t of a severe force acting
from without, although sometimes they are produced by muscular
contraction.

When the bone gives way at the point of impact of the force, the
violence is said to be _direct_, and a "fracture by compression"
results, the line of fracture being as a rule transverse. The soft
parts overlying the fracture are more or less damaged according to the
weight and shape of the impinging body. Fracture of both bones of the
leg from the passage of a wheel over the limb, fracture of the shaft
of the ulna in warding off a stroke aimed at the head, and fracture of
a rib from a kick, are illustrative examples of fractures by direct
violence.

When the force is transmitted to the seat of fracture from a distance,
the violence is said to be _indirect_, and the bone is broken by
"torsion" or by "bending." In such cases the bone gives way at its
weakest point, and the line of fracture tends to be oblique. Thus both
bones of the leg are frequently broken by a person jumping from a
height and landing on the feet, the tibia breaking in its lower third,
and the fibula at a higher level. Fracture of the clavicle in its
middle third, or of the radius at its lower end, from a fall on the
outstretched hand, are common accidents produced by indirect violence.
The ribs also may be broken by indirect violence, as when the chest is
crushed antero-posteriorly and the bones give way near their angles.
In fractures by indirect violence the soft parts do not suffer by the
violence causing the fracture, but they may be injured by displacement
of the fragments.

In fractures by _muscular action_ the bone is broken by "traction" or
"tearing." The sudden and violent contraction of a muscle may tear off
an epiphysis, such as the head of the fibula, the anterior superior
iliac spine, or the coronoid process of the ulna; or a bony process
may be separated, as, for example, the tuberosity of the calcaneus,
the coracoid process of the scapula, or the larger tubercle (great
tuberosity) of the humerus. Long bones also may be broken by muscular
action. The clavicle has snapped across during the act of swinging a
stick, the humerus in throwing a stone, and the femur when a kick has
missed its object. Fractures of ribs have occurred during fits of
coughing and in the violent efforts of parturition.

Before concluding that a given fracture is the result of muscular
action, it is necessary to exclude the presence of any of the diseased
con