Dislocation of the #inferior radio-ulnar# articulation may complicate
fracture of the lower end of the radius, or accompany sub-luxation of
the head of the radius. The head of the ulna usually passes backward.

In children, the commonest cause is lifting the child by the hand, and
the displacement is only partial. In adults, it may result from
forcible efforts at pronation or supination, as in wringing clothes,
or from direct violence, the separation being frequently complete, and
sometimes compound.

The head of the ulna is unduly prominent, and there is a depression on
the opposite aspect of the joint. The hand is generally pronated, the
rotatory movements at the wrist are restricted and painful, while
flexion and extension are comparatively free.

Reduction is effected by making pressure on the displaced bone and
manipulating the joint, especially in the direction of supination. If
the ligaments fail to unite, the head of the ulna tends to slip out of
place in pronation and supination--_recurrent dislocation_.

Dislocation at the #radio-carpal# articulation, usually spoken of as
_dislocation of the wrist_, is attended by tearing of the ligaments
and displacement of tendons, and is frequently compound. The carpus
may be displaced backward or forward, and the articular edge of the
radius towards which it passes may be chipped off.

_Backward_ dislocation is commonest, the injury resulting from a
severe form of violence, such as a fall from a height on the palm
while the hand is dorsiflexed and abducted. The clinical appearances
closely simulate those of Colles' fracture, or of separation of the
lower radial epiphysis, but the unnatural projections, both in front
and behind, are lower down, and end more abruptly (Fig. 50). The hand
is more flexed, and the palm is shortened. The styloid processes
retain their normal relations to one another, and the carpal bones lie
on a plane posterior to the styloids, the articular surfaces may be
recognised on palpation. The forearm is not shortened.

_Forward_ dislocation of the carpus may result from any form of forced
flexion, such as a fall on the back of the hand, or from direct
violence. The displaced carpus forms a marked projection on the palmar
aspect of the wrist, and there is a corresponding depression on the
dorsum. The attitude of the hand and fingers is usually one of
flexion.

In both varieties reduction is readily effected by making traction on
the hand and p