o bridge the gap in the ulna, unless it alone is the seat
of non-union.

#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