5. The os femoris may be fractured indifferently at any point between
its condyls and its neck. But the part where this accident most
frequently occurs, is about the centre of the curve of the bone, where
most of the motions and shocks impressed on it by external violence
expend their force.
6. Whatever may be the seat of the fracture, its direction is sometimes
transverse, but most frequently oblique, a variety which does not
affect the real nature of the disease, but which possesses, as to its
consequences, a very important influence. As in other affections of
the kind, so here, the bone is sometimes affected alone, and, at other
times, to a fracture simple or complicated by means of splinters,
is added an injury done to the surrounding soft parts. Hence result
compound fractures, differently varied, according to the nature of the
parts affected, and to the extent and other circumstances of these
affections. But, as Petit observes, this bone is less frequently
shattered or crushed into several pieces, than those that are more
superficially situated.
7. Extraneous causes are known to render falls more frequent in man
than in other animals, and to multiply in him the fractures of the
lower extremities, by multiplying the action of external bodies on
these extremities. This action may be exerted on the os femoris in two
modes. Sometimes only passive, it merely offers a resistance to the
power which puts the bone in motion; thus, in a fall, the os femoris,
being pressed between the ground which resists, and the weight of the
body that bears on it, bends beyond the extent of its flexibility
or pliancy, and finally gives way. At other times the influence of
external bodies is actively and directly exerted in this accident: thus
a stone, or a piece of timber, falling on the thigh, fractures the
bone, in consequence of communicating to it a degree of motion greater
than its power of resistance.
8. In common, the first mode of division is by a true counter-stroke,
similar to that which fractures the clavicle, the ribs, &c. In the
second mode, the fracture is always direct. The middle part of the bone
is generally broken in a counter-stroke: wherever the direct stroke
is received, that is the place of the fracture which it produces; the
division, most frequently oblique in the first case, is sometimes
perpendicular or transverse in the second. From a counter-stroke result
most commonly simple fractures, while compound ones are usually owing
to a direct stroke.
§ III.