A Treatise on Fractures, Luxations, and Other Affections of the Bones

by P.-J. Desault

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.

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]

Having laid down these preliminary considerations, let us proceed to examine, in particular, each kind of luxation to which the clavicle is subject.

LUXATION OF THE STERNAL EXTREMITY.

§ II.

OF THE CAUSES AND DIFFERENT KINDS OF DISPLACEMENT.

4. The sternal articulation of the clavicle experiences different changes, according to the different movements of this bone. If these movements be in a backward direction, the articulating surface is turned forward, straining the anterior part of the capsule, the corresponding ligament, and the extremity of the sterno-cleido-mastoideus muscle. If, on the other hand, they be in a forward direction, the posterior ligament, and the adjacent portion of the capsule are overstretched. In motions directed upwards, the costo-clavicular ligament, and the external and inferior part of the capsule, and in those directed downwards, the inter-clavicular ligament, and the internal portion of the capsule, experience a similar degree of tension.

5. Hence it follows, 1st. That the natural movements of the shoulder may be regarded as predisposing causes of luxation, because at the part where tension is excessive, the ligaments are disposed to give way, and suffer the sternal extremity to escape: 2dly. That the efficient causes will be, all external forces acting on the clavicle in such a way as to increase its motions beyond their natural degree, and beyond the resistance which the ligaments are capable of making. Thus a fall on the point of the shoulder, forcing it suddenly backward and inward, produces a luxation forward. But, in general, as the strength of the articular ligaments is superior to the resistance of the clavicle itself, a fracture takes place more frequently than a luxation, in the proportion of nearly six to one.