This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
The lower end of the ulna is rarely fractured, but that of the radius vies with fracture of the clavicle in being the most frequent of all fractures.
Fig. 353. - Colles's fracture of the lower end of the radius, showing the " silver fork deformity" and displacement of the fragments.
Fractures of the radius which occur at the wrist possess certain distinct characteristics and were for a long time confounded with dislocations of the wrist. These fractures are generally grouped by modern surgeons under the name of Colles's fracture. This fracture was first correctly described, according to both Hamilton and Stimson, by Pouteau (" CEuvres Posthumes," t. 11, p. 251, 1783; also Nelaton, " Chirurgie Path.," t. 1, p. 739). Mr. Colles, a Dublin surgeon, described the injury most carefully in the Edinburgh Medical and Surgical Journal, April, 1814, but it is largely due to Robt. W. Smith's "Treatise on Fractures in the Vicinity of Joints," Dublin, 1847, that the name Colles's fracture has become generally accepted. Mr. Colles placed the injury 1 1/2 inches (about 4 cm.) above the joint. Mr. Smith placed it from 1/4 in. to 1 in. (6 to 25 mm.) above the joint. Most recent writers include all fractures within 4 cm. (1 1/2 in.) of the lower edge of the radius under this name, though some few go still higher. When the line of fracture lies more than 4 cm. above the joint it loses the characteristics of a Colles's fracture and partakes of those of fractures of the shaft; hence we will not go beyond that limit.
The line of fracture is most commonly found, as stated by Robt. W. Smith, from 6 to 25 mm. (1/4 to 1 in.) above the joint. It passes almost transversely across the bone or inclines slightly downward to the ulnar side. It also lies nearer the joint on the anterior surface and inclines backward and upward toward the elbow. Hence the direction is from above downward and forward (Fig. 353).
The lower fragment is displaced upward and backward on the shaft of the radius. This causes it to be tilted backward so that the articular surface is rotated on a transverse axis more in the direction of the dorsum than normal and the hand is also carried toward the radial side. The dorsal displacement is due to the direction of the violence and not to muscular action. The radial side of the fragment is displaced upward more than the ulnar because the triangular fibrocartilage retains its radio-ulnar attachments. This prevents the ulnar side from rising, while the radial side is pulled up by the radial flexor and extensor muscles. If the fracture is not extremely close to the joint the brachioradialis will pull the lower fragment toward the radial side and up toward the elbow.
Fig. 354. - Colles's fracture of the radius, showing inclination of hand toward the radial side and prominence of the styloid process of the ulna. (From author's sketch).
As the hand is attached to the radius it follows the lower fragment; the extensor muscles of the thumb, the flexor carpi radialis, and the two extensor carpi radialis muscles all tend to aid the brachioradialis in producing the displacement toward the radial side (Fig. 354).
The lower fragment is displaced toward the dorsum and the upper fragment toward the palmar surface. This produces the " silver fork deformity" of Velpeau. This dorsal projection is sometimes increased by the presence of the "carpal tumor," a swelling due to effusion almost directly above the joint. The projection of the upper fragment toward the palmar surface and the effusion in the sheaths of the flexor tendons cause a protrusion on the anterior surface of the wrist and a marked increase in the lower anterior radiocarpal crease.
To reduce the deformity the upper fragment is firmly grasped with one hand while with the other the hand of the patient is forcibly adducted (toward the ulnar side) and then sharply flexed. This drags the distal fragment down and forward off of the proximal one. To retain the fragments in position some surgeons use a pistol-shaped splint to hold the hand turned toward the ulnar side and place a graduated compress on the palmar surface with its base opposite the line of fracture and its apex upward and another pad on the dorsal surface with its apex downward over the hand. Other surgeons place the hand in a flexed position, allowing it to hang.
The lower radial epiphysis fuses with the shaft at about the twentieth year; therefore epiphyseal separation can occur up to that time. The epiphyseal line passes across the bone from the base of the styloid process to the upper edge of the radio-ulnar joint (Fig. 355).