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

by P.-J. Desault

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;[14] 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.

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.