen opens in its upper part, and is directed upwards. The nutrient artery is branch of the anterior interosseus artery.
5. The posterior surface lies between the posterior and interosseus borders.
6. The lateral surface lies between the anterior and posterior borders.
The Lower End
The lower end is the widest part of the bone. It has five surfaces.
1. The anterior surface is in the form of a thick prominent ridge. The radial artery is palpated against this surface.
2. The posterior surface presents four grooves for the extensor tendons. The dorsal tubercle (of Lister) lies lateral to an oblique groove.
3. Tue medial surface is occupied by the ulnar notch for the head of the ulna
4. The lateral surface is prolonged downwards to form the styloid process.
5. The inferior surface bears a triangular area for the scaphoid bone, and a medial quadrangular area of the lunate bone. This surface takes part in forming the wrist joint.
Attachment on the Radius
1. The biceps brachi is inserted into the rough posterior part of the radial tuberosity. The anterior part of the tuberosity is covered by a bursa.
2. The supinator is inserted into the upper part of the lateral surface.
3. The pronator teres is inserted into the middle of the lateral surface.
4. The brachioradialis is inserted into the lowest part of the lateral surface just above the styloid process.
5. The radial head of the flexor digitorum superficialis takes origin from the anterior of oblique line (upper part of anterior border).
6. The flexor policis longus takes origin from the upper two thirds of the anterior surface.
7. The pronator quadratus is inserted into the lower part of the anterior surface and into the triangular area on the medial side of the lower end.
8. The abductor pollicis longus and the extensor pollicis brevis arise from the posterior surface.
9. The quadrate ligament is attached to the medial part of the neck.
10. The oblique cord is attached on the medial side just below the radial tuberosity.
11. The articular capsule of the wrist joint is attached to the anterior and posterior margins of the inferior articular surface.
12. The articular disc of the inferior radioulnar joint is attached to the lower border of the ulnar notch.
13. The extensor retinaculum is attached to the lower part of the anterior border.
14. The interosseus membrane is attached to the lower three fourths of the interosseus border.
Text adapted from: Human Anatomy by BD Chaurasia
Image Credit: Wikipedia