12. But, if to these indications we compare the bandage described in the foregoing case, we will perceive that they are perfectly fulfilled by it. Indeed the splints forming a kind of pullies which change the direction of the rollers, we must count on the action of these rollers only from the part of the limb which they surround, to the ends of the splints over which they are reflected: whence it follows, that the two ends of the upper roller, reflected over the superior extremities of the splints, cannot be drawn down along each of these splints, without that part of the rollers, which reaches from the leg to these extremities, being drawn up, and with it the knee and the upper fragment. In like manner, the ends of the lower roller cannot be drawn up towards the ends of the upper one, without those portions of them which run from the sole of the foot, being drawn down and pulling the foot and the inferior fragments along with them.
13. Hence it follows, that by tying on each side, one end of the upper roller to the corresponding end of the lower one with sufficient tightness, the two indications above laid down (12) are accurately fulfilled.
14. But, in general, the common bandage is sufficient, as I have already mentioned, even in cases of oblique fractures, to prevent the ascent of the lower fragments on the upper ones. Desault never employed any others in the last years of his practice, and it was only in cases of extraordinary disposition to muscular contraction, that he ever had recourse to the second kind. By means of the common apparatus, he was able to prevent the overlapping of the fragments from forming any protuberance on the anterior and internal part of the leg.
15. We must acknowledge, however, that this apparatus is liable to the same objection with most others intended for permanent extension. The roller placed below the knee, for the purpose of counter-extension, surrounds almost all the muscles, which tend to make the inferior fragments overlap the superior ones, by drawing the foot upwards. By pressing on and irritating these, it favours, and even excites their contractions, and, by that means, gives rise to a shortening of the limb, the very accident which the apparatus is intended to prevent. This inconvenience induced Desault, in a particular case, to substitute to the preceding apparatus, that used for permanent extension in fractures of the thigh.
MEMOIR XV.
ON THE DIVISION OF THE TENDO ACHILLIS.
1. It might be supposed that a work on diseases of the soft parts, would be a more proper place for this article, than the present one, where my express object is to treat of affections of the hard parts. What induces me to insert it here is, the analogy which exists between a division of the tendo Achillis and a fracture of the os calcis, the light which the treatment of the one throws on that of the other, and the example of the celebrated Petit, who, in his work on diseases of the bones, speaks also of this division.