Part 30

§ V.

OF THE MEANS OF MAINTAINING THE REDUCTION.

27. Luxations of the fore-arm have, oftentimes, a great disposition to occur anew, after having been reduced, whether they be recent, or of long standing. Extension readily dislodges the olecranon and the radius, and replaces them perfectly in their natural situation; but if any thing interrupt them, the displacement is sometimes immediately renewed: suppose the parts even remaining in contact, the slightest motion may derange this contact, and give rise to a necessity for a new reduction, more difficult, oftentimes, than the first. Hence it is always prudent to employ a retentive apparatus for some time.

28. But, on what principle and for what purpose ought it to be applied? The motions communicated to the fore-arm by external bodies, but, more particularly, the action of the muscles inserted in the bones that have been reduced, are here the causes of their displacement. Hence, 1st, to render the limb immoveable; 2dly, to push the articular ends of the bones in a direction opposite to that in which they are drawn by the muscles, and have a tendency to be displaced: such is the twofold indication of the bandage; an indication not fulfilled by the kind of bandage and the sling which Petit proposed, and which leave the arm free to move, and the muscles free to act.

29. Desault employed the following apparatus: 1st, The arm and fore-arm are first covered by oblique turns of a roller, intended both to protect them from the impression of splints, and to diminish the power and action of the muscles, by the pressure made on them: 2dly, Behind the olecranon is to be placed a thick compress, designed to retain it downwards, and which must be secured by a strong splint, situated behind, and curved at the elbow, to accommodate it to the flexion of the fore-arm: 3dly, On the sides are placed two other splints, chiefly necessary in lateral luxations: 4thly, The whole is to be secured by the remaining part of the roller, by which the arm and fore-arm are already covered.

In this bandage, the immobility of the arm is secured by the splints, while the olecranon is pushed by the compress, in a direction the reverse of that of its displacement. But these circumstances constitute the double indication that was to be fulfilled (28).

30. The period at which these means may be dispensed with, is undetermined. It belongs to the surgeon to examine and ascertain, when the natural connexions of the joint are sufficiently confirmed. Then motions, at first gentle, are to be impressed on the limb; being afterwards gradually increased, they remove by degrees that stiffness, which usually follows a dislocation, particularly an old one. But if it has existed too long, to give the limb motion, is then the only resource: the new attachments or adhesions, contracted by the articulating surfaces in their displaced state, render reduction impracticable. We must then confine ourselves merely to increasing the extent of the motions, which the displaced fore-arm is yet capable of performing.

31. There is, in general, all other things being favourable, a hope of accomplishing the reduction, till the end of the second month after the accident. Desault succeeded in it, at even a later period. What trouble or hardship is it, at last, to try extension? Should no other end be gained, but merely to bring the bones nearer to their natural cavities or situations, even without actually replacing them, this will aid their movements, the extent of which is inversely proportioned to their distance from these cavities.

MEMOIR X.

ON THE LUXATIONS OF THE RADIUS OVER THE ULNA.

1st, Most authors who have written on the luxations of the fore-arm, have omitted considering separately those confined to the radius alone. Some detached observations may be found here and there, on the luxations of the upper extremity of this bone, which Duverney alone has treated at some length. Those of its lower extremity, though more frequent, and more easily produced, appear to have almost entirely escaped the attention of the French practitioners, who have transmitted nothing to us on that point, owing, no doubt, to their having had no knowledge of it from experience. But since, at the present day, a sufficient number of facts are collected on the subject, some account of these displacements cannot be a matter of indifference to the art, and it may be traced with as much precision as the accounts of other similar accidents.

§ I.

OF THE DIFFERENCES IN POINT OF STRUCTURE BETWEEN THE TWO ARTICULATIONS OF THE RADIUS WITH THE ULNA.

2. The radius, the moveable agent in pronation and supination, rolls on the ulna its fixed basis or abutment, by means of two small articulating surfaces, the one at its upper end, slightly convex, broad within, and narrow without, corresponding to the small sigmoid cavity, in which it is lodged; and the other at its lower end, concave, semicircular, and fitted to the convex edge of the ulna, which it receives. Hence two kinds of articulation different from each other, with respect to their motions, the connexion of their surfaces, and the ligaments which strengthen them. Let us specify these differences; they will serve to shed light on those that exist between the displacements of the two extremities of the radius.

