ditions that lead to pathological fracture.

Although the force acting upon the bone is the primary factor in the
production of fractures, there are certain subsidiary factors to be
considered. Thus the age of the patient is of importance. During
infancy and early childhood, fractures are less common than at any
other period of life, and are usually transverse, incomplete, and of
the nature of bends. During adult life, especially between the ages of
thirty and forty, the frequency of fractures reaches its maximum. In
aged persons, although the bones become more brittle by the marrow
spaces in their interior becoming larger and filled with fat,
fractures are less frequent, doubtless because the old are less
exposed to such violence as is likely to produce fracture.

Males, from the nature of their occupations and recreations, sustain
fractures more frequently than do females; in old age, however,
fractures are more common in women than in men, partly because their
bones are more liable to be the seat of fatty atrophy from senility
and disease, and partly because of their clothing--a long skirt--they
are more exposed to unexpected or sudden falls.

[Illustration: FIG. 1.--Multiple Fracture of both Bones of Leg.]

#Clinical Varieties of Fractures.#--The most important subdivision of
fractures is that into simple and compound.

In a _simple_ or subcutaneous fracture there is no communication,
directly or indirectly, between the broken ends of the bone and the
surface of the skin. In a _compound_ or open fracture, on the other
hand, such a communication exists, and, by furnishing a means of
entrance for bacteria, may add materially to the gravity of the
injury.

A simple fracture may be complicated by the existence of a wound of
the soft parts, which, however, does not communicate with the broken
bone.

Fractures, whether simple or compound, fall into other clinical
groups, according to (1) the degree of damage done to the bone, (2)
the direction of the break, and (3) the relative position of the
fragments.

(1) _According to the Degree of Damage done to the Bone._--A fracture
may be incomplete, for example in _greenstick fractures_, which occur
only in young persons--usually below the age of twelve--while the
bones are still soft and flexible. They result from forcible bending
of the bone, the osseous tissue on the convexity of the curve giving
way, while that on the concavity is compressed. The clavicle and the