§ I.
1. The clavicle, which forms a moveable abutment for the shoulder, and
receives and sets bounds to most of the movements of that part, and of
the arm, exhibits at its extremities, two articulations, essentially
different from each other in their form, dispositions, and uses. These
differences give rise to differences equally essential with regard to
the dislocations to which they are subject.
2. On the sternal extremity, a small surface, convex from above
downwards, and concave from before backwards, is fitted, by means of
an intervening cartilage, to a much smaller surface of the sternum,
concave and convex in opposite directions.
One capsule, two ligaments, viz. the interclavicular and
costo-clavicular ligaments,[5] and the anterior portion of the
sterno-cleido-mastoideus muscle, strengthen the connexion of these two
surfaces, and tend, on one hand, to prevent their luxation, while, on
the other, this luxation is favoured and facilitated by the following
circumstances: 1st, the disproportion between the dimensions of the two
articulating surfaces; 2dly, the mobility of the joint; and 3dly, by
this joint’s constituting a kind of centre for the motions of the arm.
[5] I find in English books of anatomy no appropriate names for
these two ligaments. I am therefore obliged to translate the French
terms for them literally. The anatomist will have no difficulty in
recollecting their situation. TRANS.
3. On the humeral side, an elliptical surface, slightly convex, and
inclined downwards, is immediately joined to a corresponding surface of
the acromion, elliptical also, a little concave and directed upwards.
Hence two kinds of inclined plains, which would be very liable to
dislocations, by sliding easily over each other, were they not firmly
secured by a capsule, by accessory fibres, by the intersection of those
of the deltoid and trapezius muscles, and, above all, by two ligaments,
the rhomboid and the conoid.[6]
[6] I do not recollect any terms in English works of anatomy
equivalent to these. TRANS.
Having laid down these preliminary considerations, let us proceed to
examine, in particular, each kind of luxation to which the clavicle is
subject.