25. The radius, which is the moveable and almost the only support or
abutment of the hand, receives, in falls on that part, a much greater
share of the shock than the ulna, which is joined to the hand by only
a small surface. Hence, without doubt, arises the greater frequency of
the fractures of the radius; fractures which, when produced by falls on
the hand, are evidently the result of a counter-stroke. Oftentimes also
this bone is broken by the immediate action of external bodies, because
it is defended below with but a thin covering of muscles.
In whatever way the fracture may be produced, it occurs in the middle
or at the extremities of the bone; very rare near its articulation
with the os humeri, it is more common in its middle; but more frequent
still at its lower end. The difference arises probably from this
circumstance, that, in falls on the wrist or hand, the shock is
weakened and lost in proportion as it is propagated upwards.
26. In such fractures, displacement is almost constantly observable
in the thickness or cross direction of the bone and fore-arm, and is
produced by the action of the pronator muscles, which, by forcing
the fragments of the radius towards the ulna, tend to diminish the
interval between the bones. The ulna remaining unbroken, always
prevents any displacement in a longitudinal direction. The first
kind of displacement is the more perceptible, in proportion as the
fracture is nearer to the middle part of the radius, where the bones
are at the greatest distance from each other. This displacement is
seldom outwards, because the interosseous ligament prevents that: yet
experience furnishes some exceptions to this rule.
CASE I. Desault was called, in the month of July, 1781, to visit a
mason, who, sleeping at the foot of a wall, with his fore-arm stretched
out, received on the anterior part of it, a round stone, of the size
of a bowl, which, falling from a scaffold, fractured the radius in its
middle, and produced a large contusion, accompanied by an enormous
swelling, to which the usual discutient remedies were applied. On
the fifth day the swelling had in part disappeared; but then there
was discovered a very evident protuberance of the inferior fragment,
which, by pointing outwards, separated itself from the superior one,
which remained nearly in its place. The interval between the bones was
evidently increased below.
The fracture was reduced by pressing the lower fragment inwards, and,
instead of employing graduated compresses the whole length of the limb,
they reached only to its middle, along the part corresponding to the
superior fragment. The roller was drawn a little tighter below than
above, in order to keep the inferior part of the radius near to the
ulna.
By being treated afterwards in the usual mode, the fracture was cured.
But, in consequence of being over-stretched by the separation of
the bones, the ligaments of the wrist became the seat of a tedious
lymphatic swelling, which left behind it some degree of stiffness.
27. Examples of this kind occur too rarely to affect the general law
relative to the direction of the displacement of a fractured radius, a
displacement which, if not properly treated, makes the fragments unite
in such a manner as to form an angle pointing inwardly towards the
ulna, as is evinced by a perceptible depression under the cuticle. In
such a case, from this contraction or narrowing of the interval between
the bones, arise the inconveniencies already mentioned (9).
§ VIII.