slocation are also predisposing factors.

_Clinical Varieties._--The separation between the bones may be
_complete_ or _partial_. When partial, portions of the articular
surfaces remain in apposition, and the injury is known as a
_sub-luxation_. Like fractures, dislocations may be _simple_ or
_compound_, the latter being specially dangerous on account of the
risk of infection. When seen within a few days of its occurrence, a
dislocation is looked upon as _recent_; but when several weeks or
months have elapsed, it is spoken of as an _old-standing_ dislocation.
The latter will be described later.

Dislocations, like fractures, may be _complicated_ by injuries to
large blood vessels or nerve-trunks, by injuries to internal organs,
or by a wound of the soft tissues which does not communicate with the
joint. Further, a fracture may coexist with a dislocation--a most
important complication.

_Clinical Features._--The most characteristic signs of dislocation are
_preternatural rigidity_, or want of movement where movement should
naturally take place; _mobility in abnormal directions_; and
_deformity_, the part being "out of drawing" as compared with the
uninjured side (Fig. 18). The bony landmarks lose their normal
relationship to one another; and the deformity is characteristic, and
is common to all examples of the same dislocation.

Although any of the subsidiary signs may occur in lesions other than
dislocations, due weight must be given to them in making a diagnosis.
_Loss of function_ is complete as a rule. _Pain_ is much more intense
than in fracture, usually because the displaced bone presses upon
nerve-trunks, and from the same cause there is often numbness and
partial paralysis of the limb beyond. _Swelling_ of the soft parts due
to effused blood is usually less marked in dislocation than in
fracture, but is often sufficiently great to interfere with diagnostic
manipulations. The displaced bone, and sometimes the empty socket, may
be palpable. _Discoloration_ is usually later of appearing than in
fractures. _Alteration in the length_ of the injured limb--usually in
the direction of shortening--is a common feature; while girth
measurements usually show an increase. A peculiar soft _grating_ or
_creaking sensation_ is often felt on attempting to move the joint;
this is due to cartilaginous or ligamentous structures rubbing on one
another, and must not be mistaken for the crepitus of fracture. In the
majority of cas