The radius is one of the two bones of the forearm, the other is the ulna. The two bones are linked proximally by the proximal radioulnar joint, distally by the distal radioulnar joint, and along their borders by the interosseus membrane. Proximally, the radius articulates with the capitulum of the humerus and the radial notch of the ulna. Distally it articulates with the scaphoid and lunate at the radiocarpal joint.
Proximally, the flat circular head of the radius articulates with the capitulum (lateral articulating surface of the humerus), and lies within the circular annular ligament. This attaches it to the radial notch of the ulna. The joint enables the radius to rotate during pronation and supination of the forearm. Just below the head of the radius is the neck, which is the attachment point of the quadrate ligament, a quadrangular membrane that connects the neck of the radius to to a point distal to the radial notch of the ulna. Superiorly the annular ligament is supported by the radial collateral ligament, and lateral ulnar collateral ligament. The radial collateral ligament attaches from the lateral epicondyle to the annular ligament. The lateral ulna collateral ligament attaching from the lateral epicondyle to the supinator crest of the ulna. Just below the neck, we find the radial tuberosity projecting from the proximal anterior surface of the shaft. The tendon of the biceps brachii muscle inserts here, and causes supination of the forearm and flexion of the proximal radioulnar joint.
The distal surface of the radius articulates with the cashew shaped scaphoid bone laterally, and the crescent shaped lunate carpal bones medially. The scapholunate ligament connects the two carpals bones. The medial eminence of the radius is connected to the ulnar styloid process by the triangular fibrocartilage (superficial part), with the deep part of the ligament connected to the fovea on the head of the ulna. The dorsal tubercle of Lister arises from the dorsal surface of the radius, and the extensor pollicis longus wraps around the tubercle in order to pull at the appropriate angle for the thumb. The posterolateral part of the radius gives the radial styloid process, which the brachioradialis attaches to. The brachioradialis arises from the lateral epicondylar ridge and causes flexion of the elbow and supination of the forearm.
The flexor pollicis longus originates from the anterior surface of the radius, and inserts onto the distal phalanx of the thumb. The pronator teres muscle inserts onto the middle of the lateral surface of the body of the radius. The supinator originates from the lateral epicondyle of the humerus and radial collateral ligament, and inserts onto the lateral proximal radial shaft. The pronator teres originates from the distal quarter of the ulnar shaft and inserts onto the distal quarter of the radial shaft.
Galeazzi fracture- This is a fracture of the distal radial shaft, with concurrent dislocation of the distal radioulnar joint. They most commonly occur in children, and occur following a fall onto an outstretched hand.
Colles fracture- This is an extraarticular fracture of the distal radius leading to dorsal displacement of the proximal segment, leading to a ‘dinner fork’ deformity. It was first described by Abraham Colles in 1814, prior to the invention of X-rays.
Smith’s fracture- This is another fracture of the distal radius, but with volar displacement of the proximal shaft.
Hutchinson fracture- This is fracture of the radial styloid process, and is also known as a chauffeur’s fracture, when car engines used to be wound manually, and the backfire should suddenly snap the rotational ever back and lead to this fracture.
Developmental precursor- Limb bud (lateral mesodermal mesenchyme)
The muscles of pronation and supination all insert onto the radius.
Pronators: Pronator teres and pronator quadratus
Supinators: Biceps brachii and Supinator
The radius is one of the two bones of the forearm, the other is the ulna. Proximally, the radius articulates with the capitulum of the humerus and the radial notch of the ulna. Distally it articulates with the scaphoid and lunate.