Part 9

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 5.

Fig. 4.

Engrav'd by W. Kneafs.]

MEMOIR III.

ON THE LUXATION OF THE CLAVICLE.

§ 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, 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.

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.

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.

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.

Though falls on the point of the shoulder are oftentimes productive of luxation of the clavicle, they are not the exclusive causes of that accident. Desault has seen the sternal extremity forced from its cavity by the knee being pushed violently against the middle of the back, while the shoulders were drawn at the same time backwards.

CASE I. A porter dislocated his clavicle in the following manner. He was carrying a very heavy burden, suspended from his shoulders by cords that passed under each arm-pit. Being desirous of resting himself by the way, he placed on a block the burden he carried, which slipping backward, drew his shoulders in the same direction, and at the instant of his attempting to retain it and prevent it from falling, produced a luxation of the clavicle.

7. It follows from what has been said respecting the different states of the articulation, during its various motions (4), that the clavicle is not equally liable to be luxated in every direction. Inclining naturally backward, but a very slight degree of motion in that direction is necessary, to effect a luxation forward. To produce a luxation backward or inward, it is necessary, on the other hand, that the humeral extremity of the bone should make a sweep at least three times the extent of that required in the preceding case. Besides, motions in this direction are accompanied with pain, particularly if they be made by force. Luxation downward is prevented, on the one hand, by the cartilage of the first rib, which presents to the bone an insurmountable barrier. On the other hand, to produce this kind of luxation, it would be necessary for the external extremity of the clavicle to be forced upwards, an occurrence very seldom occasioned by falls. Luxation upward, or over the superior edge of the sternum, must be the effect of a stroke, which, by depressing the point of the shoulder, and forcing it at the same time forward, presses the sternal extremity against the internal and superior part of the capsule, which, being thus lacerated, suffers a luxation to take place. But such a derangement of the articulating surfaces is very rarely produced by falls. Whence it follows, that of the different kinds of luxation of the clavicle, that in a downward direction is altogether impracticable. Those backward and upward, though possible, occur but rarely in practice; while that in a forward direction, on the contrary, is not an unfrequent accident. This tends to confirm the observations of practitioners, and particularly of Desault, whose immense collection on the subject furnishes examples of the last kind of luxation only.

8. In these luxations, there is for the most part, a rupture of the capsular ligament, and an escape of the bone through the opening. But sometimes the ligament is only preternaturally distended, and then the luxation is incomplete.

§ III.

OF THE SIGNS.

9. But whatever may be the causes or kind of the luxation, its diagnosis is always easy. If it be forward, the direction of the stroke which the shoulder has received, furnishes, at first, some ground of suspicion. The accident is certainly known by the appearance of a hard and unnatural protuberance in front of the sternum, and behind the extremity of the sterno-cleido-mastoideus muscle, by the existence of a sensible depression or hollow at the joint, and by the situation of the shoulder, which is pushed further backward, and is less projecting and more approximated to the trunk, than in its natural state. Add to these, a difficulty in performing motions in a forward direction, which, when somewhat forced, reduce, in proportion as they are accomplished, the size of the protuberance formed by the displaced end. The head is always inclined towards the side where the luxation exists; an attitude which relieves the painful drawing or tension produced in the sterno-mastoideus muscle, by the humeral extremity pushing it forward.