nsmitted through the carpus to the lower end of
the radius which is broken off, the lower fragment being driven
backwards.

The fracture takes place through the cancellated extremity of the
bone, within a half to three-quarters of an inch of its articular
surface (Fig. 45). It is usually transverse, but may be slightly
oblique from above downwards and from the radial to the ulnar side. In
a considerable proportion of cases it is impacted, and not
infrequently the lower fragment is comminuted, the fracture extending
into the radio-carpal joint.

[Illustration: FIG. 43.--Colles' Fracture showing radial deviation of
hand.]

[Illustration: FIG. 44.--Colles' Fracture showing undue prominence of
ulnar styloid.]

When impaction takes place, it is usually reciprocal, the dorsal edge
of the proximal fragment piercing the distal fragment, and the palmar
edge of the distal fragment piercing the proximal. The periosteum is
usually torn and stripped from the palmar aspect of the fragments,
while it remains intact on the dorsum.

In the majority of cases the styloid process of the ulna is torn off
by traction exerted through the medial ulno-carpal (internal lateral)
ligament, and in a considerable proportion there is also a fracture of
one of the carpal bones.

The resulting _displacement_ is of a threefold character: (1) the
distal fragment is displaced backwards; (2) its carpal surface is
rotated backwards on a transverse diameter of the forearm; while (3)
the whole fragment is rotated so that the radial styloid comes to lie
at a higher level than normal.

[Illustration: FIG. 45.--Radiogram showing the line of fracture and
upward displacement of the radial styloid in Colles' Fracture.]

_Clinical Features._--In a typical case there is a prominence on the
dorsum of the wrist, caused by the displaced distal fragment, with a
depression just above it (Fig. 43); and the wrist is broadened from
side to side. The natural hollow on the palmar aspect of the radius is
filled up by the projection of the proximal fragment. The carpus is
carried to the radial side by the upward rotation of the distal
fragment, and the radial styloid is as high, or even higher, than that
of the ulna. The lower end of the ulna is rendered unduly prominent by
the flexion of the hand to the radial side. The fingers are partly
flexed and slightly deviated towards the ulnar side; and the patient
supports the injured wrist in the palm of the opposite hand,