Fracture of the shaft of the radius alone may be due to a direct blow; to indirect violence, such as a fall on the hand; or to forcible pronation against resistance, as in wringing clothes. It is rare in comparison with fracture of both bones. When broken above the insertion of the pronator teres, the upper fragment is flexed and supinated by the biceps and supinator, while the lower fragment remains semi-prone, and is drawn towards the ulna by the pronator quadratus.

When the fracture is below the pronator teres, the displacement depends upon the direction of the force and the obliquity of the fracture. In fractures of the lower third of the shaft, the hand may be flexed toward the radial side, and the styloid lies at a higher level, as in a Colles' fracture. From the frequency with which this fracture occurs while cranking a motor-car, it is conveniently described as Chauffeur's fracture; we have observed in doctors, who have sustained this fracture in their own persons, that they were under the impression that they had sustained a trivial sprain of the wrist.

In addition to the ordinary signs of fracture, there is partial or complete loss of pronation and supination. The head of the radius as a rule does not move with the lower part of the shaft, but may do so if the fracture is incomplete or impacted.

Fracture of the shaft of the ulna alone is also comparatively rare. It is almost always due to a direct blow sustained while protecting the head from a stroke, or to a fall on the ulnar edge of the forearm, as in going up a stair.

The upper third is most frequently broken, and this injury is often associated with dislocation of the head of the radius ([Fig. 40]), or some other injury implicating the elbow-joint. On account of the superficial position of the bone, this fracture is frequently compound.

The displacement depends on the direction of the force, the fragments being usually driven towards the interosseous space. There is seldom marked deformity unless the head of the radius is dislocated at the same time. The diagnosis is, as a rule, easy.

The treatment is the same as for fracture of both bones, but the splints may be discarded at the end of a fortnight.

For some unexplained reason, a fracture of the upper third of the shaft of the ulna frequently fails to unite.

CHAPTER V
INJURIES IN THE REGION OF THE WRIST AND HAND