12.3:
Bones of the Upper Limb: Radius
The radius is the lateral forearm bone that runs parallel to the ulna and joins it proximally at the radial notch and distally via the ulnar notch.
It has a nail-shaped head and a curvy shaft that ends in a pointed projection called the radial styloid process.
At the proximal end, the head joins with the humeral capitulum and the ulna, forming the elbow joint. Rotation of the radial head enables forearm movement while turning the palm upwards or downwards. During flexing of the arm, the head moves into the radial fossa of the humerus.
Just below the radial head, a narrow neck extends to the rough radial tuberosity that anchors the bicep muscles of the arm.
At the distal end, the radial styloid process joins with the wrist bones forming the radiocarpal or wrist joint.
The styloid process stabilizes the wrist joint movement via a short and a long radiolunate ligament to limit the lateral rotation of the wrist.
12.3:
Bones of the Upper Limb: Radius
The radius is longer of the two bones that make up the human antebrachium or forearm. At the proximal end, the radius articulates with the capitulum of the humerus and the radial notch of the ulna to form the elbow joint. At the distal end, the radius articulates with the ulna via the ulnar notch, forming the distal radioulnar joint. Distally, the radius also attaches to the carpal wrist bones (scaphoid and lunate) to form the radiocarpal joint.
The radius has a nail-shaped head, and a short neck that extends to the oval-shaped prominence termed the radial tuberosity. The radial tuberosity attaches to the biceps brachii muscle. The radial shaft is slightly curved and has an interosseous membrane connecting it to the ulna along its entire length. The shaft also consists of multiple attachment sites for the muscles, including pronator teres, pronator quadratus, supinator, and other hand muscles that help in the pronation, supination, flexing, and extension movements of the forearm bone.
During pronation, the radial head crosses over the ulna, so the palm faces posteriorly, while a reversal of this movement allows the palms to supinate and face anteriorly. An annular ligament surrounding the radial head stabilizes the head to the ulnar notch.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 8.2: Bones of the Upper Limb.