121. But whatever may be the precise form and figure of the fracture,
its signs are easily comprehended: a very perceptible separation
oftentimes exists between the two condyls, increasing the transverse
diameter of the knee. The rotula, sinking into this chasm between the
condyls, renders the part more flat from before backwards, than it is
in its natural state. If the rotula be pressed in a backward direction,
the condyls are separated still further from each other. If, on the
other hand, pressure be made on each side of the lower part of the
os femoris, the condyls are brought together, and the knee resumes
its usual shape. If we take hold of a condyl in each hand, it will be
easy, by moving them alternately backward and forward, to make them rub
against each other, and produce a crepitation which characterizes the
fracture beyond a doubt.
122. If the upper fracture be oblique, a shortening of the limb more
or less perceptible is always the effect of it: this appears to be
principally owing to the weight of the body which pushes the upper
fragment down, and to the action of the muscles which draws the lower
ones up (10 ... 14). In this case, the superior fragment, being
forcibly pushed against the integuments, has sometimes lacerated, and
even passed through them, giving rise to consequences of a serious
nature. Desault has published a case of this kind. A similar effect has
been produced, though more rarely, by the inferior fragment, in which
case much mischief has arisen from the admission of air into the joint.
123. Sometimes when the upper fracture extends through the whole
thickness of the os femoris, the extremity of the bone is turned round,
so that the external condyl lies behind, the internal before, and the
rotula on the outside, while the foot points in the same direction.
A case of this kind is recorded in the Journal of Surgery. The body
of the bone, being pressed into the chasm or interval between the two
condyls, may prevent their reunion, by pushing them asunder, and thus
give rise to various accidents.
124. Most of these phenomena will fail to occur, if the upper division,
passing only half way through the bone, break off but one of the
condyls, or if, passing through even the whole of the bone, it be
perfectly transverse; but cases of this description are seldom met with.
§ XX.