Part 19

9. The third were of opinion, that, in undergoing a displacement, the head of the humerus could be carried only downward, under the arm-pit, which is the most common direction, or forward, a course which it takes more rarely. Celsus is almost the only writer who has contended for this division. “Humerus, says he, modo in alam excidit, modo in partem priorem.”

10. Lastly, The fourth believe, with Hippocrates, in none but a displacement downwards, the only one which that physician has met with in his practice. “At vero humerus, inferiorem in partem excidit; aliam in partem excidere non audivi.”

11. The moderns, in borrowing from the ancients their divisions of luxations, did not, like them, determine a priori and in a vague manner, the precise spot and direction of displacement; but ascertained these points by subsequent observation, with more precision, in proportion as a knowledge of anatomy shed light on them. They also paid particular attention to the essential difference between primitive and consecutive luxations.

12. Petit admitted of four kinds of luxations, 1st, downward, on the edge of the scapula: this is a very rare occurrence: 2dly, outward, under the spine of that bone, a kind very difficult to be primitively produced. 3dly, inwards, under the hollow of the armpit. 4thly, forward, between the corocoid apophysis and the clavicle. With this illustrious practitioner, Heister acknowledged four kinds of displacements; but, here again, was a new variety, both in expression, and in meaning. The one says, downward, under the arm-pit, the other forward, under the pectoralis major; the one, backward, under the scapula, the other outward, under its spine. According to Duverney, luxations are never primitively in any other direction than downward; the others being only the subsequent effect of muscular action.

13. In the midst of these very complicated modes of treating a very simple subject, it is necessary, first, in order to acquire definite ideas, to divide luxations of the humerus into primitive, which are the immediate effect of external violence, and consecutive, which succeed the primitive, through the influence of causes which I am about to consider.

Let us suppose four lines to inscribe, in form of a parallelogram, the oval surface of the glenoid cavity, one representing the superior edge, another the inferior, a third the internal, and the fourth the external.

14. It is evident that the head of the humerus cannot be displaced towards the superior edge. In that direction, must be encountered, the acromion and corocoid apophyses, the strong ligament passing between them, the tendons of the triceps and supra-spinatus muscles, and the fleshy mass of the deltoid; all which, taken together, constitute an insurmountable obstacle to the escape of the head of the bone upwards. Besides, what power could carry it upwards? In order that this kind of luxation might take place, it would be necessary, that the head of the bone should be carried outwards at the same time, as well as upwards, a circumstance which is impossible, because the trunk prevents the lower extremity (the elbow) from being directed sufficiently inward to produce such an effect.

15. On the contrary, in other directions, but very little resistance is to be met with. Towards the inferior edge of the cavity, the long portion of the triceps; the tendon of the subscapularis, towards the internal edge; and towards the external edge, the tendons of the infra-spinatus, and teres minor, yield with ease to a force directed against them, and permit the occurrence of primitive luxations, downward, inward, and outward. Downward, between the tendon of the long portion of the triceps, and that of the subscapularis; inward, between the subscapulary muscle and fossa; and outward, between the fossa infra-spinatus and the muscle of the same name. These modes of displacement are not alike frequent, as will be mentioned presently.

(La fosse sous-scapulaire). I know of no English anatomical term for this. I therefore translate it literally. The same is true with respect to “fossa sous-epineuse,” translated here, fossa infra-spinata. TRANS.

16. Having escaped from its cavity, and being primitively placed in one of these three situations, the head of the humerus oftentimes changes its position. Then, to a primitive luxation downward or inward, succeeds a consecutive or secondary one; but never to a luxation in an outward direction, if such ever occur, because the spine of the scapula forms an obstacle to it.

A secondary luxation inward, may succeed a primitive one downward; there is nothing to oppose the head of the humerus in the course it takes, to enter between the subscapulary muscle and fossa. If, on the other hand, it be disposed to pass to the external side, the tendon of the triceps opposes it; and, notwithstanding what Petit has advanced, there is no secondary luxation in that direction.

17. It sometimes happens, that, having escaped either from the internal part, or from the inferior part of the capsule, the head passes behind the clavicle, and forms there a secondary luxation upwards, as has been observed by Ambrose Pare, and by Gallien, and of which an example or specimen was preserved in the cabinet of Desault. But, here, the secondary displacement must take place in a slow manner, and when it has taken place, art can seldom remove it, on account of the strong adhesions formed by the bony surfaces. Thus, in the example mentioned, there was a new cavity formed behind the clavicle, and the humerus adhered to the surrounding parts by a kind of new ligaments.

18. It appears from what has been said, that the humerus is subject to four different kinds of displacement. 1st, Downward: 2dly, outward, in both of which directions the luxation is always primitive; 3dly, inwards, where it is sometimes primitive, and sometimes consecutive; 4thly, upwards, where it can never be otherwise than consecutive.

The second and fourth are very rare occurrences, and bear so small a proportion to the others, that the latter alone ought to command the attention of the practitioner.

§ III.

OF THE CAUSES AND THE MECHANISM.

