t the moment of injury, and the relative
strength and capacity for effective action of the different groups of
muscles acting upon the bone.

[Illustration: FIG. 17.--Diagram of most common varieties of
Dislocation of the Shoulder.]

In the great majority of cases it passes forward and medially, and
comes to lie against the anterior surface of the neck of the
scapula, under cover of the tendons of origin of the biceps and
coraco-brachialis muscles, constituting the _sub-coracoid
dislocation_. Much less frequently it passes under cover of the
pectoralis minor and against the edge of the clavicle--the
_sub-clavicular_ variety. In rare cases the head passes backward and
lies against the spine on the dorsum of the scapula, beneath the
infra-spinatus muscle--the _sub-spinous_ variety. Other varieties are
so rare that they do not call for mention.

_Clinical Features common to all Varieties._--Dislocation of the
shoulder is commonest in adult males; in advanced life the proportion
of female sufferers increases. It is usually attended with great pain,
and there is often numbness of the limb due to pressure of the head of
the bone upon the large nerve-trunks. There is sometimes considerable
shock. The patient inclines his head towards the injured side, and,
while standing, the forearm is supported by the hand of the opposite
side. The acromion process stands out prominently, the roundness of
the shoulder giving place to a flattening or depression immediately
below it, so that a straight-edge applied to the lateral aspect of the
limb touches both the acromion and the lateral epicondyle. The
vertical circumference of the shoulder is markedly increased; this
test is easily made with a piece of tape or bandage and is compared
with a similar measurement on the normal side--we lay great stress on
this simple measure, as it is a most reliable aid in diagnosis. The
head of the bone can usually be felt in its new position, and the axis
of the humerus is correspondingly altered, the elbow being carried
from the side--forward or backward according to the position of the
head. The empty glenoid may sometimes be palpated from the axilla. In
most cases, although not in all, the patient is unable at one and the
same time to bring his elbow to the side and to place his hand upon
the opposite shoulder (Dugas' symptom). Measurements of the length of
the limb from acromion to lateral epicondyle are rarely of any
diagnostic value.

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