Subcoracoid dislocation. (Lejars.)
In the downward or subglenoid luxations the capsule is lacerated lower down. These displacements occur when the shoulder has been dislocated with the arm in the extended and elevated position. Here the head of the humerus is found in the axilla, resting against the border of the scapula, and the axillary structures, especially the circumflex nerve, usually sutler, while the external rotators are either ruptured or their insertions detached ([Fig. 345]).
Fig. 345
Subglenoid dislocation. (Lejars.)
The posterior or subspinous dislocation is the least common of all. In its production the arm is apparently adducted and the elbow raised. Here the humeral head is found beneath the posterior surface of the acromion or beneath the spine of the scapula ([Fig. 341]).
Symptoms.
—The indications of shoulder dislocation are pain; flattening of the shoulder; undue prominence of the acromion; depression opposite the glenoid cavity, with loss of the rounded contour due to the presence therein of the head of the humerus; appearance of a more or less globular mass in the position now abnormally occupied by the head of the humerus; change in the axis of this latter bone; inability to bring the elbow to the side; more or less complete loss of function, and more or less spasm of the muscles about the joint. Owing to the fact that the thorax presents a curved or warped surface, to which a straight line can be tangent only at one point, it results that the hand of the injured side cannot be made to wrap itself over the opposite shoulder while its elbow still touches the chest or side (Dugas’ test).
Diagnosis.
—As between fracture and dislocation the surgeon may be greatly helped by deciding that the head of the humerus is still in its proper position; that the deltoid is not flattened as in dislocation; that the arm is shortened rather than lengthened; that motility is increased rather than diminished; that bony crepitus is usually obtainable, and that replacement, which may be comparatively easily secured, is maintained only so long as the parts are held in position by the operator’s hands. An additional sign of value is the fact that a straight edge cannot ordinarily be made to touch the tip of the acromion and the external condyle of the humerus at the same time, because of the protrusion caused by the presence of the head of the humerus in its socket. When the straight edge can be so applied it must be either because the head of the bone is out of the socket or the upper end of the bone broken. A still more crucial test which should, however, only be applied when others prove unsatisfactory, may be furnished by passing a sterilized hat-pin through the sterilized skin over what seems to be the displaced head of the bone and into the globular mass. Rotation of the humerus will then cause its end or head to make an excursion which will be quite distinctive.