uperficial and deep (posterior interosseous) branches
of the radial nerve are liable to be pressed upon or torn by the
displaced head of the radius, especially if the ulna is fractured,
leading to disturbances in the area of their distribution.

[Illustration: FIG. 40.--Radiogram of Forward Dislocation of Head of
Radius, with Fracture of Shaft of Ulna.]

In a few cases the displacement of the head has been _backwards_ or
_laterally_.

_Treatment._--To effect reduction, the forearm should be alternately
flexed and extended, while traction is made upon it from the wrist,
and the head of the radius is pressed backward with the thumb in the
fold of the elbow. When reduction is prevented by the interposition
of a portion of the torn ligaments between the bones, it is sometimes
necessary to open the joint to ensure accurate adjustment. The joint
is fixed in acute flexion to relax the biceps, to allow of union of
the torn ligaments, and to prevent recurrence.

In old-standing cases, to obtain a useful joint, or to remove pressure
from the branches of the radial nerve, resection of the head of the
radius may be necessary.

#Sub-luxation of the head of the radius#, or "dislocation by
elongation," is a comparatively common injury in children between the
ages of two and six. It almost invariably results from the child being
lifted or dragged by the hand or forearm. The traction and torsion
thus put upon the radius causes the front part of its head to pass out
of the annular ligament, the edge of which slips between the bones.

The person holding the child may feel a click at the moment of
displacement. The child complains of pain in the region of the elbow:
the arm at once becomes useless, and is held flexed, midway between
pronation and supination. All movements are painful, but especially
movements in the direction of supination. The deformity is slight, but
the head of the radius may be unduly prominent in front. From the way
in which the injury is produced the wrist also is often swollen, and
in some cases the patient is brought to the surgeon on account of the
condition of the wrist, and attention is not directed to the elbow.

_Treatment._--Reduction frequently takes place spontaneously or during
examination, the function of the arm being at once completely
restored. In other cases it is necessary, under anaesthesia, to
manipulate the head of the bone into position. This is usually easily
done by flexing the elbow, m