40. The olecranon suffers fractures at its base and at its summit,
but more frequently in the first, than in the second situation. The
division, though very generally transverse, is sometimes oblique.
Desault met with an instance of an oblique fracture of the olecranon in
a man, who had sustained a violent blow on his fore-arm from a club.
41. The causes which produce it are, either muscular action, a
circumstance that very rarely occurs, or the direct action of external
bodies, which is by far the most common case. The reverse of this is
true with regard to fractures of the rotula, which are almost always
produced by the contraction of the muscles attached to that bone.
42. The olecranon has been at times separated from the ulna, by the act
of throwing a stone with great force. In such cases, the fracture has
been produced by the immediate action of the triceps muscle. This is
the first mode of division.
The second occurs when a violent blow is received on the elbow, or,
more particularly, from falls on that part: for example, if, when
descending a flight of stairs, our heel slip and we fall backwards, the
arm is suddenly thrown behind to save the body. In such a case, the
olecranon striking forcibly against one of the steps, and being pressed
between it and the weight of the body, is broken. In this way was the
disease produced in a majority of the patients attended by Desault for
fractures of the olecranon.
§ XIV.