.

In young subjects before the bones are fully developed the epiphyses
may be separated from the diaphyses. The use of the X-rays has added
greatly to our knowledge of these lesions.

It is useful to remember that in the upper extremity the epiphyses in
the regions of the shoulder and wrist, and, in the lower extremity,
those in the region of the knee, are the latest to unite; and that it
is in these situations that growth in length of the bone goes on
longest and most actively (twenty to twenty-one years). Injuries of
these epiphyses, therefore, are most liable to interfere with the
growth of the limb.

An epiphysis is nourished from the articular arteries and through the
vessels of the periosteum.

_Pathological Separation of Epiphyses._--There are certain
pathological conditions, such as rickets, scurvy, congenital syphilis,
tubercle, suppurative conditions, and tumour growths, which render
separation of the epiphyses liable to occur from injuries altogether
insufficient to produce such lesions under normal conditions.

#Traumatic Separations.#[2]--Speaking generally, it may be said that
injuries which in an adult would be liable to produce dislocation, are
in a young person more apt to cause separation of an epiphysis.
Indirect violence, especially when exerted in such a way as to combine
traction with torsion,--for example, when the foot is caught in the
spokes of a carriage wheel,--is the commonest cause of epiphysial
separation. Direct violence is a much less frequent cause. Muscular
action occasionally produces separation of the epiphyses--for example,
the anterior superior iliac spine, the small trochanter of the femur,
or the upper end of the fibula.

[2] We desire here to acknowledge our indebtedness to Mr. John
Poland's work on _Traumatic Separation of the Epiphyses_.

[Illustration: FIG. 8.--Partial Separation of Epiphysis, with Fracture
running into Diaphysis.]

[Illustration: FIG. 9.--Complete Separation of Epiphysis.]

[Illustration: FIG. 10.--Partial Separation with Fracture of
Epiphysis.]

[Illustration: FIG. 11.--Complete Separation with Fracture of
Epiphysis.]

The majority of separations take place between the eleventh and the
eighteenth years, chiefly because during this period the injuries
liable to produce such lesions are most common. They do not occur
after twenty-five, because by that time all the epiphyses have united.
In females this form of injury is rare, and almost invaria