tuberculous granulation tissue spreads in the marrow,
assuming the characters of a diffuse infiltration--diffuse tuberculous
osteomyelitis. The trabecular framework of the bone undergoes erosion
and absorption--rarefying ostitis--and either disappears altogether or
only irregular fragments or sequestra of microscopic dimensions remain
in the area affected. Less frequently the trabecular framework is added
to by the formation of new bone, resulting in a remarkable degree of
sclerosis, and if, following upon this, there is caseation of the
tubercle and death of the affected portion of bone, there results a
sequestrum often of considerable size and characteristic shape, which,
because of the sclerosis and surrounding endarteritis, is exceedingly
slow in separating. When the sequestrum involves an articular surface it
is often wedge-shaped; in other situations it is rounded or truncated
and lies in the long axis of the medullary canal (Fig. 125). Finally,
the sequestrum lies loose in a cavity lined by tuberculous granulation
tissue, and is readily identified in a radiogram. This type of sclerosis
preceding death of the bone is highly characteristic of tuberculosis.

[Illustration: FIG. 125.--Tuberculous Disease of Child's Tibia,
showing sequestrum in medullary cavity, and increase in girth from
excess of new bone.]

_Clinical Features._--As a rule, it is only in superficially placed
bones, such as the tibia, ulna, clavicle, mandible, or phalanges, that
tuberculous disease in the marrow gives rise to signs sufficiently
definite to allow of its clinical recognition. In the vertebrae, or in
the bones of deeply seated joints, such as the hip or shoulder, the
existence of tuberculous lesions in the marrow can only be inferred from
indirect signs--such, for example, as rigidity and curvature in the case
of the spine, or from the symptoms of grave and persistent joint-disease
in the case of the hip or shoulder.

With few exceptions, tuberculous disease in the interior of a bone does
not reveal its presence until by extension it reaches one or other of
the surfaces of the bone. In the shaft of a long bone its eruption on
the periosteal surface is usually followed by the formation of a cold
abscess in the overlying soft parts. When situated in the articular ends
of bones, the disease more often erupts in relation to the reflection of
the synovial membrane or directly on the articular surface--in either
case giving rise to disease