coracoid dislocation# (Fig. 18) is that most frequently met
with. It usually results from hyper-abduction of the arm while the
scapula is fixed, as in a fall on the medial side of the elbow when
the arm is abducted from the side. The surgical neck of the humerus is
then brought to bear upon the under aspect of the acromion, which
forms a fulcrum, and the head of the bone is pressed against the
medial and lower part of the capsule. In some cases muscular action
produces this dislocation; it may also result from force applied
directly to the upper end of the humerus.

[Illustration: FIG. 18.--Sub-coracoid Dislocation of Right Shoulder.]

The head leaves the capsule through the rent made in its lower part,
and, either from a continuation of the force or from contraction of
the muscles inserted into the inter-tubercular (bicipital) groove,
particularly the great pectoral, passes medially under cover of the
biceps and coraco-brachialis till it comes to rest against the
anterior surface of the neck of the scapula, just below the coracoid
process. The anatomical neck of the humerus presses against the
anterior edge of the glenoid, and there is frequently an _indentation
fracture of the head of the humerus_ where the two bones come into
contact (F. M. Caird). The subscapularis is bruised or torn, the
muscles inserted into the great tuberosity are greatly stretched, or
the tuberosity itself may be avulsed, allowing the long tendon of the
biceps to slip laterally, where it may form an impediment to
reduction. The axillary (circumflex) nerve is often bruised or torn,
and the head of the humerus is liable to press injuriously on the
nerves and vessels in the axilla.

The _clinical features_ common to all dislocations are prominent,
although Dugas' symptom is not constant.

[Illustration: FIG. 19.--Sub-coracoid Dislocation of Humerus.

(Sir H. J. Stiles' case. Radiogram by Dr. Edmund Price.)]

_Treatment._--The guiding principle in the reduction of these
dislocations is to make the head of the bone retrace the course it
took in leaving the socket. The main obstacles to reduction being
muscular contraction and the entanglement of the head with tendons,
ligaments, or bony points, appropriate means must be taken to
counteract each of these factors.

A general anaesthetic is an invaluable aid to reduction, and should be
given unless there is some reason for withholding it. It is specially
indicated in strong muscular subjects, a