t to mistake this condition for the effects of a
fracture which has complicated the dislocation and been overlooked at
the time of the accident.

[Illustration: FIG. 38.--Radiogram of Incomplete Backward Dislocation
of Elbow.]

_Clinical features._--The elbow is held fixed at an angle of about
120 deg., pronated or midway between pronation and supination. Any attempt
at movement causes great pain, and is followed by an elastic rebound
to the abnormal position. The antero-posterior diameter of the joint
is increased, and the forearm, as measured from the lateral epicondyle
to the tip of the styloid process of the radius, is shortened to the
extent of about an inch. If examined before swelling ensues, the
outlines of the articular surfaces may be recognised in their abnormal
positions, but swelling usually comes on rapidly, and, by obscuring
the bony landmarks, renders the diagnosis difficult.

This injury has to be diagnosed from supra-condylar fracture with
backward displacement of the lower fragment and from separation of the
lower humeral epiphysis. A general anaesthetic is often necessary to
enable an accurate diagnosis to be made. When the deformity is once
reduced, there is no tendency to its reproduction unless the
coronoid process is also fractured. In a considerable number of
cases--according to E. H. Bennett, in the majority--this dislocation
is _incomplete_, the coronoid process resting at the level of the
trochlea, and the backward projection of the olecranon being scarcely
appreciable. The head of the radius, however, is unduly prominent. In
such cases the lesion is liable to be overlooked, and therefore to go
untreated, leading to permanent stiffness at the elbow.

#Dislocation forward# is much less common than the backward variety.
It is produced by severe force acting from behind on the flexed elbow,
the ulna being driven forward, tearing the ligaments of the joint and
the muscles attached to the condyles. The olecranon is frequently
fractured at the same time (Fig. 39). When it remains intact, it may
rest below the condyles (incomplete or first stage of dislocation), or
may pass in front of them, especially if the triceps is ruptured
(complete or second stage). The forearm is lengthened, the elbow
slightly flexed, the posterior aspect of the joint flattened, and the
condyles, in their abnormal relationship, can be palpated from behind.

#Medial and Lateral Dislocations.#--Dislocation towards the uln