3. At its upper end, the radius, in performing pronation and supination, moves only on its own axis; at its lower end, it rolls round the axis of the ulna: therefore, being farther removed from their centre, its motions must have both a greater range and greater force, in the latter case than in the former. The head of the radius, turning on itself within the annular ligament, cannot distend it in any direction or part. The cellular membrane attached to this ligament is alone slightly stretched, but being loose and elastic, it yields without resistance. At its lower end, on the contrary, the radius, turning from without inwards during pronation, keeps the capsule posteriorly in a state of tension, and draws it against the immoveable head of the ulna, which tends to pass through it, if the motion be forcible. The same phenomenon occurs in a contrary direction, during supination; the radius is directed backward, and the ulna inward. Being in this case distended before, and relaxed behind, the capsule is disposed to laceration anteriorly.

4. In addition to this disposition, the ligaments of the two articulations are disproportioned in their strength. Thin and weak at the lower articulation, thick and firm at the upper one, they are in this respect strikingly different. The head of the radius, resting against the small but firmly fixed head of the humerus, finds there, in most of its movements, an obstacle to displacement. On the contrary, its lower end, drawing along with it in its movements, the bones of the carpus which are connected with it, derives from them no solid support.

§ II.

DIFFERENCES IN THE LUXATIONS OF THE RADIUS; DIFFICULTIES OF THAT AT ITS UPPER END.

5. It follows from what has been said (3 and 4), 1st, that the lower articulation of the radius is not only exposed to the action of more causes of displacement, but possesses fewer means of resisting those causes, and that, from the threefold consideration of its motions, the ligaments which connect its articulating surfaces, and their relation to each other, it must be frequently subject to luxations: 2dly, that for reasons the very reverse of these, its upper articulation must be very seldom subject to luxation.

6. Indeed, what cause is there to produce luxation in this latter joint. Is it from a forcible exertion of pronation or supination that this accident can occur? Surely not: for, on the one hand, as the lower articulation offers less resistance than the upper one, it is evident that, in either state of motion, it being the weakest, will be displaced first, and the motion being thus checked, can no longer operate to the displacement of the other. On the other hand, however forcible the motion may be, there will be in the upper articulation, nothing but a rotation of the bone on its own axis (3). How, then, without being carried forward, backward, &c. can the head be displaced? Indeed, it would be necessary that all the fastenings or bonds of attachment muscular and ligamentous, should be first broken. But these are too strong, and the motion is too weak. Can the displacement be produced by a blow impressed on the radius from below upwards? By no means: because the head of the humerus making, in this case, a solid resistance will not permit it to escape from the capsule (4). Can it arise from a violent extension or flexion of the fore-arm? No. This effort being altogether confined to the ulna, affects the radius in but a very faint degree.

7. It appears from hence, that the accidental luxation of the upper end of the radius, suddenly produced by external causes, must, if it ever occur, be extremely rare. But it is not so with respect to luxations which take place slowly in this joint, particularly in children, where, in consequence of repeated efforts, the ligaments become relaxed. But this kind of displacement, being almost always complicated with a swelling of the joint, and sometimes not to be reduced by the expedients of art, cannot be comprised in my present plan.

9. But experience would seem to have at times exposed the fallacy of these considerations and reasonings, founded merely on the structure of the parts. Duverney relates some instances of luxations of the head of the radius, produced suddenly by external causes. Two other practitioners are also of opinion that they have witnessed similar displacements. But did they examine the subject with all that attention which it required? A similar case was reported to the Academy of Surgery, by one of its associates; but doubts were entertained with regard to its reality: and, ultimately, there were so few facts in its favour, and such strong presumptions against it, that Desault was induced to deny the luxation altogether, till its reality should, by new proofs, be more certainly established.

After all, if it should occur, the same signs which announce the luxation, when the ligaments, in consequence of being gradually relaxed or in some way distended, permit the head of the radius to be insensibly displaced, would then appear as the sudden effect of external violence.

LUXATION OF THE LOWER EXTREMITY OF THE RADIUS.

§ III.

OF THE KINDS OF DISPLACEMENT.

9. The causes which produce the displacement of the lower end of the radius, are the same with those that give rise to other similar affections. 1st, The convulsive action of the pronator and supinator muscles, is doubtless a rare cause of the accident, since Desault never met with an instance of it. 2dly, The action of external bodies, which, by forcibly and suddenly producing the motions of pronation, rupture the posterior portion of the capsule, or, by those of supination, lacerate its anterior portion.

10. Hence two kinds of displacement, the one forward, the other backward. The first is somewhat frequent; the second is much less so. The latter was never seen by Desault but once, and that was in the corpse of a man who had had both his arms luxated, but respecting the circumstances of which he could receive no information. The other kind occurred frequently in his practice, of which five examples have been already published. The difference no doubt arises from this circumstance, that the greater part of our powerful motions are performed only in the direction of pronation. This appears to be proven by the following circumstances.