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.
