embrane and to the cavity of the joint. Conversely, disease
in the synovial membrane may spread to the bone in relation to it.
Infective material may escape from the joint into the surrounding
tissues through any weak point in the capsule, particularly through
the bursa which intervenes between the capsule and the ilio-psoas, and
which in one out of every ten subjects communicates with the joint.

TUBERCULOUS DISEASE

Tuberculous disease of the hip, morbus coxae, or "hip-joint disease,"
is especially common in the poorer classes. It is a frequent cause of
prolonged invalidism, and of permanent deformity, and is attended with
a considerable mortality. It is essentially a disease of early life,
rarely commencing after puberty, and almost never after maturity.

#Pathological Anatomy.#--Bone lesions bulk more largely in hip disease
than they do in disease of other joints--five cases originating in
bone to one in synovial membrane being the usual estimate. The upper
end of the femur and the acetabulum are affected with about equal
frequency.

In addition to primary tuberculous lesions, secondary changes result
from the inflamed and softened bones pressing against one another
subsequent to the destruction of their articular cartilages. The head
of the femur undergoes absorption from above downwards, becoming
flattened and truncated, or disappearing altogether. In the acetabulum
the absorption takes place in an upward and backward direction,
whereby the socket becomes enlarged and elongated towards the dorsum
ilii. To this progressive enlargement of the socket Volkmann gave the
suggestive name of "wandering acetabulum" (Fig. 108). The
displacement of the femur resulting from these secondary changes is
one of the causes of real shortening of the limb.

[Illustration: FIG. 108.--Advanced Tuberculous Disease of Acetabulum
with caries and perforation into pelvis.

(Anatomical Museum, University of Edinburgh.)]

#Clinical Features.#--It is customary to describe three stages in the
progress of hip disease, but this is arbitrary and only adopted for
convenience of description.

_Initial Stage._--At this stage the disease is confined to a focus in
the bone which has not yet opened into the joint or to the synovial
membrane. The onset is insidious, and if injury is alleged as an
exciting cause, some weeks have usually elapsed between the receipt of
the injury and the onset of symptoms. The child is brought for advice
becaus