19. The causes and the mechanism of luxations of the humerus, vary according as the displacement is primitive or consecutive.

The action of external bodies, directed against the arm, but more particularly falls, where this part strikes forcibly against a resisting body, give rise in general to primitive luxations, and, according as it is differently situated at the time of the fall, the humerus determines, by its position, the different kinds.

20. If it be separated from the trunk, without being carried either before or behind it, if the elbow be elevated, and the fall be on the side, the weight of the body, being almost entirely supported by this bone, pushes its upper extremity downward, distends the inferior part of the capsule, lacerates it, and produces a luxation downward, in which it may even be favoured by the action of the pectoralis major, the latissimus dorsi, and the teres major, as has been judiciously observed by Fabre. In such a case, these muscles, involuntarily contracting to support the trunk, act like the power or force in a lever of the second kind, the resistance to which is formed by the head of the bone, which they draw downward, while the lower extremity of the humerus, resting on the ground, constitutes the fulcrum. Some authors even regard, as an immediate cause of luxation, the powerful contraction of the deltoid muscle, which depresses the head of the bone, and forces it through the lower side of the capsule, a mode of displacement, the existence of which observation incontestibly establishes. The case of a scrivener, so often cited, is well known, who in lifting a book of records luxated his humerus in a downward direction.

21. The mechanism of a primitive luxation inwards, differs a little from the preceding. The elbow, being at once separated from the trunk, and carried backward, the person falls: the weight of the body rests on the humerus; the capsule is lacerated in its fore-part; and a displacement in the same direction supervenes.

22. In a luxation outwards, the elbow is carried forward, towards the opposite shoulder; the capsule being stretched outwardly, gives way in that part, provided the humerus be acted on by a sufficient power. But what can this power be? In a fall, the arm being pushed against the trunk, and stopped by it, cannot carry its motion to a sufficient extent to produce a laceration of the capsule. Hence a luxation outwards must be extremely rare. Indeed no instance of it is to be found in books of surgery. Desault, in particular, never witnessed it. Besides, when in a fall, the arm, separated from the body, is carried backward or forward, the weight of the body acts obliquely on it, and it is but partially subjected to the action of the latissimus dorsi, the pectoralis major, and the teres major. So that no kind of luxation ought from these considerations, to be very frequent, except that in a downward direction, where the influence of both causes is direct. Yet luxation inwards is common enough, and in many instances Desault has observed this primitive mode of displacement, though many modern authors doubt the fact, believing, with Hippocrates, that, primitively, all luxations are downwards.

23. It may so happen that in a primitive luxation, the capsule is only greatly stretched, in which case, the articulating surfaces are but partially displaced; but this membrane more frequently suffers a rupture, through which the head of the bone escapes. To this phenomenon writers, in general, have paid too little attention, notwithstanding the opening of dead bodies has oftentimes demonstrated its existence to practitioners, particularly to Desault, who has given two examples of it modelled in wax; one, of a luxation inward, and the other downward, both found in subjects that died in the Hotel-Dieu. Bell relates some analogous facts, and another English surgeon has also had occasion to meet with them.

24. Oftentimes, in compound fractures, one of the fragments passes through the integuments. In the dislocation of the humerus something similar to this occurs. The capsule is sufficiently lacerated to allow the head to escape; but the opening, being then too narrow, forms around the neck of the bone a noose or kind of collar, which prevents it from re-entering the place which it originally occupied. Thus, in the fractures of which I have just spoken, the aperture in the skin does not, at times, admit of the reduction of the fragment, without a previous dilatation.

In this case, an attempt is made to reduce the luxation: the capsule is pressed in folds against the glenoid cavity, and, interposing itself between it and the head of the humerus, renders fruitless the efforts of the surgeon who would replace the bone. Desault was the first who observed this practical fact, two instances of which are recorded in his journal, and which has frequently since occurred in the Hotel-Dieu. In such a case, the head is in general extremely moveable, because, being entirely without the capsule, there is nothing to impede its motion.

25. When, to a primitive luxation a consecutive one succeeds, several causes may concur in its production. If a second fall happen, the arm, being separated from the body, the head of the humerus having nothing to retain and secure it, obeys, with great facility, the power tending to displace it in that direction, and suffers a fresh removal from the bed which it accidentally occupies.

CASE I. A man fell in descending a ladder, and luxated his humerus in a downward direction. Desault being immediately called, discovered the nature of the disease, but deferred the reduction till evening. In the interval, the patient went to get into a chaise: his foot slipped, and he fell a second time. The pains became more severe than at the time of the first accident; and Desault, on his return, instead of finding, as in the morning, the head of the humerus under the hollow of the arm-pit, discovered it to be behind the pectoralis major.

26. Muscular action is one permanent cause of a new displacement. Suppose the humerus luxated downward, the pectoralis major, and the deltoid muscles draw its superior extremity upward and inward, which, offering to their action but a feeble resistance, changes its position and that in a two-fold direction.

27. The different motions of the arm may also, according to their direction, produce the same effect. Thus we have often witnessed a luxation inwards succeeding to a luxation downwards, in consequence of unskilful attempts to reduce it.