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

by P.-J. Desault

5. In a backward direction the olecranon and the radius may pass up behind the humerus, as the coronoid apophysis offers but little resistance in consequence of its slight curvature. On the other hand, the kind of hook formed by the olecranon, prevents it and the radius from passing before the lower articulating extremity of the humerus, and therefore, without a fracture of the olecranon, a luxation in that direction is impracticable: at the sides, the two lateral ligaments, but more particularly the reciprocal joining or interlocking of the uneven articulating surfaces, present almost insurmountable obstacles to luxations laterally. Whence it follows, that luxation backward is much more frequent than the others; compared to lateral luxations, it is, at least, in the proportion of ten to one: with luxations forward, no comparison can be made; neither Petit nor Desault having ever met with such.

6. An external force produces the whole of these luxations, but according to each, this force must vary. In a fall sideways, suppose the hand be applied to the ground, with the arm extended, to save the body. It is evident that the resistance of the ground will tend to make the bones of the fore-arm pass upwards over the humerus, while the weight of the body pushing that bone downward and forward, will make it glide over the coronoid apophysis. Thus, the capsule, being distended before by the humerus, and behind by the bones of the fore-arm, will give way in one or the other place, or in both, as Desault observed in a man, who fell on his side, as he was carrying a heavy load: the weight of the body increased by the load, had such an effect, that the bones overlapped each other nearly two inches.

7. It appears from this, that a state of extension is the position most favourable to a displacement backwards; a doctrine by no means conformable to that of most practitioners, who consider a state of flexion as necessary to the accident. But, then, in what direction should the fall take place, in order that the olecranon may pass upwards? Applied as it is against the side of the cavity that receives it when the arm is extended, would not this apophysis prevent such passage? Whatever may be the mode of displacement, the olecranon, in passing upward and backward, may incline a little to the one or the other side.

8. I have already said, that without a fracture of the olecranon, no luxation forward can occur (5). But what cause can act with sufficient power on the parts to produce both accidents at the same time? It would be necessary that a fall which had produced a fracture should be succeeded by another fall; but in such a case, the fore-arm would be half-bent, and it is in a state of extension alone (7) that the luxation can take place.

9. Lateral luxations, that is, luxations at the sides have been divided into complete, when the two articular ranges of the arm and fore-arm, have lost their connexion entirely, and incomplete, when only one bone or one part of a bone has been separated from its natural connexion with the humerus. But what cause can act with sufficient force to produce the first kind of luxation, namely, that which is complete? In such an accident so great would be the extent of the wreck and ruin of the part, that without doubt amputation would be the only resource.

10. The second kind of lateral displacement is the result of a stroke which forces violently the extremity of the fore-arm outward or inward. A footman, says Petit, in falling from a carriage, had his arm entangled between the spokes of the wheel, and suffered in consequence a luxation outwards. Another produced one inwardly, by being thrown from his horse, and falling with his arm under him, on rough ground. Strokes of this kind may, as that author remarks, vary in a singular manner. But, in general, in all of them, the fore-arm must represent a lever of the first kind, where the power acts on the end next the hand; the resistance being in the joint, and the fulcrum in the middle.

§ III.

OF THE SIGNS.

11. To form an idea of the signs or appearances of a luxation backwards, let us examine, for a moment, the natural situation of the olecranon, and the condyls of the humerus. As these eminences are easily felt under the skin, a knowledge and recollection of their situation will serve as a standard of comparison, to judge of the changes they experience in a luxation. When the fore-arm is extended, the olecranon is on a level with the internal condyl, and a little above the external one. In a state of flexion, it descends below this level, and is then farther below the internal than the external condyl. In either situation, it is nearer to the first than to the second, the radius separating it from the latter.