Overview
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.
Gross Anatomy
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.
Clinical Anatomy
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.
Quick Anatomy
Key Facts
Developmental precursor- Limb bud (lateral mesodermal mesenchyme)
Aide-Memoire
The muscles of pronation and supination all insert onto the radius.
Pronators: Pronator teres and pronator quadratus
Supinators: Biceps brachii and Supinator
Summary
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.