24. Luxations of the humeral extremity of the clavicle, take place,
according to Petit, in two ways, 1st, under, and 2dly, over the
acromion. If we attend to the disposition of the articulating surfaces,
the superior of which rests obliquely on the inferior; if we examine,
in particular, the relative position of the corocoid apophysis with
respect to the clavicle, it will be difficult to conceive how the first
kind of luxation can occur, without being accompanied by a fracture.
Yet some facts added by Desault to the doctrine of Petit, on this
point, seem to demonstrate the possibility of the clavicle sliding
under the acromion. As to luxations forward and backward, the mobility
of the shoulder, the facility with which it yields to motions impressed
on it in these two directions, and the want of a resisting power, make
the two bones that compose it, move together, still preserving their
relative position.
The luxation upward, then, is that which ought chiefly to occupy the
attention of the practitioner. Yet even this is less frequent than
the luxation of the sternal extremity, on account of the very great
strength of the retaining ligaments, which, when this luxation occurs,
must be, if not lacerated, at least very much distended.
§ VI.