12. In this case, the muscular influence is evident. Indeed the shock having produced a temporary suspension of the excitability of the part, the fragments remained in place and in proper contact with each other: but the moxa having awakened the excitability again in the muscles of the thigh, they resumed their action and caused, as usual, the inferior fragment to mount on the superior.
13. Hence it follows, 1st, that it is principally to the action of the muscles that we must attribute the displacement, in the longitudinal direction of the bone; 2dly, that, as that action, being the effect of an inherent power, is constantly exerted, the limb must have a constant tendency to this displacement, particularly in oblique fractures, where the two extremities of the bone represent two inclined plains, which readily glide along each other.
14. To this must be still added another cause, which operates injuriously in the course of the treatment. However solid the bed may be on which the patient lies, the nates or buttocks, being the most projecting part of the body, soon form a depression in it; hence arises an inclination or descent of the plain or surface on which the body lies. The body therefore sliding downwards, pushes before it the superior fragment, and makes it overlap the inferior one. In consequence of this, the muscles, being irritated by the points of the bones, increase the force of their contractions, and, as we have already observed (10), draw the inferior fragment upwards. This double movement of the two ends of the bone in contrary directions, produces only a single effect, namely, the overlapping of these ends, but carries this overlapping to a higher degree.
15. Transverse fractures are less exposed to displacement, in the longitudinal direction of the bone, because the fragments when in contact, support each other. In such a case, the inferior fragment, drawn by the muscles, finds a point of resistance against the superior one, while the latter, when pressed downward by the weight of the body, pushes the former before it, and thus both preserve their relative position.
16. A deformity of the fractured os femoris, in the direction of its cross-diameter or thickness (9), always accompanies that in its longitudinal direction, and sometimes exists alone. This takes place when, in a transverse fracture the two ends of the bone, losing their contact, are carried, the one outward, and the other inward, or when the one remains in its place, while the other is separated from it. In such a case, the superior fragment is not, as in the preceding one, immoveable by means of muscular action; because the action of the pectineus, the psoas, the illiacus, and the first adductores, derange its natural direction, and contribute to its displacement.
17. The deformity of the limb, in relation to its direction, in other words, the crookedness of the limb (9) is either the result of the stroke which fractured it, or, what is more common, of the ill directed efforts of those who lift and carry the patient, and, by an improper position, bend the two fragments, so as to make them form an angle with each other. Desault was once called to a patient, whom he found seated on a bed, in such a manner, that the upper part of the thigh was in a horizontal position, and the lower, hanging with the leg in almost a perpendicular one. Doubtless the triceps femoralis, equally attached to both fragments, bends them by its contraction, and produces a change in the direction of the limb.
18. Whatever may be the kind of the deformity, whether in a longitudinal or lateral direction, the inferior fragment may either preserve the natural position in which it is placed, or experience a rotatory motion on its axis outwards, which is a common occurrence, or inwards, a circumstance which is more rare. This rotation always renders the displacement more serious, and ought to have an influence, as I shall presently observe, on the means of reduction.
§ IV.