condensed and forms a strong
capsule, a new joint results. The occurrence of these changes in the
direction of a new ball-and-socket joint is largely dependent on the
behaviour of the patient: a vigorous man, anxious to recover the use
of the limb, will employ it with a degree of determination and
indifference to pain that could not be expected in a sensitive elderly
female. The most perfect example of a new ball-and-socket joint,
following upon an unreduced dislocation at the hip, that has come
under our observation, was in a hunting dog, given one of us by an
Australian pupil, who testified that the animal was as fleet with the
new joint as it had been with the original one. Meanwhile the
cartilage of the original socket is converted into fibrous tissue,
which may come to fill up the cavity. Changes resembling those of
arthritis deformans may occur. The large blood vessels and nerves in
the vicinity may be pressed upon or stretched by the displaced bone,
or may be implicated in fibrous adhesions. In course of time they
become lengthened or shortened in accordance with the altered attitude
of the limb.

[Illustration: FIG. 12.--Os Innominatum showing new socket formed
after old-standing dislocation. The acetabulum is almost obliterated.]

In many cases the new joint is remarkably mobile and useful; but in
others, pain, limited movement, and atrophy of muscles render it
comparatively useless, and surgical intervention is called for.

_Treatment._--It is always a difficult problem to determine the date
after which it is inadvisable to attempt reduction by manipulation in
an old dislocation and no rules can be laid down which will cover all
cases. Rather must each case be decided on its own merits, due
consideration being had to the risks that attend this line of
treatment. The chief of these are: rupture of a large blood vessel or
nerve that has formed adhesions with the displaced bone, or has become
shortened in adaptation to the altered shape or length of the limb;
tearing of muscles or tendons, or even of skin; fracture of the bone,
especially in old people; and separation of epiphyses in the young.

Before carrying out the manipulations appropriate to the particular
dislocation, all adhesions must first be broken down; and during the
proceedings no undue force is to be employed. The first attempt at
reduction may fail, and yet subsequent efforts, at intervals of a few
days, may ultimately prove successful; the vi